Hi Doug, > What's the best way to trace pilog?
Pilog clauses can indeed be traced. Unfortunately, I don't find a good description at the moment. The reference of '?' (and of 'prove' which is the internal machinery of the query front end '?') just briefly mentions it: http://software-lab.de/doc/ref_.html#? http://software-lab.de/doc/refP.html#prove It works by simply passing the names of the clauses you want to trace right after the '?' (i.e. the ['sym' ..] arguments). A simple example, using the 'append' clause: Without tracing : (? (append (a b c) @X (a b c d e f))) @X=(d e f) -> NIL With tracing : (? append (append (a b c) @X (a b c d e f))) 2 (append (a b c) @Y (a b c d e f)) 2 (append (b c) @Y (b c d e f)) 2 (append (c) @Y (c d e f)) 1 (append NIL (d e f) (d e f)) @X=(d e f) The trace output lists all clauses that _matched_, and always starts with a number indicating _which_ of the clauses in the definition matched. The definition of 'append' is : (rules 'append) 1 (be append (NIL @X @X)) 2 (be append ((@A . @X) @Y (@A . @Z)) (append @X @Y @Z)) -> append The symbolic arguments to '?' can of course also specify clauses somewhere deeply nested in the Pilog definitions, not just those passed to '?' on the top level. Cheers, - Alex -- UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe
