{- 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
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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