R6RS

R6RS, or the Revised Sixth Report on the Algorithmic Language Scheme, is a major revision of the Scheme language standard. Published in 2007, it sought to standardize both a substantial core of the language and a large standard library, with the aim of improving portability and interoperability across Scheme implementations.

R6RS introduced a formal module system, allowing libraries to declare imports and exports, and to be compiled or loaded in a uniform way. It also expanded the language’s standard library with numerous modules for I/O, data types, and system interfaces, and refined the treatment of numbers, strings, characters, and ports for more predictable behavior across platforms. The specification paid particular attention to Unicode support and to providing a clean separation between the language core and its libraries.

Reception and impact: R6RS was controversial within the Scheme community. Its size and the breadth of the standard library led to concerns that it was too heavy for practical use and difficult for smaller implementations to support. As a result, several prominent Scheme implementations chose not to adopt it or offered only partial support. The heavy direction of R6RS helped motivate the later effort to produce R7RS, which split standards development into a small, minimal core (R7RS-small) and a separate large library collection (R7RS-large).

Today, R6RS remains a reference point in discussions of Scheme standardization, and some implementations provide compatibility layers or partial implementations of its features.

See also: R5RS, R7RS.