Re: if

[Ron Stodden]

Calum Grant wrote:
> 
> A simpler variant of this problem is
> 
>         insert_set(H, L, L) :- member(H, L), !.  % A "hack" according to FH
>         insert_set(H, L, [H|L]).
> 
> which takes an item H and inserts it into a list L without duplicates, like
> a simple set.  The second clause should only be applied if the first one
> fails.  Therefore the ! is necessary.  This can be rewritten as
> 
>         insert_set(H, S0, S) :-
>         (
>                 member(H, S0) -> S0=S;  % A "hack" according to RS
>                 S = [H|S0]
>         ).
> 
> The difference is purely cosmetic, and I don't think it's worth arguing
> about.  It's a bit like saying that "|" is better than ";".

Argue?   Yes.   I would argue that the first is ultimately simpler,
more 'elegant', immediately lucid, and I suspect generates less code
and on that basis should run faster.  (Note the "should" <g>).

-- 
Regards,

Ron. [AU]