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[Caml-list] failwith, raise and type inference
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Date: -- (:)
From: Frederic van der Plancke <fvdp@d...>
Subject: Re: [Caml-list] failwith, raise and type inference

Just a small precedence bug.

failwith "The key " ^ key ^ " could not be found"

is equivalent to:

(failwith "The key ") ^ key ^ " could not be found"

and not to:

failwith ("The key " ^ key ^ " could not be found")

F.

Paul Guyot wrote:
> 
> 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.
> 
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> 
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