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?
Thanks,
Isaac
--
James "Isaac" Freeman
memotype (at) gmail.com
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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