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Re: Can I get some rules help with PARSE::RECDESCENT

by beartham (Novice)
on Mar 10, 2018 at 19:55 UTC ( [id://1210633]=note: print w/replies, xml ) Need Help??


in reply to Can I get some rules help with PARSE::RECDESCENT

It has been about 18 years since I used RecDescent, but looking at your grammar, it seems that the array reference is coming from the '@' in the Action of your expr rule coupled with the brackets in your term rule, which seems to be misplaced with the leading '|', so its regex may not be recognized as a regex, confusing RecDescent. What is the '|' supposed to be an alternative of, the operand rule parenthesized expression?

I liked RecDescent for its EBNF, because I had much previous experience with another recursive descent metacompiler, TREE META, but I found it far too slow for my design work. I ended up using Bison. I wonder if Damien has improved its speed by re-coding some of it in C since I last used it. I wish I had more time to work on it.

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Re^2: Can I get some rules help with PARSE::RECDESCENT
by 7stud (Deacon) on Mar 10, 2018 at 20:16 UTC

    What is the '|' supposed to be an alternative of, the operand rule parenthesized expression?

    A rule can have alternatives, e.g. rule_name: alt1 | alt2, and you can insert an action in the middle of a rule:

    rule_name: alt1 {action} | alt2

    [download]

    And, you can add whatever whitespace you want:

     rule_name: alt1
{action} 
 | alt2

    [download]

    And you can add an action at the end of a rule:

     rule_name: alt1
{action} 
 | alt2 {action}

    [download]
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