NAME

RE - A regular expression base class

SYNOPSIS

    use FLAT::Legacy::FA::RE;
    use FLAT::Legacy::FA::NFA;
    my $re = RE->new();
    $re->set_re('a|b|(hi)*');
    my $nfa = $re->to_nfa();
    print $nfa->info(); # see stuff on NFA
    my $dfa = $nfa->to_dfa(); 
    print $dfa->info(); # see stuff on DFA
    my @removed = $dfa->minimize();
    print $dfa->info(); # see stuff on minimized DFA
    print "Removed ".($#removed+1)." states\n";

DESCRIPTION

This module implements a regular expression parser, and supports the conversion of a RE to a deterministic finite automata. A homegrown recursive descent parser is used to build the parse tree, and the method used to conver the regular expression to a DFA uses no intermediate NFA.

Recursive Descent-safe Regex Grammar:

 R  -> O

 O  -> CO'

 O' -> '|' CO' | epsilon

 C  -> SC'

 C' -> .SC' | epsilon

 S  -> LS'

 S' -> *S' | epsilon

 L  -> a | b | c |..| 0 | 1 | 2 |..| (R) | epsilon

 Terminal symbols: a,b,c,..,z,0,1,2,..,9,|,*,(,)

 NOTE: Concatenation operator, '.', is not a terminal symbol
 and should not be included in the regex

 FAQ:
   Q: Does this support Perl regular expressions?
   A: No, just the regular expression using the terminal symbols
      listed above.

Valid terminal characters include:

a b c d e f g h i j k l m n o p q r s t u v w x y z

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

0 1 2 3 4 5 6 7 8 9 + - = ? & [ ] { } . ~ ^ @ % $

: ; < >

AUTHOR

Brett D. Estrade - <estrabd AT mailcan DOT com>

CAVEATS

Currently, all states are stored as labels. There is also no integrity checking for consistency among the start, final, and set of all states.

BUGS

to_dfa is broken, and is now listed as to_dfa_BROKEN so there is no confusion. I am currently debating whether or not to fix it, or reimplement it in FLaT 1.0.

AVAILABILITY

Perl FLaT Project Website at http://perl-flat.sourceforge.net/pmwiki

ACKNOWLEDGEMENTS

This suite of modules started off as a homework assignment for a compiler class I took for my MS in computer science at the University of Southern Mississippi. It then became the basis for my MS research. and thesis.

Mike Rosulek has joined the effort, and is heading up the rewrite of Perl FLaT, which will soon be released as FLaT 1.0.

COPYRIGHT

This code is released under the same terms as Perl.