Re: [Caml-list] How an exception could be an argument

[Vincent Aravantinos <vincent.aravantinos@gmail.com>]

The arguments are evaluated before being passed to the function.
So in your first test, "Nothing" is raised before even entering "<|||>".
In the second case you're circumventing this by copying directly "raise 
Nothing" in the body of the function: this copy-pasting is not 
equivalent since you now force the evaluation of "raise Nothing" to 
happen within the scope of "try".

* The following could be a workaround:

# let (<|||>) (f1,arg1) (f2,arg2) = try f1 arg1 with Nothing -> try f2 
arg2 with Nothing -> raise Nothing;;
val ( <|||> ) : ('a -> 'b) * 'a -> ('c -> 'b) * 'c -> 'b = <fun>

# ((fun _ -> raise Nothing),()) <|||> ((fun _ -> "jj"),());;
- : string = "jj"

It looks a bit heavy on this example because we are working with constants.
But generally the constants come from some function application so it 
can fit in a not-so-ugly way in real code.

* If you don't care about the infix, the following induces less parentheses:

# let try_or_try f1 arg1 f2 arg2 = try f1 arg1 with Nothing -> try f2 
arg2 with Nothing -> raise Nothing;;
val try_or_try : ('a -> 'b) * 'a -> ('c -> 'b) * 'c -> 'b = <fun>

# try_or_try (fun _ -> raise Nothing) () (fun _ -> "jj") ();;
- : string = "jj"

* Note that you can simplify the second try since "try blah with Nothing 
-> raise Nothing" is actually equivalent to "blah"

This yields:

# let (<|||>) (f1,arg1) (f2,arg2) = try f1 arg1 with Nothing -> f2 arg2;;
val ( <|||> ) : ('a -> 'b) * 'a -> ('c -> 'b) * 'c -> 'b = <fun>


On 02/17/2012 01:16 PM, Pierre-Alexandre Voye wrote:
> (raise Nothing) <|||> "jj";;
> Exception: Nothing.
>
> But if I try :
> try (raise Nothing)  with
>   | Nothing ->  (try "jj"with
>                    | Nothing -> raise Nothing);;
> - : string = "jj"

-- 
Vincent Aravantinos
Postdoctoral Fellow, Concordia University, Hardware Verification Group
http://users.encs.concordia.ca/~vincent