Re: goal_expansion

On 11/02/2014, at 5:38 AM, Jonathon Doran wrote:

> My thanks to everyone for your comments.  I was overthinking things.  I messed
> around with goal_expansion and have something I like:
> 
> goal_expansion(optional_param(Tag:Value, Parameters, Generator), Y) :-
>    Y = (
>            member(Tag:Value, Parameters) ->
>                true
>            ;
>                Generator
>    ).
> 
> It is possible that one or more of the list members find this offensive.
> It is hard not to fall back upon old habits when one doesn't know better.
> But I find it much easier to read/write
>   optional_param(color:Color, Parameter_List,
>      (
>         random_color(Color)
>      )),
> 
> than to have the full expansion appear in the source.

But you don't *NEED* macros of any kind for this!

optional_param(Tag:Value, Parameters, Generator) :-
    (   member(Tag:Value, Parameters) -> true
    ;   call(Generator)
    ).

And now you read/write

    optional_param(color:Color, Parameter_List, (
        random_color(Color)
    ))

and it just WORKS.  No macros required.

This is not C.
You do NOT need macros to pass code fragments as arguments!