this is how it fails now

$ cat src/glue/enum.pir
=head1 NAME

src/glue/enum.pir -- internal handling of enums

=head2 Subs

=over 4

=item !create_anon_enum(value_list)

Constructs a EnumMap, based upon the values list.

=cut

.sub '!create_anon_enum'
    .param pmc values

    # Put the values into list context, so case of a single valued enum works.
    values = values.'list'()

    # For now, we assume integer type, unless we have a first pair that says
    # otherwise.
    .local pmc cur_val
    cur_val = box 0

    # Iterate over values and make mapping.
    .local pmc result, values_it, cur_item
    result = new ['EnumMap']
    values_it = iter values
  values_loop:
    unless values_it goto values_loop_end
    cur_item = shift values_it
    $I0 = isa cur_item, 'Perl6Pair'
    if $I0 goto pair

  nonpair:
    $P0 = '&postfix:<++>'(cur_val)
    result[cur_item] = $P0
    goto values_loop

  pair:
    cur_val = cur_item.'value'()
    $P0 = cur_item.'key'()
    result[$P0] = cur_val
    cur_val = clone cur_val
    'postfix:++'(cur_val)
    goto values_loop

  values_loop_end:
    .return (result)
.end

# Local Variables:
#   mode: pir
#   fill-column: 100
# End:
# vim: expandtab shiftwidth=4 ft=pir:

$ ./perl6 -e 'enum <a b c>'
Cannot assign to readonly value
current instr.: '&die' pc 16101 (src/builtins/Junction.pir:307)
called from Sub '&infix:<=>' pc 15925 (src/builtins/Junction.pir:207)
called from Sub '&postfix:<++>' pc 338485 (src/gen/core.pir:47341)
called from Sub '!create_anon_enum' pc 742 (src/glue/enum.pir:15)
called from Sub '_block14' pc 29 (EVAL_1:0)
called from Sub '!UNIT_START' pc 1109 (src/glue/run.pir:17)
called from Sub 'perl6;PCT;HLLCompiler;eval' pc -1 ((unknown file):-1)
called from Sub 'perl6;PCT;HLLCompiler;command_line' pc 1489 (compilers/pct/src/PCT/HLLCompiler.pir:794)
called from Sub 'perl6;Perl6;Compiler;main' pc -1 ((unknown file):-1)