day9 - line simulation

yes, maybe positive example of using macro - to allow my get-x being
used as PLACE in setf

but other modifications require variable.
and that's not quite what i want.

day9-test.txt

@@ -0,0 +1,8 @@
+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2