Data.Old.Version

A general library for representation and manipulation of versions.

Versioning schemes are many and varied, so the version representation provided by this library is intended to be a compromise between complete generality, where almost no common functionality could reasonably be provided, and fixing a particular versioning scheme, which would probably be too restrictive.

So the approach taken here is to provide a representation which subsumes many of the versioning schemes commonly in use, and we provide implementations of Eq, Ord, Read, and Show, which will be appropriate for some applications, but not all.

This version of the module is forked from base, preserving the versionTags field of the Version type that will be removed in GHC 7.12 (cf. https://ghc.haskell.org/trac/ghc/ticket/2496).

This version not only preserves versionTags, but also eliminates the showing and parsing functions in favor of sensible, hand-derived Show and Read instances, such that:

show (read version) == id version

For compatibility with base, conversion functions to and from Version are provided.

The Version type

data Version

A Version represents the version of a software entity.

An instance of Eq is provided, which implements exact equality by first comparing the versionBranch fields, followed by comparing the versionTags fields.

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 by the Show and Read instances, but depending on the application a different concrete representation may be more appropriate.

Constructors

Version

Fields

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.

Instances

Eq Version

Ord Version

Read Version

Show Version

Provides one possible concrete representation for Version. For a version with versionBranch = [1,2,3] and versionTags = ["tag1","tag2"], the output will be 1.2.3-tag1-tag2.

IsString Version

Typeable * Version

Conversions from/to Version

toBase :: Version -> Version

Convert to a Version, stripping off the versionTags.

fromBase :: Version -> Version

Convert from a Version, adding an empty set of versionTags.