On Sun, 2008-05-18 at 21:16 +0400, Bulat Ziganshin wrote:
Hello Derek,
Sunday, May 18, 2008, 9:10:38 PM, you wrote:
This is incorrect. There are two (other) situations where you need type annotations in Haskell 98. One situation is when you use polymorphic recursion, but that is pretty rare unless you are writing nested data types
can you give examples?
-- untested -- all type annotations are necessary -- A nested data type example data PerfectTree a = Leaf a | Succ (PerfectTree (a,a)) size :: PerfectTree a -> Int size (Leaf _) = 1 size (Succ t) = 2 * size t -- a toy example without nested data types f :: Show a => Int -> a -> String f 0 x = show x f n x = f (n-1) (x,x) -- a less toy example bitReverse :: [a] -> [a] bitReverse [x] = [x] bitReverse xs = uncurry (++) . unzip . bitReverse . pairUp $ xs where pairUp [] = [] pairUp (x:y:xs) = (x,y):pairUp xs