Maybe everytime you use 'cell' you tell haskell to create NEW cell.
Try this:
push' i cell = modifyIORef cell (++ [i])
main = do
cell <- newIORef []
push' "x" cell {- push' 3 cell will be incorrect in this case -}
push' "o" cell
readIORef cell >>= return
Why the original code porduces [(),()] but not [] I cannot undestand.
15.03.2012, 23:53, "gladstein@gladstein.com"
Why does the following program compile and produce the results it does? It seems like 3 and "x" got interpreted as the same type, (). Thanks in advance for your help.
import Data.IORef import System.IO.Unsafe
cell = unsafePerformIO $ newIORef []
push i = modifyIORef cell (++ [i])
main = do push 3 push "x" readIORef cell >>= return
*Main> :browse cell :: GHC.IORef.IORef [a] push :: a -> IO () main :: IO [a]
*Main> main [(),()]
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