{- compile with ghc --make stm.hs -} module Main where import Control.Concurrent.STM type Account = TVar Int withdraw :: Account -> Int -> STM () withdraw acc amount = do bal <- readTVar acc writeTVar acc (bal - amount) main = do account <- atomically $ newTVar 100 atomically $ withdraw account 50 value <- atomically $ readTVar account print value On 12/23/07, Galchin Vasili wrote:

Hello,

My brain is a "out to lunch". I have read the paper "Beautiful Concurrency" (as well as a bunch of "gaming" papers regarding multi cores). I am playing with the "Account" example in the paper. In the paper, the alias "type Account = TVar Int" is used. I want to actually apply the function "withdraw" to an example "Account" parameter. I keep getting a type check error. Can someone give me a concrete example of

...

withdraw ......

??

Kind regards, Vasya

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