Hi, Does anyone know if there is a function that tells you if a haskell value has been forced or not? e.g. isWHNF :: a -> IO Bool let x = (map succ [0..]) in do putStrLn . show (isWHNF x) -- False putStrLn . show . head $ x putStrLn . show (isWHNF x) -- True putStrLn . show (isWHNF (Just undefined)) -- True If not, would it be hard/easy/possible to implement on-top-of or using GHC? I'm happy (if it's possible) to have a stab at implementing it myself, so any pointers to right directions would be helpful. I'm thinking it could be useful to allow creation of sparse-check [1] like libraries without needing a separate logic encoding, or things along those lines / in that area. Cheers, Tris [1] http://www-users.cs.york.ac.uk/~mfn/sparsecheck/index.html#lim -- Tristan Allwood PhD Student Department of Computing Imperial College London