[Caml-list] failwith, raise and type inference

[Paul Guyot <pguyot@kallisys.net>]

Hello,

My students came up with a behavior of ocaml I couldn't explain.
I have exactly the same result with 3.07pl2 and a fresh copy checked 
out from CVS.

>let rec f1 key dict =
>	match dict with
>		[] -> failwith "The key " ^ key ^ " could not be found"
>		| (aKey, aValue)::tail ->
>			if (aKey = key)
>			then aValue
>			else f1 key tail;;

is of type:

val f1 : string -> (string * string) list -> string = <fun>

while:

>exception SomeException of string;;
>
>let rec f2 key dict =
>	match dict with
>		[] -> raise (SomeException key)
>		| (aKey, aValue)::tail ->
>			if (aKey = key)
>			then aValue
>			else f2 key tail;;

is of type:

val f2 : string -> (string * 'a) list -> 'a = <fun>

Considering that failwith is of type string -> 'a and raise of type 
exn -> 'a, I couldn't figure out why the correct type for f is only 
infered with raise.

Any idea?

Paul
-- 
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