[cctalk] Re: Elliott Algol

int f1(int i) { int j; int f2(int x) { int y; y = j*2; ... f1(x+1); } f2(...); } f1(42); The local variables go into stack frames, one for each call of each function. So when recursive calls are made as in this example, there are multiple stack frames belonging to calls of f1 and of f2. Each f1 frame has a j in it. So how does the code for f2 find "the right f1 frame" to resolve the reference to j that I showed? The answer is to have a display, which is a vector of pointers, indexed by "static scope", in other words by textual nesting level. In this case that vector would have three entries: one for the program, f1, and f2. When a call to f1 is made, the stack frame is created. In the stack frame the previous value of the display entry for f1 is saved, and that entry is then set to the stack frame address. On function return, the previous display entry is restored. To resolve the reference to j in f2, the code would load the display entry for f1 (the second entry in the display vector), and add the offset to j in the stack frame.