Sha256: 17185e6382652d2483a99ff3a1d576107c1f398d09a6e188955c982b3369735c
Contents?: true
Size: 784 Bytes
Versions: 68
Compression:
Stored size: 784 Bytes
Contents
module BankAccount ( BankAccount
, openAccount, closeAccount
, getBalance, incrementBalance) where
import Control.Concurrent.STM (TVar, atomically, newTVar, readTVar, writeTVar)
newtype BankAccount = BankAccount { unBankAccount :: TVar (Maybe Int) }
openAccount :: IO BankAccount
openAccount = atomically $ BankAccount <$> newTVar (Just 0)
closeAccount :: BankAccount -> IO ()
closeAccount = atomically . flip writeTVar Nothing . unBankAccount
getBalance :: BankAccount -> IO (Maybe Int)
getBalance = atomically . readTVar . unBankAccount
incrementBalance :: BankAccount -> Int -> IO (Maybe Int)
incrementBalance acct delta = atomically $ do
let b = unBankAccount acct
bal <- fmap (delta +) <$> readTVar b
writeTVar b bal
return bal
Version data entries
68 entries across 68 versions & 1 rubygems