A Declarative Debugger of Wrong Answers for Lazy Functional Logic Programs

Rafel Caballero, Mario Rodriguez-Artalejo

In Proc. of the International Workshop on Functional and (Constraint) Logic Programming (WFLP 2001) , Report No. 2017, University of Kiel


We describe the design of a declarative debugger for diagnosing wrong answers in lazy functional logic programs with polymorphic type discipline. Following a known technique, the debugger is based on a program transformation: transformed programs return the computation trees needed for debugging, in addition to the results expected by source programs. Thanks to a careful specification of the translation, we are able to prove its correctness w.r.t. well-typing and program semantics. As additional improvements w.r.t. related approaches, we solve a previously open problem concerning the use of curried functions, and we provide a correct method for allowing "maybe" answers and avoiding redundant questions to the user during debugging. A prototype implementation of the debugger is available. Extensions of the debugger to deal with missing answers and constraints are planned as future work.