SRFIs

SRFIs, or Scheme Requests for Implementation, are community-defined specifications that propose libraries, language extensions, or other features to improve portability across Scheme implementations. They are part of the Scheme community's process for cooperative development outside of formal standards, and they cover a range of utilities from data structures to I/O.

A SRFI document typically includes a rationale, a precise specification, a reference implementation in Scheme, and tests. Proposals are numbered sequentially (for example, SRFI-1, SRFI-2) and maintained in an online repository. Each SRFI declares its authorship, status, and compatibility notes. The aim is to enable different Scheme systems to share a common API and behavior for code portability.

The SRFI process is distinct from formal language standards such as R5RS, R6RS, or R7RS, though many SRFIs are adopted by Scheme implementations and sometimes integrated into standard libraries. Implementations may selectively support SRFIs, and some SRFIs are more widely used than others. Adoption decisions are typically community-driven, with a focus on cross-implementation interoperability.

Common SRFI topics include list processing utilities, string handling, I/O, and basic data structures; there are also SRFIs that provide modules for regular expressions, ports, and testing. Some SRFIs have become de facto standards within many Scheme ecosystems, while others remain niche.

Criticism of the SRFI process notes potential fragmentation and duplication, as proposals evolve independently of formal standards. Nonetheless, SRFIs remain a central mechanism for extending Scheme libraries in a portable, collaboratively maintained way, enabling developers to write more portable code across diverse implementations.