{ lib, ... }@flakeArg:
let
  inherit (builtins)
    deepSeq
    foldl'
    groupBy
    mapAttrs
    ;
  inherit (lib.lists) singleton;
  inherit (lib.trivial) flip pipe;
in
{

  groupByMult =
    groupers:
    # TODO (maybe) make more efficient by building up grouping function from right
    # from left
    # 0= (x: x) vals
    # 1= groupBy values[0] <0>
    # 2= mapAttrs (_: groupBy values[1]) <1>
    # 3= mapAttrs (_: mapAttrs (_: groupBy values[2])) <2>
    # from right
    # 1= (groupBy values[0])
    # 2= ...
    let
      nul = {
        mapper = x: x;
        result = [ ];
      };
      op =
        { mapper, result }:
        grouper: {
          mapper = fun: mapAttrs (_: mapper fun);
          result = result ++ singleton (mapper grouper);
        };
      list = map groupBy groupers;
      pipeList = (foldl' op nul list).result;
    in
    # catch errors while building groupers before values are passed through
    deepSeq pipeList (flip pipe pipeList);

}