Curry: An Integrated Functional Logic Language

not :: Bool -> Bool
not True = False
not False = True
-- Conditional
if_then_else :: Bool -> a -> a -> a
if_then_else True t _ = t
if_then_else False _ f = f
otherwise :: Bool
otherwise = True
-- Disequality
(/=) :: a -> a -> Bool
x /= y = not (x==y)
-- Pairs
data (a,b) = (a,b)
fst :: (a,b) -> a
fst (x,_) = x
snd :: (a,b) -> b
snd (_,y) = y
-- Unit type
data () = ()
-- Lists
data [a] = [] | a : [a]
-- First element of a list
head :: [a] -> a
head (x:_) = x
-- Remaining elements of a list
tail :: [a] -> [a]
tail (_:xs) = xs
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