package Decimal(DecCounter(..), DecDigit, mkDecCounter) where
import Vector

type DecDigit = Bit 4

interface DecCounter n =
    inc :: Action
    getDigits :: Vector n DecDigit

mkDecCounter :: Module (DecCounter n)
mkDecCounter = do
    digits :: Reg (Vector n DecDigit) <- mkReg (unpack 0)
    return $
        interface DecCounter
            getDigits = digits
            inc = digits := incr digits

incr :: Vector n DecDigit -> Vector n DecDigit
incr xs =
    let addC ci x = if x+ci == 10 then (1, 0) else (0, x+ci)
        (co, xs') = mapAccumL addC 1 xs
    in  xs'