Liam Gryff

bank-kata

Implement a bank account that can deposit, withdraw and print a statement to the console.

Follow the Tell, don't ask principle. All methods should be void.

void Deposit(int)
void Withdraw(int)
void PrintStatement()

Develop an API that moves a Mars Rover around on a grid.

You are given the initial starting point (0,0,N) of a rover.
0,0 are X,Y co-ordinates on a grid of (10,10).
N is the direction it is facing (i.e. N,S,E,W).
L and R allow the rover to rotate left and right.
M allows the rover to move one point in the current direction.
The rover receives a char array of commands e.g. RMMLM and returns the finishing point after the moves e.g. 2,1,N

	-- we'll need an instance of `Writer String` for `MonadCurrentDateTime` for our test
	instance MonadCurrentDateTime (Writer String) where
	currentDateTime = pure firstOfJan2019

	testMyBank :: StateT [Transaction] (Writer String) ()
	testMyBank = do
	deposit 200
	withdraw 100
	deposit 3000
	printStatement

	instance MonadCurrentDateTime IO where
	currentDateTime = getCurrentTime -- this comes from Data.Time

	-- in our test file
	instance MonadCurrentDateTime Identity where
	currentDateTime = pure firstOfJan2019

	firstOfJan2019 = UTCTime (fromGregorian 2019 01 01) (secondsToDiffTime 0)

	-- ...
	deposit amount = modify $ \transactions -> transactions ++ [Deposit amount firstOfJan2019]

	-- same for `withdraw`, and in test functions

	-- 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]

	deposit amount = do
	now <- lift currentDateTime
	modify $ \transactions -> transactions ++ [Deposit amount now]

	deposit :: (Monad m, MonadCurrentDateTime m) => Int -> StateT [Transaction] m ()

	withdraw :: (Monad m, MonadCurrentDateTime m) => Int -> StateT [Transaction] m ()

	class MonadCurrentDateTime m where
	currentDateTime :: m UTCTime

	import Data.Time

	data Transaction = Deposit Int UTCTime \| Withdrawal Int UTCTime