Programming languages as operating systems ( or revenge of the son of the lisp machine)

Abstract

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, w e s h o w h o w MrEd denes a high-level operating system for graphical programs. Since DrScheme exposes MrEd's language constructs directly to the repl, D r S c heme can easily execute programs that use the full MrEd language, including its GUI toolbox. At the same time, DrScheme must protect its GUI against interference from the programs it executes, and it must be able to halt a program that has gone awry and To address this problem, MrEd provides a small set of new language constructs. These constructs allow a programrunning program, such a s D r S c heme, to run nested programs directly on the MrEd virtual machine without sacri cing control over the nested programs. As a result, DrScheme can execute a copy o f D r S c heme that is executing its own copy of DrScheme (see Figure 1). The inner and middle DrSchemes cannot interfere with the operation of the outer DrScheme, and the middle DrScheme cannot interfere with the outer DrScheme's control over the inner DrScheme.In this paper, we describe the key elements of the MrEd virtual machine, and we step through the implementation of a miniature version of DrScheme in MrEd. More generally, w e s h o w h o w MrEd de nes a high-level operating system (OS) for graphical programs. As in other high-level OSes, safety and security i n M r E d d e r i v e from properties of the underlying programming language. Mere safety, h o wever, provides neither the level of protection between applications nor the kind of process control that conventional OSes provide. Such protection and control is crucial for implementing many kinds of programs, including programming environments and scripting engines. By describing how w e implemented DrScheme in MrEd, we demonstrate how t o obtain key OS facilities through small extensions to a highlevel programming language.

Language support for extensible web browsers

“…We do not yet address such policies, except to note that when extensions may interact freely (unlike in Chrome), more work must be done to prevent a confused-deputy attack or outright collusion between extensions; this extends the threat model in [2]. Additional care must be taken to protect such a composite system from runaway extensions, as in [5].…”

Implementation and use of the PLT scheme Web server

“…Fortunately, PLT Scheme has facilities for fine-grained resource management: custodians [16]. A custodian records a collection of resources such as files and network ports, sockets, and network listeners, and provides a single primitive for closing them and returning them to the system.…”

“…The use of send/suspend/dispatch avoids the need to serialize the paper number in the query string, and also eliminates the need to invent names for the tags. 16 While this example uses embed/url to generate anchor elements (links) only, it is certainly possible to use it to generate a url in any other valid context, such as in the action field of a form. Unfortunately, because the action is associated with a form, not with a button, send/suspend/dispatch cannot distinguish between different form buttons: this must still be done manually in the style of figure 12.…”

“…Resource containers provide an api for separating the ownership of resources from traditional process boundaries. The custodians [16] in PLT Scheme provide similar functionality with a simpler api than those mentioned.…”

Embedding Dynamic Dataflow in a Call-by-Value Language

“…FrTime's support for dynamic dataflow graph construction saves us the need to build an interaction mode for the debugger. Instead we reuse the DrScheme REPL, inheriting its many features and also its careful handling of many subtle issues [11]. 3.…”