-------------------------- AREXX PROGRAMMING - Part 1 By Scott L. Wilcox -------------------------- (EDITOR'S NOTE: This begins a series of tutorials designed as an introduction to the ARexx programming language. You will need the ARexx software to make use of this column. It's available retail for about $30. It's published by William S. Hawes, POB 308, Maynard, MA 01754. Telephone 508-568-8695. There has been rumbling that ARexx will be supported by the yet-to-be-released Workbench 1.4, but we have no definitive word on this.) ARexx is the Amiga version of the Rexx programming language. Programs are written in plain text (ASCII) on any text editor or word-processor that saves in ASCII. It is an interpretive language and has many features that make it very useful as a macro language, but it is also a good, general purpose programming language. Instructions are the basic commands in an ARexx program. They are the built-in "commands" the interpreter executes. There are presently 32 instructions in ARexx (v.1.10). All other operations are performed by functions, which we will examine at another time. Consider the following simple ARexx program: /* A simple ARexx program. */ say 'Hello, Jumpdisk! Look, Ma, I'm programming!' This program is made of one instruction and a string. The SAY instruction writes to the console the expression that follows. It is equivalent to the PRINT command in Basic. The string can be enclosed in single or double quotes. The above program begins with a null clause. All ARexx programs must begin with a null clause or comment line. Anything within the '/* */' characters are considered null clauses. They are thrown out when read by the interpreter and do not slow down a program's execution. They may appear anywhere in a program. /* This is a comment, or null clause! */ There are other kinds of clauses (label, assignment, command), but we will concentrate on instruction clauses in this article. Instruction clauses are simply clauses that contain instructions, so are aptly named. Let's add more instructions to the above program. /* A simple ARexx program. */ say 'Hello, Jumpdisk! Look, Ma, I'm programming!' say options prompt 'Type in your name: ' pull name say say 'Hi, 'name'.' We use the SAY instruction without an expression to send a linefeed to the console. The OPTIONS instruction is used here with the PROMPT keyword to designate what the prompt string will be while waiting for user input. And the PULL instruction is the short form of PARSE UPPER PULL, which in this case reads the string the user types in and stores it in the variable 'name.' If we run the program now, the results would be something like this, assuming you typed 'Bill' at the prompt: Hello, Jumpdisk! Look, Ma, I'm programming! Type in your name: Bill Hi, BILL. A nice thing about ARexx is that it is an interpretive language, which makes it easy to check for bugs while you write a program. You can type a few lines of code, run it, debug it, run again, then type more until you are satisfied. Since this is such a laborious process with a compiler, ARexx is well suited as a prototyping language. Let's add more lines to this program. We'll add an IF / THEN / ELSE statement to check user input, and then turn on the TRACE feature so we can watch program execution. We will also use one of the built-in functions, DATATYPE(). /* A simple ARexx program. */ trace r say "Hello, Jumpdisk! Look, Ma, I'm programming!" say options prompt 'Type in your name: ' pull name say if ~datatype(name,'M') then say 'Your name should be spelled with letters from the alphabet.' else say 'Hi, 'name'.' The DATATYPE(name) function tells the program what type of data is stored in the variable 'name'. Without the option parameter, it will return either NUM or CHAR, which means the variable is either a NUMber or CHARacter. The option parameter 'M' that is after 'name' tells the function to see if the data in 'name' is Mixed alphabetics (upper and lower case letters). The function then returns a boolean value (0 if false, 1 if true). The ' ~ ' character is the 'not' operator that negates the statement. IF the result of ~DATATYPE(name,'M') is true, then 'name' does not consist of alphabetic characters, and the SAY instruction on the next line is performed. If the result is false, then 'name' consists of alphabetic characters, and the SAY clause after the ELSE instruction is performed. The first instruction is 'TRACE R', which echoes the results of each line to the console. If we press Return at the prompt, the output to the console will look like this: 4 *-* ; 5 *-* say "Hello, Jumpdisk! Look, Ma, I'm programming!"; >>> "Hello, Jumpdisk! Look, Ma, I'm programming!" Hello, Jumpdisk! Look, Ma, I'm programming! 6 *-* say; 7 *-* options prompt 'Type in your name: '; >>> "Type in your name: " 8 *-* pull name; >>> "" 9 *-* say; 10 *-* ; 11 *-* if ~datatype(name,'M') then >>> "" >>> "M" >>> "1" 11 *-* ; 12 *-* say 'Your name should be spelled with letters from the... >>> "Your name should be spelled with letters from the alph..." Your name should be spelled with letters from the alphabet. 13 *-* else; Comments are filtered out and each line is written to the screen and evaluated, after which the final results are written to the console screen. Each line is numbered, which makes it easy to find bugs. Now if we turn off tracing (TRACE OFF, instead of TRACE R), we get these results when a name is typed: Hello, Jumpdisk! Look, Ma, I'm programming! Type in your name: Bill Hi, BILL. If we type a number or other non-alphabetic character we should get these results: Hello, Jumpdisk! Look, Ma, I'm programming! Type in your name: 234 Your name should be spelled with letters from the alphabet. With just a few instructions we have written a useful and powerful program. Well, it's not so useful or powerful, but it does demonstrate the simplicity of ARexx instructions. In future ARexx tutorials we will look at more instructions, functions, interfacing with other programs, and using external libraries. The example program is in this drawer as arexx.simple. For adventurous types, there are two other ARexx listings in this drawer for study and use: ALARM.REXX INSTRUCTIONS This is a simple program that demonstrates the use of the speak: device from within Arexx, and uses the Sourceline(), and Delay() functions. I wrote it to remind me when it was time to pick up my kindergartener. You know how time slips away while computing. I originally used a "do - until" loop to wait for the time, but found it was too CPU-intensive while waiting. The Delay() function paused the program in the background and didn't grab too much CPU time. The Sourceline() function is an easy way to embed defaults, 'help' information, or any data you might want to store within the source code itself. The program listing should be fairly easy to follow. Like 'C', Arexx programs have their comments like this: /* This is a comment! */ SPELL.REXX INSTRUCTIONS Spell.rexx is an educational program to help drill lists of spelling words. It uses the built-in speech capabilities of the Amiga. The word lists are stored in an ASCII file (plain text). You can create lists from within the program, or use any text editor or word-processor that can save in ASCII. A 'SPELLFILE' is made of lines of words with spaces between words. Up to 10 lines of words can be entered. The program will prompt you for any input it needs. The listing should be fairly easy to follow. All comments look like this: /* This is a comment! */ You will need the Arexx interpreter to run this program, as well as version 1.3 of Workbench in order to use the speak: device. The program could be modified to run under the 1.2 OS. To do so, replace any line that looks like this: writeln('temptalk',phrase) with . . . address command 'say' phrase Then delete this line: open('temptalk','speak:temp','W') This modification will use the 'SAY' command on Workbench 1.2 to synthesize speech. It may even work on 1.1 OS. Does anyone still use 1.1? The program will 'read' one line at a time from the SPELLFILE, pronounce each word, then prompt you for the correct spelling. To hear the word pronounced again press Return. You can do this any number of times. The Amiga voice is difficult to understand with some words. You will get two tries to spell the word right, after which the correct spelling will be written to the screen. When all the words in the line are finished, you will be allowed to repeat that line of words, go on to the next line, or quit. In this drawer you will find the SPELLFILE needed by this program. END