%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1995
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
%
\section[Unify]{Unifier}
updatable substitution).
\begin{code}
-#include "HsVersions.h"
-
-module Unify ( unifyTauTy, unifyTauTyList, unifyTauTyLists ) where
+module Unify ( unifyTauTy, unifyTauTyList, unifyTauTyLists,
+ unifyFunTy, unifyListTy, unifyTupleTy,
+ Subst, unifyTysX, unifyTyListsX
+ ) where
-IMPORT_Trace -- ToDo: rm (debugging only)
-import Outputable
-import Pretty
+#include "HsVersions.h"
-import AbsSyn
+-- friends:
import TcMonad
-
-import CmdLineOpts ( GlobalSwitch(..) )
-import Errors ( unifyErr, UnifyErrInfo(..), UnifyErrContext )
-import Id ( Id, DataCon(..), Inst )
-import Maybes ( Maybe(..) )
-import Subst ( extendSubst, SubstResult(..), Subst )
-#if USE_ATTACK_PRAGMAS
-import Class ( Class(..), cmpClass ) -- .. for pragmas only
-import TyCon ( TyCon(..), isBoxedTyCon, isVisibleSynTyCon, cmpTyCon )
- -- .. on TyCon is for pragmas only
-import TyVar -- make all visible for pragmas
-import UniTyFuns ( pprUniType, pprTyCon )
-#else
-import Class ( Class )
-import TyVar ( TyVar(..), TyVarTemplate )
-import TyCon ( TyCon, isBoxedTyCon, isVisibleSynTyCon )
-#endif
-import UniType ( UniType(..), TauType(..)
- IF_ATTACK_PRAGMAS(COMMA cmpUniType)
- )
+import Type ( GenType(..), Type, tyVarsOfType,
+ typeKind, mkFunTy, splitFunTy_maybe, splitAppTys, splitTyConApp_maybe )
+import TyCon ( TyCon, mkFunTyCon, isTupleTyCon, tyConArity, Arity )
+import TyVar ( GenTyVar(..), TyVar, tyVarKind, tyVarSetToList,
+ TyVarEnv, lookupTyVarEnv, emptyTyVarEnv, addToTyVarEnv
+ )
+import TcType ( TcType, TcMaybe(..), TcTauType, TcTyVar,
+ newTyVarTy, tcReadTyVar, tcWriteTyVar, zonkTcType
+ )
+-- others:
+import Kind ( Kind, hasMoreBoxityInfo, mkTypeKind, mkBoxedTypeKind )
+import TysWiredIn ( listTyCon, mkListTy, mkTupleTy )
+import Maybes ( maybeToBool )
+import PprType () -- Instances
import Util
+import Outputable
\end{code}
-%************************************************************************
-%* *
-\subsection[Unify-spec]{Specification}
-%* *
-%************************************************************************
-
-CLAIM: the unifier works correctly even if the types to be unified are not
-fixed points of the substitution.
%************************************************************************
%* *
Unify two @TauType@s. Dead straightforward.
\begin{code}
-unifyTauTy :: TauType -> TauType -> UnifyErrContext -> TcM ()
-
-unifyTauTy ty1 ty2 err_ctxt = uTys ty1 ty1 ty2 ty2 err_ctxt
+unifyTauTy :: TcTauType s -> TcTauType s -> TcM s ()
+unifyTauTy ty1 ty2 -- ty1 expected, ty2 inferred
+ = tcAddErrCtxtM (unifyCtxt ty1 ty2) $
+ uTys ty1 ty1 ty2 ty2
\end{code}
-@unifyTauTyLists@ unifies corresponding elements of its two list
-arguments. The lists should be of equal length.
+@unifyTauTyList@ unifies corresponding elements of two lists of
+@TauType@s. It uses @uTys@ to do the real work. The lists should be
+of equal length. We charge down the list explicitly so that we can
+complain if their lengths differ.
\begin{code}
-unifyTauTyLists :: [TauType] -> [TauType] -> UnifyErrContext -> TcM ()
-
-unifyTauTyLists tys1 tys2 err_ctxt = uList tys1 tys2 err_ctxt
+unifyTauTyLists :: [TcTauType s] -> [TcTauType s] -> TcM s ()
+unifyTauTyLists [] [] = returnTc ()
+unifyTauTyLists (ty1:tys1) (ty2:tys2) = uTys ty1 ty1 ty2 ty2 `thenTc_`
+ unifyTauTyLists tys1 tys2
+unifyTauTyLists ty1s ty2s = panic "Unify.unifyTauTyLists: mismatched type lists!"
\end{code}
@unifyTauTyList@ takes a single list of @TauType@s and unifies them
lists, when all the elts should be of the same type.
\begin{code}
-unifyTauTyList :: [TauType] -> UnifyErrContext -> TcM ()
-
-unifyTauTyList [] _ = returnTc ()
-unifyTauTyList [ty] _ = returnTc ()
-
-unifyTauTyList (ty1:tys@(ty2:_)) err_ctxt
- = unifyTauTy ty1 ty2 err_ctxt `thenTc_`
- unifyTauTyList tys err_ctxt
-\end{code}
-
-%************************************************************************
-%* *
-\subsection[Unify-lists-of-types]{@uList@}
-%* *
-%************************************************************************
-
-@uList@ unifies corresponding elements of two lists of @TauType@s. It
-uses @uTys@ to do the real work. We charge down the list explicitly
-so that we can complain if their lengths differ.
-
-\begin{code}
-uList :: [TauType] -> [TauType]
- -> UnifyErrContext
- -> TcM ()
-
-uList [] [] _ = returnTc ()
-
-uList (ty1:tys1) (ty2:tys2) err_ctxt
- = uTys ty1 ty1 ty2 ty2 err_ctxt `thenTc_`
- uList tys1 tys2 err_ctxt
-
-uList ty1s ty2s _ = panic "Unify.uList: mismatched type lists!"
+unifyTauTyList :: [TcTauType s] -> TcM s ()
+unifyTauTyList [] = returnTc ()
+unifyTauTyList [ty] = returnTc ()
+unifyTauTyList (ty1:tys@(ty2:_)) = unifyTauTy ty1 ty2 `thenTc_`
+ unifyTauTyList tys
\end{code}
%************************************************************************
We call the first one \tr{ps_ty1}, \tr{ps_ty2} for ``possible synomym''.
\begin{code}
-uTys :: TauType -> TauType -- Error reporting ty1 and real ty1
- -> TauType -> TauType -- Error reporting ty2 and real ty2
- -> UnifyErrContext
- -> TcM ()
-\end{code}
-
-%********************************************************
-%* *
-Sanity check: should never find a UniTyVarTemplate
-%* *
-%********************************************************
-
-\begin{code}
-#ifdef DEBUG
-
-uTys ps_ty1 ty1@(UniTyVarTemplate tv1) ps_ty2 ty2 err_ctxt
- = pprPanic "Unify:uTys:unifying w/ UniTyVarTemplate(1):" (ppCat [ppr PprDebug tv1, ppr PprDebug ty2])
-
-uTys ps_ty1 ty1 ps_ty2 ty2@(UniTyVarTemplate tv2) err_ctxt
- = pprPanic "Unify:uTys:unifying w/ UniTyVarTemplate(2):" (ppCat [ppr PprDebug ty1, ppr PprDebug tv2])
-
-#endif {-DEBUG-}
-\end{code}
-
-%********************************************************
-%* *
-Both variables:
-%* *
-%********************************************************
-
-\begin{code}
-uTys ps_ty1 (UniTyVar tyvar1) ps_ty2 ty2 err_ctxt = uVar tyvar1 ps_ty2 ty2 err_ctxt
-uTys ps_ty1 ty1 ps_ty2 (UniTyVar tyvar2) err_ctxt = uVar tyvar2 ps_ty1 ty1 err_ctxt
-\end{code}
-
-%********************************************************
-%* *
-Both function constructors:
-%* *
-%********************************************************
-
-\begin{code}
-uTys _ (UniFun fun1 arg1) _ (UniFun fun2 arg2) err_ctxt
- = uList [fun1, arg1] [fun2, arg2] err_ctxt
-\end{code}
-
-%********************************************************
-%* *
-Both datatype constructors:
-%* *
-%********************************************************
-
-\begin{code}
-uTys ps_ty1 ty1@(UniData con1 args1) ps_ty2 ty2@(UniData con2 args2) err_ctxt
- = if (con1 == con2) then
- -- Same constructors, just unify the arguments
- uList args1 args2 err_ctxt
- else
- -- Different constructors: disaster
- getSrcLocTc `thenNF_Tc` \ src_loc ->
- failTc (unifyErr (UnifyMisMatch ps_ty1 ps_ty2) err_ctxt src_loc)
-\end{code}
+uTys :: TcTauType s -> TcTauType s -- Error reporting ty1 and real ty1
+ -> TcTauType s -> TcTauType s -- Error reporting ty2 and real ty2
+ -> TcM s ()
+
+ -- Always expand synonyms (see notes at end)
+uTys ps_ty1 (SynTy _ ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2
+uTys ps_ty1 ty1 ps_ty2 (SynTy _ ty2) = uTys ps_ty1 ty1 ps_ty2 ty2
+
+ -- Variables; go for uVar
+uTys ps_ty1 (TyVarTy tyvar1) ps_ty2 ty2 = uVar tyvar1 ps_ty2 ty2
+uTys ps_ty1 ty1 ps_ty2 (TyVarTy tyvar2) = uVar tyvar2 ps_ty1 ty1
+
+ -- Functions; just check the two parts
+uTys _ (FunTy fun1 arg1) _ (FunTy fun2 arg2)
+ = uTys fun1 fun1 fun2 fun2 `thenTc_` uTys arg1 arg1 arg2 arg2
+
+ -- Type constructors must match
+uTys ps_ty1 (TyConApp con1 tys1) ps_ty2 (TyConApp con2 tys2)
+ = checkTc (con1 == con2 && length tys1 == length tys2)
+ (unifyMisMatch ps_ty1 ps_ty2) `thenTc_`
+ unifyTauTyLists tys1 tys2
+
+ -- Applications need a bit of care!
+ -- They can match FunTy and TyConApp
+uTys _ (AppTy s1 t1) _ (AppTy s2 t2)
+ = uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
+
+uTys _ (AppTy s1 t1) _ (FunTy fun2 arg2)
+ = uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
+ where
+ -- Converts a -> b to (->) a b
+ s2 = TyConApp mkFunTyCon [fun2]
+ t2 = arg2
-%********************************************************
-%* *
-Type synonyms:
-%* *
-%********************************************************
+uTys _ (AppTy s1 t1) _ (TyConApp tc tys@(_:_))
+ = case snocView tys of
+ (ts2, t2) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
+ where
+ -- Not efficient, but simple
+ s2 = TyConApp tc ts2
-If just one or the other is a synonym, just expand it.
+uTys ps1 s1 ps2 s2@(AppTy _ _) = uTys ps2 s2 ps1 s1
+ -- Swap arguments if the App is in the second argument
-\begin{code}
-uTys ps_ty1 (UniSyn con1 args1 ty1) ps_ty2 ty2 err_ctxt
- | isVisibleSynTyCon con1
- = uTys ps_ty1 ty1 ps_ty2 ty2 err_ctxt
+ -- Not expecting for-alls in unification
+#ifdef DEBUG
+uTys ps_ty1 (ForAllTy _ _) ps_ty2 ty2 = panic "Unify.uTys:ForAllTy (1st arg)"
+uTys ps_ty1 ty1 ps_ty2 (ForAllTy _ _) = panic "Unify.uTys:ForAllTy (2nd arg)"
+#endif
-uTys ps_ty1 ty1 ps_ty2 (UniSyn con2 args2 ty2) err_ctxt
- | isVisibleSynTyCon con2
- = uTys ps_ty1 ty1 ps_ty2 ty2 err_ctxt
+ -- Anything else fails
+uTys ps_ty1 ty1 ps_ty2 ty2 = failWithTc (unifyMisMatch ps_ty1 ps_ty2)
\end{code}
+Notes on synonyms
+~~~~~~~~~~~~~~~~~
If you are tempted to make a short cut on synonyms, as in this
pseudocode...
\begin{verbatim}
-uTys (UniSyn con1 args1 ty1) (UniSyn con2 args2 ty2)
+uTys (SynTy con1 args1 ty1) (SynTy con2 args2 ty2)
= if (con1 == con2) then
-- Good news! Same synonym constructors, so we can shortcut
-- by unifying their arguments and ignoring their expansions.
- uList args1 args2
+ unifyTauTypeLists args1 args2
else
-- Never mind. Just expand them and try again
uTys ty1 ty2
user.
\end{quotation}
-Still, if the synonym is abstract, we can only just go ahead and try!
-
-\begin{code}
-uTys ps_ty1 (UniSyn con1 args1 ty1) ps_ty2 (UniSyn con2 args2 ty2) err_ctxt
- -- Both must be abstract (i.e., non "visible" -- not done yet)
- = if (con1 == con2) then
- -- Good news! Same synonym constructors, so we can shortcut
- -- by unifying their arguments and ignoring their expansions.
- uList args1 args2 err_ctxt
- else
- -- Bad news; mis-matched type constructors
- getSrcLocTc `thenNF_Tc` \ src_loc ->
- failTc (unifyErr (UnifyMisMatch ps_ty1 ps_ty2) err_ctxt src_loc)
-\end{code}
-
-%********************************************************
-%* *
-Catch-all case---just fails:
-%* *
-%********************************************************
-
-Anything else fails. For example, matching a @UniFun@ against
-a @UniData@.
-\begin{code}
-uTys ps_ty1 ty1 ps_ty2 ty2 err_ctxt
- = getSrcLocTc `thenNF_Tc` \ src_loc ->
- failTc (unifyErr (UnifyMisMatch ps_ty1 ps_ty2) err_ctxt src_loc)
-\end{code}
%************************************************************************
%* *
always the ones which are unified away.
\begin{code}
-uVar :: TyVar
- -> UniType -> UniType -- printing and real versions
- -> UnifyErrContext
- -> TcM ()
+uVar :: TcTyVar s
+ -> TcTauType s -> TcTauType s -- printing and real versions
+ -> TcM s ()
+
+uVar tv1 ps_ty2 ty2
+ = tcReadTyVar tv1 `thenNF_Tc` \ maybe_ty1 ->
+ case maybe_ty1 of
+ BoundTo ty1 -> uTys ty1 ty1 ps_ty2 ty2
+ other -> uUnboundVar tv1 maybe_ty1 ps_ty2 ty2
-uVar tv1 ps_ty2 ty2 err_ctxt
- = do tv1 ty2
- where
-- Expand synonyms
- do _ (UniSyn _ _ ty2) = do tv1 ty2
+uUnboundVar tv1 maybe_ty1 ps_ty2 (SynTy _ ty2)
+ = uUnboundVar tv1 maybe_ty1 ps_ty2 ty2
+
+
+ -- The both-type-variable case
+uUnboundVar tv1@(TyVar uniq1 kind1 name1 box1)
+ maybe_ty1
+ ps_ty2
+ ty2@(TyVarTy tv2@(TyVar uniq2 kind2 name2 box2))
+
+ -- Same type variable => no-op
+ | uniq1 == uniq2
+ = returnTc ()
+
+ -- Distinct type variables
+ -- ASSERT maybe_ty1 /= BoundTo
+ | otherwise
+ = tcReadTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
+ case maybe_ty2 of
+ BoundTo ty2' -> uUnboundVar tv1 maybe_ty1 ty2' ty2'
+
+ UnBound | (kind1 == kind2 && not (maybeToBool name1)) -- Same kinds and tv1 is anonymous
+ -- so update tv1
+ -> tcWriteTyVar tv1 ps_ty2 `thenNF_Tc_` returnTc ()
+
+ | kind1 `hasMoreBoxityInfo` kind2 -- Update tv2 if possible
+ -> tcWriteTyVar tv2 (TyVarTy tv1) `thenNF_Tc_` returnTc ()
+
+ | kind2 `hasMoreBoxityInfo` kind1 -- Update tv1 if possible
+ -> tcWriteTyVar tv1 ps_ty2 `thenNF_Tc_` returnTc ()
+
+ other -> failWithTc (unifyKindErr tv1 ps_ty2)
+
+ -- Second one isn't a type variable
+uUnboundVar tv1@(TyVar uniq1 kind1 name1 box1) maybe_ty1 ps_ty2 non_var_ty2
+ | typeKind non_var_ty2 `hasMoreBoxityInfo` kind1
+ = occur_check non_var_ty2 `thenTc_`
+ tcWriteTyVar tv1 ps_ty2 `thenNF_Tc_`
+ returnTc ()
+
+ | otherwise
+ = failWithTc (unifyKindErr tv1 ps_ty2)
+
+ where
+ occur_check ty = mapTc occur_check_tv (tyVarSetToList (tyVarsOfType ty)) `thenTc_`
+ returnTc ()
+
+ occur_check_tv tv2@(TyVar uniq2 _ _ box2)
+ | uniq1 == uniq2 -- Same tyvar; fail
+ = failWithTc (unifyOccurCheck tv1 ps_ty2)
+
+ | otherwise -- A different tyvar
+ = tcReadTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
+ case maybe_ty2 of
+ BoundTo ty2' -> occur_check ty2'
+ other -> returnTc ()
+\end{code}
+
+%************************************************************************
+%* *
+\subsection[Unify-fun]{@unifyFunTy@}
+%* *
+%************************************************************************
- -- Commit any open type variable
- do (OpenSysTyVar _) ty2 = tv1 `bindTo` ps_ty2
- do _ ty2@(UniTyVar tv2@(OpenSysTyVar _)) = tv2 `bindTo` ty1
+@unifyFunTy@ is used to avoid the fruitless creation of type variables.
- -- Eliminate Poly in favour of User
- do (PolySysTyVar _) ty2@(UniTyVar (UserTyVar _ _)) = tv1 `bindTo` ps_ty2
- do (PolySysTyVar _) ty2@(UniTyVar (PolySysTyVar _)) = tv1 `bindTo` ps_ty2
- do (UserTyVar _ _) ty2@(UniTyVar tv2@(PolySysTyVar _)) = tv2 `bindTo` ty1
- do (UserTyVar _ _) ty2@(UniTyVar (UserTyVar _ _)) = tv1 `bindTo` ps_ty2
+\begin{code}
+unifyFunTy :: TcType s -- Fail if ty isn't a function type
+ -> TcM s (TcType s, TcType s) -- otherwise return arg and result types
+
+unifyFunTy ty@(TyVarTy tyvar)
+ = tcReadTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of
+ BoundTo ty' -> unifyFunTy ty'
+ other -> unify_fun_ty_help ty
+
+unifyFunTy ty
+ = case splitFunTy_maybe ty of
+ Just arg_and_res -> returnTc arg_and_res
+ Nothing -> unify_fun_ty_help ty
+
+unify_fun_ty_help ty -- Special cases failed, so revert to ordinary unification
+ = newTyVarTy mkTypeKind `thenNF_Tc` \ arg ->
+ newTyVarTy mkTypeKind `thenNF_Tc` \ res ->
+ unifyTauTy ty (mkFunTy arg res) `thenTc_`
+ returnTc (arg,res)
+\end{code}
+
+\begin{code}
+unifyListTy :: TcType s -- expected list type
+ -> TcM s (TcType s) -- list element type
+
+unifyListTy ty@(TyVarTy tyvar)
+ = tcReadTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of
+ BoundTo ty' -> unifyListTy ty'
+ other -> unify_list_ty_help ty
+
+unifyListTy ty
+ = case splitTyConApp_maybe ty of
+ Just (tycon, [arg_ty]) | tycon == listTyCon -> returnTc arg_ty
+ other -> unify_list_ty_help ty
+
+unify_list_ty_help ty -- Revert to ordinary unification
+ = newTyVarTy mkBoxedTypeKind `thenNF_Tc` \ elt_ty ->
+ unifyTauTy ty (mkListTy elt_ty) `thenTc_`
+ returnTc elt_ty
+\end{code}
+
+\begin{code}
+unifyTupleTy :: Arity -> TcType s -> TcM s [TcType s]
+unifyTupleTy arity ty@(TyVarTy tyvar)
+ = tcReadTyVar tyvar `thenNF_Tc` \ maybe_ty ->
+ case maybe_ty of
+ BoundTo ty' -> unifyTupleTy arity ty'
+ other -> unify_tuple_ty_help arity ty
+
+unifyTupleTy arity ty
+ = case splitTyConApp_maybe ty of
+ Just (tycon, arg_tys) | isTupleTyCon tycon
+ && tyConArity tycon == arity
+ -> returnTc arg_tys
+ other -> unify_tuple_ty_help arity ty
+
+unify_tuple_ty_help arity ty
+ = mapNF_Tc (\ _ -> newTyVarTy mkBoxedTypeKind) [1..arity] `thenNF_Tc` \ arg_tys ->
+ unifyTauTy ty (mkTupleTy arity arg_tys) `thenTc_`
+ returnTc arg_tys
+\end{code}
+
+%************************************************************************
+%* *
+\subsection{Unification wih a explicit substitution}
+%* *
+%************************************************************************
+
+Unify types with an explicit substitution and no monad.
+
+\begin{code}
+type Subst = TyVarEnv Type -- Not necessarily idempotent
- -- Matching for boxed data types
- do (PolySysTyVar _) ty2@(UniData con _) | isBoxedTyCon con = tv1 `bindTo` ps_ty2
- do (UserTyVar _ _) ty2@(UniData con _) | isBoxedTyCon con = tv1 `bindTo` ps_ty2
+unifyTysX :: Type -> Type -> Maybe Subst
+unifyTysX ty1 ty2 = uTysX ty1 ty2 (\s -> Just s) emptyTyVarEnv
- -- Matching for unboxed data types:
- -- requires specialisation w.r.t. the unboxed type
- do (PolySysTyVar _) ty2@(UniData con _) = tv1 `bindToUnboxed` ps_ty2
- do (UserTyVar _ _) ty2@(UniData con _) = tv1 `bindToUnboxed` ps_ty2
+unifyTyListsX :: [Type] -> [Type] -> Maybe Subst
+unifyTyListsX tys1 tys2 = uTyListsX tys1 tys2 (\s -> Just s) emptyTyVarEnv
- -- Matching for function types
- do (PolySysTyVar _) ty2@(UniFun _ _) = tv1 `bindTo` ps_ty2
- do (UserTyVar _ _) ty2@(UniFun _ _) = tv1 `bindTo` ps_ty2
- -- Default
- do _ _ = getSrcLocTc `thenNF_Tc` \ src_loc ->
- failTc (unifyErr (UnifyMisMatch ty1 ps_ty2) err_ctxt src_loc)
+uTysX :: Type -> Type
+ -> (Subst -> Maybe Subst)
+ -> Subst
+ -> Maybe Subst
- ----------- END OF CASES ---------------
+uTysX ty1 (SynTy _ ty2) k subst = uTysX ty1 ty2 k subst
- ty1 = UniTyVar tv1
+ -- Variables; go for uVar
+uTysX (TyVarTy tyvar1) ty2 k subst = uVarX tyvar1 ty2 k subst
+uTysX ty1 (TyVarTy tyvar2) k subst = uVarX tyvar2 ty1 k subst
- tyvar1 `bindTo` ty2
- = extendSubstTc tyvar1 ty2 err_ctxt
+ -- Functions; just check the two parts
+uTysX (FunTy fun1 arg1) (FunTy fun2 arg2) k subst
+ = uTysX fun1 fun2 (uTysX arg1 arg2 k) subst
- tyvar1 `bindToUnboxed` ty2
- = getSwitchCheckerTc `thenNF_Tc` \ sw_chkr ->
- if sw_chkr SpecialiseUnboxed then
- extendSubstTc tyvar1 ty2 err_ctxt
- else
- getSrcLocTc `thenNF_Tc` \ src_loc ->
- failTc (unifyErr (UnifyMisMatch ty1 ps_ty2) err_ctxt src_loc)
+ -- Type constructors must match
+uTysX (TyConApp con1 tys1) (TyConApp con2 tys2) k subst
+ | (con1 == con2 && length tys1 == length tys2)
+ = uTyListsX tys1 tys2 k subst
+
+ -- Applications need a bit of care!
+ -- They can match FunTy and TyConApp
+uTysX (AppTy s1 t1) (AppTy s2 t2) k subst
+ = uTysX s1 s2 (uTysX t1 t2 k) subst
+
+uTysX (AppTy s1 t1) (FunTy fun2 arg2) k subst
+ = uTysX s1 s2 (uTysX t1 t2 k) subst
+ where
+ -- Converts a -> b to (->) a b
+ s2 = TyConApp mkFunTyCon [fun2]
+ t2 = arg2
+
+uTysX (AppTy s1 t1) (TyConApp tc tys@(_:_)) k subst
+ = case snocView tys of
+ (ts2, t2) -> uTysX s1 s2 (uTysX t1 t2 k) subst
+ where
+ -- Not efficient, but simple
+ s2 = TyConApp tc ts2
+
+uTysX s1 s2@(AppTy _ _) k subst = uTysX s2 s1 k subst
+ -- Swap arguments if the App is in the second argument
+
+ -- Not expecting for-alls in unification
+#ifdef DEBUG
+uTysX (ForAllTy _ _) ty2 k subst = panic "Unify.uTysX subst:ForAllTy (1st arg)"
+uTysX ty1 (ForAllTy _ _) k subst = panic "Unify.uTysX subst:ForAllTy (2nd arg)"
+#endif
+
+ -- Anything else fails
+uTysX ty1 ty2 k subst = Nothing
+
+
+uTyListsX [] [] k subst = k subst
+uTyListsX (ty1:tys1) (ty2:tys2) k subst = uTysX ty1 ty2 (uTyListsX tys1 tys2 k) subst
+uTyListsX tys1 tys2 k subst = Nothing -- Fail if the lists are different lengths
+\end{code}
+
+\begin{code}
+uVarX tv1 (TyVarTy tv2) k subst | tv1 == tv2 = k subst
+ -- Binding a variable to itself is a no-op
+
+uVarX tv1 ty2 k subst
+ = case lookupTyVarEnv subst tv1 of
+ Just ty1 -> -- Already bound
+ uTysX ty1 ty2 k subst
+
+ Nothing -- Not already bound
+ | typeKind ty2 `hasMoreBoxityInfo` tyVarKind tv1
+ && occur_check_ok ty2
+ -> -- No kind mismatch nor occur check
+ k (addToTyVarEnv subst tv1 ty2)
+
+ | otherwise -> Nothing -- Fail if kind mis-match or occur check
+ where
+ occur_check_ok ty = all occur_check_ok_tv (tyVarSetToList (tyVarsOfType ty))
+ occur_check_ok_tv tv | tv1 == tv = False
+ | otherwise = case lookupTyVarEnv subst tv of
+ Nothing -> True
+ Just ty -> occur_check_ok ty
\end{code}
+
+
+%************************************************************************
+%* *
+\subsection[Unify-context]{Errors and contexts}
+%* *
+%************************************************************************
+
+Errors
+~~~~~~
+
+\begin{code}
+unifyCtxt ty1 ty2 -- ty1 expected, ty2 inferred
+ = zonkTcType ty1 `thenNF_Tc` \ ty1' ->
+ zonkTcType ty2 `thenNF_Tc` \ ty2' ->
+ returnNF_Tc (err ty1' ty2')
+ where
+ err ty1' ty2' = vcat [
+ hsep [ptext SLIT("Expected:"), ppr ty1'],
+ hsep [ptext SLIT("Inferred:"), ppr ty2']
+ ]
+
+unifyMisMatch ty1 ty2
+ = hang (ptext SLIT("Couldn't match the type"))
+ 4 (sep [quotes (ppr ty1), ptext SLIT("against"), quotes (ppr ty2)])
+
+expectedFunErr ty
+ = hang (text "Function type expected, but found the type")
+ 4 (ppr ty)
+
+unifyKindErr tyvar ty
+ = hang (ptext SLIT("Compiler bug: kind mis-match between"))
+ 4 (sep [quotes (hsep [ppr tyvar, ptext SLIT("::"), ppr (tyVarKind tyvar)]),
+ ptext SLIT("and"),
+ quotes (hsep [ppr ty, ptext SLIT("::"), ppr (typeKind ty)])])
+
+unifyOccurCheck tyvar ty
+ = hang (ptext SLIT("Occurs check: cannot construct the infinite type:"))
+ 8 (sep [ppr tyvar, char '=', ppr ty])
+\end{code}
+
projects / ghc-hetmet.git / blobdiff