gleam_stdlib - v0.17.0

gleam/result

Result represents the result of something that may succeed or not. Ok means it was successful, Error means it was not successful.

Functions

all

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pub fn all(results: List(Result(a, b))) -> Result(List(a), b)

Combines a list of results into a single result. If all elements in the list are Ok then returns an Ok holding the list of values. If any element is Error then returns the first error.

Examples

> all([Ok(1), Ok(2)])
Ok([1, 2])

> all([Ok(1), Error("e")])
Error("e")

flatten

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pub fn flatten(result: Result(Result(a, b), b)) -> Result(a, b)

Merges a nested Result into a single layer.

Examples

> flatten(Ok(Ok(1)))
Ok(1)

> flatten(Ok(Error("")))
Error("")

> flatten(Error(Nil))
Error(Nil)

is_error

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pub fn is_error(result: Result(a, b)) -> Bool

Checks whether the result is an Error value.

Examples

> is_error(Ok(1))
False

> is_error(Error(Nil))
True

is_ok

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pub fn is_ok(result: Result(a, b)) -> Bool

Checks whether the result is an Ok value.

Examples

> is_ok(Ok(1))
True

> is_ok(Error(Nil))
False

lazy_or

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pub fn lazy_or(
  first: Result(a, b),
  second: fn() -> Result(a, b),
) -> Result(a, b)

Returns the first value if it is Ok, otherwise evaluates the given function for a fallback value.

Examples

> or(Ok(1), Ok(2))
Ok(1)

> or(Ok(1), Error("Error 2"))
Ok(1)

> or(Error("Error 1"), Ok(2))
Ok(2)

> or(Error("Error 1"), Error("Error 2"))
Error("Error 2")

lazy_unwrap

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pub fn lazy_unwrap(
  result: Result(a, b),
  or default: fn() -> a,
) -> a

Extracts the Ok value from a result, evaluating the default function if the result is an Error.

Examples

> lazy_unwrap(Ok(1), fn() { 0 })
1

> lazy_unwrap(Error(""), fn() { 0 })
0

map

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pub fn map(
  over result: Result(a, b),
  with fun: fn(a) -> c,
) -> Result(c, b)

Updates a value held within the Ok of a result by calling a given function on it.

If the result is an Error rather than OK the function is not called and the result stays the same.

Examples

> map(over: Ok(1), with: fn(x) { x + 1 })
Ok(2)

> map(over: Error(1), with: fn(x) { x + 1 })
Error(1)

map_error

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pub fn map_error(
  over result: Result(a, b),
  with fun: fn(b) -> c,
) -> Result(a, c)

Updates a value held within the Error of a result by calling a given function on it.

If the result is Ok rather than Error the function is not called and the result stays the same.

Examples

> map_error(over: Error(1), with: fn(x) { x + 1 })
Error(2)

> map_error(over: Ok(1), with: fn(x) { x + 1 })
Ok(1)

nil_error

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pub fn nil_error(result: Result(a, b)) -> Result(a, Nil)

Transforms any error into Error(Nil)

Examples

> nil_error(Error(1))
Error(Nil)

> nil_error(Ok(1))
Ok(1)

or

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pub fn or(
  first: Result(a, b),
  second: Result(a, b),
) -> Result(a, b)

Returns the first value if it is Ok, otherwise return the second value.

Examples

> or(Ok(1), Ok(2))
Ok(1)

> or(Ok(1), Error("Error 2"))
Ok(1)

> or(Error("Error 1"), Ok(2))
Ok(2)

> or(Error("Error 1"), Error("Error 2"))
Error("Error 2")

replace_error

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pub fn replace_error(
  result: Result(a, b),
  error: c,
) -> Result(a, c)

then

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pub fn then(
  result: Result(a, b),
  apply fun: fn(a) -> Result(c, b),
) -> Result(c, b)

Updates a value held within the Ok of a result by calling a given function on it, where the given function also returns a result. The two results are then merged together into one result.

If the result is an Error rather than OK the function is not called and the result stays the same.

This function is the equivalent of calling map followed by flatten, and it is useful for chaining together multiple functions that may fail.

Examples

> then(Ok(1), fn(x) { Ok(x + 1) })
Ok(2)

> then(Ok(1), fn(x) { Ok(#("a", x)) })
Ok(#("a", 1))

> then(Ok(1), fn(_) { Error("Oh no") })
Error("Oh no")

> then(Error(Nil), fn(x) { Ok(x + 1) })
Error(Nil)

unwrap

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pub fn unwrap(result: Result(a, b), or default: a) -> a

Extracts the Ok value from a result, returning a default value if the result is an Error.

Examples

> unwrap(Ok(1), 0)
1

> unwrap(Error(""), 0)
0

values

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pub fn values(results: List(Result(a, b))) -> List(a)

Given a list of results Return only the values inside Ok

Examples

> values([Ok(1), None, Ok(3)])
[1, 3]
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