Neil Leslie Outline Haskell Ipds4. 3 Writing Haskell Programs Scripts 4 Mastering Haskell Programming

Haskell I
Neil Leslie
Outline
Introduction
Key points about Haskell and functional programming
A session with HUGS
Writing Haskell Programs
Mastering Haskell Programming
Summary
Haskell I
Neil Leslie
March 2006
Neil Leslie Haskell I
http://www.mcs.vuw.ac.nz/~neil/ http://www.vuw.ac.nz/home/index.asp http://www.mcs.vuw.ac.nz/~neil/ http://www.mcs.vuw.ac.nz/~neil/

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
1 Introduction Texts Compilers and interpreters
2 Key points about Haskell and functional programming
3 A session with HUGS
3 Writing Haskell Programs Scripts
4 Mastering Haskell Programming
5 Summary
http://www.mcs.vuw.ac.nz/~neil/ http://www.vuw.ac.nz/home/index.asp http://www.mcs.vuw.ac.nz/~neil/

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Introduction
Functional programming languages are based on a very simple model of computation. Their simple foundations means that they provide us with a very clear setting in which to study many important ideas in programming An understanding of functional programming languages and techniques, as well as being valuable for its own sake, also provides the programmer with a new perspective on other programming paradigms.

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Texts
Haskell The Craft of Functional Programming by Simon Thompson.
Introduction to functional programming using Haskell by Richard Bird
The Haskell Road to Logic, Maths and Programming by Kees Doets and Jan van Eijck
Thompson and Bird are both on 3-day loan in the library. The web site http://www.haskell.org/ has more Haskell resources and tutorials.
http://www.mcs.vuw.ac.nz/~neil/ http://www.vuw.ac.nz/home/index.asp http://www.haskell.org/ http://www.mcs.vuw.ac.nz/~neil/

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Compilers and interpreters
In this course we will use HUGS: Hugs is an interpreter for Haskell, a standard non-strict functional programming language. Hugs implements almost all of version 1.4 of the Haskell standard, except for the module system. The name HUGS is a mnemonic (sic) for the Haskell User’s Gofer System.
There is a HUGS interpreter available on the MCS system. Type hugs at the prompt.

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Versions of Haskell are available for PC, Macs. . . which you can use at home. Look at http://www.haskell.org/ for details. There are Haskell compilers available, but for this course an interpreter is sufficient.
http://www.mcs.vuw.ac.nz/~neil/ http://www.vuw.ac.nz/home/index.asp http://www.haskell.org/ http://www.mcs.vuw.ac.nz/~neil/

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
The key points are:
functional programming is about evaluating expressions;
functions defined on inductively defined data types (e.g. Int, lists, trees) use recursion;
Haskell has a polymorphic type system;
Haskell allows us to define higher-order functions;

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
the Haskell system can infer the type of a well-typed expression;
Haskell is a sugaring of the λ-calculus;
Haskell uses lazy evaluation.

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
A session with HUGS
greta-pt: [~] % hugs __ __ __ __ ____ ___ _________________________________________ || || || || || || ||__ Hugs 98: Based on the Haskell 98 standard ||___|| ||__|| ||__|| __|| Copyright (c) 1994-2001 ||---|| ___|| World Wide Web: http://haskell.org/hugs || || Report bugs to: hugs-bugs@haskell.org || || Version: December 2001 _________________________________________
Haskell 98 mode: Restart with command line option -98 to enable extensions
Reading file "/usr/pkg/share/hugs/lib/Prelude.hs":
Hugs session for: /usr/pkg/share/hugs/lib/Prelude.hs Type :? for help Prelude>

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Prelude> :?
Prelude> :set +t +s
Prelude> 42
Prelude> 6*7
Prelude> 5 + 6 * 7

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Prelude> [1,2,3]
Prelude> ['a', 'b', 'c']
Prelude> mod
Prelude> div
Prelude> [mod, div]

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Prelude> map
Prelude> chr
Prelude> map chr [65..90]

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Prelude> [1..]
Prelude> take
Prelude> take 5 [1..10]
Prelude> take 5 [1..]

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Generally, we can think of programming as:
describing data, and
explaining how to operate with the data.
In Haskell:
we describe the data using types
we describe the algorithms using functions
Functions are defined by writing out equations, or more accurately reductions.

Haskell I
Neil Leslie
Outline
Introduction
A session with HUGS
Summary
Scripts
We write programs (often called scripts) in a text file, and then load this file. The definitions made in the script are then available to the interpreter. One file, called the Prelude i

Neil Leslie Outline Haskell Ipds4. 3 Writing Haskell Programs Scripts 4 Mastering Haskell Programming

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