arrow

Source: /nix/store/mls72plk3raskl1r5afh3cl9ik3rn969-source/nix/arrow.nix

Module Description

Arrow utilities for pure function capabilities.

Arrows are simpler than abilities - they are pure functions that can be stored in context and requested by name. Unlike abilities which return effects, arrows are just A -> B functions.

Namespace Contents

• new - Creates an arrow from a pure function
• request - Requests an arrow by name and applies it
• adapt - Transforms an arrow with pre/post functions

Difference from Abilities

• Ability: Input -> Fx<S, Output> (effectful)
• Arrow: Input -> Output (pure)

Example

runFx (
  provide { double = x: x * 2; }
    (arrow.request "double" 21)
)  # => 42

See Also

• request - For effectful abilities
• func - For state-dependent pure functions

Combinators

adapt

Transforms an arrow with pre/post processing functions.

Wraps an arrow with preprocessing (contramap) and postprocessing (map) functions, creating a new arrow with adapted types.

Type Signature

(A' -> A) -> (B -> B') -> Arrow A B -> Arrow A' B'

Parameters

• cmap: Preprocess input (A’ -> A)
• fmap: Postprocess output (B -> B’)
• f: Original arrow
• i: Input value

Example

let inc = x: x + 1;
    adapted = arrow.adapt (x: x * 2) (x: x * 10) inc;
in adapted 5  # => (5 * 2 + 1) * 10 = 110

See Also

• map - Transform effect outputs
• contraMap - Transform effect inputs

new

Creates an arrow from a pure function.

Arrows are pure functions (A -> B) that can be stored in context and requested by name. Unlike abilities which return effects, arrows perform simple transformations.

Type Signature

(A -> B) -> Arrow A B

Parameters

• f: Pure function to wrap as arrow

Example

let double = arrow.new (x: x * 2);
in double 21  # => 42

# Store in context for later use
provide {double = arrow.new (x: x * 2);} ...

See Also

• request - Retrieve arrow from context
• adapt - Transform arrows

request

Requests an arrow by name from context and applies it.

Retrieves a stored arrow function from the context and applies it to an input value, returning the result wrapped in an effect.

Type Signature

String -> A -> Fx<{name: Arrow A B}, B>

Parameters

• name: Name of arrow in context
• i: Input value

Example

runFx (
  provide {double = arrow.new (x: x * 2);} (
    arrow.request "double" 21
  )
)  # => 42

See Also

• new - Create arrows
• request.request - Request abilities (returns effects)

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