ARexx Book Review  By Arthur R. Tov von Heffen Title: Mastering Amiga ARexx Author: Paul Overaa Publisher: Bruce Smith Books ISBN: 1-873308-13-2 Printing: 1st Edition, 1st Printing, April 1993 Ed: Arthur is a video professional and can be contacted for work commissions in any kind of multimedia. Find him through Megadisc. Thanks to Bruce Smith Books for this and other books.   36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36  Description of the Package A book containing 333 pages, written by someone with a wealth of experience in the subject, gained through years of programming the Amiga at the levels of C and assembler, and from providing intelligent and in depth technical support for many readers of the British Amiga journals, throughout the same period. A disk containing source for the programmes in the book is advertised as available from the publishers, upon receipt of a cheque/postal order for £1.50p. I have not as yet seen the disk, or know if it is available in Australia. Introduction Part 1: The Language Part 2: ARexx Communications Part 3: Inside ARexx Introduction - the Entree The introduction starts with a brief history of Rexx as a language, and the history of ARexx on the Amiga. Then the notion of the ARexx Language's particularly special and quite unique feature - that of being able to communicate with other programmes running concurrently in a multi-tasking environment, and 'glue' or integrate them into coordinated systems greater than the parts - is introduced. A brief discourse on computer structure and different levels of computer programming (and therefore languages), then places ARexx as a High Level language, and presents the relative merits of programming the Amiga in a high level language. A description of what is required for producing an ARexx programme is followed by an outline of the software components that comprise the ARexx software package. The Introduction is followed by a menu of three courses: Firstly The contents of the ARexx programming language - ie the capacity of ARexx to store and process data as a programming language in it's own right. After a brief overview with some short examples to familiarize the reader with the format and layout of ARexx programmes, the author defines the components of the ARexx language with a complete description of the language's elements, followed by an explanation of how the ARexx interpreter functions. Data elements and operators are explained, followed with clause construction, a glossary of ARexx's keywords, and some short, runable examples to exemplify the descriptions. The use and value of using functions follows, illustrated with more examples, with a discussion covering parameter passing, return values, global variables, the exposing of variables, and finally external functions. A description of each of ARexx's built-in functions is then followed by an explanation of 'function libraries' and 'function hosts', and the differences between them. A chapter on 'Flow Control' follows, which covers the options ARexx provides for switching and looping within programmes. The next chapter covers hints and techniques for developing a consistant and effective programming style, and the advantages of doing so. A programme is then described which presents a menu to a shell window, and discussion on this leads into file access and handling, via input and output to the shell. ARexx's unusual but effective method of holding and referencing sets of related data is explained in the section describing Compound Variables. A recurring theme in the Paul Overaa "Programming the Amiga" series of books is the value of using programming design techniques in the process of developing a programme. This book contains a chapter describing several different algorithm design and planning methodologies, including Data-Structured Design, Data-Flow Oriented Design and Warnier Diagrams. Parsing is the technique of splitting a sentence or phrase into a number of components. As ARexx is heavily based on using strings for holding data, it is only natural that ARexx would have a large complement of tools for unpacking and manipulating them, and a chapter effectively describes the many different approaches which ARexx provides. An overview of File I/O is followed by explained examples showing file opening and closing, reading from and writing to files, and seek-locating within them. Then a project is presented, with explained ARexx source, which describes how to create a fully-functional, multi-field database with record entry, edit, store and display functions. This is the largest ARexx programme in the book, and displays many of the programme writing hints and techniques given throughout the book. This first section concludes with a section covering interrupt detection, tracing facilities and debugging techniques. The Second section extends the first by covering the extensions to ARexx provided by ARexx compatible Amiga applications, and details of the methods used for Inter-Process Communication are introduced - with music-playing examples from Octamed, Bars and Pipes and Superjam; and several examples for text editing, using SASC's LSE editor, which display the advantages and freedoms of defining macros for an application using a 'full-blown' programming language. The Third `course' is truly the 'meat' in this sandwich. Called "Interprogram Communications - The Inside Story", this 30 page chapter is a description of the essential mechanism of ARexx's message passing facility. Whereas up til now the author has been wading in the pool of ARexx capability, creating craft which manouvre on the surface, here he dives beneath the surface to uncover and show the structures and processes which occur when programmes interact via ARexx, but viewed from the lower levels of C and assembler.  a) Firstly the data structures, ie message packets, which will be encountered are described, followed by the functions provided to process them ie construct, send, receive, and interpret messages.  b) The source to two example programmes then follow - one in assembler and the other in C.  c) The first example is called ShowRexx.s. This assembly code opens a window and an ARexx port (called 'ShowRexx'), displays the programme's title in the window, then waits for an ARexx message containing the instruction 'Quit'.  d) The second example, 'ShowRexx2', is compiled from three pieces of source code - 'general.h', 'ShowRexx2.h' and 'ShowRexx2.c'. A window is opened on it's own screen, which provides a menu allowing the user to change the background window colour and to quit. An ARexx interface provides the ability to select the menu's functions with ARexx messages of the form 'SELECT MENU Fx', where x is the number of the function's menu item. Both examples are clearly presented, and both are designed to provide simple devices, complete within themselves, yet seeking extension as the path to further understanding. Several appendices close the book, giving further background information about ARexx and its link with Commodore, references to ARexx in the Fish Public Domain library (disks 227 to 466), an extensive glossary, and a bibliography of books generally useful to Amiga programmers. Review: An excellent book by one of the few who could be called the Masters of Amiga Programming. The author's rigourous approach and attention to detail, typical of an effective programmer, create a very resourceful volume. The absolute beginner may find the going a bit difficult, as the book is written with certain programming conventions understood. For those for whom ARexx is a second language, this book should be quite sufficient. For those who have outgrown their first ARexx book, this one makes a perfect complement. Errata: 1. Page 27, Line 24: 'rexxlib.library' should read 'rexxsyslib.library'  36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36 -+- 36