anchor.diff:                    [SrcVar, MsgVar, SetterFnName]);
              bool ->
                  ?f("{\n"
  -                  "    if (enif_is_identical(~s, aa_true))\n"
  +                  "    if (enif_is_identical(~s, gpb_aa_true))\n"
                     "        ~s->~s(1);\n"
                     "    else\n"
                     "        ~s->~s(0);\n"
  
positive.code:     #field{name=FName, type=FType} = Field,
      LCFName = to_lower(FName),
      [?f("    if (!~s->has_~s())\n", [MsgVar, LCFName]),
       ?f("        ~s = aa_undefined;\n", [DestVar]),
       ?f("    else\n"),
       indent_lines(
         8,
  
negative.code:                     [if I == 1 -> "";
                          I >  1 -> "else "
                       end,
                       SrcVar, mk_c_var(gpb_aa_, Sym),
                       MsgVar, SetterFnName, Sym])
                   || {I, {Sym, _Val}} <- index_seq(Enumerations)],
                  "    else\n"
  