Effect provides options to manage how effects are executed, particularly focusing on controlling how many effects run concurrently.
typeOptions= {
readonlyconcurrency?:Concurrency
}
The concurrency option is used to determine the level of concurrency, with the following values:
typeConcurrency=number|"unbounded"|"inherit"
Let’s explore each configuration in detail.
Sequential Execution (Default)
By default, if you don’t specify any concurrency option, effects will run sequentially, one after the other. This means each effect starts only after the previous one completes.
Example (Sequential Execution)
1
import {
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect,
import Duration
Duration } from"effect"
2
3
// Helper function to simulate a task with a delay
Creates an Effect that represents an asynchronous computation guaranteed to
succeed.
When to Use
Use promise when you are sure the operation will not reject.
Details
The provided function (thunk) returns a Promise that should never reject; if it does, the error
will be treated as a "defect".
This defect is not a standard error but indicates a flaw in the logic that
was expected to be error-free. You can think of it similar to an unexpected
crash in the program, which can be further managed or logged using tools like
catchAllDefect
.
Interruptions
An optional AbortSignal can be provided to allow for interruption of the
wrapped Promise API.
@see ― tryPromise for a version that can handle failures.
new <void>(executor: (resolve: (value:void|PromiseLike<void>) =>void, reject: (reason?:any) =>void) =>void) =>Promise<void>
Creates a new Promise.
@param ― executor A callback used to initialize the promise. This callback is passed two arguments:
a resolve callback used to resolve the promise with a value or the result of another promise,
and a reject callback used to reject the promise with a provided reason or error.
Promise<void>((
resolve: (value:void|PromiseLike<void>) =>void
resolve) => {
8
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Schedules execution of a one-time callback after delay milliseconds.
The callback will likely not be invoked in precisely delay milliseconds.
Node.js makes no guarantees about the exact timing of when callbacks will fire,
nor of their ordering. The callback will be called as close as possible to the
time specified.
When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.
If callback is not a function, a TypeError will be thrown.
This method has a custom variant for promises that is available using timersPromises.setTimeout().
@since ― v0.0.1
@param ― callback The function to call when the timer elapses.
@param ― delay The number of milliseconds to wait before calling the callback.
@param ― args Optional arguments to pass when the callback is called.
setTimeout(() => {
10
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Combines multiple effects into one, returning results based on the input
structure.
When to Use
Use Effect.all when you need to run multiple effects and combine their
results into a single output. It supports tuples, iterables, structs, and
records, making it flexible for different input types.
For instance, if the input is a tuple:
// ┌─── a tuple of effects
// ▼
Effect.all([effect1, effect2, ...])
the effects are executed sequentially, and the result is a new effect
containing the results as a tuple. The results in the tuple match the order
of the effects passed to Effect.all.
Concurrency
You can control the execution order (e.g., sequential vs. concurrent) using
the concurrency option.
Short-Circuiting Behavior
The Effect.all function stops execution on the first error it encounters,
this is called "short-circuiting". If any effect in the collection fails, the
remaining effects will not run, and the error will be propagated. To change
this behavior, you can use the mode option, which allows all effects to run
and collect results as Either or Option.
The mode option
The { mode: "either" } option changes the behavior of Effect.all to
ensure all effects run, even if some fail. Instead of stopping on the first
failure, this mode collects both successes and failures, returning an array
of Either instances where each result is either a Right (success) or a
Left (failure).
Similarly, the { mode: "validate" } option uses Option to indicate
success or failure. Each effect returns None for success and Some with
the error for failure.
@see ― forEach for iterating over elements and applying an effect.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
start task2 <-- task2 starts only after task1 completes
27
task2 done
28
*/
Numbered Concurrency
You can control how many effects run concurrently by setting a number for concurrency. For example, concurrency: 2 allows up to two effects to run at the same time.
Example (Limiting to 2 Concurrent Tasks)
1
import {
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect,
import Duration
Duration } from"effect"
2
3
// Helper function to simulate a task with a delay
Creates an Effect that represents an asynchronous computation guaranteed to
succeed.
When to Use
Use promise when you are sure the operation will not reject.
Details
The provided function (thunk) returns a Promise that should never reject; if it does, the error
will be treated as a "defect".
This defect is not a standard error but indicates a flaw in the logic that
was expected to be error-free. You can think of it similar to an unexpected
crash in the program, which can be further managed or logged using tools like
catchAllDefect
.
Interruptions
An optional AbortSignal can be provided to allow for interruption of the
wrapped Promise API.
@see ― tryPromise for a version that can handle failures.
new <void>(executor: (resolve: (value:void|PromiseLike<void>) =>void, reject: (reason?:any) =>void) =>void) =>Promise<void>
Creates a new Promise.
@param ― executor A callback used to initialize the promise. This callback is passed two arguments:
a resolve callback used to resolve the promise with a value or the result of another promise,
and a reject callback used to reject the promise with a provided reason or error.
Promise<void>((
resolve: (value:void|PromiseLike<void>) =>void
resolve) => {
8
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Schedules execution of a one-time callback after delay milliseconds.
The callback will likely not be invoked in precisely delay milliseconds.
Node.js makes no guarantees about the exact timing of when callbacks will fire,
nor of their ordering. The callback will be called as close as possible to the
time specified.
When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.
If callback is not a function, a TypeError will be thrown.
This method has a custom variant for promises that is available using timersPromises.setTimeout().
@since ― v0.0.1
@param ― callback The function to call when the timer elapses.
@param ― delay The number of milliseconds to wait before calling the callback.
@param ― args Optional arguments to pass when the callback is called.
setTimeout(() => {
10
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Combines multiple effects into one, returning results based on the input
structure.
When to Use
Use Effect.all when you need to run multiple effects and combine their
results into a single output. It supports tuples, iterables, structs, and
records, making it flexible for different input types.
For instance, if the input is a tuple:
// ┌─── a tuple of effects
// ▼
Effect.all([effect1, effect2, ...])
the effects are executed sequentially, and the result is a new effect
containing the results as a tuple. The results in the tuple match the order
of the effects passed to Effect.all.
Concurrency
You can control the execution order (e.g., sequential vs. concurrent) using
the concurrency option.
Short-Circuiting Behavior
The Effect.all function stops execution on the first error it encounters,
this is called "short-circuiting". If any effect in the collection fails, the
remaining effects will not run, and the error will be propagated. To change
this behavior, you can use the mode option, which allows all effects to run
and collect results as Either or Option.
The mode option
The { mode: "either" } option changes the behavior of Effect.all to
ensure all effects run, even if some fail. Instead of stopping on the first
failure, this mode collects both successes and failures, returning an array
of Either instances where each result is either a Right (success) or a
Left (failure).
Similarly, the { mode: "validate" } option uses Option to indicate
success or failure. Each effect returns None for success and Some with
the error for failure.
@see ― forEach for iterating over elements and applying an effect.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
Creates an Effect that represents an asynchronous computation guaranteed to
succeed.
When to Use
Use promise when you are sure the operation will not reject.
Details
The provided function (thunk) returns a Promise that should never reject; if it does, the error
will be treated as a "defect".
This defect is not a standard error but indicates a flaw in the logic that
was expected to be error-free. You can think of it similar to an unexpected
crash in the program, which can be further managed or logged using tools like
catchAllDefect
.
Interruptions
An optional AbortSignal can be provided to allow for interruption of the
wrapped Promise API.
@see ― tryPromise for a version that can handle failures.
new <void>(executor: (resolve: (value:void|PromiseLike<void>) =>void, reject: (reason?:any) =>void) =>void) =>Promise<void>
Creates a new Promise.
@param ― executor A callback used to initialize the promise. This callback is passed two arguments:
a resolve callback used to resolve the promise with a value or the result of another promise,
and a reject callback used to reject the promise with a provided reason or error.
Promise<void>((
resolve: (value:void|PromiseLike<void>) =>void
resolve) => {
8
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Schedules execution of a one-time callback after delay milliseconds.
The callback will likely not be invoked in precisely delay milliseconds.
Node.js makes no guarantees about the exact timing of when callbacks will fire,
nor of their ordering. The callback will be called as close as possible to the
time specified.
When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.
If callback is not a function, a TypeError will be thrown.
This method has a custom variant for promises that is available using timersPromises.setTimeout().
@since ― v0.0.1
@param ― callback The function to call when the timer elapses.
@param ― delay The number of milliseconds to wait before calling the callback.
@param ― args Optional arguments to pass when the callback is called.
setTimeout(() => {
10
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Combines multiple effects into one, returning results based on the input
structure.
When to Use
Use Effect.all when you need to run multiple effects and combine their
results into a single output. It supports tuples, iterables, structs, and
records, making it flexible for different input types.
For instance, if the input is a tuple:
// ┌─── a tuple of effects
// ▼
Effect.all([effect1, effect2, ...])
the effects are executed sequentially, and the result is a new effect
containing the results as a tuple. The results in the tuple match the order
of the effects passed to Effect.all.
Concurrency
You can control the execution order (e.g., sequential vs. concurrent) using
the concurrency option.
Short-Circuiting Behavior
The Effect.all function stops execution on the first error it encounters,
this is called "short-circuiting". If any effect in the collection fails, the
remaining effects will not run, and the error will be propagated. To change
this behavior, you can use the mode option, which allows all effects to run
and collect results as Either or Option.
The mode option
The { mode: "either" } option changes the behavior of Effect.all to
ensure all effects run, even if some fail. Instead of stopping on the first
failure, this mode collects both successes and failures, returning an array
of Either instances where each result is either a Right (success) or a
Left (failure).
Similarly, the { mode: "validate" } option uses Option to indicate
success or failure. Each effect returns None for success and Some with
the error for failure.
@see ― forEach for iterating over elements and applying an effect.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
When using concurrency: "inherit", the concurrency level is inherited from the surrounding context. This context can be set using Effect.withConcurrency(number | "unbounded"). If no context is provided, the default is "unbounded".
Example (Inheriting Concurrency from Context)
1
import {
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect,
import Duration
Duration } from"effect"
2
3
// Helper function to simulate a task with a delay
Creates an Effect that represents an asynchronous computation guaranteed to
succeed.
When to Use
Use promise when you are sure the operation will not reject.
Details
The provided function (thunk) returns a Promise that should never reject; if it does, the error
will be treated as a "defect".
This defect is not a standard error but indicates a flaw in the logic that
was expected to be error-free. You can think of it similar to an unexpected
crash in the program, which can be further managed or logged using tools like
catchAllDefect
.
Interruptions
An optional AbortSignal can be provided to allow for interruption of the
wrapped Promise API.
@see ― tryPromise for a version that can handle failures.
new <void>(executor: (resolve: (value:void|PromiseLike<void>) =>void, reject: (reason?:any) =>void) =>void) =>Promise<void>
Creates a new Promise.
@param ― executor A callback used to initialize the promise. This callback is passed two arguments:
a resolve callback used to resolve the promise with a value or the result of another promise,
and a reject callback used to reject the promise with a provided reason or error.
Promise<void>((
resolve: (value:void|PromiseLike<void>) =>void
resolve) => {
8
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Schedules execution of a one-time callback after delay milliseconds.
The callback will likely not be invoked in precisely delay milliseconds.
Node.js makes no guarantees about the exact timing of when callbacks will fire,
nor of their ordering. The callback will be called as close as possible to the
time specified.
When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.
If callback is not a function, a TypeError will be thrown.
This method has a custom variant for promises that is available using timersPromises.setTimeout().
@since ― v0.0.1
@param ― callback The function to call when the timer elapses.
@param ― delay The number of milliseconds to wait before calling the callback.
@param ― args Optional arguments to pass when the callback is called.
setTimeout(() => {
10
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Combines multiple effects into one, returning results based on the input
structure.
When to Use
Use Effect.all when you need to run multiple effects and combine their
results into a single output. It supports tuples, iterables, structs, and
records, making it flexible for different input types.
For instance, if the input is a tuple:
// ┌─── a tuple of effects
// ▼
Effect.all([effect1, effect2, ...])
the effects are executed sequentially, and the result is a new effect
containing the results as a tuple. The results in the tuple match the order
of the effects passed to Effect.all.
Concurrency
You can control the execution order (e.g., sequential vs. concurrent) using
the concurrency option.
Short-Circuiting Behavior
The Effect.all function stops execution on the first error it encounters,
this is called "short-circuiting". If any effect in the collection fails, the
remaining effects will not run, and the error will be propagated. To change
this behavior, you can use the mode option, which allows all effects to run
and collect results as Either or Option.
The mode option
The { mode: "either" } option changes the behavior of Effect.all to
ensure all effects run, even if some fail. Instead of stopping on the first
failure, this mode collects both successes and failures, returning an array
of Either instances where each result is either a Right (success) or a
Left (failure).
Similarly, the { mode: "validate" } option uses Option to indicate
success or failure. Each effect returns None for success and Some with
the error for failure.
@see ― forEach for iterating over elements and applying an effect.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
Creates an Effect that represents an asynchronous computation guaranteed to
succeed.
When to Use
Use promise when you are sure the operation will not reject.
Details
The provided function (thunk) returns a Promise that should never reject; if it does, the error
will be treated as a "defect".
This defect is not a standard error but indicates a flaw in the logic that
was expected to be error-free. You can think of it similar to an unexpected
crash in the program, which can be further managed or logged using tools like
catchAllDefect
.
Interruptions
An optional AbortSignal can be provided to allow for interruption of the
wrapped Promise API.
@see ― tryPromise for a version that can handle failures.
new <void>(executor: (resolve: (value:void|PromiseLike<void>) =>void, reject: (reason?:any) =>void) =>void) =>Promise<void>
Creates a new Promise.
@param ― executor A callback used to initialize the promise. This callback is passed two arguments:
a resolve callback used to resolve the promise with a value or the result of another promise,
and a reject callback used to reject the promise with a provided reason or error.
Promise<void>((
resolve: (value:void|PromiseLike<void>) =>void
resolve) => {
8
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Schedules execution of a one-time callback after delay milliseconds.
The callback will likely not be invoked in precisely delay milliseconds.
Node.js makes no guarantees about the exact timing of when callbacks will fire,
nor of their ordering. The callback will be called as close as possible to the
time specified.
When delay is larger than 2147483647 or less than 1, the delay will be set to 1. Non-integer delays are truncated to an integer.
If callback is not a function, a TypeError will be thrown.
This method has a custom variant for promises that is available using timersPromises.setTimeout().
@since ― v0.0.1
@param ― callback The function to call when the timer elapses.
@param ― delay The number of milliseconds to wait before calling the callback.
@param ― args Optional arguments to pass when the callback is called.
setTimeout(() => {
10
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Combines multiple effects into one, returning results based on the input
structure.
When to Use
Use Effect.all when you need to run multiple effects and combine their
results into a single output. It supports tuples, iterables, structs, and
records, making it flexible for different input types.
For instance, if the input is a tuple:
// ┌─── a tuple of effects
// ▼
Effect.all([effect1, effect2, ...])
the effects are executed sequentially, and the result is a new effect
containing the results as a tuple. The results in the tuple match the order
of the effects passed to Effect.all.
Concurrency
You can control the execution order (e.g., sequential vs. concurrent) using
the concurrency option.
Short-Circuiting Behavior
The Effect.all function stops execution on the first error it encounters,
this is called "short-circuiting". If any effect in the collection fails, the
remaining effects will not run, and the error will be propagated. To change
this behavior, you can use the mode option, which allows all effects to run
and collect results as Either or Option.
The mode option
The { mode: "either" } option changes the behavior of Effect.all to
ensure all effects run, even if some fail. Instead of stopping on the first
failure, this mode collects both successes and failures, returning an array
of Either instances where each result is either a Right (success) or a
Left (failure).
Similarly, the { mode: "validate" } option uses Option to indicate
success or failure. Each effect returns None for success and Some with
the error for failure.
@see ― forEach for iterating over elements and applying an effect.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
All effects in Effect are executed by fibers. If you didn’t create the fiber yourself, it was created by an operation you’re using (if it’s concurrent) or by the Effect runtime system.
A fiber is created any time an effect is run. When running effects concurrently, a fiber is created for each concurrent effect.
To summarize:
An Effect is a higher-level concept that describes an effectful computation. It is lazy and immutable, meaning it represents a computation that may produce a value or fail but does not immediately execute.
A fiber, on the other hand, represents the running execution of an Effect. It can be interrupted or awaited to retrieve its result. Think of it as a way to control and interact with the ongoing computation.
Fibers can be interrupted in various ways. Let’s explore some of these scenarios and see examples of how to interrupt fibers in Effect.
Effect.interrupt
A fiber can be interrupted using the Effect.interrupt effect on that particular fiber.
Example (Without Interruption)
In this case, the program runs without any interruption, logging the start and completion of the task.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Here, the fiber is interrupted after the log "start" but before the "done" log. The Effect.interrupt stops the fiber, and it never reaches the final log.
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
When a fiber is interrupted, the cause of the interruption is captured, including details like the fiber’s ID and when it started.
Interruption of Concurrent Effects
When running multiple effects concurrently, such as with Effect.forEach, if one of the effects is interrupted, it causes all concurrent effects to be interrupted as well.
Console.log(`Currently at index ${index}`).pipe(Effect.as(n *2))
)
Effect.runPromise(result).then(console.log)
// Output:
// Currently at index 0
// Currently at index 1
// Currently at index 2
// Currently at index 3
// Currently at index 4
// [ 2, 4, 6, 8, 10 ]
@example
// Title: Using discard to Ignore Results
import { Effect, Console } from "effect"
// Apply effects but discard the results
const result = Effect.forEach(
[1, 2, 3, 4, 5],
(n, index) =>
Console.log(Currently at index ${index}).pipe(Effect.as(n * 2)),
{ discard: true }
)
Effect.runPromise(result).then(console.log)
// Output:
// Currently at index 0
// Currently at index 1
// Currently at index 2
// Currently at index 3
// Currently at index 4
// undefined
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
gen allows you to write code that looks and behaves like synchronous
code, but it can handle asynchronous tasks, errors, and complex control flow
(like loops and conditions). It helps make asynchronous code more readable
and easier to manage.
The generator functions work similarly to async/await but with more
explicit control over the execution of effects. You can yield* values from
effects and return the final result at the end.
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Logs one or more messages or error causes at the current log level, which is INFO by default.
This function allows logging multiple items at once and can include detailed error information using Cause instances.
To adjust the log level, use the Logger.withMinimumLogLevel function.
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then((
exit: Exit<void[], never>
exit) =>
18
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
This function takes two effects and runs them concurrently. The first effect
that successfully completes will determine the result of the race, and the
other effect will be interrupted.
If neither effect succeeds, the function will fail with a cause containing all the errors.
This is useful when you want to run two effects concurrently, but only care
about the first one to succeed. It is commonly used in cases like timeouts,
retries, or when you want to optimize for the faster response without
worrying about the other effect.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
10
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with the specified effect,
returning the first successful A from the faster side. If one effect
succeeds, the other will be interrupted. If neither succeeds, then the
effect will fail with some error.
The foundational function for running effects, returning a "fiber" that can
be observed or interrupted.
When to Use
runFork is used to run an effect in the background by creating a
fiber. It is the base function for all other run functions. It starts a fiber
that can be observed or interrupted.
Unless you specifically need a Promise or synchronous operation,
runFork is a good default choice.
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
10
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with the specified effect,
returning the first successful A from the faster side. If one effect
succeeds, the other will be interrupted. If neither succeeds, then the
effect will fail with some error.
The foundational function for running effects, returning a "fiber" that can
be observed or interrupted.
When to Use
runFork is used to run an effect in the background by creating a
fiber. It is the base function for all other run functions. It starts a fiber
that can be observed or interrupted.
Unless you specifically need a Promise or synchronous operation,
runFork is a good default choice.
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
10
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with the specified effect,
returning the first successful A from the faster side. If one effect
succeeds, the other will be interrupted. If neither succeeds, then the
effect will fail with some error.
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
If you want to handle the result of whichever task completes first, whether it succeeds or fails, you can use the Effect.either function. This function wraps the result in an Either type, allowing you to see if the result was a success (Right) or a failure (Left):
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
10
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with the specified effect,
returning the first successful A from the faster side. If one effect
succeeds, the other will be interrupted. If neither succeeds, then the
effect will fail with some error.
Transforms an Effect into one that encapsulates both success and failure
using the Either data type.
Details
either takes an effect that could potentially fail and converts it
into an effect that always succeeds but with the result inside an Either.
The Either can either be a Left (representing failure) or a Right
(representing success). This allows you to handle both cases explicitly
without causing the effect to fail.
The resulting effect cannot fail because failure is now represented inside
the Either type.
@see ― option for a version that uses Option instead.
Transforms an Effect into one that encapsulates both success and failure
using the Either data type.
Details
either takes an effect that could potentially fail and converts it
into an effect that always succeeds but with the result inside an Either.
The Either can either be a Left (representing failure) or a Right
(representing success). This allows you to handle both cases explicitly
without causing the effect to fail.
The resulting effect cannot fail because failure is now represented inside
the Either type.
@see ― option for a version that uses Option instead.
Executes an effect and returns the result as a Promise.
When to Use
Use runPromise when you need to execute an effect and work with the
result using Promise syntax, typically for compatibility with other
promise-based code.
If the effect succeeds, the promise will resolve with the result. If the
effect fails, the promise will reject with an error.
@see ― runPromiseExit for a version that returns an Exit type instead of rejecting.
@example
// Title: Running a Successful Effect as a Promise
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
This function runs multiple effects concurrently and returns the result of the first one to succeed. If one effect succeeds, the others will be interrupted.
If none of the effects succeed, the function will fail with the last error encountered.
This is useful when you want to race multiple effects, but only care
about the first one to succeed. It is commonly used in cases like timeouts,
retries, or when you want to optimize for the faster response without
worrying about the other effects.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
10
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("150 millis"),
16
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with all the specified effects,
yielding the value of the first effect to succeed with a value. Losers of
the race will be interrupted immediately
The foundational function for running effects, returning a "fiber" that can
be observed or interrupted.
When to Use
runFork is used to run an effect in the background by creating a
fiber. It is the base function for all other run functions. It starts a fiber
that can be observed or interrupted.
Unless you specifically need a Promise or synchronous operation,
runFork is a good default choice.
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
10
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("150 millis"),
16
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with all the specified effects,
yielding the value of the first effect to succeed with a value. Losers of
the race will be interrupted immediately
The foundational function for running effects, returning a "fiber" that can
be observed or interrupted.
When to Use
runFork is used to run an effect in the background by creating a
fiber. It is the base function for all other run functions. It starts a fiber
that can be observed or interrupted.
Unless you specifically need a Promise or synchronous operation,
runFork is a good default choice.
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
10
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("150 millis"),
16
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with all the specified effects,
yielding the value of the first effect to succeed with a value. Losers of
the race will be interrupted immediately
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
This function takes two effects and runs them concurrently, returning the
result of the first one that completes, regardless of whether it succeeds or
fails.
This function is useful when you want to race two operations, and you want to
proceed with whichever one finishes first, regardless of whether it succeeds
or fails.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
12
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with the specified effect,
yielding the first result to complete, whether by success or failure. If
neither effect completes, then the composed effect will not complete.
WARNING: The raced effect will safely interrupt the "loser", but will not
resume until the loser has been cleanly terminated. If early return is
desired, then instead of performing l raceFirst r, perform
l.disconnect raceFirst r.disconnect, which disconnects left and right
interrupt signal, allowing a fast return, with interruption performed
in the background.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
Creates an Effect that represents a recoverable error.
When to Use
Use this function to explicitly signal an error in an Effect. The error
will keep propagating unless it is handled. You can handle the error with
functions like
catchAll
or
catchTag
.
@see ― succeed to create an effect that represents a successful value.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
12
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with the specified effect,
yielding the first result to complete, whether by success or failure. If
neither effect completes, then the composed effect will not complete.
WARNING: The raced effect will safely interrupt the "loser", but will not
resume until the loser has been cleanly terminated. If early return is
desired, then instead of performing l raceFirst r, perform
l.disconnect raceFirst r.disconnect, which disconnects left and right
interrupt signal, allowing a fast return, with interruption performed
in the background.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
The Effect.raceFirst function safely interrupts the “loser” effect once the other completes, but it will not resume until the loser is cleanly terminated.
If you want a quicker return, you can disconnect the interrupt signal for both effects. Instead of calling:
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
12
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with the specified effect,
yielding the first result to complete, whether by success or failure. If
neither effect completes, then the composed effect will not complete.
WARNING: The raced effect will safely interrupt the "loser", but will not
resume until the loser has been cleanly terminated. If early return is
desired, then instead of performing l raceFirst r, perform
l.disconnect raceFirst r.disconnect, which disconnects left and right
interrupt signal, allowing a fast return, with interruption performed
in the background.
Provides a way to handle timeouts in uninterruptible effects, allowing them
to continue in the background while the main control flow proceeds with the
timeout error.
The disconnect function allows an uninterruptible effect to continue
running in the background, while enabling the main control flow to
immediately recognize a timeout condition. This is useful when you want to
avoid blocking the program due to long-running tasks, especially when those
tasks do not need to affect the flow of the rest of the program.
Without disconnect, an uninterruptible effect will ignore the
timeout and continue executing until it completes. The timeout error will
only be assessed after the effect finishes, which can cause delays in
recognizing a timeout.
With disconnect, the uninterruptible effect proceeds in the
background while the main program flow can immediately handle the timeout
error or trigger alternative logic. This enables faster timeout handling
without waiting for the completion of the long-running task.
@see ― Effect.timeout for a version that interrupts the effect.
@see ― Effect.uninterruptible for creating an uninterruptible effect.
@example
import { Effect } from"effect"
constlongRunningTask= Effect.gen(function* () {
console.log("Start heavy processing...")
yield* Effect.sleep("5 seconds") // Simulate a long process
console.log("Heavy processing done.")
return"Data processed"
})
consttimedEffect= longRunningTask.pipe(
Effect.uninterruptible,
// Allows the task to finish in the background if it times out
Provides a way to handle timeouts in uninterruptible effects, allowing them
to continue in the background while the main control flow proceeds with the
timeout error.
The disconnect function allows an uninterruptible effect to continue
running in the background, while enabling the main control flow to
immediately recognize a timeout condition. This is useful when you want to
avoid blocking the program due to long-running tasks, especially when those
tasks do not need to affect the flow of the rest of the program.
Without disconnect, an uninterruptible effect will ignore the
timeout and continue executing until it completes. The timeout error will
only be assessed after the effect finishes, which can cause delays in
recognizing a timeout.
With disconnect, the uninterruptible effect proceeds in the
background while the main program flow can immediately handle the timeout
error or trigger alternative logic. This enables faster timeout handling
without waiting for the completion of the long-running task.
@see ― Effect.timeout for a version that interrupts the effect.
@see ― Effect.uninterruptible for creating an uninterruptible effect.
@example
import { Effect } from"effect"
constlongRunningTask= Effect.gen(function* () {
console.log("Start heavy processing...")
yield* Effect.sleep("5 seconds") // Simulate a long process
console.log("Heavy processing done.")
return"Data processed"
})
consttimedEffect= longRunningTask.pipe(
Effect.uninterruptible,
// Allows the task to finish in the background if it times out
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Attaches callbacks for the resolution and/or rejection of the Promise.
@param ― onfulfilled The callback to execute when the Promise is resolved.
@param ― onrejected The callback to execute when the Promise is rejected.
@returns ― A Promise for the completion of which ever callback is executed.
then(
var console:Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
constname='Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
constout=getStreamSomehow();
consterr=getStreamSomehow();
constmyConsole=new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
This function runs two effects concurrently and calls a specified “finisher” function once one of the effects completes, regardless of whether it succeeds or fails.
The finisher functions for each effect allow you to handle the results of each effect as soon as they complete.
The function takes two finisher callbacks, one for each effect, and allows you to specify how to handle the result of the race.
This function is useful when you need to react to the completion of either effect without waiting for both to finish. It can be used whenever you want to take action based on the first available result.
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("100 millis"),
5
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
constdelay: (duration:DurationInput) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+1overload)
Returns an effect that is delayed from this effect by the specified
Duration.
@since ― 2.0.0
delay("200 millis"),
12
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
consttap: <Effect.Effect<void, never, never>>(f:Effect.Effect<void, never, never>) => <A, E, R>(self:Effect.Effect<A, E, R>) =>Effect.Effect<A, E, R> (+7overloads)
Runs a side effect with the result of an effect without changing the original
value.
When to Use
Use tap when you want to perform a side effect, like logging or tracking,
without modifying the main value. This is useful when you need to observe or
record an action but want the original value to be passed to the next step.
Details
tap works similarly to flatMap, but it ignores the result of the function
passed to it. The value from the previous effect remains available for the
next part of the chain. Note that if the side effect fails, the entire chain
will fail too.
@example
// Title: Logging a step in a pipeline
import { Console, Effect, pipe } from"effect"
// Function to apply a discount safely to a transaction amount
constapplyDiscount= (
total:number,
discountRate:number
):Effect.Effect<number, Error> =>
discountRate ===0
? Effect.fail(newError("Discount rate cannot be zero"))
Returns an effect that races this effect with the specified effect, calling
the specified finisher as soon as one result or the other has been computed.
The foundational function for running effects, returning a "fiber" that can
be observed or interrupted.
When to Use
runFork is used to run an effect in the background by creating a
fiber. It is the base function for all other run functions. It starts a fiber
that can be observed or interrupted.
Unless you specifically need a Promise or synchronous operation,
runFork is a good default choice.
