Prelude> let forall :: (a -> Bool) -> [a] -> Bool ; forall f []= True; forall f (x:xs) = f x  &&  forall f  xs
Prelude> forall even  [2,4,6]
True
Prelude> forall even [2,4,5]
False
Prelude> let forall :: (a -> Bool) -> [a] -> Bool ; forall f []= True; forall f (x:xs) = if (f x)  then forall f  xs else False
Prelude> forall even [2,4,5]
False
Prelude> forall even  [2,4,6]
True
Prelude>