A Version represents the version of a software entity.
An instance of Eq is provided, which implements exact equality
modulo reordering of the tags in the versionTags field.
An instance of Ord is also provided, which gives lexicographic
ordering on the versionBranch fields (i.e. 2.1 > 2.0, 1.2.3 > 1.2.2,
etc.). This is expected to be sufficient for many uses, but note that
you may need to use a more specific ordering for your versioning
scheme. For example, some versioning schemes may include pre-releases
which have tags "pre1", "pre2", and so on, and these would need to
be taken into account when determining ordering. In some cases, date
ordering may be more appropriate, so the application would have to
look for date tags in the versionTags field and compare those.
The bottom line is, don't always assume that compare and other Ord
operations are the right thing for every Version.
Similarly, concrete representations of versions may differ. One
possible concrete representation is provided (see showVersion and
parseVersion), but depending on the application a different concrete
representation may be more appropriate.
|versionBranch :: [Int]|
The numeric branch for this version. This reflects the
fact that most software versions are tree-structured; there
is a main trunk which is tagged with versions at various
points (1,2,3...), and the first branch off the trunk after
version 3 is 3.1, the second branch off the trunk after
version 3 is 3.2, and so on. The tree can be branched
arbitrarily, just by adding more digits.
We represent the branch as a list of Int, so
version 3.2.1 becomes [3,2,1]. Lexicographic ordering
(i.e. the default instance of Ord for [Int]) gives
the natural ordering of branches.
|versionTags :: [String]||A version can be tagged with an arbitrary list of strings.
The interpretation of the list of tags is entirely dependent
on the entity that this version applies to.