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Re: [Caml-list] Cannot find Stream Parser Documentation
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Date: -- (:)
From: Wolfram Kahl <kahl@c...>
Subject: Re: [Caml-list] Cannot find Stream Parser Documentation
To my questions about streams and camlp4, I received two answers so far:
The first one from Ryan Tarpine <rtarpine@hotmail.com> unintentionally didn't
make it to the list:

 > 
 > >From: Wolfram Kahl <kahl@cas.mcmaster.ca>
 > >To: caml-list@inria.fr
 > >Subject: [Caml-list] Cannot find Stream Parser Documentation
 > >Date: Fri, 5 Apr 2002 13:58:18 -0500
 > >
 > >...
 > >
 > >The documentation for stream parsers that had been in the
 > >``Language extensions'' chapter of the OCaml manual
 > >seems to have disappeared, too.
 > >I looked for it in the camlp4 directory,
 > >but that directory doesn't even contain a README.
 > >
 > >In the OCaml distribution, camlp4 seems to come with no documentation
 > >besides the manpage!
 > >(And on the camlp4 web pages, I couldn't find anything related
 > >  to the implementation of streams.)
 > 
 > I found the most information on stream parsers to be in camlp4's tutorial 
 > section, not the reference manual like I expected.  See 
 > <http://caml.inria.fr/camlp4/tutorial/tutorial002.html> for the best info I 
 > stumbled across.  It seems that '??' is the correct syntax, and your code 
 > works if you take out the 'when' clause, so maybe this is a bug?
 > 
 > >A related issue: Among about 50 modules, only one uses stream parsers.
 > >But
 > >
 > >   ocamldep -pp camlp4o *.mli *.ml > .depend
 > >
 > >takes much longer than without camlp4.
 > >How can I tell ocamldep to use camlp4 only for this file?
 > >
 > >...
 > 
 > I recommend using Mr. Mottl's OCamlMakefile to manage your project.  See 
 > <http://www.ai.univie.ac.at/~markus/home/ocaml_sources.html#OCamlMakefile> 
 > for info.  With OCamlMakefile you just place the comment (*pp camlp4o *) at 
 > the top of any files that need to be preprocessed, and it takes care of the 
 > dirty work!
 > 
 > HTH,
 > 
 > Ryan Tarpine, rtarpine@hotmail.com
 > "To err is human, to compute divine.  Trust your computer but not its 
 > programmer."
 >   - Morris Kingston
 > 

In the second, Jean-Christophe Filliatre <Jean-Christophe.Filliatre@lri.fr>
provides a practical pattern for use in hand-made makefiles:

 > 
 > Regarding  dependencies, there are  several solutions.  As far  as I'm
 > concerned, I chose to name my camlp4 files .ml4 and to produce the .ml
 > file before computing the dependencies, like this:
 > 
 > ======================================================================
 > foo.ml: foo.ml4
 > 	camlp4o pr_o.cmo -impl $< > $@
 > 
 > depend: foo.ml
 > 	ocamldep *.ml *.mli > .depend
 > ======================================================================
 > 
 > Of course, I  do not produce the .ml file for  compiling; I use ocamlc
 > -pp:
 > 
 > ======================================================================
 > foo.cmo: foo.ml4
 > 	ocamlc -c -pp "camlp4o -impl" -impl $<
 > 
 > ======================================================================

This solves my ocamldep problem.


However, my real problem is not solved yet:
The stream language as currently supported by camlp4
apparently does not contain the full stream language of OCaml 3.02
(and many, many previous versions),
and I cannot find any document that explains the differences.

(In addition, all the OCaml sites at INRIA seem to be down since at least
 yesterday ...)


So I did a few experiments with camlp4 stream translation:

My original code (this worked for years!):

Input 1:
-------------------------------
let pc0 c = parser n
  [< '  x
        when x == c
        ?? (string_of_int n ^ ": pc '" ^ String.make 1 c ^ "'")
  >] -> ();;
-------------------------------
Message:
-------------------------------
File "streamTest.ml4", line 4, characters 8-10:
Parse error: '>]' expected after [stream_patt] (in [parser_case])
-------------------------------

The error points to `??'.
Since Ryan Tarpine points out that the ``when'' might be the problem,
but I need the condition, I try to factorise:

Input 2:
-------------------------------
let pc0 c = parser n
  [< '  x
        when (x == c)
  >] -> ();;
let pc c = parser n
  [< _ = pc0 c
        ?? (string_of_int n ^ ": pc '" ^ String.make 1 c ^ "'")
  >] -> ();;
-------------------------------
Message:
-------------------------------
File "streamTest.ml4", line 7, characters 8-10:
Parse error: '>]' expected after [stream_patt] (in [parser_case])
-------------------------------

The error points to `??', again.
This is particularly interesting given that the following works
(only difference: two invocations of pc0 before `??'):

Input 3:
-------------------------------
let pc0 c = parser n
  [< '  x
        when (x == c)
  >] -> ();;
let pc c = parser n
  [< _ = pc0 c; _ = pc0 c
        ?? (string_of_int n ^ ": pc '" ^ String.make 1 c ^ "'")
  >] -> ();;
-------------------------------
Output:
-------------------------------
let pc0 c (strm__ : _ Stream.t) =
  let n = Stream.count strm__ in
  match Stream.peek strm__ with
    Some x when x == c -> Stream.junk strm__; ()
  | _ -> raise Stream.Failure
;;
let pc c (strm__ : _ Stream.t) =
  let n = Stream.count strm__ in
  let _ = pc0 c strm__ in
  let _ =
    try pc0 c strm__ with
      Stream.Failure ->
        raise
          (Stream.Error (string_of_int n ^ ": pc '" ^ String.make 1 c ^ "'"))
  in
  ()
;;
-------------------------------

Against my expectations,
only the last invocation of pc0 is inside the try ... catch.
(Parentheses around the two invocations of pc0 are not accepted.)

I'm puzzled...  Should I rather recode all my 247 Stream parsers manually?


Wolfram
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