loop with spirit

This is a discussion on loop with spirit within the C++ Programming forums, part of the General Programming Boards category; I want to write interpreter using spirit library but i have a little problem. I don't know how to write ...

  1. #1
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    loop with spirit

    I want to write interpreter using spirit library but i have a little problem. I don't know how to write loop for example "for" with syntax "for 1 to 10 endfor". Can someone tell me how to use iterators with grammar to parse part of input 10 times, or maybe it is better to use tree?

  2. #2
    Registered User linuxdude's Avatar
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    I am not sure of your question exactly. I know personally who wrote the boost spirit library. If you pose your question a little better, I could ask him.

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    I would like to know how to parse part of file multiple times within grammar structure.

    I need this for example to interpret file like this;

    $i = 1;
    for 1 to 10
    i += 1;
    endfor

  4. #4
    Guest Sebastiani's Avatar
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    >> I want to write interpreter using spirit library but i have a little problem. I don't know how to write loop for example "for" with syntax "for 1 to 10 endfor".

    It may be a good idea to read up on the documentation at some point.

    >> I know personally who wrote the boost spirit library.

    Really - Joel de Guzman? I consider him to be at the top of the list of truly innovative and visionary software engineers. Amazing guy. Please give him my regards.
    Last edited by Sebastiani; 05-17-2009 at 01:56 AM. Reason: misquote
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

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    Doumentation only shows in simple way how to use file iterators and position iterators, but i want to use this within grammar structure. I came across some problems with trying to do this.

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    Registered User linuxdude's Avatar
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    What you want requires the context of the grammar. You could in the semantic actions of the grammar, recognize a for loop, analyze the loop variable, then in the c++, run a loop over that variable. However, I have never used boost spirit. I have just seen presentations on it. I have e-mailed one of the writers. I'll let you know when he gets back to me.

  7. #7
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by linuxdude
    I have e-mailed one of the writers. I'll let you know when he gets back to me.
    grygus, you might find it simpler to just ask on the Boost users mailing list.
    C + C++ Compiler: MinGW port of GCC
    Version Control System: Bazaar

    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    I managed to do this but I really dislike this solution;

    When i recognize for loop, I am making new grammar object and in c++ loop parse my for with this grammar. Somhow it is working correct.

    Thanks for really fast answers.

  9. #9
    Cat without Hat CornedBee's Avatar
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    The grammar of the for-loop is:

    'for' expression 'to' expression statements 'endfor'

    What's so hard about writing this in spirit? Surely you already have an expression and a statements production.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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    I didn't have problem with parsing "for loop" syntax but with semantic action on it

  11. #11
    Cat without Hat CornedBee's Avatar
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    You generally really shouldn't interpret code as you parse it. You should generate some intermediate representation (an AST, or bytecode), and then interpret that.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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