🚀 go-pugleaf

From article <ALBERTO.92Sep28113506@karna.cs.umd.edu>, by alberto@cs.umd.edu (Jose Alberto Fernandez R):

> One way to solve this is to use in the code macro commands that
> expand to the right thing for each system. Assume that your
> distributed source code is in files with extensions `.pli'. 
> In your case, the macro definitions look something like this:
> 
> 	#ifdef SEPIA
> 	#define RETRACTALL(x) retract_all(x)
> 	#else
> 	#define RETRACTALL(x) retractall(x)
> 	#endif
> 
> and in your code you use the macro RETRACTALL(x):
> 
> 	...:- ..., RETRACTALL(foo(X,Y)), ....
>... 
> It would be nice if a facility like this would have been provided as
> part of the language. Then we wouldn't need to borrow tools from 'C'.

Prolog is a sufficiently wide-spectrum language that we don't need to
borrow bolt-on programming-in-the-large languages.  I think if we write

	retract_all_unit_clause( X) :-
		(	dialect( sepia)
		->	retract_all( X)
		;	dialect( sicstus)
		->	retractall( X)
		).

then add either

	dialect( sepia).
or
	dialect( sicstus).

as a fact, and partially evaluate the program, we get the effect of macro
substitution.  Isn't this a neater way of doing things?  
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