pattern.purs

module Main where

import Prelude
import Control.Monad.Eff.Console (log)


-- give a name to an extensible record with fields common to all ducks

type Duck a = { name :: String
              , color :: String | a }


-- function that works on all ducks

display :: forall a. Duck a -> String
display duck = duck.name <> " looks " <> duck.color <> "."


-- different ways to fly abd stuff to say

woosh name = name <> " flies, woosh!"
wee name = name <> " flies, wee!"
quack name = name <> " quacks!"
squeak name = name <> " squeaks!"


-- ducks

mallard :: Duck ( fly :: String, say :: String )
mallard = 
  let name = "Mally"
  in { name, color: "blue", fly: woosh name, say: quack name } 

redhead :: Duck _
redhead = 
  let name = "Red" 
  in { name, color: "red", fly: wee name, say: quack name }

rubber = 
  let name = "Rube"
  in { name, color: "yellow", say: squeak name }


-- tests

main = do
  log mallard.fly --> Mally flies, woosh!

  log redhead.fly --> Red flies, wee!
  
  -- log rubber.fly 
  -- -- will not compile: rubber can't fly
  -- -- in OO, there is no error but nothing happens
  
  log mallard.say --: Mally quacks!
  
  log rubber.say --> Rob squeaks!

  log (display mallard) --> Mally looks red.

  
-- you can extend anything without touching anything else
-- add a way to fly or say
-- add functions common to all ducks
-- add ghost duck with new opacity attribute