I want to write a program for creating presentations. The presentation style I have in mind is very simple: few lines per slide, few words per line with a font size as large as possible, occasionally an image. (This style is close to what's called the Takahashi style).

LaTeX with the beamer class is a good candidate to make such presentations, but writing \begin{frame}...\end{frame} every time is tedious. So I wanted a program that takes the bare outline (with just the lines I want displayed) and produces the latex source for me.

One required feature of this program would be that, by default, the font size for a particular slide should be chosen so that the longest line fills the available screen width. However, it should be possible to override this mechanism and set absolute font sizes for individual lines.

Here is an example of an outline file:

First slide
Test line

Second line
Line with explicit font size @20
[download]

The "@20", or more generally the "@" character and an integer at the end of the line is the font size override.

I actually wrote the program that does all this, but it's became an unmaintainable mess, so this time I want to do it the Right Way(TM).

I figured that when it comes to Perl and parsing text files with a pre-determined structure, the Right Way is Parse::RecDescent. (I also have the ulterior motive that I want to learn P::RD.)

As a first step I set out to write a grammar that parses outline files with a structure similar to the example above.

Here is what I have so far:

#!/usr/bin/perl

use strict;
use warnings;
use Parse::RecDescent;
use Data::Dumper;

$::RD_ERRORS = 1;
$::RD_WARN   = 1;
$::RD_HINT   = 1;
$::RD_TRACE  = 1;

my $grammar = <<'END_GRAMMAR';
#<autotree>

startrule: slide(s)

slide: <skip: qr/[ \t]*/> line(s) line_end(s)

line: text fontspec(?) line_end 

text: /[^@\n]+(?:\b@[^@\n]*)*/

fontspec: <skip: ''> "@" fontspec_size

fontspec_size: /\d+/
             | <error: Invalid fontspec or unescaped '\@' at:\n$text.>

line_end: "\n"

END_GRAMMAR

my $good_text = <<'SAMPLE_TEXT';
Test
Line @20

Even more test address@test.com @20
Escaped \@text

SAMPLE_TEXT

my $bad_text =  <<'SAMPLE_TEXT';

Bad line @invalid
Also bad @foo @20

SAMPLE_TEXT

my $parser = new Parse::RecDescent ($grammar);
#$parser->startrule($text);

$parser->startrule($good_text);
print STDERR "\n" x 3;
$parser->startrule($bad_text);
[download]

I've ran into problems with the font size specifiers. I want to allow "@" characters within the text if they are not at word-initial positions (for e-mail addresses and whatnot), but I want an error to be generated if there is an unescaped or non-word-initial "@", or the font size specifier is invalid (not an integer). The version above fails at "\@", even though I want to allow that, and it does not print the error text on failure, just fails silently, as seen from the P::RD trace.

How to rephrase the grammar to make it pass the lines in $good_text, but fail on the lines in $bad_text, printing the error message?

Eventually I want to collect the parsed lines into a data structure for further processing, so I'd appreciate tips on how to that, too.