Re: how to parse this?

nojb <n.oje.bar@gmail.com> writes:


> Hi,
>
> My language has function applications like ML, i.e. f g h means f
> applied to two parameters g and h. But the rule
>
> exp: IDENT list(exp)
>
> in Yacc will parse this as f (g h). How can I fix this?


You can either fix it by post-processing the parse tree, or you can
write the production using explicit left-recursion:


exp: application


application: IDENT exp
                      | application exp


If applications are really ML-like, they don't need to start with an
identifier, so you should rather have something like


exp: exp exp


which, however, is ambiguous. You can fix this by adding a %prec
declaration or by dividing expressions into simple and complex
expressions and only allowing simple expressions as arguments to
function applications, i.e.,


exp: exp simple
      | simple


simple: IDENT
            | LPAR exp RPAR
            | ...


where LPAR and RPAR are the token names for parentheses.


Torben

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