Browsing by Author "Dewar, Alan D."
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Item Open Access A GRAPHICAL DEBUGGER FOR PROLOG(1986-01-01) Dewar, Alan D.This thesis presents the implementation of DEWLAP (DEbugging With Logical APplications), a graphical debugger for Prolog. DEWLAP is the first Prolog debugger to present program executions in an entirely graphical fashion. Instead of showing source listings for program tracing, DEWLAP displays the execution as a dynamically-changing tree. This tree shows not only the currently-active sequence of goals, but also the entire execution history. In this way, the user is provided with a much more complete view of the execution than is possible with other debuggers for Prolog or for any other language. A need for a compromise between clarity of high-level information and accessibility of low-level detail arises in a number of contexts. This problem is solved in DEWLAP by giving the user the tools needed to tailor displays and to focus attention on those parts of the execution tree which are of current interest.Item Open Access GRAPHICAL DISPLAY OF COMPLEX INFORMATION WITHIN A PROLOG DEBUGGER(1985-12-01) Dewar, Alan D.; Cleary, John G.An interactive Prolog debugger, DEWLAP, is described. Output from the debugger is in the form of graphical displays of both the derivation tree and the parameters to procedure calls. The major advantage of such displays is that they allow important information to be displayed prominently and unimportant information to be shrunk so that it is accessible but not distracting. Other advantages include the following: the control flow in Prolog is clearly shown; the control context of a particular call is readily determined; it is easy to find out whether two uninstantiated variables are bound together; and very fine control is possible over debugging and display options. A high-level graphics language is provided to allow the user to tailor the graphical display of data structures to particular applications. A number of issues raised by the need to update such displays efficiently and to control their perceived complexity are addressed. The DEWLAP system is implemented in Prolog on relatively standard hardware with a central processor running Unix and remote workstations with bitmapped displays and mice.Item Open Access A LOW-COST HIGH ACCURACY INTELLIGENT BACKTRACKING ALGORITHM(1990-03-01) Dewar, Alan D.; Cleary, John G.We present an intelligent backtracking algorithm with high accuracy and low overhead, especially for certain classes of algorithms. Information is associated with each variable binding and with each proof-tree node. Performance results indicate that our approach can attain a similar accuracy, but at a lower cost, when compared with other similar intelligent backtracking approaches.Item Open Access A LOW-COST HIGH ACCURACY INTELLIGENT BACKTRACKING ALGORITHM(1990-03-01) Dewar, Alan D.; Cleary, John G.We present an intelligent backtracking algorithm with high accuracy and low overhead, especially for certain classes of algorithms. Information is associated with each variable binding and with each proof-tree node. Performance results indicate that our approach can attain a similar accuracy, but at a lower cost, when compared with other similar intelligent backtracking approaches.