R6RS Version References (Guile Reference Manual)

6.20.5 R6RS Version References

Guile’s module system includes support for locating modules based on a declared version specifier of the same form as the one described in R6RS (see R6RS Library Form in The Revised^6 Report on the Algorithmic Language Scheme). By using the #:version keyword in a define-module form, a module may specify a version as a list of zero or more exact, nonnegative integers.

This version can then be used to locate the module during the module search process. Client modules and callers of the use-modules function may specify constraints on the versions of target modules by providing a version reference, which has one of the following forms:

 (sub-version-reference ...)
 (and version-reference ...)
 (or version-reference ...)
 (not version-reference)

in which sub-version-reference is in turn one of:

 (sub-version)
 (>= sub-version)
 (<= sub-version)
 (and sub-version-reference ...)
 (or sub-version-reference ...)
 (not sub-version-reference)

in which sub-version is an exact, nonnegative integer as above. A version reference matches a declared module version if each element of the version reference matches a corresponding element of the module version, according to the following rules:

The and sub-form matches a version or version element if every element in the tail of the sub-form matches the specified version or version element.
The or sub-form matches a version or version element if any element in the tail of the sub-form matches the specified version or version element.
The not sub-form matches a version or version element if the tail of the sub-form does not match the version or version element.
The >= sub-form matches a version element if the element is greater than or equal to the sub-version in the tail of the sub-form.
The <= sub-form matches a version element if the version is less than or equal to the sub-version in the tail of the sub-form.
A sub-version matches a version element if one is eqv? to the other.

For example, a module declared as:

 (define-module (mylib mymodule) #:version (1 2 0))

would be successfully loaded by any of the following use-modules expressions:

 (use-modules ((mylib mymodule) #:version (1 2 (>= 0))))
 (use-modules ((mylib mymodule) #:version (or (1 2 0) (1 2 1))))
 (use-modules ((mylib mymodule) #:version ((and (>= 1) (not 2)) 2 0)))