New syntax for GADT-style record declarations, and associated refactoring

[ghc-hetmet.git] / compiler / typecheck / TcTyClsDecls.lhs

diff --git a/compiler/typecheck/TcTyClsDecls.lhs b/compiler/typecheck/TcTyClsDecls.lhs
index 71e8659..633dc52 100644 (file)
--- a/compiler/typecheck/TcTyClsDecls.lhs
+++ b/compiler/typecheck/TcTyClsDecls.lhs
@@ -590,7 +590,8 @@ kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
        ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
   where
     -- doc comments are typechecked to Nothing here
-    kc_con_decl (ConDecl name expl ex_tvs ex_ctxt details res _) 
+    kc_con_decl con_decl@(ConDecl { con_name = name, con_qvars = ex_tvs
+                                  , con_cxt = ex_ctxt, con_details = details, con_res = res })
       = addErrCtxt (dataConCtxt name)  $ 
         kcHsTyVars ex_tvs $ \ex_tvs' -> do
         do { ex_ctxt' <- kcHsContext ex_ctxt
@@ -598,7 +599,8 @@ kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
            ; res'     <- case res of
                 ResTyH98 -> return ResTyH98
                 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
-           ; return (ConDecl name expl ex_tvs' ex_ctxt' details' res' Nothing) }
+           ; return (con_decl { con_qvars = ex_tvs', con_cxt = ex_ctxt'
+                              , con_details = details', con_res = res' }) }
 
     kc_con_details (PrefixCon btys) 
        = do { btys' <- mapM kc_larg_ty btys 
@@ -829,7 +831,8 @@ tcConDecl :: Bool           -- True <=> -funbox-strict_fields
          -> TcM DataCon
 
 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl       -- Data types
-         (ConDecl name _ tvs ctxt details res_ty _)
+         (ConDecl {con_name =name, con_qvars = tvs, con_cxt = ctxt
+                   , con_details = details, con_res = res_ty })
   = addErrCtxt (dataConCtxt name)      $ 
     tcTyVarBndrs tvs                   $ \ tvs' -> do 
     { ctxt' <- tcHsKindedContext ctxt
@@ -1239,7 +1242,7 @@ mkRecSelBind (tycon, sel_name)
     data_tvs   = tyVarsOfType data_ty
     is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)  
     (field_tvs, field_theta, field_tau) = tcSplitSigmaTy field_ty
-    sel_ty | is_naughty = unitTy
+    sel_ty | is_naughty = unitTy  -- See Note [Naughty record selectors]
            | otherwise  = mkForAllTys (varSetElems data_tvs ++ field_tvs) $ 
                          mkPhiTy (dataConStupidTheta con1) $   -- Urgh!
                          mkPhiTy field_theta               $   -- Urgh!
@@ -1302,10 +1305,12 @@ so that if the user tries to use 'x' as a selector we can bleat
 helpfully, rather than saying unhelpfully that 'x' is not in scope.
 Hence the sel_naughty flag, to identify record selectors that don't really exist.
 
-In general, a field is naughty if its type mentions a type variable that
-isn't in the result type of the constructor.
+In general, a field is "naughty" if its type mentions a type variable that
+isn't in the result type of the constructor.  Note that this *allows*
+GADT record selectors (Note [GADT record selectors]) whose types may look 
+like     sel :: T [a] -> a
 
-We make a dummy binding 
+For naughty selectors we make a dummy binding 
    sel = ()
 for naughty selectors, so that the later type-check will add them to the
 environment, and they'll be exported.  The function is never called, because