[Caml-list] stream parser jump-back

[Caml-list] stream parser jump-back

[Max Kirillov]

Hello!

Is it possible in a stream parser to parse again already
accepted token.

An example (a little incorrect) follows.

I'd like to make this in camlp:

A(B).c --> let module M = A(B) in M.c

To do that, i write (scematically):

expr:
[[ m = module_expr; "."; e = expr -> ... ]]

"Note" may be parsed as either module expression or a usual
one. But, expr cannot be followed by a period (that's wrong,
I know, but let's forget about it for a while). Then,
writing None, I've got the Stream.Error and parsing error.

So, can I write something like:
[[ TRY (m = module_expr); "."; ... and so on, do get parsing
failure insted of error, and push the successful head of failed
structute back into a stream, to parse it again (as an expr
now)?

Thanks for your attention.
Max.
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Re: [Caml-list] stream parser jump-back

[Daniel de Rauglaudre]

Hi,

On Mon, Aug 05, 2002 at 01:59:38AM +0700, Max Kirillov wrote:

> Is it possible in a stream parser to parse again already
> accepted token.

No.

> I'd like to make this in camlp:
> A(B).c --> let module M = A(B) in M.c
> To do that, i write (scematically):
> expr:
> [[ m = module_expr; "."; e = expr -> ... ]]

This is complicated, because "module_expr" have several rules starting
with rules already starting "expr". This extension will introduce syntax
errors in many normal cases.

> So, can I write something like:
> [[ TRY (m = module_expr); "."; ... and so on, do get parsing
> failure insted of error, and push the successful head of failed
> structute back into a stream, to parse it again (as an expr
> now)?

You can add a grammar entry defined by a parser. There are examples of
that in the "normal" syntax (pa_o.ml, in Camlp4, subdirectory etc).
See entries "test_ctyp_minusgreater", "test_label_eq",
"test_typevar_list_dot". But I consider they are "hacks" to make
some situation work.

-- 
Daniel de RAUGLAUDRE
daniel.de_rauglaudre@inria.fr
http://cristal.inria.fr/~ddr/
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Re: [Caml-list] stream parser jump-back

[Max Kirillov]

On Mon, Aug 05, 2002 at 08:40:39AM +0200, Daniel de Rauglaudre wrote:
>> Is it possible in a stream parser to parse again already
>> accepted token.
> No.

Sad.

Well, in the case I can simply note that little of module_expr
may be misparsed as expr, and define something like

module_expr_or_expr:
    [[ ... -> (<:module_expr< ...>>,<:expr< ...>>)]]
expr:
    [[ (m1,_) = module_expr_or_expr; "." ... 
    | (_,e1) = module_expr_or_expr -> e1
    ]]

and so on.

> You can add a grammar entry defined by a parser. There are examples of
> that in the "normal" syntax (pa_o.ml, in Camlp4, subdirectory etc).
> See entries "test_ctyp_minusgreater", "test_label_eq",
> "test_typevar_list_dot". But I consider they are "hacks" to make
> some situation work.

Thank you.
That funcs use Stream.npeek to get a content of the stream,
than parse it manually. Hmm...

Max.
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