<
R,
const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>,
Ret,
Fn extends (_: Types.WhenMatch<R, P>) => Ret
>(
pattern: P,
f: Fn
): <I, F, A, Pr>(
self: Matcher<I, F, R, A, Pr, Ret>
) => Matcher<
I,
Types.AddWithout<F, Types.PForExclude<P>>,
Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>,
A | ReturnType<Fn>,
Pr,
Ret
>Defines a condition for matching values.
When to use
Use to add one positive pattern case to a Match.type or Match.value
pipeline when a direct value, predicate, or structured object pattern should
run a handler for matching input.
Details
Supports both direct value comparisons and predicate functions. If the pattern matches, the associated function is executed and the matched input is removed from the remaining cases tracked by the matcher.
Example (Matching with values and predicates)
import { Match } from "effect"
// Create a matcher for objects with an "age" property
const match = Match.type<{ age: number }>().pipe(
// Match when age is greater than 18
Match.when(
{ age: (age: number) => age > 18 },
(user: { age: number }) => `Age: ${user.age}`
),
// Match when age is exactly 18
Match.when({ age: 18 }, () => "You can vote"),
// Fallback case for all other ages
Match.orElse((user: { age: number }) => `${user.age} is too young`)
)
console.log(match({ age: 20 }))
// Output: "Age: 20"
console.log(match({ age: 18 }))
// Output: "You can vote"
console.log(match({ age: 4 }))
// Output: "4 is too young"Source effect/Match.ts:53018 lines
export const const when: <
R,
P extends
| Types.PatternPrimitive<R>
| Types.PatternBase<R>,
Ret,
Fn extends (_: Types.WhenMatch<R, P>) => Ret
>(
pattern: P,
f: Fn
) => <I, F, A, Pr>(
self: Matcher<I, F, R, A, Pr, Ret>
) => Matcher<
I,
Types.AddWithout<F, Types.PForExclude<P>>,
Types.ApplyFilters<
I,
Types.AddWithout<F, Types.PForExclude<P>>
>,
A | ReturnType<Fn>,
Pr,
Ret
>
Defines a condition for matching values.
When to use
Use to add one positive pattern case to a Match.type or Match.value
pipeline when a direct value, predicate, or structured object pattern should
run a handler for matching input.
Details
Supports both direct value comparisons and predicate functions. If the
pattern matches, the associated function is executed and the matched input is
removed from the remaining cases tracked by the matcher.
Example (Matching with values and predicates)
import { Match } from "effect"
// Create a matcher for objects with an "age" property
const match = Match.type<{ age: number }>().pipe(
// Match when age is greater than 18
Match.when(
{ age: (age: number) => age > 18 },
(user: { age: number }) => `Age: ${user.age}`
),
// Match when age is exactly 18
Match.when({ age: 18 }, () => "You can vote"),
// Fallback case for all other ages
Match.orElse((user: { age: number }) => `${user.age} is too young`)
)
console.log(match({ age: 20 }))
// Output: "Age: 20"
console.log(match({ age: 18 }))
// Output: "You can vote"
console.log(match({ age: 4 }))
// Output: "4 is too young"
when: <
function (type parameter) R in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>R,
const function (type parameter) P in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>P extends Types.type Types.PatternPrimitive<A> = A | Types.PredicateA<A> | SafeRefinement<any, any>Defines primitive patterns that can match simple values.
Details
This type represents the building blocks of pattern matching: predicates,
literal values, and safe refinements. These are the atomic patterns that
can be composed into more complex matching logic.
PatternPrimitive<function (type parameter) R in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>R> | Types.type Types.PatternBase<A> = A extends readonly (infer _T)[] ? readonly any[] | Types.PatternPrimitive<A> : A extends Record<string, any> ? Partial<{ [K in keyof A]: Types.PatternPrimitive<A[K] & {}> | Types.PatternBase<A[K] & {}>; }> : neverDefines the structure for complex object and array patterns.
Details
This type represents patterns that can match against complex data structures
like objects and arrays. It supports nested pattern matching and partial
object matching, enabling sophisticated pattern compositions.
Example (Describing complex object patterns)
import { Match } from "effect"
// PatternBase enables complex object patterns
type UserPattern = Match.Types.PatternBase<{
name: string
age: number
role: "admin" | "user"
}>
// Allows: { name?: string | Predicate, age?: number | Predicate, ... }
// Example usage:
Match.value({ name: "Alice", age: 30, role: "admin" as const }).pipe(
Match.when(
{ age: (n: number) => n >= 18, role: "admin" },
(user: { name: string; age: number; role: "admin" }) =>
`Admin: ${user.name}`
),
Match.orElse(() => "Not an adult admin")
)
PatternBase<function (type parameter) R in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>R>,
function (type parameter) Ret in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Ret,
function (type parameter) Fn in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Fn extends (_: Types.WhenMatch<R, P>_: Types.type Types.WhenMatch<R, P> = [0] extends [1 & R] ? Types.ResolvePred<P, any> : P extends SafeRefinement<infer SP, never> ? SP : P extends Predicate.Refinement<infer _R, infer RP extends infer _R> ? [Extract<R, RP>] extends [infer X] ? [X] extends [never] ? RP : X : never : P extends Types.PredicateA<infer PP> ? PP : Types.ExtractMatch<R, P>Computes the matched type when a pattern P is applied to type R.
Details
This utility type determines what type a value will have after successfully
matching against a pattern. It handles refinements, predicates, and complex
object patterns to provide accurate type narrowing.
Example (Computing matched types)
import type { Match } from "effect"
// WhenMatch computes the narrowed type after pattern matching
type StringMatch = Match.Types.WhenMatch<string | number, typeof Match.string>
// Result: string
type ObjectMatch = Match.Types.WhenMatch<
{ type: "user"; name: string } | {
type: "admin"
permissions: Array<string>
},
{ type: "user" }
>
// Result: { type: "user"; name: string }
WhenMatch<function (type parameter) R in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>R, function (type parameter) P in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>P>) => function (type parameter) Ret in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Ret
>(
pattern: const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>pattern: function (type parameter) P in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>P,
f: Fn extends (_: Types.WhenMatch<R, P>) => Retf: function (type parameter) Fn in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Fn
) => <function (type parameter) I in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>I, function (type parameter) F in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>F, function (type parameter) A in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>A, function (type parameter) Pr in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Pr>(
self: Matcher<I, F, R, A, Pr, Ret>self: type Matcher<
Input,
Filters,
RemainingApplied,
Result,
Provided,
Return = any
> =
| TypeMatcher<
Input,
Filters,
RemainingApplied,
Result,
Return
>
| ValueMatcher<
Input,
Filters,
RemainingApplied,
Result,
Provided,
Return
>
Union type for matchers created by Match.type and Match.value.
Details
A Matcher carries the input type, accumulated filters, remaining cases,
result type, and, for value matchers, the provided value being matched.
Example (Matching string and number values)
import { Match } from "effect"
// Simulated dynamic input that can be a string or a number
const input: string | number = "some input"
// ┌─── string
// ▼
const result = Match.value(input).pipe(
// Match if the value is a number
Match.when(Match.number, (n) => `number: ${n}`),
// Match if the value is a string
Match.when(Match.string, (s) => `string: ${s}`),
// Ensure all possible cases are covered
Match.exhaustive
)
console.log(result)
// Output: "string: some input"
Matcher<function (type parameter) I in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>I, function (type parameter) F in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>F, function (type parameter) R in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>R, function (type parameter) A in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>A, function (type parameter) Pr in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Pr, function (type parameter) Ret in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Ret>
) => type Matcher<
Input,
Filters,
RemainingApplied,
Result,
Provided,
Return = any
> =
| TypeMatcher<
Input,
Filters,
RemainingApplied,
Result,
Return
>
| ValueMatcher<
Input,
Filters,
RemainingApplied,
Result,
Provided,
Return
>
Union type for matchers created by Match.type and Match.value.
Details
A Matcher carries the input type, accumulated filters, remaining cases,
result type, and, for value matchers, the provided value being matched.
Example (Matching string and number values)
import { Match } from "effect"
// Simulated dynamic input that can be a string or a number
const input: string | number = "some input"
// ┌─── string
// ▼
const result = Match.value(input).pipe(
// Match if the value is a number
Match.when(Match.number, (n) => `number: ${n}`),
// Match if the value is a string
Match.when(Match.string, (s) => `string: ${s}`),
// Ensure all possible cases are covered
Match.exhaustive
)
console.log(result)
// Output: "string: some input"
Matcher<
function (type parameter) I in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>I,
Types.type Types.AddWithout<A, X> = [A] extends [Types.Without<infer WX>] ? Types.Without<X | WX> : [A] extends [Types.Only<infer OX>] ? Types.Only<Exclude<OX, X>> : neverAdds a type to the exclusion filter, expanding what should be filtered out.
Details
This utility type manages the accumulation of excluded types during
pattern matching. When multiple exclusions are applied, it combines
them into a single filter representation.
Example (Accumulating excluded types)
import { Match } from "effect"
// AddWithout is used when combining multiple exclusions:
Match.type<string | number | boolean | null>().pipe(
Match.not(Match.string, () => "not string"),
Match.not(Match.number, () => "not number"),
// Type system uses AddWithout to combine exclusions
Match.orElse(() => "was string or number")
)
AddWithout<function (type parameter) F in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>F, Types.type Types.PForExclude<P> = [Types.SafeRefinementR<Types.ToSafeRefinement<P>>] extends [infer X] ? X : neverComputes the excluded type when a pattern P is used for exclusion.
Details
This utility type determines what should be excluded from a union type
when a pattern is used in filtering operations. It transforms patterns
into their exclusion-safe representations.
Example (Computing excluded patterns)
import type { Match } from "effect"
// PForExclude computes what to exclude from type operations
type ExcludeString = Match.Types.PForExclude<typeof Match.string>
// Used internally to filter out string types
type ExcludeObject = Match.Types.PForExclude<{ type: "admin" }>
// Used internally to filter out admin objects
PForExclude<function (type parameter) P in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>P>>,
Types.type Types.ApplyFilters<I, A> = A extends Types.Only<infer X> ? X : A extends Types.Without<infer X> ? Exclude<I, X> : neverApplies accumulated filters to an input type, producing the final narrowed type.
Details
This utility type takes the collected inclusion/exclusion filters and
applies them to the input type to compute the final narrowed result.
It's the culmination of the type-level filtering process.
Example (Applying accumulated filters)
import type { Match } from "effect"
// ApplyFilters computes the final narrowed type:
type Result = Match.Types.ApplyFilters<
string | number | boolean,
Match.Types.Only<string>
>
// Result: string
type ExclusionResult = Match.Types.ApplyFilters<
string | number | boolean,
Match.Types.Without<string>
>
// Result: number | boolean
ApplyFilters<function (type parameter) I in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>I, Types.type Types.AddWithout<A, X> = [A] extends [Types.Without<infer WX>] ? Types.Without<X | WX> : [A] extends [Types.Only<infer OX>] ? Types.Only<Exclude<OX, X>> : neverAdds a type to the exclusion filter, expanding what should be filtered out.
Details
This utility type manages the accumulation of excluded types during
pattern matching. When multiple exclusions are applied, it combines
them into a single filter representation.
Example (Accumulating excluded types)
import { Match } from "effect"
// AddWithout is used when combining multiple exclusions:
Match.type<string | number | boolean | null>().pipe(
Match.not(Match.string, () => "not string"),
Match.not(Match.number, () => "not number"),
// Type system uses AddWithout to combine exclusions
Match.orElse(() => "was string or number")
)
AddWithout<function (type parameter) F in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>F, Types.type Types.PForExclude<P> = [Types.SafeRefinementR<Types.ToSafeRefinement<P>>] extends [infer X] ? X : neverComputes the excluded type when a pattern P is used for exclusion.
Details
This utility type determines what should be excluded from a union type
when a pattern is used in filtering operations. It transforms patterns
into their exclusion-safe representations.
Example (Computing excluded patterns)
import type { Match } from "effect"
// PForExclude computes what to exclude from type operations
type ExcludeString = Match.Types.PForExclude<typeof Match.string>
// Used internally to filter out string types
type ExcludeObject = Match.Types.PForExclude<{ type: "admin" }>
// Used internally to filter out admin objects
PForExclude<function (type parameter) P in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>P>>>,
function (type parameter) A in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>A | type ReturnType<
T extends (...args: any) => any
> = T extends (...args: any) => infer R ? R : any
Obtain the return type of a function type
ReturnType<function (type parameter) Fn in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Fn>,
function (type parameter) Pr in <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>): Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Pr,
function (type parameter) Ret in <R, const P extends Types.PatternPrimitive<R> | Types.PatternBase<R>, Ret, Fn extends (_: Types.WhenMatch<R, P>) => Ret>(pattern: P, f: Fn): <I, F, A, Pr>(self: Matcher<I, F, R, A, Pr, Ret>) => Matcher<I, Types.AddWithout<F, Types.PForExclude<P>>, Types.ApplyFilters<I, Types.AddWithout<F, Types.PForExclude<P>>>, A | ReturnType<Fn>, Pr, Ret>Ret
> = import internalinternal.const when: <
R,
P extends
| Types.PatternPrimitive<R>
| Types.PatternBase<R>,
Ret,
Fn extends (_: Types.WhenMatch<R, P>) => Ret
>(
pattern: P,
f: Fn
) => <I, F, A, Pr>(
self: Matcher<I, F, R, A, Pr, Ret>
) => Matcher<
I,
Types.AddWithout<F, Types.PForExclude<P>>,
Types.ApplyFilters<
I,
Types.AddWithout<F, Types.PForExclude<P>>
>,
A | ReturnType<Fn>,
Pr,
Ret
>