First of all thanks for the advice!

This looks like a classical application of a recursive descending parser that I introduced in RFC: Parsing with perl - Regexes and beyond.

I have difficulty understanding the article. In my humble opinion it is rather theoretical. Maybe I am not worthy ;-)

In fact I think I wrote a similar parser for a SoPW the other, see Design hints for a file processor. Since some of your tokens stretch multiple files you need a slightly more intelligent tokenizer though.

The "slightly" is an understatement. Some of my nightmare examples to illustrate the point:

In general: KEYWORD = value with value being of a certain type. The comments should be ignored and are not part of the value.

/* A 2-dimensional sequence as the value is being called in ODL */
KEYWORD = ((1,2) (3,4) (5,8) /* some comment */
            9,11))
[download]

/* A set as the value is being called in ODL */
KEYWORD = { RED, BLUE, /* some comment */
            GREEN, HAZEL }
[download]

/* A text string spanning multiple lines */
KEYWORD = "some text /* not a comment but part of the value! */
          more text
          even more text" /* this is again a comment*/
[download]

I have difficulty understanding the article. In my humble opinion it is rather theoretical. Maybe I am not worthy ;-)

No, it probably means that you are not the intended target audience. Or that I did a bad job at writing.

The "slightly" is an understatement. Some of my nightmare examples to illustrate the point:

You're right, I underestimated the complexity. I thought you could just take lines, and multiple lines if they contained non-closed quoted strings.

Still you should not give up hope. I wrote a simple lexer that works for the example you gave:

use strict;
use warnings;
use Data::Dumper;
use Math::Expression::Evaluator::Lexer qw(lex);

my $d = do { local $/; <DATA> };

my @tokens = (
    ['Commment',    qr{/\*.*?\*/}s, sub { return }],
    ['Identifier',  qr{[a-zA-Z_]\w+}],
    ['Number',      qr{\d+}],
    ['Operator',    qr{[=(),+-/*{}]}],
    ['Quoted String', qr{"[^"]*"}],
    ['Newline',     qr{\n}],
    ['Whitespace',  qr{\s+}, sub { return }],
);

print Dumper lex($d, \@tokens);

__DATA__
/* A 2-dimensional sequence as the value is being called in ODL */
KEYWORD = ((1,2) (3,4) (5,8) /* some comment */
            9,11))

/* A set as the value is being called in ODL */
KEYWORD = { RED, BLUE, /* some comment */
            GREEN, HAZEL }

/* A text string spanning multiple lines */
KEYWORD = "some text /* not a comment but part of the value! */
          more text
          even more text" /* this is again a comment*/
[download]

This is far from ideal, but it does tokenize the data in a meaningful way, and strips comments, but not those inside quoted strings.

(The lexer in Math::Expression::Evaluator::Lexer is quite simple and not iterator-like. If you don't want to read all input at once, you need to come up with something more sophisticated.)