[9fans] forgotten rc hack

[erik quanstrom]

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);
}