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GHC 9.10.3 · lts/ghc-9.10.x · 248f8f0 · 2026-10-05

ModuleCabal-syntax-3.12.1.0Haskell2010

Distribution.Version

Exports the Version type along with a parser and pretty printer. A version is something like "1.3.3". It also defines the VersionRange data types. Version ranges are like ">= 1.2 && < 2".

  • 8 types
  • 44 values

Package versions

7 declarations
datadata Version
#

A Version represents the version of a software entity.

Instances of Eq and Ord are provided, which gives exact equality and lexicographic ordering of the version number components (i.e. 2.1 > 2.0, 1.2.3 > 1.2.2, etc.).

This type is opaque and distinct from the Version type in Data.Version since Cabal-2.0. The difference extends to the Binary instance using a different (and more compact) encoding.

Instances12Eq, Data, Ord, Read, Show, Generic, …
valuemkVersion :: [Int] -> Version
#

Construct Version from list of version number components.

For instance, mkVersion [3,2,1] constructs a Version representing the version 3.2.1.

All version components must be non-negative. mkVersion [] currently represents the special null version; see also nullVersion.

Version ranges

1 declaration
datadata VersionRange
#
Instances13Eq, Data, Ord, Read, Show, Generic, …

Constructing

The version range -any. That is, a version range containing all versions.

withinRange v anyVersion = True

The empty version range -none, that is a version range containing no versions.

This can be constructed using any unsatisfiable version range expression, for example < 0.

withinRange v noVersion = False

The version range == v.*.

For example, for version 1.2, the version range == 1.2.* is the same as >= 1.2 && < 1.3.

withinRange v' (withinVersion v) = v' >= v && v' < upper v
  where
    upper (Version lower t) = Version (init lower ++ [last lower + 1]) t

The version range ^>= v.

For example, for version 1.2.3.4, the version range ^>= 1.2.3.4 is the same as >= 1.2.3.4 && < 1.3.

Note that ^>= 1 is equivalent to >= 1 && < 1.1.

Inspection

Does this VersionRange place any restriction on the Version or is it in fact equivalent to AnyVersion.

Note this is a semantic check, not simply a syntactic check. So for example the following is True (for all v).

isAnyVersion (EarlierVersion v `UnionVersionRanges` orLaterVersion v)

This is the converse of isAnyVersion. It check if the version range is empty, if there is no possible version that satisfies the version range.

For example this is True (for all v):

isNoVersion (EarlierVersion v `IntersectVersionRanges` LaterVersion v)

Simplify a VersionRange expression. For non-empty version ranges this produces a canonical form. Empty or inconsistent version ranges are left as-is because that provides more information.

If you need a canonical form use fromVersionIntervals . toVersionIntervals

It satisfies the following properties:

withinRange v (simplifyVersionRange r) = withinRange v r
    withinRange v r = withinRange v r'
==> simplifyVersionRange r = simplifyVersionRange r'
 || isNoVersion r
 || isNoVersion r'
valuefoldVersionRange
  1. :: a

    "-any" version

  2. -> (Version -> a)
    "== v"
  3. -> (Version -> a)
    "> v"
  4. -> (Version -> a)
    "< v"
  5. -> (a -> a -> a)

    "_ || _" union

  6. -> (a -> a -> a)

    "_ && _" intersection

  7. -> VersionRange
  8. -> a
#

Fold over the basic syntactic structure of a VersionRange.

This provides a syntactic view of the expression defining the version range. The syntactic sugar ">= v", "<= v" and "== v.*" is presented in terms of the other basic syntax.

For a semantic view use asVersionIntervals.

Does the version range have an explicit lower bound?

Note: this function only considers the user-specified lower bounds, but not the implicit >=0 lower bound.

Cata & ana

datadata VersionRangeF a
#

F-Algebra of VersionRange. See cataVersionRange.

Constructors

Instances9Functor, Foldable, Traversable, Eq, Data, Read, …

Utilities

Increment the last version number.

Example: For 1.2 this returns 1.3 so that it can be used as upper bound when resolving == 1.2.*. For 0.4.1 it returns 0.4.2.

Compute next greater major version to be used as upper bound.

Example: 0.4.1 produces the version 0.5 which then can be used to construct a range >= 0.4.1 && < 0.5

Modification

Version intervals view

5 declarations

View a VersionRange as a union of intervals.

This provides a canonical view of the semantics of a VersionRange as opposed to the syntax of the expression used to define it. For the syntactic view use foldVersionRange.

Each interval is non-empty. The sequence is in increasing order and no intervals overlap or touch. Therefore only the first and last can be unbounded. The sequence can be empty if the range is empty (e.g. a range expression like && 2).

Other checks are trivial to implement using this view. For example:

isNoVersion vr | [] <- asVersionIntervals vr = True
               | otherwise                   = False
isSpecificVersion vr
   | [(LowerBound v  InclusiveBound
      ,UpperBound v' InclusiveBound)] <- asVersionIntervals vr
   , v == v'   = Just v
   | otherwise = Nothing

VersionIntervals abstract type

The VersionIntervals type and the accompanying functions are exposed primarily for completeness and testing purposes. In practice asVersionIntervals is the main function to use to view a VersionRange as a bunch of VersionIntervals.

newtypenewtype VersionIntervals
#

A complementary representation of a VersionRange. Instead of a boolean version predicate it uses an increasing sequence of non-overlapping, non-empty intervals.

The key point is that this representation gives a canonical representation for the semantics of VersionRanges. This makes it easier to check things like whether a version range is empty, covers all versions, or requires a certain minimum or maximum version. It also makes it easy to check equality or containment. It also makes it easier to identify 'simple' version predicates for translation into foreign packaging systems that do not support complex version range expressions.

Instances2Eq, Show