Cabal- A framework for packaging Haskell softwareSource codeContentsIndex
This is about the cabal configurations feature. It exports finalizePackageDescription and flattenPackageDescription which are functions for converting GenericPackageDescriptions down to PackageDescriptions. It has code for working with the tree of conditions and resolving or flattening conditions.
finalizePackageDescription :: Package pkg => FlagAssignment -> Maybe (PackageIndex pkg) -> OS -> Arch -> CompilerId -> [Dependency] -> GenericPackageDescription -> Either [Dependency] (PackageDescription, FlagAssignment)
flattenPackageDescription :: GenericPackageDescription -> PackageDescription
parseCondition :: ReadP r (Condition ConfVar)
freeVars :: CondTree ConfVar c a -> [FlagName]
:: Package pkg
=> FlagAssignmentExplicitly specified flag assignments
-> Maybe (PackageIndex pkg)Available dependencies. Pass Nothing if this is unknown.
-> OSOS-name
-> ArchArch-name
-> CompilerIdCompiler + Version
-> [Dependency]Additional constraints
-> GenericPackageDescription
-> Either [Dependency] (PackageDescription, FlagAssignment)Either missing dependencies or the resolved package description along with the flag assignments chosen.

Create a package description with all configurations resolved.

This function takes a GenericPackageDescription and several environment parameters and tries to generate PackageDescription by finding a flag assignment that result in satisfiable dependencies.

It takes as inputs a not necessarily complete specifications of flags assignments, an optional package index as well as platform parameters. If some flags are not assigned explicitly, this function will try to pick an assignment that causes this function to succeed. The package index is optional since on some platforms we cannot determine which packages have been installed before. When no package index is supplied, every dependency is assumed to be satisfiable, therefore all not explicitly assigned flags will get their default values.

This function will fail if it cannot find a flag assignment that leads to satisfiable dependencies. (It will not try alternative assignments for explicitly specified flags.) In case of failure it will return a minimum number of dependencies that could not be satisfied. On success, it will return the package description and the full flag assignment chosen.

flattenPackageDescription :: GenericPackageDescription -> PackageDescriptionSource

Flatten a generic package description by ignoring all conditions and just join the field descriptors into on package description. Note, however, that this may lead to inconsistent field values, since all values are joined into one field, which may not be possible in the original package description, due to the use of exclusive choices (if ... else ...).

XXX: One particularly tricky case is defaulting. In the original package description, e.g., the source directory might either be the default or a certain, explicitly set path. Since defaults are filled in only after the package has been resolved and when no explicit value has been set, the default path will be missing from the package description returned by this function.

parseCondition :: ReadP r (Condition ConfVar)Source
Parse a configuration condition from a string.
freeVars :: CondTree ConfVar c a -> [FlagName]Source
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