ALS PrologĀ® was an incremental native code compiler for a superset of Edinburg Prolog that quickly produces Prolog code. The compiler supported a two-way C interface, which enableded calls both from Prolog to Objective C and from Objective C to Prolog.

ALS Prolog provided full access to NeXTStep, including complete integration with Interface Builder. After generating interface code with Interface Builder, the programmer simply added callbacks to ALS Prolog in the .m file. The ALS Prolog windowed development environment was fully interactive and included a source code trace debugger and other powerful cools.

Applied Logic Systems