evaluating logical boolean expressions
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Thread: evaluating logical boolean expressions

  1. #1
    Join Date
    Jun 2012
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    evaluating logical boolean expressions

    hi,

    I am looking for a library to aid me in evaluating Boolean expressions.
    For example, i have an expression like this:

    (1*(5+3)+9*65/5-(354*4565*5643+98) >= 12345) && ( 654*987+123 || (2345 > 23423 && 1 != 2)))
    (it can alos be much longer!)

    and would like to evaluate them to a true/false boolean.
    My dear gcc would kick some *** here with its static evaluation, but it`s way too complicated to use a compiler or the like for this.

    There are tons of libraries to calculate the (numerical) result of a mathematical expression, but this is not what i want to do.

  2. #2
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    Re: evaluating logical boolean expressions

    Perhaps you should start by defining the grammar of these boolean expressions. After that, it becomes a question of whether you want to write your own parser or use some tool to create a parser for you.
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  3. #3
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    Jun 2012
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    Re: evaluating logical boolean expressions

    forgot that, sorry.

    Standard math/c++ set of expressions, i would say, ie:

    <,>,>=,<=,&&,||, nested brevets,*,+,-,/, etc.

    If i was to write my own parser, would you know of any "reference" project i could learn from or base on?

  4. #4
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    Re: evaluating logical boolean expressions

    Quote Originally Posted by tuli View Post
    forgot that, sorry.

    Standard math/c++ set of expressions, i would say, ie:

    <,>,>=,<=,&&,||, nested brevets,*,+,-,/, etc.

    If i was to write my own parser, would you know of any "reference" project i could learn from or base on?
    Look up "grammar" and "recursive descent parsers". You need to formally define the grammar first, then from the grammar (production) rules, you create the parser.

    Regards,

    Paul McKenzie

  5. #5
    Join Date
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    Re: evaluating logical boolean expressions

    Quote Originally Posted by tuli View Post
    I am looking for a library to aid me in evaluating Boolean expressions.
    you can use the boost.Spirit library to write a BNRF based parser relatively quickly ( the "Qi" library component, more specifically; there are also a lexer and an output generator library components but you'll probably not need them ... ). Used in conjunction with boost.Phoenix you can process the expression in-place while parsing, including grammar error handling.

    Quote Originally Posted by tuli View Post
    (it can alos be much longer!)
    so, are those expressions human or computed generated ? in the latter case you don't need a parser, just store the expression in a computer-understandable representation directly.

  6. #6
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    Re: evaluating logical boolean expressions

    An alternative approach would be to load a linkable script language. Writing your own expression parser of "mini language" to do this will take a considerable amount of development time.

    One example is LUA (www.lua.org) which is pretty easy to integrate into a C/C++ program. But there are many others.

    Another way out would be to take the expression and form it into a VBScript or javascript and use the wscript.exe to evaluate it for you.

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