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, 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 and conversion to/from String which will be appropriate for some applications, but not all.
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.
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.
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.
The version of compilerName with which the program was compiled or is being interpreted.
A parser for versions in the format produced by showVersion.
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.
A library that performs fast, accurate conversion between double precision floating point and text.
This library is implemented as bindings to the C++ double-conversion library written by Florian Loitsch at Google: http://code.google.com/p/double-conversion/.
The Text versions of these functions are about 30 times faster than the default show implementation for the Double type.
The ByteString versions are slower than the Text versions; roughly half the speed. (This seems to be due to the cost of allocating ByteString values via malloc.)
As a final note, be aware that the bytestring-show package is about 50% slower than simply using show.
getRequestVersion req returns the HTTP protocol version of the request req. If Nothing, the default httpVersion can be assumed.
getResponseVersion rsp returns the HTTP protocol version of the response rsp. If Nothing, the default httpVersion can be assumed.
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