Re: [Caml-list] exn vs option

[Julien Verlaguet <julien.verlaguet@gmail.com>]

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2 more use cases:

1) When writing a deep recursion
Throwing an exception will directly jump to your "catch" block without
having to unfold every return call site on the stack one by one. Which can
be much faster if the recursion is very "deep".

2) When your exception is exceptional :-)
If Not_found is never caught, then using exceptions is faster than option
because you don't have to allocate to perform the "find" operation (the
difference should be minimal though).
Plus it makes your code more readable, you don't have to match on the
return value of the find.
This use case makes sense if you don't intend to catch Not_found, when
Not_found is a bug, period.

Le 4 avril 2012 13:38, John Carr <jfc@mit.edu> a écrit :

>
> When thinking about performance, consider the "try" keyword to take time
> to execute.  A try block pushes an exception handler onto a stack and
> pops the stack on exit.  The try block may also interfere with tail call
> optimizations.
>
> A loop like
>
>  for i = 0 to 10000000 do try ... done
>
> executes "try" 10000001 times and will run much more slowly than
>
>  try for i = 0 to 10000000 do ... done
>
> where "try" only executes once.
>
> I use options where performance matters, in frequently executed code
> where the amount of computation is not much more than the overhead of
> a try...with.  For example, I have variants of List.assoc that return
> options instead of raising exceptions.
>
> Where performance doesn't matter, i.e. the amount of code in the block
> is large or the block is rarely executed, I use exceptions or options
> based on convenience.
>
> > I benchmarked two programs, in one case the main function throw an
> exception
> > that is caught, in the other the function returns an option that is
> pattern
> > matched on.
> >
> > I noticed that, whether the exception is thrown or not, the option
> version is
> > always faster.
> >
> > Is there any case where it makes sense, performance wise, to use
> exception
> > instead of 'a option ?
>
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