Search icon CANCEL
Arrow left icon
Explore Products
Best Sellers
New Releases
Books
Videos
Audiobooks
Learning Hub
Conferences
Free Learning
Arrow right icon
Arrow up icon
GO TO TOP
Haskell Design Patterns

You're reading from   Haskell Design Patterns Take your Haskell and functional programming skills to the next level by exploring new idioms and design patterns

Arrow left icon
Product type Paperback
Published in Nov 2015
Publisher
ISBN-13 9781783988723
Length 166 pages
Edition 1st Edition
Languages
Arrow right icon
Author (1):
Arrow left icon
Ryan Lemmer Ryan Lemmer
Author Profile Icon Ryan Lemmer
Ryan Lemmer
Arrow right icon
View More author details
Toc

Monad

The Monad class inherits from the Applicative class (only from GHC 7.10 onward; see the Monad as applicative section for more on this):

class (Applicative m) => Monad m where
  return :: a -> m a
  (>>=) :: m a -> (a -> m b) -> m b

The return function looks just like the pure function of the Applicative class (it wraps a value in a Monad class).

The bind operator (>>=) combines a Monad (m a) with a function (a -> m b), which we'll call a monadic function. The monadic function acts on type a of the first monad and returns a new monad of type (m b).

Let's make our Maybe' type a Monad class:

import Control.Monad
import Control.Applicative

data Maybe' a = Just' a | Nothing'
  deriving (Show)

instance Functor Maybe' where
–- ...

instance Applicative Maybe' where
–- ...

instance Monad Maybe' where
  return x = Just' x
  Nothing'  >>= _   = Nothing'
  (Just' x) >>= f ...
lock icon The rest of the chapter is locked
Register for a free Packt account to unlock a world of extra content!
A free Packt account unlocks extra newsletters, articles, discounted offers, and much more. Start advancing your knowledge today.
Unlock this book and the full library FREE for 7 days
Get unlimited access to 7000+ expert-authored eBooks and videos courses covering every tech area you can think of
Renews at $19.99/month. Cancel anytime