-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello everyone, I am trying to write a generalisation of memoisation for a couple of backtracking algorithms that I wrote (which don't specify a memoisation technique), by keeping a local destructive update using unsafePerformIO and IORef - neither of which I have used before and I am struggling to figure out. I am going from the document: http://haskell.org/hawiki/GlobalMutableState I am not sure if: a) this is even possible b) if a) holds, if this is a good thing Here is some code to help demonstrate what I intend: {-# OPTIONS_GHC -fglasgow-exts #-} import Data.Ix - -- implementations must guarantee that - -- memo f k is equivalent to f k - -- but may otherwise use local destructive updates class Memo k v where memo :: (k -> v) -> k -> v instance (Ix k) => Memo k v where memo f k = error("todo: array") instance (Ord k) => Memo k v where memo f k = error("todo: binary tree") - -- Tony Morris http://tmorris.net/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGkZlFmnpgrYe6r60RArT8AJ4iFVyzmUN1pdxpMBokZpj48CiqRgCfReIe 2yZ55LMcFs24TJOVeCV4tbo= =IR5s -----END PGP SIGNATURE-----