Schemelet

Schemelet is a conceptual unit of software organization in the Scheme family of programming languages. It describes a small, self-contained collection of Scheme code that provides a narrowly focused API while encapsulating its internal implementation. Schemelets are intended to be lightweight building blocks that are easy to reuse, compose, and reason about, functioning like mini-modules built from a handful of procedures.

Origin and scope: The term combines "Scheme" with the diminutive -let to convey smallness. It is not a formal standard in the Scheme specifications, but it appears in educational literature and among library designers as a convenient label for micro-modules or library fragments that expose a limited surface area.

Core characteristics: A schemelet typically has a compact, well-defined interface and hides implementation details behind a small export list. It relies on lexical scoping and closures to protect private state, minimizes external dependencies, and is designed to be importable or require-able alongside other schemelets.

Relation to other constructs: Schemelets sit between plain functions and full modules. They share module-like properties such as an explicit API but stay lighter weight than traditional libraries. In practice, a schemelet may be implemented as a module file or a package containing code, tests, and a manifest of exports.

Usage pattern: Authors create schemelets for focused concerns, document the public surface, and ensure internal helpers remain private. They can be composed by linking the exported procedures of multiple schemelets to assemble larger systems, reducing cross-cutting dependencies and improving testability.

See also: Scheme, modules, libraries, closures, macros.