<A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (
self: Chunk<A>
) => Option<B>
<A>(predicate: Predicate<NoInfer<A>>): (self: Chunk<A>) => Option<A>
<A, B extends A>(self: Chunk<A>, refinement: Refinement<A, B>): Option<B>
<A>(self: Chunk<A>, predicate: Predicate<A>): Option<A>Finds the last element for which a predicate holds.
Example (Finding the last matching element)
import { Chunk, Option } from "effect"
const chunk = Chunk.make(1, 2, 3, 4, 5)
const result = Chunk.findLast(chunk, (n) => n < 4)
console.log(Option.isSome(result)) // true
console.log(Option.getOrElse(result, () => 0)) // 3
// No match found
const notFound = Chunk.findLast(chunk, (n) => n > 10)
console.log(Option.isNone(notFound)) // true
// Find last even number
const lastEven = Chunk.findLast(chunk, (n) => n % 2 === 0)
console.log(Option.getOrElse(lastEven, () => 0)) // 4export const const findLast: {
<A, B extends A>(
refinement: Refinement<NoInfer<A>, B>
): (self: Chunk<A>) => Option<B>
<A>(predicate: Predicate<NoInfer<A>>): (
self: Chunk<A>
) => Option<A>
<A, B extends A>(
self: Chunk<A>,
refinement: Refinement<A, B>
): Option<B>
<A>(
self: Chunk<A>,
predicate: Predicate<A>
): Option<A>
}
Finds the last element for which a predicate holds.
Example (Finding the last matching element)
import { Chunk, Option } from "effect"
const chunk = Chunk.make(1, 2, 3, 4, 5)
const result = Chunk.findLast(chunk, (n) => n < 4)
console.log(Option.isSome(result)) // true
console.log(Option.getOrElse(result, () => 0)) // 3
// No match found
const notFound = Chunk.findLast(chunk, (n) => n > 10)
console.log(Option.isNone(notFound)) // true
// Find last even number
const lastEven = Chunk.findLast(chunk, (n) => n % 2 === 0)
console.log(Option.getOrElse(lastEven, () => 0)) // 4
findLast: {
<function (type parameter) A in <A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (self: Chunk<A>) => Option<B>A, function (type parameter) B in <A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (self: Chunk<A>) => Option<B>B extends function (type parameter) A in <A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (self: Chunk<A>) => Option<B>A>(refinement: Refinement<NoInfer<A>, B>refinement: interface Refinement<in A, out B extends A>A predicate that also narrows the input type when it returns true.
When to use
Use when you want a runtime check that refines A to B for TypeScript,
especially when composing type guards with
compose
or safely
checking unknown values.
Details
A refinement returns a type predicate (a is B). Use it with if or
filter to narrow types.
Example (Narrowing unknown values)
import { Predicate } from "effect"
const isString: Predicate.Refinement<unknown, string> = (u): u is string => typeof u === "string"
const data: unknown = "hello"
if (isString(data)) {
console.log(data.toUpperCase())
}
Type-level utilities for working with
Refinement
types.
When to use
Use when you need to extract input and output types from refinement
signatures while writing generic helpers over refinements.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting refinement types)
import { Predicate } from "effect"
type IsString = Predicate.Refinement<unknown, string>
type Input = Predicate.Refinement.In<IsString>
type Output = Predicate.Refinement.Out<IsString>
Refinement<type NoInfer<A> = [A][A extends any ? 0 : never]Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) A in <A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (self: Chunk<A>) => Option<B>A>, function (type parameter) B in <A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (self: Chunk<A>) => Option<B>B>): (self: Chunk<A>(parameter) self: {
length: number;
right: Chunk<A>;
left: Chunk<A>;
backing: Backing<A>;
depth: number;
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
interface Chunk<out A>A Chunk is an immutable, ordered collection optimized for efficient concatenation and access patterns.
Example (Inspecting chunk values)
import { Chunk } from "effect"
const chunk: Chunk.Chunk<number> = Chunk.make(1, 2, 3)
console.log(chunk.length) // 3
console.log(Chunk.toArray(chunk)) // [1, 2, 3]
A namespace containing utility types for Chunk operations.
Example (Working with Chunk utility types)
import type { Chunk } from "effect"
// Extract the element type from a Chunk
declare const chunk: Chunk.Chunk<string>
type ElementType = Chunk.Chunk.Infer<typeof chunk> // string
// Create a preserving non-emptiness
declare const nonEmptyChunk: Chunk.NonEmptyChunk<number>
type WithString = Chunk.Chunk.With<typeof nonEmptyChunk, string> // Chunk.NonEmptyChunk<string>
Chunk<function (type parameter) A in <A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (self: Chunk<A>) => Option<B>A>) => type Option<A> = O.None<A> | O.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) B in <A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (self: Chunk<A>) => Option<B>B>
<function (type parameter) A in <A>(predicate: Predicate<NoInfer<A>>): (self: Chunk<A>) => Option<A>A>(predicate: Predicate<NoInfer<A>>predicate: interface Predicate<in A>A function that decides whether a value of type A satisfies a condition.
When to use
Use when you want a reusable boolean check for A, especially when you plan
to combine checks with
and
/
or
or pass a predicate to arrays
and iterables.
Details
A predicate returns true or false and never throws by itself. It does not
narrow types unless you use Refinement.
Example (Defining a predicate)
import { Predicate } from "effect"
const isPositive: Predicate.Predicate<number> = (n) => n > 0
console.log(isPositive(1))
Type-level utilities for working with
Predicate
types.
When to use
Use when you need to extract input types from predicate signatures while
writing generic helpers over predicate types.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting predicate input)
import { Predicate } from "effect"
type IsString = Predicate.Predicate<string>
type Input = Predicate.Predicate.In<IsString>
Predicate<type NoInfer<A> = [A][A extends any ? 0 : never]Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) A in <A>(predicate: Predicate<NoInfer<A>>): (self: Chunk<A>) => Option<A>A>>): (self: Chunk<A>(parameter) self: {
length: number;
right: Chunk<A>;
left: Chunk<A>;
backing: Backing<A>;
depth: number;
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
interface Chunk<out A>A Chunk is an immutable, ordered collection optimized for efficient concatenation and access patterns.
Example (Inspecting chunk values)
import { Chunk } from "effect"
const chunk: Chunk.Chunk<number> = Chunk.make(1, 2, 3)
console.log(chunk.length) // 3
console.log(Chunk.toArray(chunk)) // [1, 2, 3]
A namespace containing utility types for Chunk operations.
Example (Working with Chunk utility types)
import type { Chunk } from "effect"
// Extract the element type from a Chunk
declare const chunk: Chunk.Chunk<string>
type ElementType = Chunk.Chunk.Infer<typeof chunk> // string
// Create a preserving non-emptiness
declare const nonEmptyChunk: Chunk.NonEmptyChunk<number>
type WithString = Chunk.Chunk.With<typeof nonEmptyChunk, string> // Chunk.NonEmptyChunk<string>
Chunk<function (type parameter) A in <A>(predicate: Predicate<NoInfer<A>>): (self: Chunk<A>) => Option<A>A>) => type Option<A> = O.None<A> | O.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) A in <A>(predicate: Predicate<NoInfer<A>>): (self: Chunk<A>) => Option<A>A>
<function (type parameter) A in <A, B extends A>(self: Chunk<A>, refinement: Refinement<A, B>): Option<B>A, function (type parameter) B in <A, B extends A>(self: Chunk<A>, refinement: Refinement<A, B>): Option<B>B extends function (type parameter) A in <A, B extends A>(self: Chunk<A>, refinement: Refinement<A, B>): Option<B>A>(self: Chunk<A>(parameter) self: {
length: number;
right: Chunk<A>;
left: Chunk<A>;
backing: Backing<A>;
depth: number;
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
interface Chunk<out A>A Chunk is an immutable, ordered collection optimized for efficient concatenation and access patterns.
Example (Inspecting chunk values)
import { Chunk } from "effect"
const chunk: Chunk.Chunk<number> = Chunk.make(1, 2, 3)
console.log(chunk.length) // 3
console.log(Chunk.toArray(chunk)) // [1, 2, 3]
A namespace containing utility types for Chunk operations.
Example (Working with Chunk utility types)
import type { Chunk } from "effect"
// Extract the element type from a Chunk
declare const chunk: Chunk.Chunk<string>
type ElementType = Chunk.Chunk.Infer<typeof chunk> // string
// Create a preserving non-emptiness
declare const nonEmptyChunk: Chunk.NonEmptyChunk<number>
type WithString = Chunk.Chunk.With<typeof nonEmptyChunk, string> // Chunk.NonEmptyChunk<string>
Chunk<function (type parameter) A in <A, B extends A>(self: Chunk<A>, refinement: Refinement<A, B>): Option<B>A>, refinement: Refinement<A, B>refinement: interface Refinement<in A, out B extends A>A predicate that also narrows the input type when it returns true.
When to use
Use when you want a runtime check that refines A to B for TypeScript,
especially when composing type guards with
compose
or safely
checking unknown values.
Details
A refinement returns a type predicate (a is B). Use it with if or
filter to narrow types.
Example (Narrowing unknown values)
import { Predicate } from "effect"
const isString: Predicate.Refinement<unknown, string> = (u): u is string => typeof u === "string"
const data: unknown = "hello"
if (isString(data)) {
console.log(data.toUpperCase())
}
Type-level utilities for working with
Refinement
types.
When to use
Use when you need to extract input and output types from refinement
signatures while writing generic helpers over refinements.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting refinement types)
import { Predicate } from "effect"
type IsString = Predicate.Refinement<unknown, string>
type Input = Predicate.Refinement.In<IsString>
type Output = Predicate.Refinement.Out<IsString>
Refinement<function (type parameter) A in <A, B extends A>(self: Chunk<A>, refinement: Refinement<A, B>): Option<B>A, function (type parameter) B in <A, B extends A>(self: Chunk<A>, refinement: Refinement<A, B>): Option<B>B>): type Option<A> = O.None<A> | O.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) B in <A, B extends A>(self: Chunk<A>, refinement: Refinement<A, B>): Option<B>B>
<function (type parameter) A in <A>(self: Chunk<A>, predicate: Predicate<A>): Option<A>A>(self: Chunk<A>(parameter) self: {
length: number;
right: Chunk<A>;
left: Chunk<A>;
backing: Backing<A>;
depth: number;
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
interface Chunk<out A>A Chunk is an immutable, ordered collection optimized for efficient concatenation and access patterns.
Example (Inspecting chunk values)
import { Chunk } from "effect"
const chunk: Chunk.Chunk<number> = Chunk.make(1, 2, 3)
console.log(chunk.length) // 3
console.log(Chunk.toArray(chunk)) // [1, 2, 3]
A namespace containing utility types for Chunk operations.
Example (Working with Chunk utility types)
import type { Chunk } from "effect"
// Extract the element type from a Chunk
declare const chunk: Chunk.Chunk<string>
type ElementType = Chunk.Chunk.Infer<typeof chunk> // string
// Create a preserving non-emptiness
declare const nonEmptyChunk: Chunk.NonEmptyChunk<number>
type WithString = Chunk.Chunk.With<typeof nonEmptyChunk, string> // Chunk.NonEmptyChunk<string>
Chunk<function (type parameter) A in <A>(self: Chunk<A>, predicate: Predicate<A>): Option<A>A>, predicate: Predicate<A>predicate: interface Predicate<in A>A function that decides whether a value of type A satisfies a condition.
When to use
Use when you want a reusable boolean check for A, especially when you plan
to combine checks with
and
/
or
or pass a predicate to arrays
and iterables.
Details
A predicate returns true or false and never throws by itself. It does not
narrow types unless you use Refinement.
Example (Defining a predicate)
import { Predicate } from "effect"
const isPositive: Predicate.Predicate<number> = (n) => n > 0
console.log(isPositive(1))
Type-level utilities for working with
Predicate
types.
When to use
Use when you need to extract input types from predicate signatures while
writing generic helpers over predicate types.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting predicate input)
import { Predicate } from "effect"
type IsString = Predicate.Predicate<string>
type Input = Predicate.Predicate.In<IsString>
Predicate<function (type parameter) A in <A>(self: Chunk<A>, predicate: Predicate<A>): Option<A>A>): type Option<A> = O.None<A> | O.Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) A in <A>(self: Chunk<A>, predicate: Predicate<A>): Option<A>A>
} = import RARA.findLast