lib: deprecate fold

    min

    id

    warn

    pipe

    ;

  inherit (lib.attrsets) mapAttrs attrNames;

  inherit (lib) max;

    fold' 0;

  /**

    `fold` is an alias of `foldr` for historic reasons

    `fold` is an alias of `foldr` for historic reasons.

    ::: {.warning}

    This function will be removed in 26.05.

    :::

  */

  # FIXME(Profpatsch): deprecate?

  fold = foldr;

  fold = warn "fold has been deprecated, use foldr instead" foldr;

  /**

    “left fold”, like `foldr`, but from the left:

    expected = [ 15 ];

  };

  testFold =

  testFoldr =

    let

      f = op: fold: fold op 0 (range 0 100);

      # fold with associative operator

      f = op: foldr: foldr op 0 (range 0 100);

      # foldr with associative operator

      assoc = f builtins.add;

      # fold with non-associative operator

      # foldr with non-associative operator

      nonAssoc = f builtins.sub;

    in

    {

      expr = {

        assocRight = assoc foldr;

        # right fold with assoc operator is same as left fold

        # foldr with assoc operator is same as foldl

        assocRightIsLeft = assoc foldr == assoc foldl;

        nonAssocRight = nonAssoc foldr;

        nonAssocLeft = nonAssoc foldl;

        # with non-assoc operator the fold results are not the same

        # with non-assoc operator the foldr results are not the same

        nonAssocRightIsNotLeft = nonAssoc foldl != nonAssoc foldr;

        # fold is an alias for foldr

        foldIsRight = nonAssoc fold == nonAssoc foldr;

      };

      expected = {

        assocRight = 5050;

        nonAssocRight = 50;

        nonAssocLeft = (-5050);

        nonAssocRightIsNotLeft = true;

        foldIsRight = true;

      };

    };