Bison - handling non LALR(1) grammars

Question

I am making a simple calculator using flex, bison.

I developed a grammar which includes two type of expressions - integer expressions and real expressions.

The grammar is similar to this:

exp -> intExp | realExp

intExp -> INT | intExp '+' intExp

realExp -> REAL | realExp '+' realExp | intExp '+' realExp | realExp '+' intExp

This is not LALR(1).

For example consider the string INT '+' REAL. At 'INT' the lookahead is '+' and based on just this it is impossible to tell whether the string is an intExp or a realExp.

I tried rewriting the grammar to resolve the ambiguity but nothing came of it.

I know I could defer making computations during parsing and instead build a parse tree. Then with type checking, the issue could be resolved. But that seems a bit too much for such a simple problem.

Is there any way bison itself can be made to handle this ambiguity? Or can the grammar be re-written in a better way?

Answer 1

No, if it's not LALR(1) then it's not. However in your language you cannot have a type mismatch error. Why then have separate productions for int and real expressions? Just make the node value contain an integer, a real and a type code.