{
  lib ? import <nixpkgs/lib>,
}: let
  t = lib.types;
in lib.fix (self: {
  /** Perform module-system type checking and resolving on a single option value. */
  typeCheck = loc: optionType: value:
    assert lib.isOptionType optionType;
    assert lib.isList loc;
    assert lib.all lib.isString loc;
  let
    merged = lib.modules.mergeDefinitions loc optionType [ {
      inherit value;
      file = "«inline»";
    } ];
  in merged.mergedValue;

  /** Either a list of strings, or a dotted string that will be split. */
  convenientAttrPath = t.coercedTo t.str (lib.splitString ".") (t.listOf t.str);

  concatFoldl = f: list: lib.foldl' (acc: value: acc ++ (f value)) [ ] list;
  recUpdateFoldl = f: list: lib.foldl' (acc: value: lib.recursiveUpdate acc (f value)) { } list;
  recUpdateFoldlAttrs = f: attrs: lib.foldlAttrs (acc: name: value: lib.recursiveUpdate acc (f name value)) { } attrs;
})