Proposal: (a -> Bool) -> a -> f a
Roman Cheplyaka
roma at ro-che.info
Sun Dec 21 11:14:53 UTC 2014
I like the idea.
This is similar to guard (MonadPlus m => Bool -> m ()), so maybe exploit
that similarity for naming.
Suggestions:
* guardp (for "predicate")
* guardf (for "function")
* guardWith
I wouldn't be opposed to cond, either.
On 21/12/14 12:54, Nikita Volkov wrote:
> I propose to add the following utility function into |Control.Applicative|:
>
> |cond :: (Alternative f) => (a -> Bool) -> a -> f a
> cond p a = if p a then pure a else empty
> |
>
> Following is a typical use case:
>
> |\x -> fromMaybe 0 $ cond (> 0) $ x - 10
> |
>
> which is the same as
>
> |\x -> let y = x - 10 in if y > 0 then y else 0
> |
>
> Why the first one is better:
>
> 1.
>
> The control flow is evident and goes from right to left step by step.
> It’s not scattered around like in the second example.
>
> 2.
>
> No need to interrupt to imagine a name for a temporary variable.
>
> 3.
>
> Less noise.
>
> Now, since it’s generalised to |Alternative| one can imagine tons of
> other useful cases for this.
>
> Alternative titles:
>
> *
>
> |conditional|
>
> *
>
> |partial|
>
> Best regards,
> Nikita
>
>
>
>
> _______________________________________________
> Libraries mailing list
> Libraries at haskell.org
> http://www.haskell.org/mailman/listinfo/libraries
>
More information about the Libraries
mailing list