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From: Louis Krupp <lkrupp@nospam.pssw.com.invalid>
Newsgroups: comp.compilers
Subject: Re: Add nested-function support in a language the based on a stack-machine
Date: Tue, 13 Feb 2018 00:42:00 -0700
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On Mon, 12 Feb 2018 11:25:36 -0800 (PST), dror.openu@gmail.com wrote:

>Suppose I have a simple C-like programming language: ...
>Like you can see, it supports nested functions.

gcc supports nested functions as an extension to C. Compiling this
program with -O0 -fdump-tree-all and looking at the generated files
might give you an idea of one way to do it:

#include <stdio.h>

int main(void)
{
	int k1 = 1;
	int p1(void)
	{
		int k2 = 2;
		int p2(void)
		{
			int k3 = 3;
			int p3(void)
			{
				return k1 + k2 + k3;
			}
			return p3();
		}
		return p2();
	}
	int n;

	n = p1();
	printf("%d\n", n);

	return 0;
}

Apparently, gcc chains stack frames, and accessing uplevel variables,
as when p3 uses k1 and k2, seems like it would take O(n) time, where n
is the nesting level.

The alternative, a display vector, seems like it would be easier to
implement unless you're doing this for a real machine with a real (and
therefore limited) set of registers.

Louis