Re: [Groff] Question about .substring

[Ralph Corderoy]

Hi Ingo,

> > for example, and without introducing lengthy calculations
> 
> Lengthy?  If you have the offset and length (> 0), all it takes is one
> addition and decrementing by one.

I think his point is given string s of `abcdefghij', one wants the
substring starting at index 2, `c', of length 0, 1, or 2.  `2 2' gives
`c', `2 3' `cd'.  `2 1' is swapped to `1 2' giving `bc'.  There's no
second parameter that gives an empty string, unlike the [startindex,
endindex) interval where endindex is exclusive, e.g. Python.

    $ python -c 'print "abcdefghij"[2:2]' | od -c
    0000000  \n
    0000001
    $

So that means testing the length number register to see if it's zero and
defining the string to be empty if it is, or doing the maths for
.substring otherwise.

Obviously, ;-)
the new expression syntax would have a substring function that returns
rather than modifies and uses the normal [) interval.

Cheers, Ralph.