On 4/5/07, Martin Jambon <[EMAIL PROTECTED]> wrote:
>
> On Thu, 5 Apr 2007, Hugo Ferreira wrote:
>
> >
> > Hello,
> >
> > I would like to use a reserved word and substitute that by a function
> > call. For example, the following:
> >
> > let _ = HEAP in
> > let h1 = HEAP in
> >
> > would become
> >
> > let __heap = new_heap () in
> > let h1 = new_heap () in
As always it will be a lot simpler to do that kind of thing using a
filter in camlp4 3.10.
...
match (* do things bottom-up *) super#expr e with
| <:[EMAIL PROTECTED]< let _ = HEAP in $e$ >> ->
<:[EMAIL PROTECTED]< let __heap = new_heap () in $e$ >>
| <:[EMAIL PROTECTED]< let $p$ = HEAP in $e$ >> ->
<:[EMAIL PROTECTED]< let $p$ = new_heap () in $e$ >>
| e -> e
...
> You shouldn't try to do this because the parser looks only one token ahead
> to make its decision. If you add a rule that starts from "let" (it has
> to), the token which enables the parser to select this rule is in position
> 3, so it comes too late. Camlp4 will not warn you about the conflict but
> fail during preprocessing because it will choose either the predefined
> "let" rule or yours without knowing if it's the right one.
In fact it's wrong camlp4 can takes more than one token of look ahead.
It will try to match the input with all the firsts terminals of a rule.
However you're right to discourage him to try that kind of thing.
Indeed it's highly dependent on the left factorization mechanism
performed by camlp4.
--
Nicolas Pouillard
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