Re: Which one is "better" ?

[Hans Aberg]

On 31 Jul 2005, at 01:07, Baldurien (club internet) wrote:

> I  have  a  grammar  to do for my self, and since this grammar add the
> same  expression  than  the one we could have in a SQL query language,
> I'm wondering which grammar is better in term of performance.
>
> My first one is the classical "one production per precedence" :
...
> With %left, and %nonassoc (and %right too) it give this :

There is no big practical difference between these two methods, as a  
typical compiler spends most time in the actions and the lexer. So  
choose the method you are most comfortable with. Using precedence  
rules %left, etc. produces a more compact grammar that is also more  
structured, which might help human programming. Otherwise, using  
precedence rules cuts down the number of states, so that parser will  
be somewhat faster; the transitions, independent of number, are put  
in a lookup array, so the number does not affect parser size.

  Hans Aberg