labs/lib/src/default.nix

let
  files = [
    ./attrs
    ./bools
    ./dag
    ./errors
    ./fp
    ./generators
    ./importers
    ./licenses
    ./lists
    ./math
    ./modules
    ./numbers
    ./options
    ./packages
    ./paths
    ./points
    ./strings
    ./types
    ./versions
  ];

  libs = builtins.map (f: import f) files;

  ## Calculate the fixed point of a function. This will evaluate the function `f`
  ## until its result settles (or Nix's recursion limit is reached). This allows
  ## us to define recursive functions without worrying about the order of their
  ## definitions.
  ##
  ## @type (a -> a) -> a
  fix =
    f:
    let
      x = f x;
    in
    x;

  ## Merge two attribute sets recursively until a given predicate returns true.
  ## Any values that are _not_ attribute sets will be overridden with the value
  ## from `y` first if it exists and then `x` otherwise.
  ##
  ## @type Attrs a b c => (String -> Any -> Any -> Bool) -> a -> b -> c
  mergeAttrsRecursiveUntil =
    predicate: x: y:
    let
      process =
        path:
        builtins.zipAttrsWith (
          name: values:
          let
            currentPath = path ++ [ name ];
            isSingleValue = builtins.length values == 1;
            isComplete = predicate currentPath (builtins.elemAt values 1) (builtins.elemAt values 0);
          in
          if isSingleValue || isComplete then builtins.elemAt values 0 else process currentPath values
        );
    in
    process [ ] [
      x
      y
    ];

  ## Merge two attribute sets recursively. Any values that are _not_ attribute sets
  ## will be overridden with the value from `y` first if it exists and then `x`
  ## otherwise.
  ##
  ## @type Attrs a b c => a -> b -> c
  mergeAttrsRecursive = mergeAttrsRecursiveUntil (
    path: x: y:
    !(builtins.isAttrs x && builtins.isAttrs y)
  );

  lib = fix (
    self:
    let
      merge = acc: create: mergeAttrsRecursive acc (create self);
    in
    builtins.foldl' merge { } libs
  );
in
lib.points.withExtend (lib.fp.const lib)