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Re: Random Tips on Parse::RecDescent

by educated_foo (Vicar)
on Jul 11, 2002 at 15:49 UTC ( #181053=note: print w/replies, xml ) Need Help??

in reply to Random Tips on Parse::RecDescent

Excellent node! I have a couple of questions:
  1. Why do you do [@item[0..$#item]] rather than just [@item]? IIRC, the second will copy the array as well, so there's no need to take a slice.
  2. re: number 15 -- I've noticed that it complains about RD_AUTOACTION when you use Precompile (which is the same as the command-line?), but it seems to still append auto-actions just fine. Is this the behavior you saw?
And finally, one additional suggestion to add: Do as little as possible in your actions, particularly in the ones in lower-level rules. Building up and tearing down parse trees can be awfully slow, so it may be faster to just do the fastest thing possible during the parse, and post-process it afterwards.


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Re: Re: Random Tips on Parse::RecDescent
by hsmyers (Canon) on Jul 11, 2002 at 16:49 UTC

    About the [@item[@0..$#item]] reason other than using the supplied example from the docs (after all, good enough for damian, good enough for me). chromatic caught this when I posted, I checked and as you say, there is no difference other than less typing!

    As far as the #15 goes, the problem is that the grammar file has no way to contain the RD_AUTOACTION specification with the command line as given. I also played with the expanded .pl version but still couldn't get it to provide identical behavior. What did work was the suggested sledge hammer approach--fix each instance by hand! There may have been a discernable pattern to what was used as default, but I didn't see it and didn't have the time to track it down.

    I like your final 'additional suggestion', the Parse::RecDescent version of 'do as little as possible to get the job done'.


    "Never try to teach a pig to sing…it wastes your time and it annoys the pig."

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