Comment author: administrator

Full_Name: Hugo Herbelin
Version: 3.06
OS: linux
Submission from: herbelin.net1.nerim.net (62.212.105.93)

Bonjour,

I fell on a funny behaviour of ast-based preprocessing wrt to useless pattern
detection.

When preprocessed with camlp4o the following program reports an incorrect
useless pattern.

% cat foo.ml
let f = function
| 'b' -> 1
| 'a'..'c' -> 2
| _ -> 3
% ocamlc -pp 'camlp4o' -c -impl ~/foo.ml
File "/home/herbelin/toto.ml", line 3, characters 4-12:
Warning: this pattern is unused.

When communicating via ocaml parser, it is correct though (no warning).

% ocamlc -pp 'camlp4o pr_o.cmo' -c -impl ~/foo.ml

In both cases, the .cmo is the same, so it really just seems to be that the
useless pattern detection is not happy with the abstract syntax tree returned by
camlp4 (perhaps is 'a'..'c' then expanded) ?

Thanks for all.

Hugo

Hi, I think you are right, at least the observed behavior can be
explained as you do : 'a'..'c' is expanded by camlp4.
However some << ghost location >> mecanism shoud prevent the warning.
I probably missed something here.

--Luc

Comment author: administrator

Fixed on 02.24/2003 --Luc