Re: Unifying with partially ground terms without unifying with

Robert Oschler wrote:
>
> I have a program where I want to take certain action on various list items
,
> if certain elements match a certain predicate name only.
>
> For example, given the list:
>
> [Var1, op(SubVar1), Var2, ...]
>
> I have a predicate that 'walks' the list and only manipulates the term if 
it
> is a op() predicate element.  To do this I wrote the following predicate:
>
> % Determine if an element is an op() predicate without unifying with
> unground variables.
> is_op_term(OpTerm, Innards):-
>  OpTerm =.. [X | Args],
>  ground(X),
>  X = op,
>  Innards =.. Args,
>  !.
>
> This works fine but it I wonder if there is a more elegant way to do this.
> The problem with attempting to handle the op() predicate elements with a
> clause like:
>
> do_op([op(X) | T]):- % etc.
>
> Is that the head of the list in the clause will unify with completely
> unground variables, which is what I don't want. I only want grounded or
> partially grounded variables that are currently instantiated to an op()
> term.
>
> I tried using 'not', hoping to test the element without unifying with it,
> but ended up with a control error:
>
> do_op([H | T]):-
>     not (H = op(X)),
>     !,
>     ... % etc.
>
> So what's a better way to do this?

if you want to check if two variables unify without unification been
made
try this

\+ \+ X = Y

double negation (seen in nlp in prolog by shieber and perreira)


Have fun


Djamé