Equality constraint solver is now externally pure

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

diff --git a/compiler/typecheck/TcRnTypes.lhs b/compiler/typecheck/TcRnTypes.lhs
index 28bfd8e..cbc0fe4 100644 (file)
--- a/compiler/typecheck/TcRnTypes.lhs
+++ b/compiler/typecheck/TcRnTypes.lhs
@@ -34,7 +34,7 @@ module TcRnTypes(
        plusLIEs, mkLIE, isEmptyLIE, lieToList, listToLIE,
 
        -- Misc other types
-       TcId, TcIdSet, TcDictBinds,
+       TcId, TcIdSet, TcDictBinds, TcTyVarBind(..), TcTyVarBinds
        
   ) where
 
@@ -98,6 +98,18 @@ type RnM  a = TcRn a         -- Historical
 type TcM  a = TcRn a           -- Historical
 \end{code}
 
+Representation of type bindings to uninstantiated meta variables used during
+constraint solving.
+
+\begin{code}
+data TcTyVarBind = TcTyVarBind TcTyVar TcType
+
+type TcTyVarBinds = Bag TcTyVarBind
+
+instance Outputable TcTyVarBind where
+  ppr (TcTyVarBind tv ty) = ppr tv <+> text ":=" <+> ppr ty
+\end{code}
+
 
 %************************************************************************
 %*                                                                     *
@@ -343,15 +355,20 @@ data TcLclEnv             -- Changes as we move inside an expression
                -- We still need the unsullied global name env so that
                --   we can look up record field names
 
-       tcl_env  :: NameEnv TcTyThing,  -- The local type environment: Ids and TyVars
-                                       -- defined in this module
+       tcl_env  :: NameEnv TcTyThing,  -- The local type environment: Ids and
+                                       -- TyVars defined in this module
                                        
        tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
                        -- Namely, the in-scope TyVars bound in tcl_env, 
-                       -- plus the tyvars mentioned in the types of Ids bound in tcl_lenv
-                       -- Why mutable? see notes with tcGetGlobalTyVars
+                       -- plus the tyvars mentioned in the types of Ids bound
+                       -- in tcl_lenv. 
+                        -- Why mutable? see notes with tcGetGlobalTyVars
+
+       tcl_lie   :: TcRef LIE,         -- Place to accumulate type constraints
 
-       tcl_lie   :: TcRef LIE          -- Place to accumulate type constraints
+        tcl_tybinds :: TcRef TcTyVarBinds -- Meta and coercion type variable
+                                          -- bindings accumulated during
+                                          -- constraint solving
     }