61: Getting Haskell Unit 2 (TypeClass)

Follow up

• Elm does not currently support type classes.

  • Does it need to?

Using TypeClasses

• Implement your own type classes
• Understand polymorphism in Haskell
• `Know when to use deriving
• Search for documentation with Hackage and Hoogle

Show

class Show a where
  show :: a -> String

• turns any value into a string for output
• So the output we see from GHCI
• automatically derived typeclass Vanillia | Chocolate

Ord

class Eq a => Ord a where
  compare :: a -> a -> Ordering
  (<) :: a -> a -> Bool
  (<=) :: a -> a -> Bool
  (>) :: a -> a -> Bool
  (>=) :: a -> a -> Bool
  max :: a -> a -> a
  min :: a -> a -> a

• Cool, Ord is defined as a Eq class. oh that’s rad
• well i guess if you’re gonna order something you’ll need to compare it’s equally, just like it says in the the compare definition.
• compare :: Ord a => a -> a -> Ordering
• man it makes so much sense it’s a bit frightening.

EQ

class Eq a where
  (==) :: a -> a -> Bool
  (/=) :: a -> a -> Bool

• pretty straight forward takes, 2 values and returns a bool, True or False

Bounded

class Bounded a where
  minBound :: a
  maxBound :: a

• no functions just values.
• members of bounded must provide a way to get their Upper and Minimum limit. Char and Int are bounded

• Now on to programming with Types, Things are getting pretty good.

  • Creating types with and | or
  • Semigroups
  • Parameterized Types
  • The Maybe type

The podcast space

• Dynamic Ad Insertion and other monitizations

• Wild World of Podcast Ads

Resources

• Pushed code to exercise repo

Get Programming With Haskell

• Why type classes aren’t important in Elm yet
• Monads are like burittos

Follow

• JavaScript to Elm

  • Twitter: @jstoelm
  • Email: jesse@jstoelm.com

• Jesse Tomchak

  • Twitter: @jtomchak