Re: shift/reduce conflict with unary

[Evan Lavelle]

cwcaceres wrote:
> But I'm not trying to list. I'm trying to do the add operation. So the
> expression "5 6 +4" wouldn't be valid. An example of a valid operation would
> be "+5 + -6 - -2" which should have an output of 1. My grammar file
> currently outputs the correct result.
>
> I agree with trying to remove the conflict but I'm putting that on hold for
> now since I can't think of how to remove it.

I'm writing this with the benefit of 10 minutes exposure to your 
problem, so I may well be wrong. However, I think you need to stop and 
think a bit more.

The expression "5 6 +4" *is* valid according to the grammar; try it. It 
may not be valid according to your intent, which is a rather different 
matter.

Read the debug output, and walk through a scan of "5 6 +4". After 
scanning '6', the parser has to decide whether the '+' marks the start 
of a new unary expression, or is an addition operator. If it's the 
former, then it has to reduce a summation expression; if the latter, it 
has to shift for the addition. That's your conflict. The default is to 
reduce, ie. to push onto the expression list, which I don't think is 
what you want.

You say that you're "not trying to list". But that's exactly what

> expression_list
>                 : /* empty */
>                 | expression_list summation_expression
>                 ;

does; it parses a list of summation expressions. What is the intent of 
expression_list?

Evan