#9628: Add Annotations to the AST to simplify source to source conversions -------------------------------------+------------------------------------- Reporter: alanz | Owner: alanz Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.9 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | Differential Revisions: D297 | -------------------------------------+------------------------------------- Comment (by simonpj): Thanks for the wiki page -- extremely helpful. I'm concerned about the proliferation of data types. As I read it you intend to have a new data type for each constructor of each data type in `HsSyn`. That's a LOT of new data types! And I bet you'll soon want Eq, Ord, Data instances for them as well as Typeable. Indeed you say {{{ data AnnClassDecl = AnnClassDecl { aclassdecl_class :: SrcSpan , aclassdecl_mwhere :: Maybe SrcSpan , aclassdecl_mbraces :: Maybe (SrcSpan,SrcSpan) } deriving (Eq,Data,Typeable,Show) }}} I wonder if something simpler and more dynamically-typed might do. Suppose you had {{{ lookupApiAnns :: Typeable value => ApiAnns -> SrcSpan -> String -> Maybe value }}} so that `ApiAnns` is really a map from `(SrcSpan, String, TypeRep)` to values, where `TypeRep` there is the `TypeRep` of the value. The `String` is the dynamic bit. Now you could say {{{ processHsClassDecl :: ApiAnns -> LTyClDecl n -> ... processHsClassDecl anns (L l (ClassDecl { ..} )) = r where Just kwd_loc = lookupAPiAnns anns loc "class-keyword" :: Maybe SrcSpan Just mb_loc = lookupApiAnns anns loc "class-mwhere" :: Maybe (Maybe SrcSpan) ... }}} OK so you might type those strings in wrong -- but if you do the look up will fail. I don't want this to sink under the sheer weight of gratuitous declarations. Oh and you could use the same string in lots of places. e.g. "where- keyword" might be used in a number of constructs. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9628#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler