Introduction to algebraic datatypes in Haskell

2015-07-21 2043 speaker: S"onke Hahn event: Haskell.SG meetup

using a Haskell module and doctest

** product type data Position

• = Position Int Int
• deriving (Show)

date Position2 =

• Position2 {
  • posX :: Int,
  • posY :: Int
• }
• deriving (Show)

posX and posY takes a Position2 and return an Int

** sum type data Color

• = White
• | Black
• deriving (Show)

isBlack :: Color -> Bool isBlack color = case color of

• Black -> True
• White -> False

** sum of product data Piece

• = Pawn Position Color
• | Rook Position Color
• …

case construct reports a warning for non-exhaustive matches, it can throw an exception at runtime

** random thoughts case vs function definitions with patterns as parmeters the later would reqire changes to multiple lines if you add a new parameter

** newtype for the case of simple wrapper type, for better performance newtype Minute = Minute Int