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Functional Programming Lecture 1 - Introduction

Functional Programming Lecture 1 - Introduction. Professor Muffy Calder. About the Course. the Haskell functional language Lectures + Laboratories + Problem Sessions 2 Assignments Web site Lecture notes Assignments and problem sheets Resources Textbook

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Functional Programming Lecture 1 - Introduction

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  1. Functional ProgrammingLecture 1 - Introduction Professor Muffy Calder

  2. About the Course • the Haskell functional language • Lectures + Laboratories + Problem Sessions • 2 Assignments • Web site • Lecture notes • Assignments and problem sheets • Resources • Textbook Functional Programming in Haskell by Simon Thompson

  3. Programming Languages • imperative: Ada, C, Pascal, … • object: Java, C++, Smalltalk … • logic: Prolog, ... • functional: Haskell, ML, Lisp, Scheme, … • Haskell named after Haskell B. Curry • Not Schoenfinkel • Haskell is lazy • ML is strict

  4. What is Functional Programming? • Based on mathematical functions • Example • A function to compute whether or not an integer is in a list of integers inlist :: Int -> [Int] -> Bool inlist x [] = False inlist x (y:ys) = | (x == y) = True | otherwise = inlist x ys inlist 3 [5,3,6] inlist 2 [5,3,6] • Key concepts • Types • Recursion

  5. Why use Functional Languages? • Concise and powerful style • Rapid prototyping • Strong error checking by intepreter/compiler • Reduced debugging time • Reliable, correct software • Formal reasoning • Why teach it in second year? • Good discipline + more abstract way of thinking

  6. Haskell • Standard functional language • developed by international committee • 3 people from GU on that committee • Used as the basis for numerous projects, in numerous countries • Has technical characteristics that support software engineering and formal methods

  7. Hugs • An interactive interpreter for Haskell98 • Hugs98 for windows • Very quick ‘compilation’ and error checking • Available on nearly all computers • Free software • See http://haskell.org/hugs

  8. Overview of Functional Programming 2 slogans • everything is a function • every function has a type FP consists of • defining types • defining functions • applying functions and calculating the resulting expression typed inputs typed output f

  9. Types, Constants and Expressions • type - set of possible values Int • constant - a particular value in a type 27:: Int • expression - can be evaluated 2+3*x • notation: 2+2 => 4 “2+2 evaluates to 4” The type of + is Int->Int-Int, i.e. _+_ :: Int->Int->Int

  10. Int and Integer • Int - 32-bit integers • Integer - genuine integers • no limit on size (except memory) • all operations give correct result • programmer doesn’t have to worry about how much memory to allocate You will usually use Int.

  11. Float and Double • Single and double precision floating point numbers • Does not give exact real arithmetic - there can be roundoff errors • It is unlikely that you will use these types in this course.

  12. Char • ASCII characters • constant - surround with single quote ‘x‘ :: Char • can compare characters `c` < ‘Z’ • case conversion • toUpper ‘ w ‘ => ‘ W ‘ • toLower ‘Q ‘ => ‘ q ‘ • toUpper :: Char -> Char

  13. Bool • Boolean values, used to control conditionals • only two constants: False :: Bool and True :: Bool • b && c (conjunction) • b || c (disjunction) • not b (negation) Example: ( 3 <= x) && (x <= 10) :: Bool

  14. Function application • Write the name of the function followed by the arguments • Sometimes use terminology rator and rand • Don’tput parentheses around the argument sqrt 9.0 fcn 2 8 13 3.4 + (sqrt x) * 100 2 * (sqrt (pi*r*r)) + y E.g. In Maths f(x) In FP (f x)

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