R5RS

R5RS, the Fifth Revised Report on the Algorithmic Language Scheme, is a standard for the Scheme programming language. Published in 1998 by the IEEE Computer Society as a revision of R4RS, it defines a portable, practical subset of Scheme intended to support both teaching and real-world programming while preserving Scheme’s essential features.

The standard specifies the core language and its semantics, including lexical scoping, first-class procedures, and proper tail recursion, along with a collection of primitives, control forms (such as if, cond, and let), and higher-level constructs like begin and letrec. It also introduces a hygienic macro system based on define-syntax and syntax-rules, enabling portable macro definitions without unintended variable capture.

R5RS also provides a standard library for basic data types (numbers, characters, strings, lists), input/output, and port-based I/O operations, enabling common tasks such as file access and display of values. It deliberately keeps the core small and emphasizes extensibility, with many features left to implementations as extensions or libraries.

In the broader history of Scheme, R5RS succeeded R4RS and was later superseded in part by R6RS and by later efforts under the R7RS umbrella. It remains influential in legacy code and in teaching, and many Scheme implementations provide compatibility with R5RS while offering additional features.