Handling newlines in P::RD

spurperl has asked for the wisdom of the Perl Monks concerning the following question:

Fellow monks,

I want to use Parse::RecDescent to parse a certain assembly language. In assembly, data is "line oriented", that is newline is the statement separator. Simplified demonstration:

command1 arg1 \n
command2 arg2 \n

Defines two statements. More than one statement on a line is illegal, a statement broken to two lines is also illegal.

Now, P::RD has an issue with newlines. It swallows them by default. There is a workaround using the "skip" directive, but it became tedious and my grammar code is full of <skip: qr/ \t*/> directives.

Is there an easier way ?

What I want, for starters, is a trivial "command arg" pairs for statements:

line -> command arg "\n"

Comment on Handling newlines in P::RD

Replies are listed 'Best First'.
•Re: Handling newlines in P::RD by merlyn (Sage) on Nov 15, 2004 at 17:34 UTC
Seeting `<skip: ... >` is exactly the way to handle this. It stays set through all invoked rules as well. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply] [d/l]
Re^2: Handling newlines in P::RD by ikegami (Patriarch) on Nov 15, 2004 at 18:23 UTC
Just to clarify for the OP, "It stays set through all invoked rules as well" means if you place it in your start rule, it'll affect all your rules.	[reply]
Re^3: Handling newlines in P::RD by spurperl (Priest) on Nov 16, 2004 at 10:50 UTC
Thanks, this is the approach I've eventually taken. Still, looking at my grammar and at the attemps I did trying stuff, it's clear that P::RD has an issue with line-oriented input. It's possible, but adds difficulties, mainly because its default "skippable" chars include a newline. This can be trivially solved with a tiny bit of preprocessing, but I tried a pure P::RD approach. To conclude - it works, it even looks clean enough and not too complicated. Thanks for the feedback !	[reply]
Re: Handling newlines in P::RD by Boots111 (Hermit) on Nov 16, 2004 at 04:25 UTC
spurperl~ I cannot suggest a good method, but you could always cheat by doing a `s/\n/MONKEY/g` on your text before hand and have Parse::RecDescent use "MONKEY" as its statement delimiter... Boots --- Computer science is merely the post-Turing decline of formal systems theory. --???	[reply] [d/l]
Re: Handling newlines in P::RD by metaperl (Curate) on Dec 03, 2004 at 02:13 UTC
Your question is answered in the FAQ right here Also, the parse-recdescent mailing list recently had a post by TheDamian with an nice example.	[reply]