Tentative answer to https://groups.google.com/d/msg/marpa-parser/8QK1x69MmXA/SyjyeryTOa8J

transitiongg.pl

#!env perl

use strict;
use diagnostics;
use Marpa::R2;
use POSIX;
use Data::Dumper;

my $source = do { local $/; <DATA> };
my $grammar = Marpa::R2::Scanless::G->new( { bless_package => 'test', source  => \$source });

my @input;
push(@input, "first; second; if(a) b; else c; d;");
push(@input, "
   Some \x{263a}Unicode\x{05d0} in\x{10a0}put; 
 // comment which needs to be parsed, not ignored
   Second expression;
   if(Something)
      First thing
   else
      Other thing;
   End
");
print "Rules:\n" . $grammar->show_rules() . "\n";
foreach (@input) {
  print "Input:\n<CUT HERE>\n$_</CUT HERE>\n";
  my $recce = Marpa::R2::Scanless::R->new( { grammar => $grammar } );
  $recce->read(\$_);
  my $value_ref = $recce->value();
  print Dumper($value_ref);
}

exit(EXIT_SUCCESS);

__DATA__

####################################
# Defaults
####################################
:default ::= action => [values] bless => ::lhs


####################################
# G1 rules
####################################
:start           ::= instructions

expression       ::= text3 ';'
                 |   text3

elseblock        ::= 'else' instruction

ifblock          ::= 'if' '(' text ')'  instruction 

ifschain         ::= ifblock elseblock
                 |   ifblock

instruction      ::= comment
                 |   ifschain
                 |   expression

instructions     ::= instruction+

####################################
# G0 rules
####################################
text_0      ~ '\\'| '\)'| '\(' | [\w] | [^\s()]
text        ::= text_0+
text3_0     ~ '\\' | '\[' | '\}' | '\{' | '\;' | [\w] | [^\s\[;{}]
text3       ::= text3_0+

#
## C comment, c.f. https://gist.github.com/jeffreykegler/5015057
#  -------------------------------------------------------------
<C style comment> ~ '/*' <comment interior> '*/'
<comment interior> ~
    <optional non stars>
    <optional star prefixed segments>
    <optional pre final stars>
<optional non stars> ~ [^*]*
<optional star prefixed segments> ~ <star prefixed segment>*
<star prefixed segment> ~ <stars> [^/*] <optional star free text>
<stars> ~ [*]+
<optional star free text> ~ [^*]*
<optional pre final stars> ~ [*]*
comment ~ <C style comment>
 
#
## C++ comment
#  -----------
<Cplusplus style comment> ~ '//' <Cplusplus comment interior>
<Cplusplus comment interior> ~ [^\n]*
comment ~ <Cplusplus style comment>

#
## Generic discard
#  ---------------
ws ~ [\s]+
:discard ~ ws