constr.hs

{-# LANGUAGE DeriveDataTypeable #-}

-- See http://www.reddit.com/r/haskell/comments/pb7dd/how_would_i_write_a_haskell_function_to_do_this/

import Data.Data

data Foo = Bar Int
         | Baz String
  deriving (Show, Eq, Typeable, Data)

hasTypes :: Data a => [a] -> [Constr] -> Bool
hasTypes vs ts = all (uncurry (==)) (zipWith (\v t -> (toConstr v, t)) vs ts)

main :: IO ()
main = do
    print $ hasTypes [Bar 1, Bar 2, Baz "A"] [r, r]
    print $ hasTypes [Bar 1, Baz "A", Bar 2] [r, z]
    print $ hasTypes [Bar 1, Baz "A"] [z, r]
    print $ hasTypes [Bar 1] []
  where
    r = toConstr $ Bar undefined
    z = toConstr $ Baz undefined