S while E do S1 S.begin := newlabel S. begin : S.after := newlabel E.code   if E.place = 0 goto S.after S.code := gen(S.begin:) || S1 .code E.code || goto S.begin gen(if E.place = 0 goto S.after) || S.after : S 1 .code ||   gen(goto S.begin) ||   gen(S.after:)

The syntax directed definition is shown in the slide. A new label S .begin is created and attached to the first instruction for E. Another new label S. after is created. The code for E generates a jump to the label if E is true, a jump to S.next if E is false; again, we set E.false to be S.next. After the code for S1 we place the instruction goto S.begin, which causes a jump back to the beginning of the code for the Boolean expression. Note that S1.next is set to this label S.begin, so jumps from within S1.code can directly to S.begin.