SumProduct.hs

module SumProduct (
    KnownColor (..)
  , RGB (..)

  , redColor
  , magenta
  , red
  ) where


-- | To calculate how many possible values the new type has, we count and sum
--   all the possible values, therefore "sum type"
data KnownColor -- the new type's name
  = Red         -- One possible value
  | Blue
  | Green

redColor :: KnownColor
redColor =
  Red

-- | To calculate how many possible values the new type has, we count and
--   multiply the amount of possible values for each type. Therefore "product
--   type"
--

-- data RGB
--   = MkRGB Int Int Int
{-
      ^    ^   ^   ^
      |    |   |   |
      |    |   |   +- This is the blue component
      |    |   |
      |    |   +----- This is the green component
      |    |
      |    +--------- This is the red component
      |
      +------------- This is called the value constructor, or "tag"
-}

magenta :: RGB
magenta =
  MkRGB 255 0 255

-- | Records allow us to name the fields in a product type
--   There is more to records, but we won't talk too much about it here
--
data RGB =
  MkRGB {
    rgbRed   :: Int
  , rgbGreen :: Int
  , rgbBlue  :: Int
  }

red :: RGB
red =
  MkRGB {
    rgbRed   = 255
  , rgbGreen = 0
  , rgbBlue  = 0
  }