expand advice on importing these modules
[packages/old-time.git] / Data / Version.hs
1 -----------------------------------------------------------------------------
2 -- |
3 -- Module : Data.Version
4 -- Copyright : (c) The University of Glasgow 2004
5 -- License : BSD-style (see the file libraries/base/LICENSE)
6 --
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable (local universal quantification in ReadP)
10 --
11 -- A general library for representation and manipulation of versions.
12 --
13 -- Versioning schemes are many and varied, so the version
14 -- representation provided by this library is intended to be a
15 -- compromise between complete generality, where almost no common
16 -- functionality could reasonably be provided, and fixing a particular
17 -- versioning scheme, which would probably be too restrictive.
18 --
19 -- So the approach taken here is to provide a representation which
20 -- subsumes many of the versioning schemes commonly in use, and we
21 -- provide implementations of 'Eq', 'Ord' and conversion to\/from 'String'
22 -- which will be appropriate for some applications, but not all.
23 --
24 -----------------------------------------------------------------------------
25
26 module Data.Version (
27 -- * The @Version@ type
28 Version(..),
29 -- * A concrete representation of @Version@
30 showVersion, parseVersion,
31 ) where
32
33 import Prelude -- necessary to get dependencies right
34
35 -- These #ifdefs are necessary because this code might be compiled as
36 -- part of ghc/lib/compat, and hence might be compiled by an older version
37 -- of GHC. In which case, we might need to pick up ReadP from
38 -- Distribution.Compat.ReadP, because the version in
39 -- Text.ParserCombinators.ReadP doesn't have all the combinators we need.
40 #if __GLASGOW_HASKELL__ >= 603 || __HUGS__ || __NHC__
41 import Text.ParserCombinators.ReadP
42 #else
43 import Distribution.Compat.ReadP
44 #endif
45
46 #if !__GLASGOW_HASKELL__
47 import Data.Typeable ( Typeable, TyCon, mkTyCon, mkTyConApp )
48 #elif __GLASGOW_HASKELL__ < 602
49 import Data.Dynamic ( Typeable(..), TyCon, mkTyCon, mkAppTy )
50 #else
51 import Data.Typeable ( Typeable )
52 #endif
53
54 import Data.List ( intersperse, sort )
55 import Control.Monad ( liftM )
56 import Data.Char ( isDigit, isAlphaNum )
57
58 {- |
59 A 'Version' represents the version of a software entity.
60
61 An instance of 'Eq' is provided, which implements exact equality
62 modulo reordering of the tags in the 'versionTags' field.
63
64 An instance of 'Ord' is also provided, which gives lexicographic
65 ordering on the 'versionBranch' fields (i.e. 2.1 > 2.0, 1.2.3 > 1.2.2,
66 etc.). This is expected to be sufficient for many uses, but note that
67 you may need to use a more specific ordering for your versioning
68 scheme. For example, some versioning schemes may include pre-releases
69 which have tags @\"pre1\"@, @\"pre2\"@, and so on, and these would need to
70 be taken into account when determining ordering. In some cases, date
71 ordering may be more appropriate, so the application would have to
72 look for @date@ tags in the 'versionTags' field and compare those.
73 The bottom line is, don't always assume that 'compare' and other 'Ord'
74 operations are the right thing for every 'Version'.
75
76 Similarly, concrete representations of versions may differ. One
77 possible concrete representation is provided (see 'showVersion' and
78 'parseVersion'), but depending on the application a different concrete
79 representation may be more appropriate.
80 -}
81 data Version =
82 Version { versionBranch :: [Int],
83 -- ^ The numeric branch for this version. This reflects the
84 -- fact that most software versions are tree-structured; there
85 -- is a main trunk which is tagged with versions at various
86 -- points (1,2,3...), and the first branch off the trunk after
87 -- version 3 is 3.1, the second branch off the trunk after
88 -- version 3 is 3.2, and so on. The tree can be branched
89 -- arbitrarily, just by adding more digits.
90 --
91 -- We represent the branch as a list of 'Int', so
92 -- version 3.2.1 becomes [3,2,1]. Lexicographic ordering
93 -- (i.e. the default instance of 'Ord' for @[Int]@) gives
94 -- the natural ordering of branches.
95
96 versionTags :: [String] -- really a bag
97 -- ^ A version can be tagged with an arbitrary list of strings.
98 -- The interpretation of the list of tags is entirely dependent
99 -- on the entity that this version applies to.
100 }
101 deriving (Read,Show
102 #if __GLASGOW_HASKELL__ >= 602
103 ,Typeable
104 #endif
105 )
106
107 #if !__GLASGOW_HASKELL__
108 versionTc :: TyCon
109 versionTc = mkTyCon "Version"
110
111 instance Typeable Version where
112 typeOf _ = mkTyConApp versionTc []
113 #elif __GLASGOW_HASKELL__ < 602
114 versionTc :: TyCon
115 versionTc = mkTyCon "Version"
116
117 instance Typeable Version where
118 typeOf _ = mkAppTy versionTc []
119 #endif
120
121 instance Eq Version where
122 v1 == v2 = versionBranch v1 == versionBranch v2
123 && sort (versionTags v1) == sort (versionTags v2)
124 -- tags may be in any order
125
126 instance Ord Version where
127 v1 `compare` v2 = versionBranch v1 `compare` versionBranch v2
128
129 -- -----------------------------------------------------------------------------
130 -- A concrete representation of 'Version'
131
132 -- | Provides one possible concrete representation for 'Version'. For
133 -- a version with 'versionBranch' @= [1,2,3]@ and 'versionTags'
134 -- @= [\"tag1\",\"tag2\"]@, the output will be @1.2.3-tag1-tag2@.
135 --
136 showVersion :: Version -> String
137 showVersion (Version branch tags)
138 = concat (intersperse "." (map show branch)) ++
139 concatMap ('-':) tags
140
141 -- | A parser for versions in the format produced by 'showVersion'.
142 --
143 #if __GLASGOW_HASKELL__ >= 603 || __HUGS__
144 parseVersion :: ReadP Version
145 #elif __NHC__
146 parseVersion :: ReadPN r Version
147 #else
148 parseVersion :: ReadP r Version
149 #endif
150 parseVersion = do branch <- sepBy1 (liftM read $ munch1 isDigit) (char '.')
151 tags <- many (char '-' >> munch1 isAlphaNum)
152 return Version{versionBranch=branch, versionTags=tags}