Kima- an Automated Error Correction System for Concurrent Logic Programs

Abstract. We have implemented Kima, an automated error correction system for concurrent logic programs. Kima corrects near-misses such as wrong variable occurrences in the absence of explicit declarations of program properties. Strong moding/typing and constraint-based analysis are turning to play fundamental roles in debugging concurrent logic programs as well as in establishing the consistency of communication protocols and data types. Mode/type analysis of Moded Flat GHC is a constraint satisfaction problem with many simple mode/type constraints, and can be solved efficiently. We proposed a simple and efficient technique which, given a non-well-moded/typed program, diagnoses the "reasons " of inconsis- tency by finding minimal inconsistent subsets of mode/type constraints. Since each constraint keeps track of the symbol occurrence in the pro- gram, a minimal subset also tells possible sources of program errors. Kima realizes automated correction by replacing symbol occurrences around the possible sources and recalculating modes and types of the rewritten programs systematically. As long as bugs are near-misses, Kima proposes a rather small number of alternatives that include an intended program. Search space is kept small because the minimal subset confines possible sources of errors in advance. This paper presents the basic al- gorithm and various optimization techniques implemented in Kima, and then discusses its effectiveness based on quantitative experiments. 1 Introduction In our previous work [1], we proposed a framework of automated debugging of program errors based on static, constraint-based program analysis in the absence of programmers ' declarations. The framework was then implemented in Kima, an automated error correction system for concurrent logic programs, which featured several improvements to make the system more practical and efficient. The mechanism of error correction in Kima is based on the mode and type system of Moded Flat GHC [8][9]. Moded Flat GHC is a concurrent logic (and consequently, a concurrent constraint) language with a constraint-based mode system designed by one of the authors. Languages equipped with strong typ