FDBG, the CLPFD Debugger Library of SICStus Prolog

FDBG (short for Finite domain DeBuGger) is a tool addressing the problems of debugging nite domain (FD) constraint programs. Implemented as a SICStus Prolog library, it allows CLP(FD) programmers to trace FD variable domain changes. FDBG is capable of detecting the wake-up of constraints as well as the steps of labeling, and it reports the e ects of these events on the variables. The simplest way to use FDBG is to produce a wallpaper trace of the run of the constraint program. The trace is analyzed (typically post-mortem) either manually or by a tool designed for this purpose. However, program behavior may also be observed in real time exploiting the modular design and the exible output redirecting capabilities. FDBG was written almost entirely in Prolog as user space code, no native routines were used directly. It is also included (with source) in the o cial SICStus distribution in versions 3.9 and upwards.