I'm looking into it, but meanwhile I discovered a bug in
/n/sources/plan9/sys/src/cmd/grap/input.c
In function "eprint" the second occurrence of
for (; p < q; p++)
should be
for (; p < ep; p++)
(p has already passed q due to the previous loop).
Also I found a bug in your "eg" implementation:
In function "set_defaults" add the line
start_drawing = 0
