Fix Trac #1814 (staging interaction in Template Haskell and GHCi), and add comments

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

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index 63b73fc..a23795c 100644 (file)
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -47,7 +47,7 @@ module TcEnv(
 
        -- Template Haskell stuff
        checkWellStaged, spliceOK, bracketOK, tcMetaTy, thLevel, 
-       topIdLvl, 
+       topIdLvl, thTopLevelId,
 
        -- New Ids
        newLocalName, newDFunName, newFamInstTyConName,
@@ -110,7 +110,7 @@ tcLookupGlobal name
   = do { env <- getGblEnv
        
                -- Try local envt
-       ; case lookupNameEnv (tcg_type_env env) name of {
+       ; case lookupNameEnv (tcg_type_env env) name of { 
                Just thing -> return thing ;
                Nothing    -> do 
         
@@ -123,12 +123,12 @@ tcLookupGlobal name
 
                -- Should it have been in the local envt?
        { case nameModule_maybe name of
-               Nothing -> notFound name        -- Internal names can happen in GHCi
+               Nothing -> notFound name env -- Internal names can happen in GHCi
 
                Just mod | mod == tcg_mod env   -- Names from this module 
-                        -> notFound name       -- should be in tcg_type_env
+                        -> notFound name env -- should be in tcg_type_env
                         | mod == thFAKE        -- Names bound in TH declaration brackets
-                        -> notFound name       -- should be in tcg_env
+                        -> notFound name env -- should be in tcg_env
                         | otherwise
                         -> tcImportDecl name   -- Go find it in an interface
        }}}}}
@@ -553,12 +553,12 @@ thLevel (Brack l _ _) = l
 
 
 checkWellStaged :: SDoc                -- What the stage check is for
-               -> ThLevel      -- Binding level
+               -> ThLevel      -- Binding level (increases inside brackets)
                -> ThStage      -- Use stage
                -> TcM ()       -- Fail if badly staged, adding an error
 checkWellStaged pp_thing bind_lvl use_stage
-  | bind_lvl <= use_lvl        -- OK!
-  = returnM () 
+  | use_lvl >= bind_lvl        -- OK! Used later than bound
+  = returnM ()                 -- E.g.  \x -> [| $(f x) |]
 
   | bind_lvl == topLevel       -- GHC restriction on top level splices
   = failWithTc $ 
@@ -566,7 +566,7 @@ checkWellStaged pp_thing bind_lvl use_stage
         nest 2 (ptext SLIT("is used in a top-level splice, and must be imported, not defined locally"))]
 
   | otherwise                  -- Badly staged
-  = failWithTc $ 
+  = failWithTc $               -- E.g.  \x -> $(f x)
     ptext SLIT("Stage error:") <+> pp_thing <+> 
        hsep   [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
                ptext SLIT("but used at stage") <+> ppr use_lvl]
@@ -604,6 +604,10 @@ tcMetaTy :: Name -> TcM Type
 tcMetaTy tc_name
   = tcLookupTyCon tc_name      `thenM` \ t ->
     returnM (mkTyConApp t [])
+
+thTopLevelId :: Id -> Bool
+-- See Note [What is a top-level Id?] in TcSplice
+thTopLevelId id = isGlobalId id || isExternalName (idName id)
 \end{code}
 
 
@@ -708,9 +712,11 @@ pprBinders :: [Name] -> SDoc
 pprBinders [bndr] = quotes (ppr bndr)
 pprBinders bndrs  = pprWithCommas ppr bndrs
 
-notFound name 
-  = failWithTc (ptext SLIT("GHC internal error:") <+> quotes (ppr name) <+> 
-               ptext SLIT("is not in scope"))
+notFound name env
+  = failWithTc (vcat[ptext SLIT("GHC internal error:") <+> quotes (ppr name) <+> 
+                     ptext SLIT("is not in scope during type checking, but it passed the renamer"),
+                     ptext SLIT("tcg_type_env of environment:") <+> ppr (tcg_type_env env)]
+                    )
 
 wrongThingErr expected thing name
   = failWithTc (pprTcTyThingCategory thing <+> quotes (ppr name) <+>