Practical OCaml

483 Pages·2006·1.955 MB·English

by  Joshua B Smith

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Practical OCaml
P
Dear Reader, r
a
OCaml, like many functional programming languages, has historically managed
to maintain a low profile despite widespread use in industries ranging from c
microchip fabrication to financial analysis. Yet with functional programming
t
recently experiencing a renaissance of sorts, interest in this powerful language is Practical
i
picking up sharply. And for good reason. Sporting features such as a robust object c
system, type safety, and an expansive standard library, OCaml is a language that
a
encourages pragmatic instead of dogmatic solutions.
I wrote this book to teach you all about this general-purpose language’s won- l
derful array of talents. Beginning with an overview of the OCaml installation
O OCaml
process and toplevel, the interactive OCaml interpreter, you’ll have a solid
framework in place for investigating the language’s syntax, semantics, and
types in the chapters that follow. You’ll also learn about advanced features such
as the ocamldoc documentation-generation tool, threading, and the Camlp4
C
preprocessor and pretty printer.
Along the way, you’ll apply what you’ve learned by implementing a number of
practical OCaml-driven applications. I’ve omitted the typical and tired Towers
of Hanoi and four-function calculator examples. Instead, I choose to focus on a
building applications capable of performing complex log-file processing, web
crawling, filtering spam, and even broadcasting audio over a network using the
Shoutcast protocol.
m
Adding to the excitement, I’ll occasionally delve into tangential topics such
as OCaml’s impurities from the functional programming perspective and show
you how to overcome them by using mutability, references, and classes.
Joshua B. Smith
l
Master the OCaml functional programming language
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Practical
OCaml
Joshua B. Smith
620Xfmfinal.qxd 9/22/06 4:21 PM Page ii
Practical OCaml
Copyright © 2006 by Joshua B.Smith
All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means,
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Contents at a Glance
About the Author .................................................................xxi
About the Technical Reviewer .....................................................xxiii
Acknowledgments ...............................................................xxv
nCHAPTER 1 Why Objective Caml (OCaml)?...................................1
nCHAPTER 2 Interacting with OCaml:The Toplevel...........................11
nCHAPTER 3 Syntax and Semantics.........................................21
nCHAPTER 4 Understanding Functions ......................................33
nCHAPTER 5 Practical:Creating a Simple Database..........................51
nCHAPTER 6 Primitive and Composite Types ................................61
nCHAPTER 7 Practical:Simple Database Reports,Exports,and Imports ......73
nCHAPTER 8 Collections ....................................................89
nCHAPTER 9 Files and File I/O..............................................113
nCHAPTER 10 Exception Handling...........................................123
nCHAPTER 11 Practical:A URI Library .......................................135
nCHAPTER 12 Using Ocamldoc..............................................145
nCHAPTER 13 Modules and Functors ........................................155
nCHAPTER 14 Practical:A Spam Filter.......................................169
nCHAPTER 15 Practical:A Network-Aware Scoring Function .................179
nCHAPTER 16 Ocamllex and Ocamlyacc .....................................193
nCHAPTER 17 Practical:Complex Log File Parsing ...........................213
nCHAPTER 18 The Objective Part of Caml....................................225
nCHAPTER 19 Digression: OCaml Is Not Pure ................................249
nCHAPTER 20 Digression: Functional Programming..........................261
nCHAPTER 21 Practical:Web Programming..................................273
nCHAPTER 22 Practical:A Shoutcast Server .................................293
nCHAPTER 23 Using Threads................................................309
nCHAPTER 24 Practical:A Concurrent Web Crawler..........................329
nCHAPTER 25 Interfacing with OCaml .......................................349
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nCHAPTER 26 Practical:Time and Logging Libraries .........................359
nCHAPTER 27 Processing Binary Files.......................................375
nCHAPTER 28 OCaml Development Tools ....................................401
nCHAPTER 29 Camlp4.......................................................411
nCHAPTER 30 Conclusion ...................................................431
nINDEX .......................................................................445
v
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Contents
About the Author .................................................................xxi
About the Technical Reviewer .....................................................xxiii
Acknowledgments ...............................................................xxv
nCHAPTER 1 Why Objective Caml (OCaml)? ..............................1
Who Benefits from Learning OCaml?................................1
WhatIs OCaml Good For? .........................................2
Who Uses OCaml?................................................3
Where Did OCaml Come From? ....................................3
WhatIs the Current State of the Art?................................4
Why This Book?..................................................4
What Is Covered?.................................................4
Interacting with OCaml:The Toplevel (Chapter 2)................4
Syntax and Semantics (Chapter 3).............................5
Understanding Functions (Chapter 4)...........................5
Practical:Creating a Simple Database (Chapter 5) ...............5
Primitive and Composite Types (Chapter 6) .....................5
Practical:Simple Database Reports,Exports,and
Imports (Chapter 7) .......................................5
Collections (Chapter 8).......................................5
Files and File I/O (Chapter 9)..................................5
Exception Handling (Chapter 10)...............................6
Practical:AURI Library(Chapter 11) ...........................6
Using OCamldoc (Chapter 12).................................6
Modules and Functors (Chapter 13)............................6
Practical:ASpam Filter (Chapter 14)...........................6
Practical:A Network-Aware Scoring Function (Chapter 15)........6
Ocamllex and Ocamlyacc (Chapter 16) .........................6
Practical:Complex Log File Parsing (Chapter 17) ................6
The Objective Part of Caml (Chapter 18)........................7
Digression:OCaml Is Not Pure (Chapter 19).....................7
Digression:Functional Programming (Chapter 20) ...............7
vii
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viii nCONTENTS
Practical:Web Programming (Chapter 21) ......................7
Practical:A Shoutcast Server (Chapter 22)......................7
Using Threads (Chapter 23)...................................7
Practical:A Concurrent Web Crawler (Chapter 24) ...............7
Interfacing with OCaml (Chapter 25) ...........................7
Practical:Time and Logging Libraries (Chapter 26)...............8
Practical:Processing Binary Files (Chapter 27) ..................8
OCaml Development Tools (Chapter 28)........................8
Camlp4 (Chapter 29).........................................8
Conclusion (Chapter 30)......................................8
What Isn’t Covered? ..............................................8
What Are My Expectations for You?.................................8
Conclusion ......................................................9
nCHAPTER 2 Interacting with OCaml: The Toplevel .....................11
Distributions of OCaml...........................................12
Official Distribution .........................................12
Unofficial Releases .........................................12
Installing OCaml.................................................12
Windows ..................................................12
Linux .....................................................14
Interacting with the Toplevel.................................16
Hello World................................................17
Final Notes ................................................18
Code Files......................................................18
Basic Code Files............................................19
Custom Toplevel ................................................20
Why Would You Do This?....................................20
HowDo You Do This?.......................................20
Conclusion .....................................................20
nCHAPTER 3 Syntax and Semantics......................................21
Variables in a Constant Language .................................21
WhatVariables Are Not......................................21
Let Bindings ...............................................22
Understanding Scope .......................................23
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nCONTENTS ix
Records and Types..............................................23
Creating Enums and Simple User-Defined Types ...............26
Defining Records...........................................28
More About Math................................................29
Integers and Floats .........................................29
Others ....................................................29
Defining Functions...............................................30
Imperative Programming ....................................30
Recursion .................................................30
Pattern Matching...........................................31
Signatures......................................................32
Conclusion .....................................................32
nCHAPTER 4 Understanding Functions...................................33
Creating Values and Functions....................................33
Functions Must Have One Return Type ........................35
Constraining Types in Function Calls..........................35
Using Higher-Order Functions.....................................36
Using Lists.................................................37
Anonymous Functions.......................................37
Why Use Anonymous Functions? .............................39
Understanding Consequences of Functions As Data.............39
Curried Functions...........................................41
Working with the Distance Type...................................41
Creating Recursive Functions.....................................44
Why Do Recursive Functions Need a Special Designation?.......45
Tail Recursion and Efficient Programming .....................45
Doing More Pattern Matching.....................................46
Understanding the Default Match.............................47
Bindings Within Pattern Matches .............................47
Guarded Matches:AReturn to the Distance Calculator ..........48
Understanding Built-in Functions..................................48
Using Labels and Optional Arguments..............................49
Conclusion .....................................................50