Grammer rules

This is a discussion on Grammer rules within the C++ Programming forums, part of the General Programming Boards category; in a programing language how do you represent grammer rules? For example say we have a hypothetical programming language called ...

  1. #1
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    Grammer rules

    in a programing language how do you represent grammer rules?

    For example

    say we have a hypothetical programming language called ABED

    ABED can have only one type of loop. And it's a while loop. The while loop condition should be a int and if the value of the int is greater than zero it means true otherwise it means false;


    How do i represent the above grammer in C.

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    Super Moderator VirtualAce's Avatar
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    What?

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    now the above rules can be defined using backus naur form. So how do i store these rules in a program so that these rules can be used later to check for syntax validity?

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    spurious conceit MK27's Avatar
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    You might want to investigate something like Lex.

    Using BNF may (or may not) be of much use in actual parsing.

    Quote Originally Posted by iamnew View Post
    So how do i store these rules in a program so that these rules can be used later to check for syntax validity?
    This is really not very different from someone saying, "How do I store the rules of chess in a program so that I can check if a move in a game is valid?" Certainly, there are many chess games and syntax parsers around, so there should be no shortage of existing source code for you to examine, but if you are looking for some function API like:

    Code:
    int DefineMyChessGame (char *rules);  // "rules" is a string definition
    int DefineMyBNF_lexer (char *rules);  // "rules" is a string definition
    Well, you may (or may not) find some library around to suit your needs, there is certainly no standard procedure here. Like I said, google lex and yacc.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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    Quote Originally Posted by iamnew
    now the above rules can be defined using backus naur form. So how do i store these rules in a program so that these rules can be used later to check for syntax validity?
    Along the lines of what MK27 suggested, you can write those rules in C++ masquerading as a kind of extended BNF using Boost.Spirit.
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    Can't you use a parse tree to validate syntax?

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    When you parse, you check source codes syntatical validaty. Parsers output (or are able to output) parse trees. So yes.

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    say if you have a code like this

    Code:
    int a=4;
    if(a){
    }
    else{
    }
    How many parse tree's should i create? Is it Two?

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    No. One translation unit produces one parse tree.

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