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

[Goswin von Brederlow <goswin-v-b@web.de>]

On Tue, May 27, 2014 at 09:42:35AM +0100, Ben Millwood wrote:
> One particularly galling aspect of exceptions not showing up in types is
> that they can't easily be refactored. If you decide to change which
> exceptions a given function throws, you can't rely on the typechecker to
> flag up where code was written to the old specification and needs changing.
> You can't even just eyeball the code to see where the function was used and
> see if the exception was caught, because who knows where in the call stack
> it might have been handled? Explicit error types, on the other hand, will
> refuse to compile unless you have changed your code to deal with it, so you
> can make your errors richer or more precise with a high level of confidence
> that you haven't introduced any "holes" for exceptional conditions to sneak
> out where previously they couldn't.
> 
> This is essentially why we still have a few Not_found exceptions in Core,
> because it's really pretty hard to know where they might be relied upon, so
> it's easier to leave them in than purge them and risk silent breakage.

HUH?

Say you have a function

val f : ('a, 'b) t -> 'a -> 'b   (raise [Not_found])

then eliminating Not_found that function would become

val f : ('a, 'b) t -> 'a -> 'b option

That should fail to compile if the return type is used or a signature
exists. Where do you think a change would go unnoticed?

MfG
	Goswin