Currently, `HsModule` is defined to be polymorphic over GHC passes. That is, it is defined like so: ```hs data HsModule pass = HsModule { hsmodName :: Maybe (Located ModuleName), hsmodExports :: Maybe (Located [LIE pass]), hsmodImports :: [LImportDecl pass], hsmodDecls :: [LHsDecl pass], hsmodDeprecMessage :: Maybe (Located WarningTxt), hsmodHaddockModHeader :: Maybe LHsDocString } deriving instance Data (HsModule GhcPs) deriving instance Data (HsModule GhcRn) deriving instance Data (HsModule GhcTc) ``` However, every single use site for `HsModule` that I can find only instantiates `pass` to `GhcPs`, which suggests that `HsModule` is only ever used for parsed code, but not renamed or typechecked code. In light of this, is there any good reason to keep around the `pass` parameter? We could make the code simpler by removing it: ```diff diff --git a/compiler/GHC/Hs.hs b/compiler/GHC/Hs.hs index 103539a41b..ecd891b52e 100644 --- a/compiler/GHC/Hs.hs +++ b/compiler/GHC/Hs.hs @@ -63,12 +63,12 @@ import Data.Data hiding ( Fixity ) -- | Haskell Module -- -- All we actually declare here is the top-level structure for a module. -data HsModule pass +data HsModule = HsModule { hsmodName :: Maybe (Located ModuleName), -- ^ @Nothing@: \"module X where\" is omitted (in which case the next -- field is Nothing too) - hsmodExports :: Maybe (Located [LIE pass]), + hsmodExports :: Maybe (Located [LIE GhcPs]), -- ^ Export list -- -- - @Nothing@: export list omitted, so export everything @@ -82,11 +82,11 @@ data HsModule pass -- ,'ApiAnnotation.AnnClose' -- For details on above see note [Api annotations] in ApiAnnotation - hsmodImports :: [LImportDecl pass], + hsmodImports :: [LImportDecl GhcPs], -- ^ We snaffle interesting stuff out of the imported interfaces early -- on, adding that info to TyDecls/etc; so this list is often empty, -- downstream. - hsmodDecls :: [LHsDecl pass], + hsmodDecls :: [LHsDecl GhcPs], -- ^ Type, class, value, and interface signature decls hsmodDeprecMessage :: Maybe (Located WarningTxt), -- ^ reason\/explanation for warning/deprecation of this module @@ -113,12 +113,10 @@ data HsModule pass -- hsmodImports,hsmodDecls if this style is used. -- For details on above see note [Api annotations] in ApiAnnotation --- deriving instance (DataIdLR name name) => Data (HsModule name) -deriving instance Data (HsModule GhcPs) -deriving instance Data (HsModule GhcRn) -deriving instance Data (HsModule GhcTc) +deriving instance Data HsModule ``` If this sounds like a good idea, I can offer a patch. I have already confirmed that the test suite passes even with this change (after updating one type signature in the test suite).