Unifying with partially ground terms without unifying with completely unground terms?

From: Robert Oschler (no-mail-please_at_nospam.com)
Date: 10/21/04

  • Next message: Bart Demoen: "Re: Unifying with partially ground terms without unifying with completely unground terms?" 
    Date: Thu, 21 Oct 2004 12:27:12 -0400

    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?

    Thanks,
    Robert. 

    -- 
Robert Oschler
http://www.robotsrule.com/phpBB2/
Robot & Android Discussion Forum
  • Next message: Bart Demoen: "Re: Unifying with partially ground terms without unifying with completely unground terms?"

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