fp_utils - v1.0.0

fp/option

Values

and_then

</> 
pub fn and_then(
  o: option.Option(a),
  f: fn(a) -> option.Option(b),
) -> option.Option(b)

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

Examples

and_then(Some(5), fn(x) { Some(x * 2) }) // Some(10)
and_then(Some(5), fn(_) { None }) // None
and_then(None, fn(x) { Some(x * 2) }) // None

filter

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pub fn filter(
  o: option.Option(a),
  predicate: fn(a) -> Bool,
) -> option.Option(a)

Filters an Option based on a predicate. Returns None if the predicate fails.

Examples

filter(Some(5), fn(x) { x > 3 }) // Some(5)
filter(Some(2), fn(x) { x > 3 }) // None
filter(None, fn(x) { x > 3 }) // None

flatten

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pub fn flatten(
  o: option.Option(option.Option(a)),
) -> option.Option(a)

Flattens a nested Option. Converts Option(Option(a)) to Option(a).

Examples

flatten(Some(Some(5))) // Some(5)
flatten(Some(None)) // None
flatten(None) // None

from_result

</> 
pub fn from_result(r: Result(a, b)) -> option.Option(a)

Converts a Result to an Option, discarding any error information.

Examples

from_result(Ok(5)) // Some(5)
from_result(Error("failed")) // None

is_none

</> 
pub fn is_none(o: option.Option(a)) -> Bool

Returns True if the option is None.

Examples

is_none(Some(5)) // False
is_none(None) // True

is_some

</> 
pub fn is_some(o: option.Option(a)) -> Bool

Returns True if the option contains a value.

Examples

is_some(Some(5)) // True
is_some(None) // False

map

</> 
pub fn map(
  o: option.Option(a),
  f: fn(a) -> b,
) -> option.Option(b)

Transforms the value inside Some, leaving None unchanged.

Examples

map(Some(5), fn(x) { x * 2 }) // Some(10)
map(None, fn(x) { x * 2 }) // None

or

</> 
pub fn or(
  first: option.Option(a),
  second: option.Option(a),
) -> option.Option(a)

Returns the first Option if it’s Some, otherwise returns the second Option. Useful for providing fallback values.

Examples

or(Some(5), Some(10)) // Some(5)
or(None, Some(10)) // Some(10)
or(Some(5), None) // Some(5)
or(None, None) // None

or_else

</> 
pub fn or_else(
  first: option.Option(a),
  f: fn() -> option.Option(a),
) -> option.Option(a)

Like or, but the second Option is computed lazily. Only evaluates the function if the first Option is None.

Examples

or_else(Some(5), fn() { Some(10) }) // Some(5)
or_else(None, fn() { Some(10) }) // Some(10)

tap_none

</> 
pub fn tap_none(
  o: option.Option(a),
  f: fn() -> b,
) -> option.Option(a)

Applies a function for side effects when the option is None, returning the original option. Useful for logging when values are missing.

Examples

import gleam/io

None
|> tap_none(fn() { io.println("No value found") })
|> unwrap_or(0)
// Prints "No value found" and returns 0

tap_some

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pub fn tap_some(
  o: option.Option(a),
  f: fn(a) -> b,
) -> option.Option(a)

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

Examples

import gleam/io

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

to_result

</> 
pub fn to_result(o: option.Option(a), error: e) -> Result(a, e)

Converts an Option to a Result, using the provided error for None.

Examples

to_result(Some(5), "missing") // Ok(5)
to_result(None, "missing") // Error("missing")

unwrap_or

</> 
pub fn unwrap_or(o: option.Option(a), default: a) -> a

Extracts the value from Some or returns the default for None.

Examples

unwrap_or(Some(5), 0) // 5
unwrap_or(None, 0) // 0

unwrap_or_else

</> 
pub fn unwrap_or_else(o: option.Option(a), f: fn() -> a) -> a

Extracts the value from Some or computes a default for None. The function is only called if the option is None.

Examples

unwrap_or_else(Some(5), fn() { 0 }) // 5
unwrap_or_else(None, fn() { 0 }) // 0

when

</> 
pub fn when(condition: Bool, value: a) -> option.Option(a)

Returns Some(value) if the condition is true, otherwise None. Useful for conditional Option creation.

Examples

when(True, 42) // Some(42)
when(False, 42) // None

when_some

</> 
pub fn when_some(
  o: option.Option(a),
  f: fn(a) -> b,
) -> option.Option(b)

Applies a function that returns an Option, but only if the input Option is Some. This is like and_then but the function doesn’t need to return an Option.

Examples

when_some(Some(5), fn(x) { x > 3 }) // Some(True)
when_some(Some(2), fn(x) { x > 3 }) // Some(False)
when_some(None, fn(x) { x > 3 }) // None

zip

</> 
pub fn zip(
  first: option.Option(a),
  second: option.Option(b),
) -> option.Option(#(a, b))

Combines two Options into a tuple. Returns None if either Option is None.

Examples

zip(Some(5), Some("hello")) // Some(#(5, "hello"))
zip(Some(5), None) // None
zip(None, Some("hello")) // None

zip_with

</> 
pub fn zip_with(
  first: option.Option(a),
  second: option.Option(b),
  f: fn(a, b) -> c,
) -> option.Option(c)

Combines two Options using a function. Returns None if either Option is None.

Examples

zip_with(Some(5), Some(3), fn(a, b) { a + b }) // Some(8)
zip_with(Some(5), None, fn(a, b) { a + b }) // None
zip_with(None, Some(3), fn(a, b) { a + b }) // None
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