HASKELL Installation and exercises Installation http www haskell

HASKELL Installation and exercises

Installation • http: //www. haskell. org • Main Page Download Haskell • Haskell Engine + GHCi – In Windows: Also Win. GHCi • GHCi: Haskell Compiler/Interpreter

GHCi

Interpreter: Try it out! • Math Operations and Functions – 2+2 – 10^2 – log(10) • Lists – – [1, 2, 3] [1. . 10] [“x”, ”y”, ”z”] [‘x’, ’y’, ’z’] • Variable Assignment – let x = 5 in x^2 + 2*x + 4

Running Haskell Script Files • Create a new file, “Hello. World. hs” – main = do put. Str. Ln "Hello, world!" • Change the current directory: – : cd <Directory of HS file> • Load the file: – : load Hello. World. hs • Run the file: – main

Running Haskell Files

Basic List Manipulation • • • Get first element: head <list> Get last element: tail <list> Get nth element: <list> !! N Get first n elements: take n <list> Remove first n elements: drop n <list> Length of list: length <list> Sum of numbers: sum <list> Product of numbers: product <list> Append lists: <list 1> ++ <list 2> Reverse list: reverse <list>

Functions in Haskell • Prefix Operations: Operation before operands. – In Math: f(x, y) + z – In Haskell: f x y + z • Function has higher priority – In Math: f(x, y+z) – In Haskell: f x (y+z) • Function of functions – In Math: f(x, g(y)) – In Haskell: f x (g y) • Recursion is highly encouraged

Defining functions • Defined in a Haskell script file – The “=“ operator – Arguments • Example: – double x = x + x – squared x = x * x – hypothenuse x y = sqrt(x^2 + y^2)

Implicit Grouping • Used when defining functions • Same spacing/tabbing to denote groups hypothenuse 2 x y = sqrt(z) where z = x 2 + y 2 x 2 = x^2 y 2 = y^2

Exercises • Fix the syntax error and try the following program: N = a ’div’ length xs where a = 10 xs = [1, 2, 3, 4, 5]

Exercises • Write two possible definitions of the ‘last. One’ function that selects the last element of a list. • Write two possible definitions of an ‘init’ function that removes the last element of a list. • Write a function that receives a list and returns a list of the original values of the list plus two

Exercises • Write a function for the factorial operation • Write a function that receives a numerical user input and returns the factorial of that number – To obtain user input: • X <- read. Ln • Write a function that receives a numerical user input ‘x’ and returns a list from 0 to x

Exercises • EXTRA: Write a function that calculates the nth number of the Fibonacci sequence – Fibonacci numbers: • f(n) = f(n-1) + f(n-2) • f(0) = 1 • f(1) = 1