Visual languages and the conflict between single assignment and iteration

Abstract

Many visual languages follow the principle of single assignment, particularly those based on declarative programming paradigms. However, the notion of single assignment seems at odds with most forms of iteration. The authors survey a variety of approaches to this problem and then present the approach used in the visual language Forms/2. Forms/2 treats iteration in a form as a temporal sequence of instances of the form. Termination is controlled rather uniquely in Forms/2 as a direct result of the dependence-resolution evaluation mechanism.<>