Incremental type systems and implicit parametric overloading in visual languages

A primary goal of much visual language research is ultimately to further the ability of visual languages to be used for realistic programming projects. As a step in this direction one expects much of incremental type systems in order to prevent run-time errors as early as possible and to preserve the user´s conceptual model of a visual language at the same time. The paper reports on the integration of both an incremental type system and the support of user-definable overloaded functions in an implicit manner for the higher order visual language VisaVis. As a consequence the idea of parametric polymorphism used in many approaches for type systems is not sufficient in our approach. The concept is based upon a generalization of definite databases leading to a PROLOG interface being a main part of the type checker. Beside this, data structures are discussed performing the required unification process as well as the preparation of queries for the database