Haskell的“功能”在哪里？

Question

If you use pointfree on the code \\btf -> if b then t else f , the answer you get is if' .

Where is if' defined?

Answer 1

It's worth mentioning that the if' function exists in base since version 4.7, but it's called bool (in style with either and maybe ).

bool :: a -> a -> Bool -> a
bool f _ False = f
bool _ t True  = t

is defined in Data.Bool .

Answer 2

According to Hayoo , it is defined in the following three packages:

if' :: Bool -> a -> a -> a

1. utility-ht - Data.Bool.HT

   if-then-else as function.

   Example:

    if' (even n) "even" $ if' (isPrime n) "prime" $ "boring" 

2. plailude - Plailude

   If True then the first value, else the second.

3. CLASE - Data.Cursor.CLASE.Util

The two main search engines for Haskell that I know of are Hoogle and Hayoo .