[project @ 1999-01-27 14:51:14 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcInstDcls.lhs b/ghc/compiler/typecheck/TcInstDcls.lhs
index aa21d98..8005b0b 100644 (file)
--- a/ghc/compiler/typecheck/TcInstDcls.lhs
+++ b/ghc/compiler/typecheck/TcInstDcls.lhs
@@ -183,8 +183,16 @@ tcInstDecl1 unf_env mod_name (InstDecl poly_ty binds uprags (Just dfun_name) src
     in
 
        -- Check for respectable instance type, and context
-    scrutiniseInstanceHead clas inst_tys       `thenNF_Tc_`
-    mapNF_Tc scrutiniseInstanceConstraint theta        `thenNF_Tc_`
+       -- but only do this for non-imported instance decls.
+       -- Imported ones should have been checked already, and may indeed
+       -- contain something illegal in normal Haskell, notably
+       --      instance CCallable [Char] 
+    (if isLocallyDefined dfun_name then
+       scrutiniseInstanceHead clas inst_tys    `thenNF_Tc_`
+       mapNF_Tc scrutiniseInstanceConstraint theta
+     else
+       returnNF_Tc []
+     )                                         `thenNF_Tc_`
 
        -- Make the dfun id and constant-method ids
     let