Re: Parsing expressions without outer parentheses

Hannah Schroeter <hannah@schlund.de> wrote:


> Frank Heckenbach <frank@g-n-u.de> wrote:
> >[...]
>
> >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.
>
> >[...]
>
> How about creating a syntax tree node for parens, too? ...
>
> Then you could just check whether the expression tree's root is a
> "()" node and if so, reject the input.
>
> Afterwards, you can remove the paren nodes (except if you want to use
> them to inhibit optimizing transforms that would change the associative
> order, like required in Fortran).


Thanks for the hint. I might try this. Though this solution seems a
little "unclean" from a grammar point of view. But perhaps I've just
got to take such a compromise if the alternative would blow up the
grammar too much.


Frank


--
Frank Heckenbach, frank@g-n-u.de, http://fjf.gnu.de/
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Free GNU Pascal Compiler: http://www.gnu-pascal.de/
[In the absence of attribute grammars, if you want to add N bits of
state to a token, you have to represent it as 2^N tokens. That's why
yacc parsers usually move a lot of work into the semantics to keep
the grammar to a reasonable size. -John]

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