Add ifThenElse and (?) to Data.Bool

[winter]

Ah Yeah, i see. It’s indeed a rare use case.

From all your feedback, I guess i will make a package with (?) for someone who want to save keystrokes like me ;)



Cheers~
Winter


> On 17 Nov 2016, at 12:03, Edward Kmett <ekmett at gmail.com> wrote:
> 
> (?) <$> fFlag <$> flagEnabled <*> flagDisabled
> 
> You probably don't want this. This performs both effects (!), regardless of the flag, but only keeps one result.
> 
> -Edward
> 
> 
> On Wed, Nov 16, 2016 at 11:01 PM, winter <drkoster at qq.com <mailto:drkoster at qq.com>> wrote:
> And here’s some other stuff i can came up with it(without obscured readability IMHO):
> 
> ...
>    -- replacement for ifM in various package, similar to (>>= when)
>    
>    (mFlag >>= (?)) flagEnabled        -- mFlag :: Monad m => m Bool
>                  $ flagDisabled
>   
>    -- nicer if-then-else in applicative style
>    (?) <$> fFlag <$> flagEnabled
>                  <*> flagDisabled
> 
>    -- compose with predicates to define your own if
>    ifLower =  (?) . isLower
>    ifLower ‘X’ lower
>                upper 
> ...
> 
> 
> Basically it's a good if-then-else replacement if you’re comfortable with point-free style.
> 
> 
>> On 17 Nov 2016, at 11:16, winter <drkoster at qq.com <mailto:drkoster at qq.com>> wrote:
>> 
>> I’m totally aware of the existence of bool, i suppose (?) is mainly used in fully application to get a different style than if-then-else syntax, say,
>> 
>> ...
>>     isGoo <- checkGoo
>>     isGoo ? goo
>>           $ woo
>> ...
>> 
>> 
>> But like what the wiki suggested, (?) can be used in some high-order situations. I like this operator because the mnemonic of questioning meaning.
>> 
>> 
>> 
>>> On 17 Nov 2016, at 11:03, David Feuer <david.feuer at gmail.com <mailto:david.feuer at gmail.com>> wrote:
>>> 
>>> If ifThenElse is good for RebindableSyntax, then I'm +1 on that (but I've never played with that extension, so I don't really know). I'm -1 on (?). We already have bool, which tends to be rather more useful when partially applied.
>>> 
>>> 
>>> On Nov 16, 2016 9:43 PM, "winter" <drkoster at qq.com <mailto:drkoster at qq.com>> wrote:
>>> It seems this’s a very old request, see https://wiki.haskell.org/If-then-else <https://wiki.haskell.org/If-then-else>. I’d like to see following:
>>> 
>>> ifThenElse :: Bool -> a -> a -> a
>>> ifThenElse True  x _ = x
>>> ifThenElse False _ y = y
>>> 
>>> infixr 1 ?
>>> (?) :: Bool -> a -> a -> a
>>> (?) = ifThenElse
>>> 
>>> in Date.Bool module, it will have advantages that:
>>> 
>>> + It’s more composable than syntax.  
>>> + Write (xxx ? yyy $ zzz) instead of (if xxx then yyy else zzz) is more consistent with (f . g $ x) style, and save key strokes.
>>> + In module with RebindableSyntax enabled, you can import ifThenElse to get default behavior.
>>> 
>>> Whether or not to be exported by Prelude is another question, but Data.Bool seems a good place to start with.
>>> 
>>> Cheers~
>>> Winter
>>> 
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>> 
> 
> 
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