Re: Parsing expressions without outer parentheses

Hello!


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'd have


        +
      / \
    () ()
    | |
    1 2


for (1) + (2) and


      ()
        |
        +
      / \
    1 2


for (1 + 2).


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).


Kind regards,


Hannah.

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