[9fans] forgotten rc hack

[erik quanstrom <quanstro@quanstro.net>]

some time ago, i had a want for es-style subscripting like

	; x=(1 2 3)
	; echo $x(1-2)
	1 2
	; echo $x(2-)
	2 3
	; x = $x(2-)	# shift x

i'd forgotten all about it.  the following replacement for
exec.c:subwords() is all that you need to enable this.

- erik

----

word*
copynwords(word *a, word *tail, int n)
{
	word *v = 0, **end;
	for(end=&v;a && n-- != 0;a = a->next,end=&(*end)->next)
		*end = newword(a->word, 0);
	*end = tail;
	return v;
}

word*
subwords(word *val, int len, word *sub, word *a)
{
	int n, m;
	char *s;
	if(!sub)
		return a;
	s = sub->word;
	deglob(s);
	a = subwords(val, len, sub->next, a);
	n = 0; m = 0;
	while('0'<=*s && *s<='9') n = n*10+ *s++ -'0';
	if(*s++ == '-'){
		if(*s)	while('0'<=*s && *s<='9') m = m*10+ *s++ -'0';
		else	m = len;
		m -= n;
	}
	if(n<1 || len<n)
		return a;
	while(--n) val = val->next;
	return copynwords(val, a, m+1);
}