Re: [Caml-list] Uncaught exceptions in function type.

[Thomas Blanc <thomas.blanc@crans.org>]

Le 26/05/2014 16:23, Philippe Veber a écrit :
> Hi everyone,
>
> Out of curiosity, I was wondering how difficult it would be in theory 
> to extend the type system so that exceptions that can pop out of a 
> function when it is called would be included in the type of the 
> function. Could this type information be infered automatically? Could 
> this be used to have an exhaustivity check in the "with" part of a try 
> ... with expression?
>
> I guess that if it was so easy, we would already be enjoying it within 
> our favorite compiler, but I fail to see how hairy is the question.
>
> Cheers,
>   Philippe.
>
>

This as already been analyzed by François Pessaux and Xavier Leroy, see 
[1] that does a very good survey on the matter.

The main problem for it is (as Romain pointed out) the problem of 
higher-order functions:
you would have to reannotate all of your .mli to add the exception 
annotations.
([1] solved it by doing a separate type analysis)

This would lead to a lot of problems (along with breaking existing code):
* "exceptions we know won't be throwed":
Typing analysis can't know that "x/2" or a.((Array.length a) - 1) 
wouldn't raise anything, so you'd have a lot of unexpected
exceptions that would come up.
* An arbitrary big number of exceptions
At the time [1] was wrote, there was necessarily a finite number of 
exceptions in your program, with nifty stuff like first class modules 
and generative functors it is no longer the case.

[1] http://pauillac.inria.fr/~xleroy/publi/exceptions-popl.ps.gz