{- 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 <[EMAIL PROTECTED]> 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
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> [email protected]
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>
>
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