[project @ 2003-03-27 08:25:31 by simonpj]

-------------------------------------
      Fix a wibble in default-type setting for TH
	-------------------------------------

When a bunch of declarations contains no 'default' declaration,
we were setting 'defaultDefaultTys' as appropriate default types.
This isn't right for Template Haskell, which may have more than
one bunch of top-level decls.  (The bunches are separated by
top-level declaration splices.)

Instead, if there is no 'default' declaration we should do nothing.

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index 82290db..f107451 100644 (file)
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -22,14 +22,24 @@ import HscTypes             ( TyThing(..) )
 
 \begin{code}
 tcDefaults :: [DefaultDecl Name]
-          -> TcM [Type]            -- defaulting types to heave
+          -> TcM [Type]            -- Defaulting types to heave
                                    -- into Tc monad for later use
                                    -- in Disambig.
 
-tcDefaults [] = returnM defaultDefaultTys
+tcDefaults [] 
+  = getDefaultTys              -- No default declaration, so get the
+                               -- default types from the envt; 
+                               -- i.e. use the curent ones
+                               -- (the caller will put them back there)
+       -- It's important not to return defaultDefaultTys here (which
+       -- we used to do) because in a TH program, tcDefaults [] is called
+       -- repeatedly, once for each group of declarations between top-level
+       -- splices.  We don't want to carefully set the default types in
+       -- one group, only for the next group to ignore them and install
+       -- defaultDefaultTys
 
 tcDefaults [DefaultDecl [] locn]
-  = returnM []         -- no defaults
+  = returnM []                 -- Default declaration specifying no types
 
 tcDefaults [DefaultDecl mono_tys locn]
   = tcLookupGlobal_maybe numClassName  `thenM` \ maybe_num ->