lib.fixedPoints.composeManyExtensions

Composes a list of overlays and returns a single overlay function that combines them.

Inputs

extensions

A list of overlay functions

The order of the overlays in the list is important.

Each overlay function takes two arguments, by convention final and prev, and returns an attribute set.

• final is the result of the fixed-point function, with all overlays applied.
• prev is the result of the previous overlay function(s).

Type

# Pseudo code
let
  #               final      prev
  #                 ↓          ↓
  OverlayFn = { ... } -> { ... } -> { ... };
in
  composeManyExtensions :: ListOf OverlayFn -> OverlayFn

Examples

let
  # The "original function" that is extended by the overlays.
  # Note that it doesn't have prev: as argument since no overlay function precedes it.
  original = final: { a = 1; };

  # Each overlay function has 'final' and 'prev' as arguments.
  overlayA = final: prev: { b = final.c; c = 3; };
  overlayB = final: prev: { c = 10; x = prev.c or 5; };

  extensions = composeManyExtensions [ overlayA overlayB ];

  # Caluculate the fixed point of all composed overlays.
  fixedpoint = lib.fix (lib.extends extensions original );

in fixedpoint
=>
{
  a = 1;
  b = 10;
  c = 10;
  x = 3;
}

Noogle detected

• lib.composeManyExtensions

composeManyExtensions = lib.foldr (x: y: composeExtensions x y) (final: prev: { });