To keep following the TTG goal of a GHC-independent AST, we want to remove all imports of `GHC.*` from the `Language.Haskell.*` hierarchy. One of these imports is `FastString`. ~~After some discussion below we've decided to move `FastString` from the `GHC.Data` module hierarchy to the "independent" `Data` one.~~ ~~This issue should be closed after `FastString` lives in this independent space, and all `Language.Haskell.*` imports of `FastString` then import `Data.FastString` rather than `GHC.Data.FastString`~~ Currently, `FastString` from `GHC.Data.FastString` is used multiple times in the client-independent AST living in `Language.Haskell.Syntax`. The occurrences are: ```hs data HsExpr id = ... | HsOverLabel (XOverLabel p) FastString ... | HsQuasiQuote -- See Note [Quasi-quote overview] in GHC.Tc.Gen.Splice (XQuasiQuote id) (IdP id) -- Splice point (IdP id) -- Quoter SrcSpan -- The span of the enclosed string FastString -- The enclosed string ... data HsLit id = ... | HsString (XHsString x) {- SourceText -} FastString data OverLitVal = ... | HsIsString !SourceText !FastString -- ^ String-looking literals data HsTyLit = ... | HsStrTy SourceText FastString newtype ModuleName = ModuleName FastString ``` I am wondering about how I can get rid of FastString in Language.Haskell.Syntax, and so by raising this issue I mean to discuss ways to solve this, and get started on implementing said solution Perhaps some strategy resembling `IdP`... Thank you, romes CC: @Ericson2314