checkWellStaged: reverse comparsion (no change in semantics), plus some comments

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index 63b73fc..58bda52 100644 (file)
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -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]