bank-kata-haskell-date-1.hs

-- our Transaction type
data Transaction = Deposit Int | Withdrawal Int

-- our bank functions
deposit :: Monad m => Int -> StateT [Transaction] m ()
deposit amount = modify $ \transactions -> transactions ++ [Deposit amount]

withdraw :: Monad m => Int -> StateT [Transaction] m ()
withdraw amount = modify $ \transactions -> transactions ++ [Withdrawal amount]

printStatement :: (Monad m, MonadStatementPrinter m) => StateT [Transaction] m ()
printStatement = do
  transactions <- get
  let statement = toStatement transactions
  lift $ printSt statement

-- in our test file
it "deposits money" $ do
  runIdentity (execStateT (deposit 100) newBank) `shouldBe` [Deposit 100]

it "withdraws money" $ do
  runIdentity (execStateT (withdraw 100) newBank) `shouldBe` [Withdrawal 100]

it "prints a statement" $ do
  execWriter (evalStateT printStatement [Deposit 100]) `shouldBe` "Desposited 100 | Balance 100\n"