Re: Parsing expressions without outer parentheses

Pete Jinks <pjj@cs.man.ac.uk> wrote:


> Frank Heckenbach wrote:
>
> > expression: simple_expression | expression '=' simple_expression;
> > simple_expression: term | simple_expression '+' term;
> > term: factor | term '*' factor;
> > factor: primary | factor '^' primary;
> > primary: constant | '(' expression ')';
> >
> > Now I want to accept only expressions which are not completely
> > enclosed in a pair of parentheses, e.g. `(1) + (2)' would be
> > accepted, but `(1 + 2)' would not.
>
> is this any more useful?
>
> expression: constant
> | factor '^' primary
> | term '*' factor
> | simple_expression '+' term
> | fullexp '=' simple_expression
> ;
> fullexp : expression
> | '(' fullexp ')'
> ;
> primary : constant | '(' fullexp ')'
> ;
> (simple_expression, term, factor as before)


This doesn't increase the number of nonterminals so much, but OTOH, it
requires duplication of all the actions for the operators. I guess
I'll have to weigh the disadvantages ...


Frank


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Frank Heckenbach, frank@g-n-u.de, http://fjf.gnu.de/
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