+
+%************************************************************************
+%* *
+\subsection{The global tyvars}
+%* *
+%************************************************************************
+
+\begin{code}
+tcExtendGlobalTyVars extra_global_tvs thing_inside
+ = tcGetEnv `thenNF_Tc` \ env ->
+ tc_extend_gtvs (tcTyVars env) extra_global_tvs `thenNF_Tc` \ gtvs' ->
+ tcSetEnv (env {tcTyVars = gtvs'}) thing_inside
+
+tc_extend_gtvs gtvs extra_global_tvs
+ = tcReadMutVar gtvs `thenNF_Tc` \ global_tvs ->
+ tcNewMutVar (global_tvs `unionVarSet` extra_global_tvs)
+\end{code}
+
+@tcGetGlobalTyVars@ returns a fully-zonked set of tyvars free in the environment.
+To improve subsequent calls to the same function it writes the zonked set back into
+the environment.
+
+\begin{code}
+tcGetGlobalTyVars :: NF_TcM TcTyVarSet
+tcGetGlobalTyVars
+ = tcGetEnv `thenNF_Tc` \ (TcEnv {tcTyVars = gtv_var}) ->
+ tcReadMutVar gtv_var `thenNF_Tc` \ gbl_tvs ->
+ zonkTcTyVarsAndFV (varSetElems gbl_tvs) `thenNF_Tc` \ gbl_tvs' ->
+ tcWriteMutVar gtv_var gbl_tvs' `thenNF_Tc_`
+ returnNF_Tc gbl_tvs'
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{The instance environment}
+%* *
+%************************************************************************
+
+\begin{code}
+tcGetInstEnv :: NF_TcM InstEnv
+tcGetInstEnv = tcGetEnv `thenNF_Tc` \ env ->
+ returnNF_Tc (tcInsts env)
+
+tcSetInstEnv :: InstEnv -> TcM a -> TcM a
+tcSetInstEnv ie thing_inside
+ = tcGetEnv `thenNF_Tc` \ env ->
+ tcSetEnv (env {tcInsts = ie}) thing_inside
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{The InstInfo type}
+%* *
+%************************************************************************
+
+The InstInfo type summarises the information in an instance declaration
+
+ instance c => k (t tvs) where b
+
+\begin{code}
+data InstInfo
+ = InstInfo {
+ iLocal :: Bool, -- True <=> it's defined in this module
+ iDFunId :: DFunId, -- The dfun id
+ iBinds :: RenamedMonoBinds, -- Bindings, b
+ iPrags :: [RenamedSig] -- User pragmas recorded for generating specialised instances
+ }
+
+pprInstInfo info = vcat [ptext SLIT("InstInfo:") <+> ppr (idType (iDFunId info)),
+ nest 4 (ppr (iBinds info))]
+
+simpleInstInfoTy :: InstInfo -> Type
+simpleInstInfoTy info = case splitDFunTy (idType (iDFunId info)) of
+ (_, _, _, [ty]) -> ty
+
+simpleInstInfoTyCon :: InstInfo -> TyCon
+ -- Gets the type constructor for a simple instance declaration,
+ -- i.e. one of the form instance (...) => C (T a b c) where ...
+simpleInstInfoTyCon inst = tyConAppTyCon (simpleInstInfoTy inst)
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Errors}
+%* *
+%************************************************************************
+