to try it out on the gap source code. Is there a "system.c" file for DOS
and do I need anything else to generate the executable myself?

Yes, there is a "system.c" for DOS, called "system.dos". This file
however is not in the orginal release but in the upgrade to 3.1
PatchLevel 2. So you need (in addition to "src3r1.zoo" or
"src3r1.tar.Z") the files "upg3r1.dif.Z" and "upg3r1p2.dif.Z".

"Edit(filename)" command which I could not get to work; but since
Exec("myeditor filename") works fine, that hasn't been much of an abstacle.)

Try
EDITOR := "myeditor";
in your .gaprc file.

mfg
Frank Celler