In fact 'assert false' is explicitely replaced by 'raise Assert_failure(...)' by the parser. See the documentation about that in the "Language extensions" section.
With any other argument than false, assert is considered to have type bool -> unit Esther Baruk On Wed, Aug 31, 2011 at 1:40 AM, Philippe Wang <[email protected]>wrote: > On Wed, Aug 31, 2011 at 12:31 AM, John Carr <[email protected]> wrote: > > # let f () = assert false; 0;; > > Warning 21: this statement never returns (or has an unsound type.) > > val f : unit -> int = <fun> > > > Assert behaves like a function with type bool -> 'a. The return type is > > an unconstrained type, a type variable not mentioned on the left hand > > side of the arrow. > > Actually, assert is more like a function with type bool -> unit. > Indeed, (assert false) is a special case where it is "so obvious that > it'll raise an exception that it's made type 'a". > > Notably, if you write > assert(1=2) > it's not "obvious enough" for the compiler to assume it will raise an > exception. > (Which is normal, by the way, because it's generally an undecidable > problem: in general, it's not possible to know that the evaluation of > assert's argument will return a value, especially when there is a > function application such as in "1=2".) > > So, > in > let f () = assert false > f : unit -> 'a > let f () = assert (1=2) > f : unit -> unit > > And while > let f () = assert false; 0;; > raises a warning, > let f () = assert (1=2); 0;; > won't raise any. > > Somehow, the choice of discriminating (assert false) is not so perfect... > > Cheers, > > -- > Philippe Wang > > > N.B. Sorry for double-replying. > I wonder if "reply-to: [email protected]" field could be added > automatically to headers of all mails received by the list... > > > -- > Caml-list mailing list. Subscription management and archives: > https://sympa-roc.inria.fr/wws/info/caml-list > Beginner's list: http://groups.yahoo.com/group/ocaml_beginners > Bug reports: http://caml.inria.fr/bin/caml-bugs > > -- Caml-list mailing list. Subscription management and archives: https://sympa-roc.inria.fr/wws/info/caml-list Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
