sub_string/5 (was Re: Ann: SWI-Prolog 6.5.3)

On 11/22/2013 01:57 AM, Richard A. O'Keefe wrote:
> 
> On 22/11/2013, at 2:33 AM, Boris Vassilev wrote:
> 
>> P.S. And there is actually no immediately obvious "sub_list" built-in list
>> predicate for efficient searching for (overlapping) substrings in a
>> list.... Or again, I have not paid enough attention when reading.
> 
> It's not quite clear to me what you want here.
> 
> The Quintus library included
> 
> substring(Whole, Part, Before, Length, After)
>     is true when Whole = Front ++ Part ++ Back
>     and length(Front, Before)
>     and length(Part, Length)
>     and length(Back, After).
> 
> substring(Whole, Part, Before, Length) :-
>     substring(Whole, Part, Before, Length, _).
> 
> substring(Whole, Part, Before) :-
>     substring(Whole, Part, Before, _, _).
> 
> substring(Whole, Part) :-
>     substring(Whole, Part, _, _, _).
> 
> SWI Prolog has
> 
> sub_string(Whole, Start, Length, After, Part)
> 
>   -- The argument order is not friendly to dropping
>   -- unwanted length arguments.

It is modelled after ISO sub_atom/5.  I think that is the
most sensible thing to do.

>   -- The name Start suggests a 1-origin *position*,
>   -- in fact, like substring/5 it uses a 0-origin *offset*.

The ISO standard describes this argument as `Before'.  I now
copied that.  Made the docs a bit more elaborate and consistent.

	Cheers --- Jan