Cabal-1.11.2: A framework for packaging Haskell software





This should be a much more sophisticated abstraction than it is. Currently it's just a bit of data about the compiler, like it's flavour and name and version. The reason it's just data is because currently it has to be in Read and Show so it can be saved along with the LocalBuildInfo. The only interesting bit of info it contains is a mapping between language extensions and compiler command line flags. This module also defines a PackageDB type which is used to refer to package databases. Most compilers only know about a single global package collection but GHC has a global and per-user one and it lets you create arbitrary other package databases. We do not yet fully support this latter feature.


Haskell implementations

Support for package databases

data PackageDB

Some compilers have a notion of a database of available packages. For some there is just one global db of packages, other compilers support a per-user or an arbitrary db specified at some location in the file system. This can be used to build isloated environments of packages, for example to build a collection of related packages without installing them globally.

type PackageDBStack = [PackageDB]

We typically get packages from several databases, and stack them together. This type lets us be explicit about that stacking. For example typical stacks include:

 [GlobalPackageDB, UserPackageDB]
 [GlobalPackageDB, SpecificPackageDB "package.conf.inplace"]

Note that the GlobalPackageDB is invariably at the bottom since it contains the rts, base and other special compiler-specific packages.

We are not restricted to using just the above combinations. In particular we can use several custom package dbs and the user package db together.

When it comes to writing, the top most (last) package is used.

registrationPackageDB :: PackageDBStack -> PackageDB

Return the package that we should register into. This is the package db at the top of the stack.

Support for optimisation levels

data OptimisationLevel

Some compilers support optimising. Some have different levels. For compliers that do not the level is just capped to the level they do support.

Support for language extensions

type Flag = String

extensionsToFlags :: Compiler -> [Extension] -> [Flag]

For the given compiler, return the flags for the supported extensions.

unsupportedExtensions :: Compiler -> [Extension] -> [Extension]

For the given compiler, return the extensions it does not support.