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Is it function??
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{-# LANGUAGE DataKinds, TypeOperators, KindSignatures, TypeFamilies #-} | |
{-# LANGUAGE UndecidableInstances, FlexibleInstances, FlexibleContexts #-} | |
module IsFun ( | |
Proxy | |
, isFun | |
, cntArgs | |
) where | |
import Data.Proxy | |
import GHC.TypeLits | |
type family CntArgs (a :: *) :: Nat where | |
CntArgs (a -> b) = 1 + CntArgs b | |
CntArgs a = 0 | |
proxy' :: a -> Proxy (CntArgs a) | |
proxy' _ = Proxy | |
cntArgs :: KnownNat (CntArgs a) => a -> Integer | |
cntArgs x = natVal $ proxy' x | |
isFun :: KnownNat (CntArgs a) => a -> Bool | |
isFun x = cntArgs x > 0 | |
f1 :: Int -> Int | |
f1 = id | |
f2 :: Int -> Int -> Int | |
f2 = const | |
v :: Int | |
v = 0 | |
main = do | |
print $ isFun f1 -- a -> a の a が曖昧で数えられない | |
print $ isFun f2 | |
print $ isFun v | |
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