Re: Add ifThenElse and (?) to Data.Bool

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 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 mailto:david.feuer@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" mailto:drkoster@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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