Haskell Cheat Sheet

Basics:

• Function Definition:

add :: Int -> Int -> Int
add x y = x + y

• Type Declarations:

name :: String
name = "John"

age :: Int
age = 25

• Lists:

numbers :: [Int]
numbers = [1, 2, 3, 4, 5]

strings :: [String]
strings = ["apple", "banana", "cherry"]

Pattern Matching:

• Matching on Values:

isZero :: Int -> Bool
isZero 0 = True
isZero _ = False

• Matching on Lists:

head' :: [a] -> a
head' (x:_) = x
head' []    = error "Empty list"

Higher-Order Functions:

• Map Function:

square :: Int -> Int
square x = x * x

squares :: [Int] -> [Int]
squares = map square

• Filter Function:

isEven :: Int -> Bool
isEven x = x `mod` 2 == 0

evens :: [Int] -> [Int]
evens = filter isEven

Lambda Expressions:

• Anonymous Function:

double :: Int -> Int
double = \x -> x * 2

Typeclasses:

• Defining Typeclasses:

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

• Implementing Instances:

instance Eq Bool where
    True  == True  = True
    False == False = True
    _     == _     = False

Monads:

• Maybe Monad:

divide :: Double -> Double -> Maybe Double
divide _ 0 = Nothing
divide x y = Just (x / y)

IO Operations:

• Printing to Console:

main :: IO ()
main = putStrLn "Hello, Haskell!"

• Reading from Console:

main :: IO ()
main = do
    putStrLn "What's your name?"
    name <- getLine
    putStrLn $ "Hello, " ++ name ++ "!"

This Haskell cheat sheet covers basic syntax, common constructs, and functional programming concepts. Haskell’s expressive and concise syntax makes it a powerful language for various applications, including mathematical modeling, compiler