Tuesday, 15 January 2013

expression - Bison - handling non LALR(1) grammars -


I am making a simple calculator using flex, bison.

I have developed a grammar in which two types of expression - integer expression and actual expression.

Grammar is similar to this:

  exp -> IntExp | RealExp intExp - & gt; INT | IntExp '+' intExp realExp - & gt; Real | RealExp '+' realExp | IntExp '+' realExp | RealExp '+' intExp   

This is not LLRR (1).

For example, consider the string 'INT' + 'real' INT 'is' +' on INT and based on this, it can tell that the string is an intExp or a real expression.

I tried to write the grammar again to solve the ambiguity but nothing came of it.

I know that I can make computation during parsing and in the form of a parse tree. Then with type inquiry, this issue can be solved but it seems that there is a little too much for such a simple problem.

Can a season be made to control such ambiguity? Or can a grammar be rewritten in a better way?

No, if it is not LALR (1) then it is not. However, you can not have a type of mismatch error in your language. Then why is there different presentations for int and real expression? Just node values ​​have an integer, a real and a type code.

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