fp_utils - v1.0.0

fp/result

Values

and_then

</> 
pub fn and_then(
  r: Result(a, e),
  f: fn(a) -> Result(b, e),
) -> Result(b, e)

Chains operations that return Result, flattening the result. Also known as bind or >>= in other functional languages.

Examples

and_then(Ok(5), fn(x) { Ok(x * 2) }) // Ok(10)
and_then(Ok(5), fn(_) { Error("failed") }) // Error("failed")
and_then(Error("failed"), fn(x) { Ok(x * 2) }) // Error("failed")

is_error

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pub fn is_error(r: Result(a, e)) -> Bool

Returns True if the result is Error.

Examples

is_error(Ok(5)) // False
is_error(Error("failed")) // True

is_ok

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pub fn is_ok(r: Result(a, e)) -> Bool

Returns True if the result is Ok.

Examples

is_ok(Ok(5)) // True
is_ok(Error("failed")) // False

map

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pub fn map(r: Result(a, e), f: fn(a) -> b) -> Result(b, e)

Transforms the Ok value, leaving Error unchanged.

Examples

map(Ok(5), fn(x) { x * 2 }) // Ok(10)
map(Error("failed"), fn(x) { x * 2 }) // Error("failed")

map_error

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pub fn map_error(r: Result(a, e), f: fn(e) -> f) -> Result(a, f)

Transforms the Error value, leaving Ok unchanged.

Examples

map_error(Ok(5), fn(e) { e <> "!" }) // Ok(5)
map_error(Error("failed"), fn(e) { e <> "!" }) // Error("failed!")

tap_error

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pub fn tap_error(r: Result(a, e), f: fn(e) -> b) -> Result(a, e)

Applies a function to the Error value for side effects, returning the original result. Useful for logging errors in a pipeline.

Examples

import gleam/io

Error("failed")
|> tap_error(fn(e) { io.println("Error: " <> e) })
|> map_error(fn(e) { e <> "!" })
// Prints "Error: failed" and returns Error("failed!")

tap_ok

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pub fn tap_ok(r: Result(a, e), f: fn(a) -> b) -> Result(a, e)

Applies a function to the Ok value for side effects, returning the original result. Useful for logging or debugging in a pipeline.

Examples

import gleam/io

Ok(42)
|> tap_ok(fn(x) { io.println("Success: " <> int.to_string(x)) })
|> map(fn(x) { x * 2 })
// Prints "Success: 42" and returns Ok(84)

unwrap_or

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pub fn unwrap_or(r: Result(a, e), default: a) -> a

Extracts the Ok value or returns the default for Error.

Examples

unwrap_or(Ok(5), 0) // 5
unwrap_or(Error("failed"), 0) // 0

unwrap_or_else

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pub fn unwrap_or_else(r: Result(a, e), f: fn(e) -> a) -> a

Extracts the Ok value or computes a default from the Error. The function is only called if the result is Error.

Examples

unwrap_or_else(Ok(5), fn(_) { 0 }) // 5
unwrap_or_else(Error("failed"), fn(e) {
  case e {
    "failed" -> -1
    _ -> 0
  }
}) // -1
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