L. Naish. Negation and control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, New York, 1986.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....domain is required to be a complete lattice (when this is not the case, and it is just a cpo, an additional widening operation is usually provided by the domain) 2. the derivation 7 produces a decreasing chain in its rst argument. Example 4. 1 Consider the program PERMUTE discussed by Naish in [16]. perm(Xs,Ys) Ys is a permutation of the lists Xs perm(Xs,Ys) Xs = Ys = perm(Xs,Ys) Xs = X X1s] delete(X,Ys,Zs) perm(X1s,Zs) delete(X,Ys,Zs) Zs is the list obtained by removing X from the list Ys delete(X,Ys,Zs) Ys = X Zs] delete(X,Ys,Zs) Ys = X Y1s] Zs = ....

L. Naish. Negation and control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, New York, 1986.

....calling it. Negation is another problematic area for developing a declarative view of Mercury programs. Lots of work has been done in the area of understanding negation, and we note that negation can be dealt with in reasonable ways. The best approach for Mercury is to follow Naish s treatment [68], which was the basis for Mercury s handling of negation. Somogyi s proposal for Ptah [94] also presents a declarative view of negation which is much the same. The basic constraint in both these approaches is that negations may not bind any non local variables, and therefore not upset the ....

Lee Naish. Negation and control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, New York, 1986.

....of a negated goal until it becomes ground, and an approach which, within a negated goal s computation, blocks only the unification of variables which are free 17 outside the scope of the negation. The latter methods have been implemented in a variety of systems, for instance Naish s NU Prolog [Nai86] Here we are motivated by our interest in the features implemented in the most widely used Prolog systems. Most Prolog systems implement the simple negation as failure studied in this paper. The restrictions captured by the conservative semantics are enough to achieve the witness properties; ....

Lee Naish. Negation and Control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer, 1986.

....selection rule specified by such delay declarations are various. Amongst others, it can provide a synchronization mechanism by coroutining the execution of atoms in a computation, or it can be used to avoid infinite derivations by suspending parts of the computation which would cause loops ( Nai86, Nai92] As a consequence, the run time behaviour of logic programs with dynamic scheduling is rather subtle, because atoms in a derivation can be suspended . Therefore, it is important to provide the programmer with suitable tools for studying the suspension behaviour. The techniques most ....

Lee Naish. Negation and Control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, 1986.

....as failure : it computes a goal :G by the regular negation as failure (NAF) method only if G is ground, and terminates query processing immediately with an error indication if G is not ground. This is preferable to the unsound negation of most Prologs for some applications, but Naish points out [Nai86] that even the slightly more liberal form of NAF used in IC Prolog gives the error indication frequently. More useful is the form of NAF in which the call to :G is delayed until G is ground [Dah80, Nai84] However, it is theoretically interesting that this form of negation can be given a logical ....

Lee Naish. Negation and Control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer, 1986.

....satisfy the delay declaration DELAY app(X, Z) UNTIL nonvar(X) nonvar(Z) A contradiction. 2 This isolated result shows how elaborate arguments are sometimes needed to prove simple termination results in presence of delay declarations. In this connection let us mention a related work of Naish [Nai86] and LuttringhausKappel [LK93] who automatically generate delay declarations which ensure that a given program terminates with respect to a selection rule according to which the leftmost non delayed atom is selected. 7 Conclusions In this paper we dealt with the correctness of logic programs ....

L. Naish. Negation and Control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, 1986.

.... straight forward once you are in possession of the necessary data flow information 1 , so it should be easy to extend our results to include 1 For example, Lee Naish s nac preprocessor does determinism analysis using the data flow information provided by NU Prolog s when declarations [Nai86] determinism analysis. For our prototype implementation, we have a safe destructive assignment primitive, which trails all destructive assignments to terms that are older than the most recent choice point; such destructive assignments are then undone on backtracking. In the case where ....

Lee Naish. Negation and control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, New York, 1986.

....is that the definitions implicitly state the mode of use. Similarly, functions are implicitly deterministic and this can also be used as control information. In contrast, reasonable control information for predicates is much more difficult to determine, though some heuristics can be used [Nai86a] Third, the fact that a procedure will be used in a particular mode and is completely deterministic can be used to improve the implementation in a variety of ways. It is much easier to determine this information from the syntax than to analyse programs [DW86] An example of the use of mode ....

....many benefits of knowing what things are functions. Furthermore, we consider that some of the work on reversibility of functions using narrowing is a little simplistic. Like Prolog, reversibility for non trivial programs requires additional control information and a more flexible computation rule [Nai86a] Another approach is to include some of the features of functional programs (lazy evaluation, higher order functions) into a relational language, or develop programming techniques to support these styles of programming [Nar86] She90] This approach does not take advantage 13 of the ....

Lee Naish. Negation and control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, New York, 1986.

....logic programs. This is somewhat of a departure from trends in control languages. IC Prolog [CG83] used a form of mode information to specify eager consumers and lazy producers. MU Prolog and many subsequent systems have based control on single procedures rather than conjunctions. It was argued in [Nai86] that such control was easier to generate automatically, was more modular and often resulted in a better computation rule than that in IC Prolog. We believe that mode information can also be generated and expressed locally and result in efficient computation rules. However, it also enables more ....

Lee Naish. Negation and control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, New York, 1986.

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L. Naish. Negation and control in Prolog. Number 238 in Lecture Notes in Computer Science. Springer-Verlag, New York, 1986.

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