The Logo Programming Language is a dialect of Lisp dating from 1967, and designed as a tool for learning. Its features (interactivity, modularity, extensibility, flexibility of data types) are intended to support this goal, rooted in constructivist educational philosophy, and are designed to support constructive learning. Logo is usually implemented as an interpreted language, though some versions compile. The interactivity of this approach gives the user immediate feedback on individual instructions, thus aiding in the debugging and learning process. Error messages are descriptive.