KeyValueStore

The @effect/platform/KeyValueStore module provides a robust and effectful interface for managing key-value pairs. It supports asynchronous operations, ensuring data integrity and consistency, and includes built-in implementations for in-memory, file system-based, and schema-validated stores.

Basic Usage

The module provides a single KeyValueStore tag, which acts as the gateway for interacting with the store.

Example (Accessing the KeyValueStore Service)

1
import { 
import KeyValueStore
KeyValueStore } from "@effect/platform"
2
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
3

4
const 
const program: Effect.Effect<void, never, KeyValueStore.KeyValueStore>
program = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const gen: <YieldWrap<Tag<KeyValueStore.KeyValueStore, KeyValueStore.KeyValueStore>>, void>(f: (resume: Effect.Adapter) => Generator<...>) => Effect.Effect<...> (+1 overload)
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.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.
@example 
import { Effect } from "effect"

const addServiceCharge = (amount: number) => amount + 1

const applyDiscount = (
  total: number,
  discountRate: number
): Effect.Effect<number, Error> =>
  discountRate === 0
    ? Effect.fail(new Error("Discount rate cannot be zero"))
    : Effect.succeed(total - (total * discountRate) / 100)

const fetchTransactionAmount = Effect.promise(() => Promise.resolve(100))

const fetchDiscountRate = Effect.promise(() => Promise.resolve(5))

export const program = Effect.gen(function* () {
  const transactionAmount = yield* fetchTransactionAmount
  const discountRate = yield* fetchDiscountRate
  const discountedAmount = yield* applyDiscount(
    transactionAmount,
    discountRate
  )
  const finalAmount = addServiceCharge(discountedAmount)
  return `Final amount to charge: ${finalAmount}`
})
@since ― 2.0.0
gen(function* () {
5
  const 
const kv: KeyValueStore.KeyValueStore
kv = yield* 
import KeyValueStore
KeyValueStore.
const KeyValueStore: Tag<KeyValueStore.KeyValueStore, KeyValueStore.KeyValueStore>@since ― 1.0.0
@since ― 1.0.0
@since ― 1.0.0
KeyValueStore
6

7
  // Use `kv` to perform operations on the store
8
})

The KeyValueStore interface includes the following operations:

Operation	Description
get	Returns the value as `string` of the specified key if it exists.
getUint8Array	Returns the value as `Uint8Array` of the specified key if it exists.
set	Sets the value of the specified key.
remove	Removes the specified key.
clear	Removes all entries.
size	Returns the number of entries.
modify	Updates the value of the specified key if it exists.
modifyUint8Array	Updates the value of the specified key if it exists.
has	Check if a key exists.
isEmpty	Check if the store is empty.
forSchema	Create a SchemaStore for the specified schema.

Example (Working with Key-Value Pairs)

1
import {
2
  
const KeyValueStore: Tag<KeyValueStore, KeyValueStore>@since ― 1.0.0
@since ― 1.0.0
@since ― 1.0.0
KeyValueStore,
3
  
const layerMemory: Layer<KeyValueStore, never, never>@since ― 1.0.0
layerMemory
4
} from "@effect/platform/KeyValueStore"
5
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect } from "effect"
6

7
const 
const program: Effect.Effect<void, PlatformError, KeyValueStore>
program = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const gen: <YieldWrap<Tag<KeyValueStore, KeyValueStore>> | YieldWrap<Effect.Effect<void, PlatformError, never>>, void>(f: (resume: Effect.Adapter) => Generator<...>) => Effect.Effect<...> (+1 overload)
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.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.
@example 
import { Effect } from "effect"

const addServiceCharge = (amount: number) => amount + 1

const applyDiscount = (
  total: number,
  discountRate: number
): Effect.Effect<number, Error> =>
  discountRate === 0
    ? Effect.fail(new Error("Discount rate cannot be zero"))
    : Effect.succeed(total - (total * discountRate) / 100)

const fetchTransactionAmount = Effect.promise(() => Promise.resolve(100))

const fetchDiscountRate = Effect.promise(() => Promise.resolve(5))

export const program = Effect.gen(function* () {
  const transactionAmount = yield* fetchTransactionAmount
  const discountRate = yield* fetchDiscountRate
  const discountedAmount = yield* applyDiscount(
    transactionAmount,
    discountRate
  )
  const finalAmount = addServiceCharge(discountedAmount)
  return `Final amount to charge: ${finalAmount}`
})
@since ― 2.0.0
gen(function* () {
8
  const 
const kv: KeyValueStore
kv = yield* 
const KeyValueStore: Tag<KeyValueStore, KeyValueStore>@since ― 1.0.0
@since ― 1.0.0
@since ― 1.0.0
KeyValueStore
9

10
  // Initially, the store is empty
11
  
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(new Error('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

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = 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(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
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()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(yield* 
const kv: KeyValueStore
kv.
KeyValueStore.size: Effect.Effect<number, PlatformError, never>
Returns the number of entries.
size)
12

13
  // Set a key-value pair
14
  yield* 
const kv: KeyValueStore
kv.
KeyValueStore.set: (key: string, value: string | Uint8Array) => Effect.Effect<void, PlatformError>
Sets the value of the specified key.
set("key", "value")
15
  
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(new Error('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

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = 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(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
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()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(yield* 
const kv: KeyValueStore
kv.
KeyValueStore.size: Effect.Effect<number, PlatformError, never>
Returns the number of entries.
size)
16

17
  // Retrieve the value for the specified key
18
  const 
const value: Option<string>
value = yield* 
const kv: KeyValueStore
kv.
KeyValueStore.get: (key: string) => Effect.Effect<Option<string>, PlatformError>
Returns the value of the specified key if it exists.
get("key")
19
  
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(new Error('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

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = 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(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
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()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(
const value: Option<string>
value)
20

21
  // Remove the key-value pair
22
  yield* 
const kv: KeyValueStore
kv.
KeyValueStore.remove: (key: string) => Effect.Effect<void, PlatformError>
Removes the specified key.
remove("key")
23
  
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(new Error('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

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = 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(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
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()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(yield* 
const kv: KeyValueStore
kv.
KeyValueStore.size: Effect.Effect<number, PlatformError, never>
Returns the number of entries.
size)
24
})
25

26
// Provide an in-memory KeyValueStore implementation
27
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const runPromise: <void, PlatformError>(effect: Effect.Effect<void, PlatformError, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<...>
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
import { Effect } from "effect"

Effect.runPromise(Effect.succeed(1)).then(console.log)
// Output: 1
@example 
//Example: Handling a Failing Effect as a Rejected Promise
import { Effect } from "effect"
Effect.runPromise(Effect.fail("my error")).catch(console.error)
// Output:
// (FiberFailure) Error: my error
@since ― 2.0.0
runPromise(
const program: Effect.Effect<void, PlatformError, KeyValueStore>
program.
Pipeable.pipe<Effect.Effect<void, PlatformError, KeyValueStore>, Effect.Effect<void, PlatformError, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<void, PlatformError, KeyValueStore>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const provide: <KeyValueStore, never, never>(layer: Layer<KeyValueStore, never, never>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<...> (+9 overloads)
Provides the necessary Layers to an effect, removing its dependency on the
environment.
You can pass multiple layers, a Context, Runtime, or ManagedRuntime to
the effect.
@see ― provideService for providing a service to an effect.
@example 
import { Context, Effect, Layer } from "effect"

class Database extends Context.Tag("Database")<
  Database,
  { readonly query: (sql: string) => Effect.Effect<Array<unknown>> }
>() {}

const DatabaseLive = Layer.succeed(
  Database,
  {
    // Simulate a database query
    query: (sql: string) => Effect.log(`Executing query: ${sql}`).pipe(Effect.as([]))
  }
)

//      ┌─── Effect<unknown[], never, Database>
//      ▼
const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  return result
})

//      ┌─── Effect<unknown[], never, never>
//      ▼
const runnable = Effect.provide(program, DatabaseLive)

Effect.runPromise(runnable).then(console.log)
// Output:
// timestamp=... level=INFO fiber=#0 message="Executing query: SELECT * FROM users"
// []
@since ― 2.0.0
provide(
const layerMemory: Layer<KeyValueStore, never, never>@since ― 1.0.0
layerMemory)))
28
/*
29
Output:
30
0
31
1
32
{ _id: 'Option', _tag: 'Some', value: 'value' }
33
0
34
*/

Built-in Implementations

The module provides several built-in implementations of the KeyValueStore interface, available as layers, to suit different needs:

Implementation	Description
In-Memory Store	`layerMemory` provides a simple, in-memory key-value store, ideal for lightweight or testing scenarios.
File System Store	`layerFileSystem` offers a file-based store for persistent storage needs.
Schema Store	`layerSchema` enables schema-based validation for stored values, ensuring data integrity and type safety.

SchemaStore

The SchemaStore interface allows you to validate and parse values according to a defined schema. This ensures that all data stored in the key-value store adheres to the specified structure, enhancing data integrity and type safety.

Example (Using Schema Validation in KeyValueStore)

1
import {
2
  
const KeyValueStore: Tag<KeyValueStore, KeyValueStore>@since ― 1.0.0
@since ― 1.0.0
@since ― 1.0.0
KeyValueStore,
3
  
const layerMemory: Layer<KeyValueStore, never, never>@since ― 1.0.0
layerMemory
4
} from "@effect/platform/KeyValueStore"
5
import { 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect, 
import Schema
Schema } from "effect"
6

7
// Define a schema for the values
8
const 
const Person: Schema.Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}>
Person = 
import Schema
Schema.
function Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}>(fields: {
    name: typeof Schema.String;
    age: typeof Schema.Number;
}): Schema.Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}> (+1 overload)@since ― 3.10.0
Struct({
9
  
name: typeof Schema.String
name: 
import Schema
Schema.
class String
export String@since ― 3.10.0
String,
10
  
age: typeof Schema.Number
age: 
import Schema
Schema.
class Number
export Number@since ― 3.10.0
Number
11
})
12

13
const 
const program: Effect.Effect<void, PlatformError | ParseError, KeyValueStore>
program = 
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const gen: <YieldWrap<Tag<KeyValueStore, KeyValueStore>> | YieldWrap<Effect.Effect<void, PlatformError | ParseError, never>>, void>(f: (resume: Effect.Adapter) => Generator<...>) => Effect.Effect<...> (+1 overload)
Provides a way to write effectful code using generator functions, simplifying
control flow and error handling.
When to Use
Effect.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.
@example 
import { Effect } from "effect"

const addServiceCharge = (amount: number) => amount + 1

const applyDiscount = (
  total: number,
  discountRate: number
): Effect.Effect<number, Error> =>
  discountRate === 0
    ? Effect.fail(new Error("Discount rate cannot be zero"))
    : Effect.succeed(total - (total * discountRate) / 100)

const fetchTransactionAmount = Effect.promise(() => Promise.resolve(100))

const fetchDiscountRate = Effect.promise(() => Promise.resolve(5))

export const program = Effect.gen(function* () {
  const transactionAmount = yield* fetchTransactionAmount
  const discountRate = yield* fetchDiscountRate
  const discountedAmount = yield* applyDiscount(
    transactionAmount,
    discountRate
  )
  const finalAmount = addServiceCharge(discountedAmount)
  return `Final amount to charge: ${finalAmount}`
})
@since ― 2.0.0
gen(function* () {
14
  // Create a SchemaStore based on the Person schema
15
  const 
const kv: SchemaStore<{
    readonly name: string;
    readonly age: number;
}, never>
kv = (yield* 
const KeyValueStore: Tag<KeyValueStore, KeyValueStore>@since ― 1.0.0
@since ― 1.0.0
@since ― 1.0.0
KeyValueStore).
KeyValueStore.forSchema: <{
    readonly name: string;
    readonly age: number;
}, {
    readonly name: string;
    readonly age: number;
}, never>(schema: Schema.Schema<{
    readonly name: string;
    readonly age: number;
}, {
    readonly name: string;
    readonly age: number;
}, never>) => SchemaStore<...>
Create a SchemaStore for the specified schema.
forSchema(
const Person: Schema.Struct<{
    name: typeof Schema.String;
    age: typeof Schema.Number;
}>
Person)
16

17
  // Add a value that adheres to the schema
18
  const 
const value: {
    name: string;
    age: number;
}
value = { 
name: string
name: "Alice", 
age: number
age: 30 }
19
  yield* 
const kv: SchemaStore<{
    readonly name: string;
    readonly age: number;
}, never>
kv.
SchemaStore<{ readonly name: string; readonly age: number; }, never>.set: (key: string, value: {
    readonly name: string;
    readonly age: number;
}) => Effect.Effect<void, PlatformError | ParseError, never>
Sets the value of the specified key.
set("user1", 
const value: {
    name: string;
    age: number;
}
value)
20
  
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(new Error('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

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = 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(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
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()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(yield* 
const kv: SchemaStore<{
    readonly name: string;
    readonly age: number;
}, never>
kv.
SchemaStore<{ readonly name: string; readonly age: number; }, never>.size: Effect.Effect<number, PlatformError, never>
Returns the number of entries.
size)
21

22
  // Retrieve and log the value
23
  
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(new Error('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

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = 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(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void
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()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(yield* 
const kv: SchemaStore<{
    readonly name: string;
    readonly age: number;
}, never>
kv.
SchemaStore<{ readonly name: string; readonly age: number; }, never>.get: (key: string) => Effect.Effect<Option<{
    readonly name: string;
    readonly age: number;
}>, PlatformError | ParseError, never>
Returns the value of the specified key if it exists.
get("user1"))
24
})
25

26
// Use the in-memory store implementation
27
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const runPromise: <void, PlatformError | ParseError>(effect: Effect.Effect<void, PlatformError | ParseError, never>, options?: {
    readonly signal?: AbortSignal;
} | undefined) => Promise<...>
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
import { Effect } from "effect"

Effect.runPromise(Effect.succeed(1)).then(console.log)
// Output: 1
@example 
//Example: Handling a Failing Effect as a Rejected Promise
import { Effect } from "effect"
Effect.runPromise(Effect.fail("my error")).catch(console.error)
// Output:
// (FiberFailure) Error: my error
@since ― 2.0.0
runPromise(
const program: Effect.Effect<void, PlatformError | ParseError, KeyValueStore>
program.
Pipeable.pipe<Effect.Effect<void, PlatformError | ParseError, KeyValueStore>, Effect.Effect<void, PlatformError | ParseError, never>>(this: Effect.Effect<...>, ab: (_: Effect.Effect<...>) => Effect.Effect<...>): Effect.Effect<...> (+21 overloads)
pipe(
import Effect@since ― 2.0.0
@since ― 2.0.0
@since ― 2.0.0
Effect.
const provide: <KeyValueStore, never, never>(layer: Layer<KeyValueStore, never, never>) => <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<...> (+9 overloads)
Provides the necessary Layers to an effect, removing its dependency on the
environment.
You can pass multiple layers, a Context, Runtime, or ManagedRuntime to
the effect.
@see ― provideService for providing a service to an effect.
@example 
import { Context, Effect, Layer } from "effect"

class Database extends Context.Tag("Database")<
  Database,
  { readonly query: (sql: string) => Effect.Effect<Array<unknown>> }
>() {}

const DatabaseLive = Layer.succeed(
  Database,
  {
    // Simulate a database query
    query: (sql: string) => Effect.log(`Executing query: ${sql}`).pipe(Effect.as([]))
  }
)

//      ┌─── Effect<unknown[], never, Database>
//      ▼
const program = Effect.gen(function*() {
  const database = yield* Database
  const result = yield* database.query("SELECT * FROM users")
  return result
})

//      ┌─── Effect<unknown[], never, never>
//      ▼
const runnable = Effect.provide(program, DatabaseLive)

Effect.runPromise(runnable).then(console.log)
// Output:
// timestamp=... level=INFO fiber=#0 message="Executing query: SELECT * FROM users"
// []
@since ― 2.0.0
provide(
const layerMemory: Layer<KeyValueStore, never, never>@since ― 1.0.0
layerMemory)))
28
/*
29
Output:
30
1
31
{ _id: 'Option', _tag: 'Some', value: { name: 'Alice', age: 30 } }
32
*/