debugfindx(expression,sentence,factset,ruleset) → expression / false
The debugfindx subroutine takes as arguments an expression (called the aspect), a sentence (called the query), a dataset, and a ruleset. It uses the facts in the dataset and the rules in the ruleset (and the definitions of predefined functions and relations) to derive an instance of the query. If it succeeds, it returns the corresponding instance of the aspect; if it fails to derive an instance of the query, it returns false.
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Call: definefacts(repository,readdata('p(art,bob) p(bob,cal) p(bob,cam)'))
Exit: true
Call: definerules(library,readdata('g(X,Z) :- p(X,Y) & p(Y,Z)'))
Exit: true
Call: debugfindx('Z',read('g(art,Z)'),repository,library)
Exit: cal
Call: debugfindx('X',read('g(art,cal)'),repository,library)
Exit: art
Call: grind(debugfindx(read('answer(X,Z)'),read('g(X,Z)'),repository,library))
Exit: answer(art,cal)
Call: grind(debugfindx(read('answer(X,Z)'),read('p(X,Y) & p(Y,Z)'),repository,library))
Exit: answer(art,cal)
Call: debugfindx('Z',read('g(bob,Z)'),repository,library)
Exit: false
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The subroutine debugfindx differs from compfindx in two ways. (1) It limits the depth of recursion based on the value of the global variable depth. (2) It allows the user to trace attempts to compute relations specified via the value of the variable traces (which can be modified directly or using the trace and untrace subroutines). Trace output is printed using the Javascript subroutine console.log.
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