Re^2: Parse::RecDescent trouble

I absolutely don't mind. Actually I am extremely happy I got an answer like this. Thank you a ton, it is full of very helpful advices. Particularly I had no idea I can add a closure to the grammar and use it as part of a virtual main package (I did not find it nowhere in the docs).
I have an additional question if you do not mind. Can you decipher this:

line       : ''               # Skip blank lines.
                 <skip:'[ \t]*'>  # Don't treat newlines as whitespace
+.
                 key_value /\n/
                 <skip: $item[2]>
                 { $item[3] }
[download]

for me please? I particularly do not understand the '' construct (it will always match right?) neither do I understand how can you have several tokens in one rule without the | mark (you have '' then a skip pragma then key_value then /\n/ and then another skip pragma)
Once again thanks a lot for the insights!

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Re^3: Parse::RecDescent trouble by ikegami (Patriarch) on Jan 12, 2007 at 22:26 UTC
Particularly I had no idea I can add a closure to the grammar and use it as part of a virtual main package It's not really a closure. The block is inlined at the start of the generated parser code. You should check out `Grammar.pm` after executing: `use Parse::RecDescent my $grammar = ...; Parse::RecDescent->Precompile($grammar, "Grammar");` [download] That block is documented as Start-up Actions. I particularly do not understand the `''` construct. it will always match right? Yes, but remember that P::RD removes `/$skip/` from the input before every terminal in the grammar. The current value of skip is `'\\s*'`, so `''` removes all leading whitespace. That whole thing allows blank lines between `key_value`, but not within `key_value`.	[reply] [d/l] [select]

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Re^3: Parse::RecDescent trouble
by ikegami (Patriarch) on Jan 12, 2007 at 22:26 UTC

Particularly I had no idea I can add a closure to the grammar and use it as part of a virtual main package

It's not really a closure. The block is inlined at the start of the generated parser code. You should check out Grammar.pm after executing:

use Parse::RecDescent
my $grammar = ...;
Parse::RecDescent->Precompile($grammar, "Grammar");
[download]

That block is documented as Start-up Actions.

I particularly do not understand the '' construct. it will always match right?

Yes, but remember that P::RD removes /$skip/ from the input before every terminal in the grammar. The current value of skip is '\\s*', so '' removes all leading whitespace.

That whole thing allows blank lines between key_value, but not within key_value.

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