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1987-12-04
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December 4, 1987
GFATIP14.DOC
by John B. Holder
Senior Software Engineer
Marathon Computer Press
Asst. Sysop on GEnie's MichTron Roundtable
This is the 14th in a planned series of GFA Tip files. The
topic of this issue is effective use of DEFFN & FN to expand GFA
Basic's vocabulary. In this archive you will find the following
files:
GFATIP14.DOC
GFATIP14.BAS
GEMDEFS.LST
In this issue you will be receiving a .BAS file that contains
a very complete description of GEMDOS, the Bios & Xbios. Since
very informative manuals have been written on the ATARI ST
operating system, I'll leave it to them. I would suggest that you
purchase a copy of ATARI ST INTERNALS by ABACUS Software to fully
grasp and utilize this GFATIP. Some of the presented OS
(operating system) calls (through the use of DEFFN & FN) are quite
complex, and some are DESTRUCTIVE. My suggestion to you is this:
If you are going to use some of the OS calls that either delete or
add data to your disk, that you use a floppy disk set up
specifically for this purpose. Just place a copy of GFABASIC.PRG
on the working disk along with either GFATIP14.BAS, or
GEMDEFS.LST. *** Nothing is destructive about GFATIP14.BAS,
unless you add it. ***
At the top of the GEMDEFS Library portion of the TIP File,
you will find several examples of how the User defined Functions
can be used. They just scratch the surface of the potential
contained in the functions, but are a good example of how to
properly use DEFFN & FN.
By MERGING the GEMDEFS.LST file in your GFA Basic programs &
using FN to call the function, you can effectively increase the
vocabulary and functionality of the language. Have fun with these
library functions, but be careful. You really should buy the
reference material before attempting to use functions not
demonstrated, or at least experiment with a backup disk.
John B. Holder
GEnie => GRIFJOHN
CIS => 75766,505