We show how a parallel logic programming system is produced as the result of stepwise improvements of a series of minimal interpreters. This paper exposes typical problems and solutions in a clear way. One result is a full implementation of the language Fleng, including built-in functions, suspension mechanism, and one-way unification. We also give a version of the same interpreter using a freeze primitive. The Fleng interpreter is further developed into a Flat GHC interpreter, and then into a Full GHC interpreter.