DrScheme is a programming environment for Scheme. It fully integrates a graphics-enriched editor, a parser for multiple variants of Scheme, a functional read-eval-print loop, and an algebraic printer. The environment is especially useful for students, because it has a tower of syntactically restricted variants of Scheme that are designed to catch typical student mistakes and explain them in terms the students understand. The environment is also useful for professional programmers, due to its sophisticated programming tools, such as the static debugger, and its advanced language features, such as units and mixins. Beyond the ordinary programming environment tools, DrScheme provides an algebraic stepper, a context-sensitive syntax checker, and a static debugger. The stepper reduces Scheme programs to values, according to the reduction semantics of Scheme. It is useful for explaining the semantics of linguistic facilities and for studying the behavior of small programs. The syntax checker annotates programs with font and color changes based on the syntactic structure of the program. On demand, it draws arrows that point from bound to binding occurrences of identifiers. It also supports α-renaming. Finally, the static debugger provides a type inference system that explains specific inferences in terms of a value-flow graph, selectively overlaid on the program text.

Abstract PLT Scheme (DrScheme and MzScheme) supports the Component Object Model (COM) standard with two pieces of software. The first piece is MzCOM, a COM class that makes a Scheme evaluator available to COM clients. With MzCOM, programmers can embed Scheme code in programs written in mainstream languages such as C++ or Visual BASIC. Some applications can also be used as MzCOM clients. The other piece of component‐support software is MysterX, which makes COM classes available to PLT Scheme programs. When needed, MysterX uses a programmable Web browser to display COM objects. We describe the technical issues encountered in building these two systems and sketch some applications. Copyright © 2002 John Wiley & Sons, Ltd.

We consider the problem of lightweight closure conversion, in which multiple procedure call protocols may coexist in the same code. A lightweight closure omits bindings for some of the free variables of the procedure that is represents. Flow analysis is used to match the protocol expected by each procedure and the protocol used at its possible call sites. We formulate the flow analysis as a deductive system that generates a labeled transition system and a set of constraints. We show that any solution to the constraints justifies the resulting transformation. Some of the techniques used are similar to those of abstract interpretation, but others appear to be novel.

We consider the problem of selective and lightweight closure conversion, in which multiple procedure-calling protocols may coexist in the same code. Flow analysis is used to match the protocol expected by each procedure and the protocol used at each of its possible call sites. We formulate the flow analysis as the solution of a set of constraints, and show that any solution to the constraints justifies the resulting transformation. Some of the techniques used are suggested by those of abstract interpretation, but others arise out of alternative approaches.