GFA Basic Compiler

Reviewed by Matthew Jones

 

Issue 30

Nov/Dec 87

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Glentop Press Ltd.

THE BASIC

As a programmer who learnt the BASIC language many years ago but then left for the brave new world of C, the opportunity to review GFA BASIC was an interesting chance to see what BASIC has been getting up to since I left.

GFA BASIC comes in a video cassette style box, and includes a 293 page ring bound manual and a single floppy disk. The disk contains two versions of the BASIC (both unprotected please don't abuse), a full featured one for program development, and a run-only version to allow you to give away or sell your programs.

IT DOESN'T USE GEM!

Being a normal user, the first thing I did was not study the manual but run the BASIC program. I have had my ST since the first shipment hit the U.K., and since then have become very familiar with the GEM interface, using windows, icons, menus and mice. When I ran GFA BASIC therefore I had quite a shock. GFA BASIC is a standard text mode program, though it does use a mouse. I fully expected to find GFA BASIC using windows, but having used it for a while, I have to admit that even without windows, it still presents a good environment to work in. GFA uses a 'Command line' menu at the top for mouse selections which is similar to a drop down menu but nothing drops down! There are ten options, doubled up to make twenty. Clicking on the command text, or pressing a function key (shifted for the extra ten), activates the command. Commands include load, save, run, program check, search, replace and block functions, as well as options like insert and overwrite mode toggles, and (on monochrome screens) a 50 line mode.

The BASIC program is not entered in the traditional form with line numbers, but is entered with one command to a line and automatically 'tabbed' within loops (GFA is a procedural BASIC, also incorporating DO...LOOP, REPEAT...UNTIL and WHILE...WEND). A nice touch is that keywords can be differentiated by automatically capitalising the first letter. I did miss a scroll bar to reflect the current position within the program and to provide easy movement to anywhere in the program, but for those who do not like GEM, this may be not be a problem.

IT DOES USE GEM!

GEM is not neglected by the program though, for whilst the programming environment is not GEM based, very good provision has been made within the commands for incorporating GEM into a user's program. As an example, it is possible to define an array of text strings, which can then be used with a command to build a proper GEM menu bar across the top of the screen. Activating the menu is then just a case of using the command 'ON MENU GOSUB'. The user must know a bit about the GEM system, but other commands allow much more transparent access to GEM facilities, like the window commands, and an alert handler. So the programmer who wants to use GEM is not held back by GFA (an interface to the heart of GEM is provided if you want to sidestep or enhance the standard facilities).

GFA BASIC is not just about working GEM however, as a lot of new and useful functions have been added to make programming in BASIC a lot easier and more powerful. I cannot include them all, but for a few examples: access to the address of a variable, and passing of pointers to procedures; single operand maths functions like ADD A%,5 (which is twice as fast as LET A% = A% + 5); graphics primitives (lines, boxes, circles, ellipses); chaining of other programs; date and time functions; structured file read/writing and random access files; PRINT USING; form inputs (limiting input to a set length); local variables in procedures; reading of all mouse actions (x,y, buttons, leaving/entering boxes); sprite definition; sound command; upper/lower case of a string; butter type block moves; screen save/restores; an 'approximately' equal to comparison; and both user and supervisor mode POKE functions (byte, word and long sized) for twiddling within the computer. I can't cover them all here, and I haven't included the more basic (no pun intended) functions that have been added. Overall this is a function packed BASIC.

THE MANUAL

Considering the number of functions and the general power of GFA BASIC, it is a great pity that it is let down by the manual.

Despite its size, and at least one page per command, it does not give as much information as I would have liked, and it is often not very clear, partly because of its (obvious) German translated origin. Another point is that it has been printed on a bright red paper, a technique used to stop photocopying. I tested this and found that with a bit of experimentation, the photocopy was easier to read than the original manual! Glentop told me they were doing a new manual, and may be dropping the red paper. I hope that existing owners will be able to send back their manual with a SMALL fee to upgrade to a new one. At the current time, the manual is a disappointment, but it does contain all the information you just have to spend a long time finding it as there is no index.

CONVERTING PROGRAMS

My experiments with the system included an attempt to convert an old 8 bit Atari BASIC program ('Matthews Label Maker') to run on the ST. GFA provide a program which converts Atari ST BASIC programs (with line numbers and multiple statements per line), and converts it to a file suitable for GFA BASIC (single command per line, using labels in gotos). After a few unsuccessful runs (the program picks up on FORs in REMs), the program was in a form suitable for reading into GFA BASIC. It seemed too good to be true, and was, for my original program seems to have had some convoluted system of conditional NEXTs in it, and I got a 'procedure in a loop' error, which meant I was totally unable to use my original (I can't remember how it works any more!). This may not be typical though, and if I were to write it again today, I would make much more use of the structuring capability of languages like GFA BASIC.

A set of public domain programs for GFA BASIC is also included, which really show off the program to its best. Some are quite astonishing (for instance an animation of a horse by blitting), and if I hadn't run them myself I might not have believed they were written in BASIC (and interpreted BASIC at that). More GFA BASIC programs are available from other public domain sources.

THE COMPILER

The separately bought compiler comes in the same style box, with a 31 page manual and disk. Compiling is very simple. A dialog is presented which shows the possible options, and when you have chosen you select a file to compile, then a file to save it as, and then it is done. Simple as that. The available options are: whether the program can be stopped by pressing the Shift/Alternate/Control keys together (and how often checks are made for them); whether integer overflow will be trapped; whether run-time error messages are text and number or number only; whether bombs are to be trapped (e.g. erroneous instructions which cause three bombs can be stopped and made to create an error 103, and thus detected by ON ERROR GO SUB). All the options can be specified in the source code if desired.

Only a few commands cannot be compiled, and they are only because they are not applicable (like LIST and SAVE). No separate compilation is possible, so it is not possible to split your code up into smaller files, but this is not too much of a drawback. The only requirement for distributing the compiled code is that you acknowledge GFA BASIC.

CONCLUSION

GFA BASIC is a very capable programming system, and would be quite suitable for any level of programming, from beginner to very advanced. It is a pity that GEM is not used when writing programs, but not having it probably contributes to the claimed interpreter size of only 55k, and the program is quite usable anyway. The only drawback to GFA BASIC is the manual, but this may be replaced soon. The compiler is a nice option, but with the run-only version of the interpreter supplied, only the commercial user will need it as the interpreter does a very fast job on its own. If GFA BASIC is representative, BASIC has come a long way in the last few years.

GFA BASIC interpreter and compiler cost 45.95 each, and are available from: Glentop Press Ltd, Standfast House, Bath Place, Barnet, Herts, ENS SXE

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