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

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

On Tue, May 27, 2014 at 11:39:20PM +0200, Daniel Bünzli wrote:
> Le mardi, 27 mai 2014 à 10:49, Goswin von Brederlow a écrit :
> > Sometimes arguments are computed and suddenly exceed aceptable
> > parameters. E.g. the user specifies a data file that needs to be read
> > into a string. If the file is too large you get Invalid_argument.
> > Programms can catch and handle such cases, at least to the point of
> > giving a good error message.
> 
> 
> Bad api. Neither exceptional error, neither programming error, *should* not raise Invalid_argument, of course you???ll have to handle it but don't forget to send hate emails to the API designer.  
> 
> > That is a matter of taste and with recursions in the mix exceptions
> > can be a great way to abort the recursion while keeping the code flow
> > simple. They also allow you to use things like List.fold_left and
> > abort early.
> 
> It???s not a matter of taste. What you are describing here is usage of exceptions by a programmer that wants to shoot himself in the foot. Libraries themselves should never disrupt the control flow of clients.  
> 
> Best,
> 
> Daniel

Who said anything about disrupting the codeflow of clients?

The use case is like

exception Result of int

let find_less_than x list =
  try
    List.iter (fun y -> if x > y then raise (Result y)) list;
    None
  with Result y -> Some y


# find_less_than 10 [100; 23; 3; 42; 17];;
- : int option = Some 3

You hrow the exception internally and catch it internally. Nothing of
the clients gets disruppted.

Obviously this is a constructed simplistic example. But in more
complex code an exception can be far more readable than 50 ifs and
checks of None/Some all over the place.

MfG
	Goswin