FACWHAT?

FACSKELL is the Founders & Coders Haskell Club. We are currently learning Haskell by reading CIS 194: Introduction to Haskell (Spring 2013) by Brent Yorgey. We are also learning from other books:

• Learn you a Haskell for great good
• Real world Haskell

Find and post your questions on Reddit Haskell, Reddit Haskell Questions or on Stackoverflow

For a more detail list of documentation you can have a look at the Haskell website

Why

Because learning Haskell is cool!

What is Haskell

Haskell is:

• Functional
• Pure
  • Immutable
  • No side effects
  • A same function with the same arguments will return the same outputs
• Lazy
• Typed

Types

Haskell has the usual types : Bool, Int, Integer, Char, String. The Char type is represented with single quote 'C', the Sting type is represented with double quotes "myString". Haskell has also some more useful types:

• Pairs:

p :: (Int, Char)

• List:

l :: [Integer] -- a list is a head and a tail (x:xs)

Alias type

You can use the keyword type to create an alias for a type.

type St = String
f :: St -> St

Algebraic Data Type

You can create a new type with the keyword data:

data Tree = Empty | Leaf Int | Node Tree Tree

Here we create the type constructor Tree whith the following data constructors:

• Empty
• Leaf Int
• Node Tree Tree

Leaf and Node take parameters! type constructor and data constructor must begin with a capital letter!

Combining functions

You can combine functions:

 myOtherFunc (myFirstFunc a)

Two useful operators:

. Which correspond to the mathematic composition. The result of the fist function become the input of the second function

(myOtherFunc . myFirstFunc) a

$ Replace parenthesis. Everything after $ will be executed before the things before the $ (everything after $ has a higher precedence)

myOtherFunc $ myFirstFunc a

Haskell load by default the Prelude module which contains a lot of useful functions

You can find all the documentation of Haskell on Hoogle