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  • HOP::Lexer didn't do the trick because what you need (and wrote) is a parser, not just a lexer.

  • Your code has bugs. It doesn't recognie the bold in <uc><b>...</b></uc>, and it silently ignores the </uc> in <b>...</uc></b>. While this is not too hard to fix, you'll notice adding a third tag to your model will be very hard (and introduce lots of redundancy and fragility), and introducing a fourth will be near-impossible.

    (
    2 tags => 4 hashes in %$lexer
    3 tags => 16 hashes in %$lexer
    4 tags => 65 hashes in %$lexer
    5 tags => 326 hashes in %$lexer
    )

    Part of the problem is that it's not proper (i.e. maintainable, expandable) for each tag to be a seperate token. <b> and <uc> should consist of the same one (opentag) or three (opentagopen, tagname, tagclose) tokens.

  • I love using /.../xgc for lexing (aka tokenizing). See What good is \G in a regular expression? for more on this topic. My version below uses this. ( Oops! So does yours! )

My version:

use strict; use warnings; my %VALID_ELEMENTS = map { $_ => 1 } qw( b uc ); my %state; my @to_close; sub output_text { my ($text) = @_; $text =~ s/([[:print:]])/$1$1/g if $state{b}; $text = uc($text) if $state{uc}; print($text); } sub open_tag { /\G ( \w+ ) /xgc or die("Expecting tag name\n"); my $ele = lc($1); $VALID_ELEMENTS{$ele} or die("Unknown element name $ele\n"); /\G > /xgc or die("Expecting closing bracket\n"); !$state{$ele} or die("Attempting to open previously opened element\n"); $state{$ele} = 1; push @to_close, $ele; } sub close_tag { /\G (\w+) /xgc or die("Expecting tag name\n"); my $ele = lc($1); $VALID_ELEMENTS{$ele} or die("Unknown element name $ele\n"); /\G > /xgc or die("Expecting closing bracket\n"); $state{$ele} or die("Attempting to close unopened element\n"); my $to_close = $to_close[$#to_close]; $to_close eq $ele or die("Missing closing tag for element $to_close\n"); $state{$ele} = 0; pop @to_close; } sub process { # The following "for" aliases $_ to $text and # provides a target for the upcoming "redo" stmts. for ($_[0]) { /\G <\/ /xsgc && do { close_tag(); redo }; /\G < /xsgc && do { open_tag(); redo }; /\G ( [^<]+ ) /xsgc && do { output_text("$1"); redo }; # Falls through at the end of the string. } } process("This is a nifty <b><uc>uppercase</uc> test</b> to see what <u +c>this</uc> thing can do.\n");

In reply to Re: Lexical Analyzer with Actions : Continue Development? by ikegami
in thread Lexical Analyzer with Actions : Continue Development? by Velaki

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