Types and Type Inference in a Visual Programming Language

In this paper, the uses of types and type inference in visual languages are explored. First, we discuss how the goals of a type system must differ for visual languages from those of a type system for textual languages. We then present a type system developed under these goals for the visual language Forms/3. Within the context of this system, issues of particular importance in visual languages are examined, including maintaining the user's conceptual model, the avoidance of language restrictions solely to support a type system, and how the visual process of programming can provide additional information to the type system. 1: Introduction One approach to types in visual programming languages (VPLs) is to hide them. The rationale would be to keep the simple, flexible spirit of programming in a visual language. This philosophy appears to be shared by many researchers, because few have introduced the concept of types into visual languages. But it seems contradictory to allow the user to u..