msg: {
  actual,
  expected ? {},
  asString ? false,
  asJSON ? false,
  removeDunders ? false,
  safeToPrint ? true,
  throws ? false,
}: let
  preProcess = v:
    if removeDunders
    then undunder v
    else if asString
    then toString v
    else if asJSON
    then builtins.toJSON v
    else v;

  a = preProcess actual;
  e = preProcess expected;

  undunder = v:
    if builtins.isAttrs v
    then builtins.removeAttrs v ["__toString" "__functor"]
    else v;

  out =
    if safeToPrint
    then
      builtins.toJSON (undunder (
        if throws
        then (builtins.tryEval actual).value
        else {
          inherit actual expected;
        }
      ))
    else ''{"msg": "cannot be stringified ):"}'';

  success =
    if throws
    then (builtins.tryEval actual).success == false
    else (a == e);
in
  {
    inherit success msg;
  }
  // (
    if success
    then {}
    else builtins.trace "FAILED ${msg}" {inherit actual expected;}
  )