In previous sections, we learned how to create and use sinks. Now, let’s explore some operations that let you transform or filter sink behavior.
Adapting Sink Input
At times, you may have a sink that works with one type of input, but your current stream uses a different type. The Sink.mapInput function helps you adapt your sink to a new input type by transforming the input values. While Sink.map changes the sink’s output, Sink.mapInput changes the input it accepts.
Example (Converting String Input to Numeric for Summing)
Suppose you have a Sink.sum that calculates the sum of numbers. If your stream contains strings rather than numbers, Sink.mapInput can convert those strings into numbers, allowing Sink.sum to work with your stream:
Transforming Both Input and Output
When you need to transform both the input and output of a sink, Sink.dimap provides a flexible solution. It extends mapInput by allowing you to transform the input type, perform the operation, and then transform the output to a new type. This can be useful for complete conversions between input and output types.
Example (Converting Input to Integer, Summing, and Converting Output to String)
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()).
Sinks can also filter incoming elements based on specific conditions with Sink.filterInput. This operation allows the sink to process only elements that meet certain criteria.
Example (Filtering Negative Numbers in Chunks of Three)
In the example below, elements are collected in chunks of three, but only positive numbers are included:
1
import {
import Stream
Stream,
import Sink
Sink,
import Effect
@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from"effect"
2
3
// Define a stream with positive, negative, and zero values
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((
chunk: Chunk<Chunk<number>>
chunk) =>
14
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()).