Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!nuchat!sugar!peter
From: peter@sugar.hackercorp.com (Peter da Silva)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Can you nest subroutines in C?
Message-ID: <3996@sugar.hackercorp.com>
Date: 7 Jul 89 02:51:59 GMT
References: <3982@sugar.hackercorp.com> <268@hitech.ht.oz>
Organization: Sugar Land Unix - Houston
Lines: 62

In article <268@hitech.ht.oz>, clyde@hitech.ht.oz (Clyde Smith-Stubbs) writes:
> From article <3982@sugar.hackercorp.com>, by peter@sugar.hackercorp.com (Peter da Silva):
> > And nested procedures can be implemented by explicitly passing the frame
> > pointer. In fact, you can implement nested procedures efficiently in 'C',

> What do you mean by "explicitly passing the frame pointer".

I mean, explicitly passing a ponter to the stack frame that contains that
particular set of variables. Maybe you call it the display pointer:

struct outer_display {
	type outer_var;
	...
};

struct middle_display {
	type middle_var;
	...
};

static inner_func(mid, out, myvars)
struct middle_display *mid;
struct outer_display *out;
type myvars;
{
	mid->middle_var = myvar;
	...
}

static middle_func(out, myvars)
struct outer_display *out;
type myvars;
{
	struct middle_display mid;
	...
	inner_func(&mid, out, out->outer_var);
	...
	out->outer_var += mid->middle_var;
	...
}

outer_func(myvars)
type myvars;
{
	struct outer_display out;
	...
	middle_func(&out, 7);
	...
}

This is an example of three levels of nested functions implemented in C by
explicitly passing the display pointers. The code generated will be
equivalent to the equivalent modula code. It's a little messier, yes, but
it *is* possible to do the job in C.

> Implementation of displays in C is not difficult, and properly done need
> not add much overhead.

I agree entirely, see above.
-- 
Peter "Have you hugged your wolf today" da Silva      `-_-'
...texbell!sugar!peter, or peter@sugar.hackercorp.com  'U`