I'm fully on board with cleaning up the story around package keys, so +1 on the mission, but I have very few preferences on the particulars. -Edward On Fri, May 1, 2015 at 1:06 PM, Edward Z. Yang wrote:

In GHC 7.10, we changed the internal representation of names to be based on package keys (base_XXXXXX) rather than package IDs (base-4.7.0.1), however, we forgot to update the Template Haskell API to track these changes. This lead to some bugs in TH code which was synthesizing names by using package name and version directly, e.g. https://ghc.haskell.org/trac/ghc/ticket/10279

We now propose the following changes to the TH API in order to track these changes:

1. Currently, a TH NameG contains a PkgName, defined as:

newtype PkgName = PkgName String

This is badly misleading, even in the old world order, since these needed version numbers as well. We propose that this be renamed to PkgKey:

newtype PkgKey = PkgKey String mkPackageKey :: String -> PackageKey mkPackageKey = PkgKey

2. Package keys are somewhat hard to synthesize, so we also offer an API for querying the package database of the GHC which is compiling your code for information about packages. So, we introduce a new abstract data type:

data Package packageKey :: Package -> PkgKey

and some functions for getting packages:

searchPackage :: String -- Package name -> String -- Version -> Q [Package]

reifyPackage :: PkgKey -> Q Package

We could add other functions (e.g., return all packages with a package name).

3. Commonly, a user wants to get the package key of the current package. Following Simon's suggestion, this will be done by augmenting ModuleInfo:

data ModuleInfo = ModuleInfo { mi_this_mod :: Module -- new , mi_imports :: [Module] }

We'll also add a function for accessing the module package key:

modulePackageKey :: Module -> PkgKey

And a convenience function for accessing the current module:

thisPackageKey :: Q PkgKey thisPackageKey = fmap (modulePackageKey . mi_this_mod) qReifyModule

thisPackage :: Q Package thisPackage = reifyPackage =<< thisPackageKey

Discussion period: 1 month

Thanks, Edward