Re: Labyrinth problem

From: houdini (presto_at_this.address.is_INVALID)
Date: 04/12/04

  • Next message: reader: "Re: Any Crossword puzzle example?" 
    Date: Mon, 12 Apr 2004 18:54:59 GMT

    Negator wrote:
    >>Several things are not clear in what you ask:
    >>
    >>how vould the query ?-path(room1,room2).
    >> produce the list of answers [room1,room2,room1,room2...]
    >>
    >>your program calls a predicate pass/2, but you
    >>didn't give clauses for it
    >>
    >>Finally, one answer to you question would be: get rid of recursive
    >>calls. But I guess that's not what you want. Did you mean to ask:
    >>
    >>How can I get rid of multiple answers ?
    >>or
    >>How can I get rid of an infinite loop ?
    >>
    >>Please, more precise details about your program and your questions and
    >>then the net can (maybe try to) answer your problem.
    >
    >
    > I'm sorry, I meant "link" instead of "pass" - that happend because of
    > different versions of the predicate. The right version looks like:
    >
    > path(A,A,L):-length(L,1).
    > path(From,To,A):-A=[From|Rest],
    > Rest=[SecondInPair|_],
    > (link(SecondInPair,From); /* recursion*/
    > link(From,SecondInPair)),
    > path(SecondInPair,To,Rest).
    >
    > but still doesn't work)
    > You are right - the qestion isn't correctly formulated.

       In Prolog and in logic programming generally, capturing the essence
    of the problem in as few rules or axioms as possible is pretty much the
    name of the game.

    It isn't really a
    > Prolog qestion, but I'm sure, it can be solved here much easier than in any
    > other programming language.

      [?]

    > How to make a rule, that will exclude the recursion. I.e.
    >
    > ?-path(room1,room2).
    >
    > or
    >
    > ?-path(room2,room1).
    >
    > if there is a
    >
    > link(room1,room2).
    >
    > instructs Prolog to find all paths between room1 and room2. Prolog finds the
    > first correct variant - [room1,room2], but we need all possible paths
    > between two roms, that's why it finds the next variant -
    > [room1,room2,room1,room2] - that is a correct variant too, but we don't need
    > it.
    > So the qestion is: how to exclude these variants, and infinite loops with
    > them?
    >
    >

       Suppose you had to explore a huge mansion that had hundreds of
    interconnected rooms and you were not allowed to leave markers of any
    kind and you didn't want to visit any room twice: put into words the
    rule that governs the question of whether you are allowed to go from
    room A to room B.

       With no restrictions, you have

            possible_to_go(A,B) if link(A,B).
            possible_to_go(A,B) if link(B,A).

       In these rules, the only factors that enter into consideration are
    the respective names of the rooms. If there is another factor, it has to
    be represented, maybe like

             allowed_to_go(A,B,OtherFactor) if
                    possible_to_go(A,B)
                    and not rules_out(OtherFactor,A,B). 

    --
sequitur AT sonic DOT net
  • Next message: reader: "Re: Any Crossword puzzle example?"

    Relevant Pages