Emacs Lisp

Abstract: While Emacs proponents largely agree that it is the world’s greatest text editor, it is almost as much a Lisp machine disguised as an editor. Indeed, one of its chief appeals is that it is programmable via its own programming language. Emacs Lisp is a Lisp in the classic tradition. In this article, we present the history of this language over its more than 30 years of evolution. Its core has remained remarkably stable since its inception in 1985, in large part to preserve compatibility with the many third-party packages providing a multitude of extensions. Still, Emacs Lisp has evolved and continues to do so. Important aspects of Emacs Lisp have been shaped by concrete requirements of the editor it supports as well as implementation constraints. These requirements led to the choice of a Lisp dialect as Emacs’s language in the first place, specifically its simplicity and dynamic nature: Loading additional Emacs packages or changing the ones in place occurs frequently, and having to restart the editor in order to re-compile or re-link the code would be unacceptable. Fulfilling this requirement in a more static language would have been difficult at best. One of Lisp’s chief characteristics is its malleability through its uniform syntax and the use of macros. This has allowed the language to evolve much more rapidly and substantively than the evolution of its core would suggest, by letting Emacs packages provide new surface syntax alongside new functions. In particular, Emacs Lisp can be customized to look much like Common Lisp, and additional packages provide multiple-dispatch object systems, legible regular expressions, programmable pattern-matching constructs, generalized variables, and more. Still, the core has also evolved, albeit slowly. Most notably, it acquired support for lexical scoping. The timeline of Emacs Lisp development is closely tied to the projects and people who have shaped it over the years: We document Emacs Lisp history through its predecessors, Mocklisp and MacLisp, its early development up to the “Emacs schism” and the fork of Lucid Emacs, the development of XEmacs, and the subsequent rennaissance of Emacs development.

Abstract: It is possible to translate code written in Emacs Lisp or another Lisp dialect which uses dynamic scoping to a more modern programming language with lexical scoping while largely preserving structure and readability of the code. The biggest obstacle to such an idiomatic translation from Emacs Lisp is the translation of dynamic binding into suitable instances of lexical binding: Many binding constructs in real programs in fact exhibit identical behavior under both dynamic and lexical binding. An idiomatic translation needs to detect as many of these binding constructs as possible and convert them into lexical binding constructs in the target language to achieve readability and efficiency of the target code. The basic prerequisite for such an idiomatic translation is thus a dynamic scope analysis which associates variable occurrences with binding constructs. We present such an analysis. It is an application of the Nielson/Nielson framework for flow analysis to a semantics for dynamic binding akin to Moreau's. Its implementation handles a substantial portion of Emacs Lisp, has been applied to realistic Emacs Lisp code, and is highly accurate and reasonably efficient in practice.

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Abstract: Volume IV begins with the Logic Programming group, all descended from John McCarthy's LISP of the late 1960s. The Volume begins with a few pages from the LISP 1.5 Programmers Manual, a vital token of things to come and moves on to LISP's offspring: LISP, Scheme, Guile, and CLOS. Finally, Jamie Andrews provides a substantial essay on the most important Functional programming language, Prolog. The contributions are designed to enable the programmer to evaluate the languages and to understand the ways in which each works. -- Bob Chassell on Emacs LISP -- Brian Harvey on Scheme -- Jim Blandy on Guile -- Jim Veitch on CLOS -- Jamie Andrews on Prolog