On Thu, Sep 27, 2007 at 05:31:51PM +0200, apfelmus wrote:
Tristan Allwood wrote:
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
Note that this function is not referentially transparent since
isWHNF 2 = True
but
isWHNF (1+1) = False
although 1+1 = 2. In other words, it messes up the language semantics (extensional equality) which is bad. Indeed. Does it still mess up with the result in IO Bool (as was my intent)?
Ah, I do realise my example use case above needs some =<<'s inserting into it which may have led to some confusion. Tris -- Tristan Allwood PhD Student Department of Computing Imperial College London