Successful Scheme

Thought up any great programming schemes lately? The attendees at the Workshop on Scheme and Functional Programming 2000 -- held in Montreal on Sept. 17 -- have. The recent conference means the time is ripe to introduce the Scheme programming language and mention a bit of what's new in the Scheme world.

Scheme goes to school

Scheme, for the most part, is a simplified Lisp: one with extremely regular syntax, lexical interpretation, and semantics. That means it's easy to teach computers how to interpret Scheme, and to teach humans how to program in it.

That duality has made Scheme an academic language in two senses. Its regularity renders it a good construction material for research into new language structures and verification mechanisms; its powerful simplicity invites its use as a language for instruction.

In fact, one of Scheme's greatest advantages is the pedagogic classic, Structure and Interpretation of Computer Programs (SICP). Also known as The Wizard Book or The Purple Book because of its unique cover, SICP has been lauded since its inception in 1984 for its cogent, well-organized explanations of the fundamental abstractions of computing. SICP presents its algorithms and data in Scheme.

Scheme's place in the world of languages

Consequently, Scheme has been the mother tongue for many of the last generation's best computing students. However, Scheme is not stuck in the classroom or its own past. It's a very productive language for application development, and modern Schemes include extensive libraries that give it the Web, GUI, and networking capabilities that most programs need.

Many Scheme aspects appear in other languages and are familiar to loyal readers of Regular Expressions. Scheme shares its grounding in denotational semantics with REBOL, the subject of our last column. Scheme is the first prominent dialect of Lisp to demonstrate static lexical scoping, and is also properly tail-callable. The spirit of its coding is much like Forth's, although the two languages are at odds regarding garbage collection and the hardware-dependence of values. Guile, introduced in our November 1998 column, is itself a specialization of Scheme, crafted for portability and embeddability.

Papers at the Montreal workshop touched on several other topics that we consider important. Two speakers demonstrated the interoperability between Scheme as a scripting language and legacy objects coded in either C or Java; another explained advanced models for distributed computing.

The pieces of the Scheme world are relatively common, but Scheme's combination of them is uniquely potent.

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