Version française
Home     About     Download     Resources     Contact us    
Browse thread
[Caml-list] failwith, raise and type inference
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: -- (:)
From: Paul Guyot <pguyot@k...>
Subject: [Caml-list] failwith, raise and type inference
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
-- 
Philosophie de baignoire - consultations sur rendez-vous.

NPDS/NewtonOS: http://newton.kallisys.net:8080/
Apache/FreeBSD: http://www.kallisys.com/

-------------------
To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr
Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/
Beginner's list: http://groups.yahoo.com/group/ocaml_beginners