Functional Programming Lecture 1 Introduction

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Functional ProgrammingLecture 1 - Introduction

• Professor Muffy Calder

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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

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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

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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 -gt Int -gt Bool
• inlist x False
• inlist x (yys) (x y) True
• otherwise
  inlist x ys
• inlist 3 5,3,6
• inlist 2 5,3,6
• Key concepts
• Types
• Recursion

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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

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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

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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

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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
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Types, Constants and Expressions

• type - set of possible values
• Int
• constant - a particular value in a type
• 27 Int
• expression - can be evaluated
• 23x
• notation 22 gt 4
• 22 evaluates to 4
• The type of is Int-gtInt-Int, i.e.
• __ Int-gtInt-gtInt

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Int and Integer

• Int - 32-bit integers
• Integer - genuine integers
• no limit on size (except memory)
• all operations give correct result
• programmer doesnt have to worry about how much
  memory to allocate
• You will usually use Int.

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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.

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Char

• ASCII characters
• constant - surround with single quote x
  Char
• can compare characters
• c lt Z
• case conversion
• toUpper w gt W
• toLower Q gt q
• toUpper Char -gt Char

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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 lt x) (x lt 10) Bool

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Function application

• Write the name of the function followed by the
  arguments
• Sometimes use terminology rator and rand
• Dont put parentheses around the argument
• sqrt 9.0
• fcn 2 8 13
• 3.4 (sqrt x) 100
• 2 (sqrt (pirr)) y
• E.g. In Maths f(x)
• In FP (f x)