🚀 go-pugleaf

I have a doubt to clarify from an example that is given in the book
mentioned above. This is an example on pages 470-471. The example has
been given in the context of trimming environments for a clause. The whole
example and the insruction in doubt are as follows: 
(WPE is another name for WAM)

Prolog Source 			WPE Machine Code
p(A,D) :-		     p: alloc
	q(A,B), r(B,C),		getVar	r2, 2	% D is first in frame
	s(C,D).			putVar	r2, 4	% B is last in frame
				call	q:, 5	% space for D,C,B
				putUVal	r1, 4	% B to r1
				putVar	r2, 3	% C is second in frame
				call	r:, 4	% space for D,C
	/*****/ ---------->     putVal	r1, 3	% C to r1
				putVal	r2, 2	% D to r2
				dealloc
				exec	s:


 My objection is to the instruction marked by /*****/. I think it
should be "putUVal r1, 3" for the same reason as putUVal has been
used for B. C might still be unbound after the call to r, and since
we are deallocating the frame for the clause before the call to s:, C 
becomes unsafe.

All explanations are welcome.

Apart from the doubt mentioned above, I found the section on the WAM
(#11.8) very useful and well written.

Sanjeev Kumar.
-- 
Sanjeev Kumar. ( skumar@paul.rutgers.edu ) 
Phone: Off. (201)932-3766, Res. (201)878-1841.
Dept. of Computer Science, RUTGERS, New Brunswick, NJ08903.