From: "Nicolas Pouillard" <nicolas.pouillard@gmail.com>
To: "Isaac Freeman" <memotype@gmail.com>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] camlp4 and streams
Date: Sun, 13 May 2007 22:28:28 +0200 [thread overview]
Message-ID: <cd67f63a0705131328u36990373i66d893b5b1c92cd0@mail.gmail.com> (raw)
In-Reply-To: <6ff764650705130858s7bbc2263sc3d99ed9e8a4760c@mail.gmail.com>
On 5/13/07, Isaac Freeman <memotype@gmail.com> wrote:
> Hello,
>
> I am having some problems using streams in my camlp4 extentions. The code:
>
> EXTEND
> expr: LEVEL "expr1"
> [[ "yield"; e1 = expr LEVEL "simple";
> "continue"; e2 = expr LEVEL "simple" ->
> <:expr< [< $e1$; $e2$ >] >> ]];
> END;;
>
> produces the error:
>
> isaac@lappy:~/stuff/ocaml$ ocamlc -pp "camlp4o pa_extend.cmo
> q_MLast.cmo" -I +camlp4 -c gen-syntax.ml
> File "gen-syntax.ml", line 8, characters 18-20:
> While expanding quotation "expr":
> Parse error: illegal begin of expression
> Uncaught exception: Pcaml.Qerror("expr", 1, _)
> Preprocessor error
>
> However, when I change the stream into a list, it works fine, so I'm
> sure there is just some technicality in using streams here that I'm
> not accounting for properly. Any ideas?
You are hitting a limitation of the old camlp4 implementation. The
thing is that the quotation expander <:expr<...>> provided by
q_MLast.cmo is somewhat limited to the revised syntax.
BTW in revised streams syntax is: [: ... :] (instead of [< ... >]) and
elements starts with a backquote instead of a single quote.
Indeed the stream syntax is provided as a syntactic sugar over regular
OCaml code using the Stream module from the standard library.
However the new Camlp4 implementation provided in 3.10 lift that
shortcoming by giving a full reflection system. So if you want to use
the original syntax everywhere you can use camlp4of that provided
quotation (<:expr<...>>, patt, ctyp...) in the original syntax
including syntactic sugars.
Here is a 3.10 valid extension:
$ cat ext.ml
open Camlp4.PreCast;;
open Syntax;;
EXTEND Gram
expr: LEVEL "top"
[[ "yield"; e1 = expr LEVEL "simple";
"continue"; e2 = expr LEVEL "simple" ->
<:expr< [< $e1$; $e2$ >] >> ]];
END;;
$ ocamlc -c -I +camlp4 -pp camlp4of ext.ml
$ camlp4o ./ext.cmo -str 'yield e1 continue e2'
Stream.lapp (fun _ -> e1) (Stream.slazy (fun _ -> e2))
Best regards,
--
Nicolas Pouillard
prev parent reply other threads:[~2007-05-13 20:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-13 15:58 Isaac Freeman
2007-05-13 20:28 ` Nicolas Pouillard [this message]
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