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Date: Wed, 15 Dec 1999 08:39:36 -0800 (PST)
To: Norman Ramsey <nr@eecs.harvard.edu>
Cc: caml-list@inria.fr
Subject: my stupidity and non-tail calls
In-Reply-To: <199912141953.OAA04635@labrador.eecs.harvard.edu>
References: <199912141953.OAA04635@labrador.eecs.harvard.edu>
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From: David Brown <caml-list@davidb.org>
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Norman Ramsey writes:
 > OK, I apologize for bothering everyone.  My `tail calls' are actually
 > sitting inside `try ... with' blocks, so I recognize that these cannot be
 > optimized since they are in the scope of different handlers.  I will
 > have to find a way to restructure my code.  A great pity, since
 > I like it the way it is... suggestions are welcome.

I wonder if this is worthy of the FAQ.  I have done the same thing as
well.  It comes kind of as a consequence of ocaml's philosophy of
using exceptions for things such as not-found, and end of file.  Doing
this cleans up a lot of code, and a few things get a little messier.

I don't know if there is a "clean" way to do it, but what I usually do
is wrap the item around an option.

e.g.
   let maybe_input_char infile =
     try
       Some (input_char infile)
     with End_of_file ->
       None
   
   then in the code...
   
      let next' = maybe_input_char infile in
      match next' with
	Some next ->
	  let () = Queue.add next q in
	  ...
	  compressLoop instr' b q csum infile
      | None ->
	  finishCompressing instr' b q

It isn't quite as clean as the exception code, but it is
tail-recursive.

David Brown