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Re: how to parse this?

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  Re: how to parse this? torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-02-01 13:35 +0100

#976 — 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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