Jonathan Cast wrote:
Xiao-Yong Jin wrote:
> > Xiao-Yong Jin wrote:
> > > So I have another question. Is the following function safe
> > > and legitimate?
> > >
> > >> safeDiv :: (Exception e, Integral a) =>
> > >> a -> a -> Either e a
> > >> safeDiv x y = unsafePerformIO . try . evaluate $ div x y
>
>> safeDiv' :: (Exception e, Integral a) =>
>> a -> a -> Either e a
>> safeDiv' _ 0 = Left e
>> safeDiv' x y = Right $ div x y
[...]
Other than that, I think the imprecise exceptions paper guarantees that
these two functions are equivalent (albeit unwisely: see below).
I don't think so. The evaluation of x and y may throw errors before we
get around to div.
* safeDiv' will evaluate y (to pattern match against 0) and may return
an error, e, whereas safeDiv will return Left e if div is strict in y.
* safeDiv' postpones evaluating x and so may return Right e, whereas
safeDiv will return Left e if div is strict in x.
--
Live well,
~wren
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