This is an implementation of enumerated types for Scheme, based on a pre-SRFI specification by John Cowan. It should be portable to any R7RS-small implementation with SRFIs 1, 125, 128, and 146.
From the pre-SRFI's Rationale:
Many procedures in many libraries accept arguments from a finite set (usually a fairly small one), or subsets of a finite set to describe one or more modes of operation. Offering a mechanism for dealing with such values fosters portable and readable code, much as records do for compound values, or multiple values for procedures computing several results.
This SRFI ... provides something related to the enums of Java version 5 and later. These are objects of a type disjoint from all others that are grouped into enumeration types (called enum classes in Java). In Java, each enumeration type is allowed to declare the number and types of values associated with each object, but in this SRFI an enumeration object has exactly one value; this is useful when translating from C to record the numeric value, but has other uses as well.
The current enums spec states that the set-theoretical enum set
enum-set-union!, etc.) may mutate their first enum-set
argument. Enum sets are currently implemented in terms of SRFI 146
mappings, and their linear update set-theoretical procedures
mapping-union!, etc.). SRFI 146 does not specify which arguments
may be mutated by these procedures.
Email: wcm at sigwinch dot xyzzy minus the zy
This is free software released under the MIT/X license. See LICENSE for details.