The MrEd virtual machine serves both as the implementation platform for the DrScheme programming environment, and as the underlying Scheme engine for executing expressions and programs entered into DrScheme's read-eval-print loop. We describe the key elements of the MrEd virtual machine for building a programming environment, and we step through the implementation of a miniature version of DrScheme in MrEd. More generally, we show how MrEd defines a high-level operating system for graphical programs. 1 MrEd: A Scheme Machine The DrScheme programming environment [10] provides students and programmers with a user-friendly environment for developing Scheme programs. To make programming accessible and attractive to novices, DrScheme provides a thoroughly graphical environment and runs under several major windowing systems (Windows, MacOS, and Unix/X). More than 60 universities and high schools currently employ DrScheme in their computing curriculum, and new schools adopt DrScheme every s...

this paper, we outline a vision of analysis techniques for this design domain and argue that most conventional compositional verification techniques, such as are found in the model checking literature, are poorly suited for this domain

Most existing modular model checking techniques betray their hardware roots: they assume that modules compose in parallel. In contrast, feature-oriented software designs, which have proven very successful in several domains, are sequential in the simplest case. Most interesting feature-oriented designs are really quasi-sequential compositions of parallel compositions. These designs demand and inspire new verification techniques. This paper presents algorithms that exploit the software's modular decomposition to verify feature-oriented designs. Our technique can verify most properties locally in the features; we also characterize when a global state space construction is unavoidable. We have validated our proposal by testing it on several designs.

The effectiveness of modular model checking for hardware makes it tempting to apply these techniques to software. Existing modular techniques have been driven by the parallel-composition semantics of hardware. New architectures for software, however, combine sequential and parallel composition.