[Caml-list] parsing: old and new ways

[Philippe Esperet <philippe.esperet@wanadoo.fr>]

%--------------------
/dosc/esperet/tex/email/@ocaml9.tex Fri Dec 14 2001 20:36:20
caml-list@inria.fr

Trying to parse the grammar S->aSa|bSb|c
with the old stream syntax, I get

# mirror_parse (Stream.of_string "abcba");;
- : string = "abba"

but with the new camlp4 syntax, the natural translation fails:

# Grammar.Entry.parse mirror (Stream.of_string "abcba");;
Exception:
Stdpp.Exc_located ((0, 5), Stream.Error "illegal begin of mirror").

What am I missing?

Best regards


[old code]
let rec mirror_parse=parser
| [<''a';s=mirror_parse;''a'>] -> "a"^s^"a"
| [<''b';s=mirror_parse;''b'>] -> "b"^s^"b"
| [<''c'>]                     -> "";;

[brand new code]
let gram_mirror=Grammar.create (Plexer.make ());; 
let mirror=Grammar.Entry.create gram_mirror "mirror";;

EXTEND
  mirror:
  [   [  "a" ; x=mirror ; "a" -> "a"^x^"a"
       | "b" ; x=mirror ; "b" -> "b"^x^"b"
       | "c"                  ->  ""]
  ];
END;;
-- 
esperet@gage.polytechnique.fr
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