FORTH is an increasingly popular
language, and E. S. FORTH is one of several versions available
for ATARI computers. It will run on 400, 800 and XL models having at
least 32K. Cassette and disc versions are available, and both are very
good value.
Operations are carried out in FORTH by
executing commands, known as "words". Every version of FORTH
contains a "dictionary" of these words. A FORTH program is
written by defining new words, which are added to the dictionary, to
perform new functions. This is done by writing chunks (or
"screens") of source code containing the definitions, which
are then compiled into the dictionary.
FORTH is a structured language, in that
the program flow is not controlled by jumping between numbered program
lines, as in BASIC. This forces the programmer to think more carefully
before he starts writing his program, and results in the program being
much better organised. It also means that it is much easier to keep
lots of different program utilities which are loaded in at will
without worrying about conflicts between line numbers.
FORTH is claimed to have a number of
advantages over BASIC, especially that of speed. It is indeed much
faster than BASIC, but this does not mean that you can use FORTH to
write arcade-quality programs with the same ease as ordinary BASIC
programs. If necessary though you can speed things up further by using
machine code routines. FORTH is much more versatile than BASIC, and
allows the user far more control over what is happening inside the
computer. For this reason I find it a much more pleasing and
interesting language to use.
E. S. FORTH is based on a standard
called fig-FORTH, but claims to have been internally optimised for
speed and efficiency. I tried a few crude bench tests and found that
it did indeed run noticeably faster than two other fig- FORTH based
ATARI languages. The version of E. S. FORTH I tried was cassette
based. This reduces costs when compared with cartridges, and renders
it available to those users who do not have disc drives. However, like
all RAM based languages a program crash often means switching off the
computer and starting again from scratch, which can be time consuming
when you have to load the language off a cassette.
An area of RAM is set aside to simulate
a disc, and contains a number of screens into which the user can write
source code for his FORTH program. The size of the area (and hence the
number of screens) is set by the user at the start of a programming
session. Screens are written using the ATARI screen editor, as in
BASIC, except that the user must remember when altering a line to
insert "P"' between the line number and the line's text.
Otherwise strange things happen. Other editing facilities are also
provided, these are standard FORTH editing commands, although in E. S.
FORTH they are permanently resident and operational, which is not
usual.
Once the screens have been written they
can be stored individually or as a set on a cassette, and can be
compiled into the language's dictionary to enable the program to be
run. Five screens can be simultaneously stored in a 32K system and
still leave room for a complex compiled program. More screens can be accommodated
by sacrificing display and/or dictionary memory. However this is not necessary
if you are willing to write your program in separate sections which
are successively retrieved from cassette and compiled which, with a
little thought, could be done automatically.
The basic dictionary of E. S. FORTH
contains nearly all the standard fig-FORTH commands. Those that are
missing relate mainly to the use of discs. It should be noted that one
of the beauties of FORTH is that in principle adding new words, for
example to make up for omissions in the basic dictionary, should not
present problems, so long as the functions of the words are
understood.
The E. S. FORTH dictionary is also
well-stocked with commands specifically for the ATARI These are mostly
like corresponding BASIC commands They include I/O words such as OPEN,
CLOSE PUT GET. graphics words such as GRAPHICS, COLOR, PLOT, DRAW, as
well as other types of words, e.g.. STICK, SOUND, etc. There are
however a number of commands which do not have BASIC counterparts.
There is for example a very useful PLAY command, which is like SOUND
except that it has a time parameter, so that the sound stops after a
preset duration. Processing continues while the sound is playing.
There are also commands to make it much
easier to design and use custom character sets, but the most useful of
these extra commands are the Player-Missile utilities. A single
command sets up the registers and allocates screen memory. Other
commands are provided, e.g. for defining and switching between player
shapes (to permit animation), for moving the players and missiles,
setting their colours and widths, etc. Controlling player movement in
response to a joystick is made particularly easy. Anyone who has tried
writing even simple Player-Missile routines in BASIC will know how
tedious this can be, especially if you have to resort to clever little
programming tricks to get the players to move quickly enough. Having a
language that can handle this for you makes a very pleasant change,
and for this reason alone I would recommend E. S. FORTH.
Some versions of FORTH are provided
with an assembler, which enables new words to be defined in machine
code to increase speed, but unfortunately E. S. FORTH does not have
one. Instead it is possible to run the language with the ATARI
ASSEMBLER/EDITOR cartridge in place, and switch control between FORTH
and the cartridge. This is useful in some situations, but makes saving
and loading FORTH programs written partly in assembly language
awkward. However, some public domain assemblers have been written in
FORTH, and the interested user should be able to get hold of a source
listing without too much difficulty.
A more serious omission is the lack of
any command to allow the FORTH dictionary (including any new words
which the user has defined) to be saved on cassette. This means that
every time you wish to run a program or utility, you have to load the
language itself and then load in and compile the source code (i. e.
the screens), which could take a considerable time particularly if you
have several different utilities which you want to use together. The
experienced user would find a way to solve this problem, but for the
beginner it could be a real nuisance.
The documentation supplied with E. S.
FORTH is not, and does not claim to be, adequate for the beginner. No
attempt is made to teach FORTH, and as this language is so different
from BASIC, especially in its "backward" looking syntax, the
novice would need to buy a suitable book. As E. S. FORTH is so cheap
this is not unreasonable. Much of the book supplied with E. S. FORTH
is taken up with a reproduction of literature issued by the FORTH
Interest Group, including a glossary of fig-FORTH words and a
"model" which explains in detail the inner workings of the
language and which would be useful (and comprehensible) only to the
very experienced user. The rest of the book contains enough to explain
those features specific to E. S. FORTH, and includes short programs to
demonstrate the Player-Missile utilities.
Anyone who likes programming but only
knows BASIC doesn't know what he's missing. Even ignoring the
usefulness of the FORTH language, just learning how to use it and what
it can do is fascinating. If you are interested in computing, rather
than simply playing games you have bought, then you can't fail to get
excellent value by buying E. S. FORTH.
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