[Caml-list] ocaml 4.03 and warning 52 : argument of this constructor should not be matched against a constant pattern

[William <r.3@libertysurf.fr>]

Hello,

with ocaml 4.03, I came with many warnings such as this one :

let lst = [] in
try
    let fst = List.hd lst in
    Printf.printf "fst:%s\n" fst
with
| Failure "hd" -> Printf.printf "empty list\n";;

Characters 123-127:
| Failure "hd" -> Printf.printf "empty list\n";;
            ^^^^
Warning 52: the argument of this constructor should not be matched against a
constant pattern; the actual value of the argument could change
in the future.



It occurs typically for Failure "hd", Failure "tl", Failure 
"float_of_string", Failure "int_of_string", Failure "lexing: empty 
token", Invalid_argument "Filename.chop_extension", ...

How are we supposed to handle this nicely with the standard library ? Is 
there a better approach to catch those exceptions ?


Best regards,

William