This provides an abstraction which deals with configuring and running programs. A Program is a static notion of a known program. A ConfiguredProgram is a Program that has been found on the current machine and is ready to be run (possibly with some user-supplied default args). Configuring a program involves finding its location and if necessary finding its version. There is also a ProgramConfiguration type which holds configured and not-yet configured programs. It is the parameter to lots of actions elsewhere in Cabal that need to look up and run programs. If we had a Cabal monad, the ProgramConfiguration would probably be a reader or state component of it.

The module also defines all the known built-in Programs and the defaultProgramConfiguration which contains them all.

One nice thing about using it is that any program that is registered with Cabal will get some "configure" and ".cabal" helpers like --with-foo-args --foo-path= and extra-foo-args.

There's also good default behavior for trying to find "foo" in PATH, being able to override its location, etc.

There's also a hook for adding programs in a Setup.lhs script. See hookedPrograms in UserHooks. This gives a hook user the ability to get the above flags and such so that they don't have to write all the PATH logic inside Setup.lhs.

Make a simple named program.

By default we'll just search for it in the path and not try to find the version name. You can override these behaviours if necessary, eg:

 simpleProgram "foo" { programFindLocation = ... , programFindVersion ... }

The Read/Show instance does not preserve all the unconfigured Programs because Program is not in Read/Show because it contains functions. So to fully restore a deserialised ProgramConfiguration use this function to add back all the known Programs.

• It does not add the default programs, but you probably want them, use builtinPrograms in addition to any extra you might need.

Try to configure a specific program. If the program is already included in the colleciton of unconfigured programs then we use any user-supplied location and arguments. If the program gets configured sucessfully it gets added to the configured collection.

Note that it is not a failure if the program cannot be configured. It's only a failure if the user supplied a location and the program could not be found at that location.

The reason for it not being a failure at this stage is that we don't know up front all the programs we will need, so we try to configure them all. To verify that a program was actually sucessfully configured use requireProgram.

Check that a program is configured and available to be run.

Additionally check that the version of the program number is suitable. For example AnyVersion or orLaterVersion (Version [1,0] [])

It raises an exception if the program could not be configured or the version is unsuitable, otherwise it returns the configured program.