Installation and exercises HASKELL Installation and exercises

Installation http://www.haskell.org Main Page  Download Haskell Haskell Engine + GHCi In Windows: Also WinGHCi 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, “HelloWorld.hs” main = do putStrLn "Hello, world!" Change the current directory: :cd <Directory of HS file> Load the file: :load HelloWorld.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: <list1> ++ <list2> 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 Example: 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 hypothenuse2 x y = sqrt(z) where z = x2 + y2 x2 = x^2 y2 = 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 ‘lastOne’ 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 <- readLn 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