<K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <
OutElem,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>
) => Channel<
OutElem,
| Types.ExcludeTag<OutErr, K>
| Types.ReasonOf<Types.ExtractTag<OutErr, K>>,
OutDone,
InElem,
InErr,
InDone,
Env
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
K extends TagsWithReason<OutErr>
>(
self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>,
errorTag: K
): Channel<
OutElem,
| Types.ExcludeTag<OutErr, K>
| Types.ReasonOf<Types.ExtractTag<OutErr, K>>,
OutDone,
InElem,
InErr,
InDone,
Env
>Promotes nested reason errors into the channel error, replacing the parent error.
Example (Promoting nested reasons)
import { Channel, Data } from "effect"
class RateLimitError extends Data.TaggedError("RateLimitError")<{
retryAfter: number
}> {}
class QuotaExceededError extends Data.TaggedError("QuotaExceededError")<{
limit: number
}> {}
class AiError extends Data.TaggedError("AiError")<{
reason: RateLimitError | QuotaExceededError
}> {}
const channel = Channel.fail(
new AiError({ reason: new RateLimitError({ retryAfter: 60 }) })
)
const unwrapped = channel.pipe(Channel.unwrapReason("AiError"))error handling
Source effect/Channel.ts:548565 lines
export const const unwrapReason: {
<K extends TagsWithReason<OutErr>, OutErr>(
errorTag: K
): <
OutElem,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
OutElem,
| Types.ExcludeTag<OutErr, K>
| Types.ReasonOf<Types.ExtractTag<OutErr, K>>,
OutDone,
InElem,
InErr,
InDone,
Env
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
K extends TagsWithReason<OutErr>
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
errorTag: K
): Channel<
OutElem,
| Types.ExcludeTag<OutErr, K>
| Types.ReasonOf<Types.ExtractTag<OutErr, K>>,
OutDone,
InElem,
InErr,
InDone,
Env
>
}
Promotes nested reason errors into the channel error, replacing the parent error.
Example (Promoting nested reasons)
import { Channel, Data } from "effect"
class RateLimitError extends Data.TaggedError("RateLimitError")<{
retryAfter: number
}> {}
class QuotaExceededError extends Data.TaggedError("QuotaExceededError")<{
limit: number
}> {}
class AiError extends Data.TaggedError("AiError")<{
reason: RateLimitError | QuotaExceededError
}> {}
const channel = Channel.fail(
new AiError({ reason: new RateLimitError({ retryAfter: 60 }) })
)
const unwrapped = channel.pipe(Channel.unwrapReason("AiError"))
unwrapReason: {
<
function (type parameter) K in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K extends type TagsWithReason<E> = {
[T in Types.Tags<E>]: Types.ReasonTags<
Types.ExtractTag<E, T>
> extends never
? never
: T
}[Types.Tags<E>]
function (type parameter) OutErr in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr>,
function (type parameter) OutErr in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr
>(
errorTag: K extends TagsWithReason<OutErr>errorTag: function (type parameter) K in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K
): <function (type parameter) OutElem in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutDone in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(parameter) self: {
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; <…;
}
interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env>
) => interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<
function (type parameter) OutElem in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem,
import TypesTypes.type ExcludeTag<
E,
K extends string
> = E extends {
readonly _tag: K
}
? never
: E
Excludes members of a tagged union by their _tag value.
When to use
Use to remove tagged-union members whose _tag matches a specific value in
type-level code.
Details
Non-tagged members of the union are preserved.
Example (Removing a variant)
import type { Types } from "effect"
type MyError =
| { readonly _tag: "NotFound"; readonly id: string }
| { readonly _tag: "Timeout"; readonly ms: number }
| string
type WithoutTimeout = Types.ExcludeTag<MyError, "Timeout">
// { readonly _tag: "NotFound"; readonly id: string } | string
ExcludeTag<function (type parameter) OutErr in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) K in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K> | import TypesTypes.type ReasonOf<E> = E extends {
readonly reason: infer R
}
? R
: never
Extracts the reason type from an error that has a reason field.
When to use
Use when an error type stores nested sub-errors in a reason field and you
need that field's full union type as a standalone type.
Details
Returns never if E has no reason field.
Example (Extracting reason types)
import type { Types } from "effect"
type RateLimitError = { readonly _tag: "RateLimitError"; readonly retryAfter: number }
type QuotaError = { readonly _tag: "QuotaError"; readonly limit: number }
type ApiError = { readonly _tag: "ApiError"; readonly reason: RateLimitError | QuotaError }
type Reasons = Types.ReasonOf<ApiError>
// RateLimitError | QuotaError
ReasonOf<import TypesTypes.type ExtractTag<
E,
K extends string
> = E extends {
readonly _tag: infer T
}
? K extends T
? E
: never
: never
Extracts a specific member of a tagged union by its _tag value.
When to use
Use to select tagged-union members whose _tag matches a specific value in
type-level code.
Details
Returns never if no member matches the tag.
Example (Extracting a variant)
import type { Types } from "effect"
type MyError =
| { readonly _tag: "NotFound"; readonly id: string }
| { readonly _tag: "Timeout"; readonly ms: number }
type TimeoutError = Types.ExtractTag<MyError, "Timeout">
// { readonly _tag: "Timeout"; readonly ms: number }
ExtractTag<function (type parameter) OutErr in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) K in <K extends TagsWithReason<OutErr>, OutErr>(errorTag: K): <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K>>,
function (type parameter) OutDone in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone,
function (type parameter) InElem in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem,
function (type parameter) InErr in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr,
function (type parameter) InDone in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone,
function (type parameter) Env in <OutElem, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env
>
<
function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem,
function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr,
function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone,
function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem,
function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr,
function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone,
function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env,
function (type parameter) K in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K extends type TagsWithReason<E> = {
[T in Types.Tags<E>]: Types.ReasonTags<
Types.ExtractTag<E, T>
> extends never
? never
: T
}[Types.Tags<E>]
function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr>
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(parameter) self: {
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; <…;
}
interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env>,
errorTag: K extends TagsWithReason<OutErr>errorTag: function (type parameter) K in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K
): interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<
function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem,
import TypesTypes.type ExcludeTag<
E,
K extends string
> = E extends {
readonly _tag: K
}
? never
: E
Excludes members of a tagged union by their _tag value.
When to use
Use to remove tagged-union members whose _tag matches a specific value in
type-level code.
Details
Non-tagged members of the union are preserved.
Example (Removing a variant)
import type { Types } from "effect"
type MyError =
| { readonly _tag: "NotFound"; readonly id: string }
| { readonly _tag: "Timeout"; readonly ms: number }
| string
type WithoutTimeout = Types.ExcludeTag<MyError, "Timeout">
// { readonly _tag: "NotFound"; readonly id: string } | string
ExcludeTag<function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) K in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K> | import TypesTypes.type ReasonOf<E> = E extends {
readonly reason: infer R
}
? R
: never
Extracts the reason type from an error that has a reason field.
When to use
Use when an error type stores nested sub-errors in a reason field and you
need that field's full union type as a standalone type.
Details
Returns never if E has no reason field.
Example (Extracting reason types)
import type { Types } from "effect"
type RateLimitError = { readonly _tag: "RateLimitError"; readonly retryAfter: number }
type QuotaError = { readonly _tag: "QuotaError"; readonly limit: number }
type ApiError = { readonly _tag: "ApiError"; readonly reason: RateLimitError | QuotaError }
type Reasons = Types.ReasonOf<ApiError>
// RateLimitError | QuotaError
ReasonOf<import TypesTypes.type ExtractTag<
E,
K extends string
> = E extends {
readonly _tag: infer T
}
? K extends T
? E
: never
: never
Extracts a specific member of a tagged union by its _tag value.
When to use
Use to select tagged-union members whose _tag matches a specific value in
type-level code.
Details
Returns never if no member matches the tag.
Example (Extracting a variant)
import type { Types } from "effect"
type MyError =
| { readonly _tag: "NotFound"; readonly id: string }
| { readonly _tag: "Timeout"; readonly ms: number }
type TimeoutError = Types.ExtractTag<MyError, "Timeout">
// { readonly _tag: "Timeout"; readonly ms: number }
ExtractTag<function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) K in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K>>,
function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone,
function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem,
function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr,
function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone,
function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env
>
} = dual<(...args: Array<any>) => any, <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>>(arity: 2, body: <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>): ((...args: Array<any>) => any) & (<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K) => Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>) (+1 overload)Creates a function that can be called in data-first style or data-last
(pipe-friendly) style.
When to use
Use to expose one implementation through both direct and pipe-friendly
call styles.
Details
Pass either the arity of the uncurried function or a predicate that decides
whether the current call is data-first. Arity is the common case. Use a
predicate when optional arguments make arity ambiguous.
Example (Selecting data-first or data-last style by arity)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(2, (self, that) => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Defining overloads with call signatures)
import { Function, pipe } from "effect"
const sum: {
(that: number): (self: number) => number
(self: number, that: number): number
} = Function.dual(2, (self: number, that: number): number => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Selecting data-first or data-last style with a predicate)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(
(args) => args.length === 2,
(self, that) => self + that
)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
dual(2, <
function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem,
function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr,
function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone,
function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem,
function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr,
function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone,
function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env,
function (type parameter) K in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K extends type TagsWithReason<E> = {
[T in Types.Tags<E>]: Types.ReasonTags<
Types.ExtractTag<E, T>
> extends never
? never
: T
}[Types.Tags<E>]
function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr>
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(parameter) self: {
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; <…;
}
interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env>,
errorTag: K extends TagsWithReason<OutErr>errorTag: function (type parameter) K in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K
): interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<
function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutElem,
import TypesTypes.type ExcludeTag<
E,
K extends string
> = E extends {
readonly _tag: K
}
? never
: E
Excludes members of a tagged union by their _tag value.
When to use
Use to remove tagged-union members whose _tag matches a specific value in
type-level code.
Details
Non-tagged members of the union are preserved.
Example (Removing a variant)
import type { Types } from "effect"
type MyError =
| { readonly _tag: "NotFound"; readonly id: string }
| { readonly _tag: "Timeout"; readonly ms: number }
| string
type WithoutTimeout = Types.ExcludeTag<MyError, "Timeout">
// { readonly _tag: "NotFound"; readonly id: string } | string
ExcludeTag<function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) K in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K> | import TypesTypes.type ReasonOf<E> = E extends {
readonly reason: infer R
}
? R
: never
Extracts the reason type from an error that has a reason field.
When to use
Use when an error type stores nested sub-errors in a reason field and you
need that field's full union type as a standalone type.
Details
Returns never if E has no reason field.
Example (Extracting reason types)
import type { Types } from "effect"
type RateLimitError = { readonly _tag: "RateLimitError"; readonly retryAfter: number }
type QuotaError = { readonly _tag: "QuotaError"; readonly limit: number }
type ApiError = { readonly _tag: "ApiError"; readonly reason: RateLimitError | QuotaError }
type Reasons = Types.ReasonOf<ApiError>
// RateLimitError | QuotaError
ReasonOf<import TypesTypes.type ExtractTag<
E,
K extends string
> = E extends {
readonly _tag: infer T
}
? K extends T
? E
: never
: never
Extracts a specific member of a tagged union by its _tag value.
When to use
Use to select tagged-union members whose _tag matches a specific value in
type-level code.
Details
Returns never if no member matches the tag.
Example (Extracting a variant)
import type { Types } from "effect"
type MyError =
| { readonly _tag: "NotFound"; readonly id: string }
| { readonly _tag: "Timeout"; readonly ms: number }
type TimeoutError = Types.ExtractTag<MyError, "Timeout">
// { readonly _tag: "Timeout"; readonly ms: number }
ExtractTag<function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) K in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>K>>,
function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>OutDone,
function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InElem,
function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InErr,
function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>InDone,
function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, K extends TagsWithReason<OutErr>>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, errorTag: K): Channel<OutElem, Types.ExcludeTag<OutErr, K> | Types.ReasonOf<Types.ExtractTag<OutErr, K>>, OutDone, InElem, InErr, InDone, Env>Env
> =>
const catchFilter: {
<
OutErr,
EB,
X,
OutElem1,
OutErr1,
OutDone1,
InElem1,
InErr1,
InDone1,
Env1,
OutElem2 = Types.unassigned,
OutErr2 = never,
OutDone2 = never,
InElem2 = unknown,
InErr2 = unknown,
InDone2 = unknown,
Env2 = never
>(
filter: Filter.Filter<OutErr, EB, X>,
f: (
failure: EB
) => Channel<
OutElem1,
OutErr1,
OutDone1,
InElem1,
InErr1,
InDone1,
Env1
>,
orElse?:
| ((
failure: X
) => Channel<
OutElem2,
OutErr2,
OutDone2,
InElem2,
InErr2,
InDone2,
Env2
>)
| undefined
): <
OutElem,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
| OutElem
| OutElem1
| Exclude<OutElem2, Types.unassigned>,
| OutErr1
| OutErr2
| (OutElem2 extends Types.unassigned
? X
: never),
OutDone | OutDone1 | OutDone2,
InElem & InElem1 & InElem2,
InErr & InErr1 & InErr2,
InDone & InDone1 & InDone2,
Env | Env1 | Env2
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
EB,
X,
OutElem1,
OutErr1,
OutDone1,
InElem1,
InErr1,
InDone1,
Env1,
OutElem2 = Types.unassigned,
OutErr2 = never,
OutDone2 = never,
InElem2 = unknown,
InErr2 = unknown,
InDone2 = unknown,
Env2 = never
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
filter: Filter.Filter<OutErr, EB, X>,
f: (
failure: EB
) => Channel<
OutElem1,
OutErr1,
OutDone1,
InElem1,
InErr1,
InDone1,
Env1
>,
orElse?:
| ((
failure: X
) => Channel<
OutElem2,
OutErr2,
OutDone2,
InElem2,
InErr2,
InDone2,
Env2
>)
| undefined
): Channel<
| OutElem
| OutElem1
| Exclude<OutElem2, Types.unassigned>,
| OutErr1
| OutErr2
| (OutElem2 extends Types.unassigned
? X
: never),
OutDone | OutDone1 | OutDone2,
InElem & InElem1 & InElem2,
InErr & InErr1 & InErr2,
InDone & InDone1 & InDone2,
Env | Env1 | Env2
>
}
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(parameter) self: {
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; <…;
}
error: OutErrerror) =>
isTagged<K>(self: unknown, tag: K): self is {
_tag: K;
} (+1 overload)
Checks whether a value has a _tag property equal to the given tag.
When to use
Use when you model tagged unions with a _tag field and want a quick
Predicate guard for tagged values.
Details
Uses hasProperty and strict equality on _tag.
Example (Guarding tagged values)
import { Predicate } from "effect"
const isOk = Predicate.isTagged("Ok")
console.log(isOk({ _tag: "Ok", value: 1 }))
isTagged(error: OutErrerror, errorTag: K extends TagsWithReason<OutErr>errorTag) && hasProperty<"reason">(self: unknown, property: "reason"): self is { [K in "reason"]: unknown; } (+1 overload)Checks whether a value has a given property key.
When to use
Use when you need a Predicate guard for property access on unknown
values with a simple structural object check.
Details
Uses the in operator and isObjectKeyword. This does not check property
value types.
Example (Guarding object properties)
import { Predicate } from "effect"
const hasName = Predicate.hasProperty("name")
const data: unknown = { name: "Ada" }
if (hasName(data)) {
console.log(data.name)
}
hasProperty(error: OutErr & {
_tag: K
}
import ResultResult.const succeed: <A>(right: A) => Result<A>Creates a Result holding a Success value.
Details
- Use when you have a value and want to lift it into the
Result type
- The error type
E defaults to never
Example (Wrapping a value)
import { Result } from "effect"
const result = Result.succeed(42)
console.log(Result.isSuccess(result))
// Output: true
succeed(error: OutErr & {
_tag: K
} & {
reason: unknown
}
reason: unknownreason) : import ResultResult.const fail: <E>(
left: E
) => Result<never, E>
Creates a Result holding a Failure value.
When to use
Use to represent a failed Result with a typed failure value.
Details
- The success type
A defaults to never
Example (Creating a failure)
import { Result } from "effect"
const result = Result.fail("Something went wrong")
console.log(Result.isFailure(result))
// Output: true
fail(error: OutErrerror),
const fail: <E>(
error: E
) => Channel<never, E, never>
Constructs a channel that fails immediately with the specified error.
Example (Failing with an error)
import { Channel } from "effect"
// Create a channel that fails with a string error
const failedChannel = Channel.fail("Something went wrong")
// Create a channel that fails with a custom error
class CustomError extends Error {
constructor(message: string) {
super(message)
this.name = "CustomError"
}
}
const customErrorChannel = Channel.fail(new CustomError("Custom error"))
// Use in error handling by piping to another channel
const channelWithFallback = Channel.concatWith(
failedChannel,
() => Channel.succeed("fallback value")
)
fail
) as any)