Gracjan Polak wrote:
Hello all,
I've got two questions, both are space related so I'll put them in one e-mail.
1. I'd like to have function intern, that behaves essentially like id, but with the following constraint: if x==y then makeStableName(intern x)==makeStableName(intern y) Reasoning behind this hack: objects equal (as in Eq) should occupy the same place in memory. I've got to parse quite large file, most tokens are the same. Haskell speed is very good, but I constantly run out of memory. Here is something I wrote, but it doesn't work :(
The code below seems to work for strings, and should be generalizable to any type for which you have a hash function: import Data.HashTable as H import System.IO.Unsafe (unsafePerformIO) {-# NOINLINE stringPool #-} stringPool :: HashTable String String stringPool = unsafePerformIO $ new (==) hashString {-# NOINLINE shareString #-} shareString :: String -> String shareString s = unsafePerformIO $ do mv <- H.lookup stringPool s case mv of Just s' -> return s' Nothing -> do H.insert stringPool s s return s It seems very similiar to your code, except that it uses HashTable instead of Map. /Björn