in reply to When the only tool you have is a screwdriver...

Do you have a good set of test cases ? 

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1144184

use strict;
use warnings;

sub e
  {
  /\Guc*/gc or return 0;                     # rule 1. & 5.
  /\Ga/gc and return e();                    # rule 2.
  /\Gc+/gc;                                  # rule 5.
  /\Gd/gc and return e() && /\Gf/gc && e();  # rule 3.
  /\Gb/gc and return e();                    # rule 4.
  return 1;
  }
  
for (qw( u udufu uau uu uc ubu ucbuc uaau ua uauau uccc ))
  {
  print e() && /\G\z/ ? "matches" : "   fail", "  $_\n";
  }

[download]

outputs:

matches  u
matches  udufu
matches  uau
   fail  uu
matches  uc
matches  ubu
matches  ucbuc
   fail  uaau
   fail  ua
matches  uauau
matches  uccc

[download]

Which of these is wrong, if any? Let's keep tweaking until it works :)

Replies are listed 'Best First'.
Re^2: When the only tool you have is a screwdriver...
by Anonymous Monk on Oct 08, 2015 at 18:22 UTC

    Cleaning up (and making more clear) the parsing.

    #!/usr/bin/perl

# http://perlmonks.org/?node_id=1144184

use strict;
use warnings;

sub e
  {
  /\Gua/gc ? return e() : /\Gu/gc || return 0;
  1 while (/\Gd/gc && e() && /\Gf/gc or /\Gb/gc) && e() or /\Gc/gc;
  return 1;
  }

for (qw( u udufu uau uu uc ubu ucbuc uaau ua uauau uccc uauuau ))
  {
  print e() && /\G\z/ ? "matches" : "   fail", "  $_\n";
  }

    [download]

    Again, do you have a good set of test cases ?

[reply]
[d/l]

      Adding random test cases found a weird frankenbug. Fixing backup seems to have fixed it. Do you have any good test cases ? 

      #!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1144184

use strict;
use warnings;

sub e
  {
  my $p; 
  /\Gua/gc ? return e() : /\Gu/gc || return 0;
  1 while /\Gc/gc or
    ($p = pos(), /\Gb/gc && e() || (pos() = $p, 0)) or
    ($p = pos(), /\Gd/gc && e() && /\Gf/gc && e() || (pos() = $p, 0));
  return 1;
  }

for (qw( u udufu uau uu uc ubu ucbuc uaau ua uauau uccc uauuau
  udufuaua uaua uauau uccbucdc ))
  {
  print e() && /\G\z/gc ? "matches" : "   fail", "  $_";
  }

      [download]
[reply]
[d/l]

        s/frankenbug/heisenbug/

[reply]

In Section Seekers of Perl Wisdom