Re: [Haskell-cafe] Re: isWHNF :: a - IO Bool ?
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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: isWHNF :: a - IO Bool ?
On Thu, 2007-09-27 at 16:57 +0100, Tristan Allwood wrote: 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)? In IO this should be fine, as IO is explicitly a non-determinism monad (along with everything else). jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
