<E extends string>(): Getter<string, E>Decodes a hexadecimal string to a UTF-8 string.
Details
- Fails with
SchemaIssue.InvalidValueif the input is not valid hex.
Example (Decoding hex to string)
import { SchemaGetter } from "effect"
const decode = SchemaGetter.decodeHexString<string>()
// Getter<string, string>export function function decodeHexString<
E extends string
>(): Getter<string, E>
Decodes a hexadecimal string to a UTF-8 string.
Details
- Fails with
SchemaIssue.InvalidValue if the input is not valid hex.
Example (Decoding hex to string)
import { SchemaGetter } from "effect"
const decode = SchemaGetter.decodeHexString<string>()
// Getter<string, string>
decodeHexString<function (type parameter) E in decodeHexString<E extends string>(): Getter<string, E>E extends string>(): class Getter<out T, in E, R = never>class Getter {
run: (input: Option.Option<E>, options: SchemaAST.ParseOptions) => Effect.Effect<Option.Option<T>, SchemaIssue.Issue, R>;
map: <T2>(f: (t: T) => T2) => Getter<T2, E, R>;
compose: <T2, R2>(other: Getter<T2, T, R2>) => Getter<T2, E, R | R2>;
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; <…;
}
Represents a composable transformation from an encoded type E to a decoded type T.
When to use
Use when you need a schema getter to build and compose custom transformations
for Schema.decodeTo or Schema.decode.
Details
A getter wraps a function Option<E> -> Effect<Option<T>, Issue, R>. It
receives Option.None when the encoded key is absent, such as a missing
struct field, and returns Option.None to omit the value from the decoded
output. It fails with Issue on invalid input and may require Effect
services via R. .map(f) applies f to the decoded value inside Some
while leaving None unchanged. .compose(other) chains two getters by
feeding the output of this into other; passthrough getters on either side
are optimized away.
Example (Creating and composing getters)
import { SchemaGetter } from "effect"
const parseNumber = SchemaGetter.transform<number, string>((s) => Number(s))
const double = SchemaGetter.transform<number, number>((n) => n * 2)
const composed = parseNumber.compose(double)
// composed: Getter<number, string> — parses then doubles
Getter<string, function (type parameter) E in decodeHexString<E extends string>(): Getter<string, E>E> {
return function transformOrFail<T, E, R = never>(
f: (
e: E,
options: SchemaAST.ParseOptions
) => Effect.Effect<T, SchemaIssue.Issue, R>
): Getter<T, E, R>
Creates a getter that applies a fallible, effectful transformation to present values.
When to use
Use when you need a schema getter for a transformation that may fail, require
Effect services, or run asynchronously.
Details
- Skips
None inputs — only called when a value is present.
- On success, wraps the result in
Some.
- On failure, propagates the
Issue.
Example (Parsing with failure)
import { Effect, Option, SchemaGetter, SchemaIssue } from "effect"
const safeParseInt = SchemaGetter.transformOrFail<number, string>(
(s) => {
const n = parseInt(s, 10)
return isNaN(n)
? Effect.fail(new SchemaIssue.InvalidValue(Option.some(s), { message: "not an integer" }))
: Effect.succeed(n)
}
)
transformOrFail((input: E extends stringinput) =>
import ResultResult.const match: {
<E, B, A, C = B>(options: {
readonly onFailure: (error: E) => B
readonly onSuccess: (ok: A) => C
}): (self: Result<A, E>) => B | C
<A, E, B, C = B>(
self: Result<A, E>,
options: {
readonly onFailure: (error: E) => B
readonly onSuccess: (ok: A) => C
}
): B | C
}
import EncodingEncoding.const decodeHexString: (
str: string
) => Result.Result<string, Encoding.EncodingError>
Decodes a hexadecimal string into a UTF-8 string safely.
When to use
Use to decode hexadecimal text into UTF-8 text without throwing on invalid
input.
Details
Returns Result.succeed with the decoded text when decoding succeeds, or
Result.fail with an EncodingError when the input is not valid hex.
Example (Decoding hex strings)
import { Encoding, Result } from "effect"
const result = Encoding.decodeHexString("68656c6c6f")
if (Result.isSuccess(result)) {
console.log(result.success) // "hello"
}
decodeHexString(input: E extends stringinput), {
onFailure: (
error: Encoding.EncodingError
) => Effect.Effect<
never,
SchemaIssue.InvalidValue,
never
>
e: Encoding.EncodingError(parameter) e: {
name: string;
message: string;
stack: string;
cause: unknown;
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;
_tag: Tag;
kind: 'Decode' | 'Encode';
module: string;
input: unknown;
}
import EffectEffect.const fail: <E>(
error: E
) => Effect<never, E>
Creates an Effect that represents a recoverable error.
When to use
Use to explicitly signal a recoverable error in an Effect.
Details
The error keeps propagating unless it is handled. You can handle tagged
errors with functions like
catchTag
or
catchTags
.
Example (Creating a failed effect)
import { Data, Effect } from "effect"
class OperationFailedError extends Data.TaggedError("OperationFailedError")<{}> {}
// ┌─── Effect<never, OperationFailedError, never>
// ▼
const failure = Effect.fail(
new OperationFailedError()
)
fail(new import SchemaIssueSchemaIssue.constructor InvalidValue(actual: Option.Option<unknown>, annotations?: Schema.Annotations.Issue | undefined): SchemaIssue.InvalidValueRepresents a schema issue produced when the input has the correct type but its value violates a
constraint (e.g. a string that is too short, a number out of range).
When to use
Use when you need to detect constraint violations from Schema.filter,
Schema.minLength, Schema.greaterThan, or similar checks.
Details
actual is Option.some(value) when the failing value is known, or
Option.none() when absent.annotations optionally carries a message string for formatting.- The default formatter renders this as
"Invalid data <actual>" unless a
custom message annotation is provided.
Example (Returning InvalidValue from a custom filter)
import { Option, SchemaIssue } from "effect"
const issue = new SchemaIssue.InvalidValue(
Option.some(""),
{ message: "must not be empty" }
)
console.log(String(issue))
// "must not be empty"
InvalidValue(import OptionOption.const some: <A>(value: A) => Option<A>Wraps the given value into an Option to represent its presence.
When to use
Use to wrap a known present value as Option
- Returning a successful result from a partial function
Details
- Always returns
Some<A>
- Does not filter
null or undefined; use
fromNullishOr
for that
Example (Wrapping a value)
import { Option } from "effect"
// ┌─── Option<number>
// ▼
const value = Option.some(1)
console.log(value)
// Output: { _id: 'Option', _tag: 'Some', value: 1 }
some(input: E extends stringinput), { Annotations.Issue.message?: string | undefinedmessage: e: Encoding.EncodingError(parameter) e: {
name: string;
message: string;
stack: string;
cause: unknown;
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;
_tag: Tag;
kind: 'Decode' | 'Encode';
module: string;
input: unknown;
}
Error.message: stringmessage })),
onSuccess: <A>(value: A) => Effect<A>onSuccess: import EffectEffect.const succeed: <A>(value: A) => Effect<A>Creates an Effect that always succeeds with a given value.
When to use
Use when an effect should complete successfully with a specific value without any errors
or external dependencies.
Example (Creating a successful effect)
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)
succeed
})
)
}