#10820 on Trac [1] and D1200 on Phabricator [2] discuss adding the capababilty to Template Haskell to detect which language extensions enabled. Unfortunately, since template-haskell can't depend on ghc (as ghc depends on template-haskell), it can't simply re-export the ExtensionFlag type from DynFlags to the user. There is a second data type encoding the list of possible language extensions in the Cabal package, in Language.Haskell.Extension [3]. But template-haskell doesn't already depend on Cabal, and doing so seems like it would cause difficulties, as the two packages can be upgraded separately. So adding this new feature to Template Haskell requires introducing a *third* data type for language extensions. It also requires enumerating this full list in two more places, to convert back and forth between the TH Extension data type and GHC's internal ExtensionFlag data type. Is there another way here? Can there be one single shared data type for this somehow? [1] https://ghc.haskell.org/trac/ghc/ticket/10820 [2] https://phabricator.haskell.org/D1200 [3] https://hackage.haskell.org/package/Cabal-1.22.4.0/docs/Language-Haskell-Ext...