Parametric polymorphism (generics)

length :: [a] -> Int

Type constraint after :: and before => 

(+) :: (Num a) => a -> a -> a

Num is a typeclass.

Guards

mySignum x
    | x < 0     = -1
    | x > 0     = 1
    | otherwise = 0


Pattern matching
pts :: Int -> Int
pts 1 = 10
pts 2 = 6
pts 3 = 4
pts 4 = 3
pts 5 = 2
pts 6 = 1
pts _ = 0


Where

log2 x = higher x 0
        where
        higher x n
                | power 2 n > x = n - 1
                | otherwise     = higher x (n + 1)

map 

{- higher order function (has a function as an argument) -}

Modules

import Data.List

foldr f acc xs -- fold right associative

foldl -- left associative

foldl' -- eager evaluation

foldr1 -- use last element as initial accumulator

Lists

init -- all but last element

List Comprehensions

evensMinusOne es = [n - 1 | n <- es, isEven n]

Data

data Anniversary = Birthday String Int Int Int       -- name, year, month, day
                 | Wedding String String Int Int Int -- spouse name 1, spouse name 2, year, month, day

As patterns

contrivedMap f list@(x:xs) = f list x : contrivedMap f xs

Do

main = do  
    putStrLn "What's your first name?"  
    firstName <- getLine  
    putStrLn "What's your last name?"  
    lastName <- getLine  
    let bigFirstName = map toUpper firstName  
        bigLastName = map toUpper lastName  
    putStrLn $ "hey " ++ bigFirstName ++ " " ++ bigLastName ++ ", how are you?"