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 Ubiq
+#include "HsVersions.h"
-- friends:
import TcMonad
-import Type ( GenType(..), getTypeKind )
-import TyCon ( TyCon(..), ConsVisible, NewOrData )
-import TyVar ( GenTyVar(..), TyVar(..) )
-import TcType ( TcType(..), TcMaybe(..), TcTauType(..), TcTyVar(..),
- tcReadTyVar, tcWriteTyVar
+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, isSubKindOf )
-import PprType ( GenTyVar, GenType ) -- instances
-import Pretty
-import Unique ( Unique ) -- instances
+import Kind ( Kind, hasMoreBoxityInfo, mkTypeKind, mkBoxedTypeKind )
+import TysWiredIn ( listTyCon, mkListTy, mkTupleTy )
+import Maybes ( maybeToBool )
+import PprType () -- Instances
import Util
+import Outputable
\end{code}
\begin{code}
unifyTauTy :: TcTauType s -> TcTauType s -> TcM s ()
-unifyTauTy ty1 ty2
- = tcAddErrCtxt (unifyCtxt ty1 ty2) $
+unifyTauTy ty1 ty2 -- ty1 expected, ty2 inferred
+ = tcAddErrCtxtM (unifyCtxt ty1 ty2) $
uTys ty1 ty1 ty2 ty2
\end{code}
unifyTauTyLists [] [] = returnTc ()
unifyTauTyLists (ty1:tys1) (ty2:tys2) = uTys ty1 ty1 ty2 ty2 `thenTc_`
unifyTauTyLists tys1 tys2
-unifyTauTypeLists ty1s ty2s = panic "Unify.unifyTauTypeLists: mismatched type lists!"
+unifyTauTyLists ty1s ty2s = panic "Unify.unifyTauTyLists: mismatched type lists!"
\end{code}
@unifyTauTyList@ takes a single list of @TauType@s and unifies them
-> 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
- -- Applications and functions; just check the two parts
-uTys _ (FunTy fun1 arg1 _) _ (FunTy fun2 arg2 _)
- = uTys fun1 fun1 fun2 fun2 `thenTc_` uTys arg1 arg1 arg2 arg2
-uTys _ (AppTy fun1 arg1) _ (AppTy fun2 arg2)
+ -- 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 (TyConTy con1 _) ps_ty2 (TyConTy con2 _)
- = checkTc (con1 == con2) (unifyMisMatch ps_ty1 ps_ty2)
-
- -- Always expand synonyms (see notes at end)
-uTys ps_ty1 (SynTy con1 args1 ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2
-uTys ps_ty1 ty1 ps_ty2 (SynTy con2 args2 ty2) = uTys ps_ty1 ty1 ps_ty2 ty2
-
- -- Special case: converts (->) a b to a -> b
-uTys ps_ty1 (AppTy (AppTy (TyConTy FunTyCon u) fun) arg) ps_ty2 ty2
- = uTys ps_ty1 (FunTy fun arg u) ps_ty2 ty2
-uTys ps_ty1 ty1 ps_ty2 (AppTy (AppTy (TyConTy FunTyCon u) fun) arg)
- = uTys ps_ty1 ty1 ps_ty2 (FunTy fun arg u)
+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
+
+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
+
+uTys ps1 s1 ps2 s2@(AppTy _ _) = uTys ps2 s2 ps1 s1
+ -- Swap arguments if the App is in the second argument
+
+ -- 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
-- Anything else fails
-uTys ps_ty1 ty1 ps_ty2 ty2 = failTc (unifyMisMatch ps_ty1 ps_ty2)
+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 (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.
+ unifyTauTypeLists args1 args2
+ else
+ -- Never mind. Just expand them and try again
+ uTys ty1 ty2
+\end{verbatim}
+
+then THINK AGAIN. Here is the whole story, as detected and reported
+by Chris Okasaki \tr{<Chris_Okasaki@loch.mess.cs.cmu.edu>}:
+\begin{quotation}
+Here's a test program that should detect the problem:
+
+\begin{verbatim}
+ type Bogus a = Int
+ x = (1 :: Bogus Char) :: Bogus Bool
+\end{verbatim}
+
+The problem with [the attempted shortcut code] is that
+\begin{verbatim}
+ con1 == con2
+\end{verbatim}
+is not a sufficient condition to be able to use the shortcut!
+You also need to know that the type synonym actually USES all
+its arguments. For example, consider the following type synonym
+which does not use all its arguments.
+\begin{verbatim}
+ type Bogus a = Int
+\end{verbatim}
+
+If you ever tried unifying, say, \tr{Bogus Char} with \tr{Bogus Bool},
+the unifier would blithely try to unify \tr{Char} with \tr{Bool} and
+would fail, even though the expanded forms (both \tr{Int}) should
+match.
+
+Similarly, unifying \tr{Bogus Char} with \tr{Bogus t} would
+unnecessarily bind \tr{t} to \tr{Char}.
+
+... You could explicitly test for the problem synonyms and mark them
+somehow as needing expansion, perhaps also issuing a warning to the
+user.
+\end{quotation}
+
+
%************************************************************************
%* *
\subsection[Unify-uVar]{@uVar@: unifying with a type variable}
= tcReadTyVar tv1 `thenNF_Tc` \ maybe_ty1 ->
case maybe_ty1 of
BoundTo ty1 -> uTys ty1 ty1 ps_ty2 ty2
- UnBound -> uUnboundVar tv1 ps_ty2 ty2
+ other -> uUnboundVar tv1 maybe_ty1 ps_ty2 ty2
-- Expand synonyms
-uUnboundVar tv1 ps_ty2 (SynTy _ _ ty2) = uUnboundVar tv1 ps_ty2 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))
= returnTc ()
-- Distinct type variables
+ -- ASSERT maybe_ty1 /= BoundTo
| otherwise
= tcReadTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
case maybe_ty2 of
- BoundTo ty2' -> uUnboundVar tv1 ty2' ty2'
- UnBound -> if kind2 `isSubKindOf` kind1 then
- tcWriteTyVar tv1 ty2 `thenNF_Tc_` returnTc ()
- else if kind1 `isSubKindOf` kind2 then
- tcWriteTyVar tv2 (TyVarTy tv1) `thenNF_Tc_` returnTc ()
- else
- failTc (unifyKindErr tv1 ps_ty2)
+ 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) ps_ty2 non_var_ty2
- = occur_check non_var_ty2 `thenTc_`
- checkTc (getTypeKind non_var_ty2 `isSubKindOf` kind1)
- (unifyKindErr tv1 ps_ty2) `thenTc_`
- tcWriteTyVar tv1 non_var_ty2 `thenNF_Tc_`
- returnTc ()
+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 (TyVarTy tv2@(TyVar uniq2 _ _ box2))
+ occur_check ty = mapTc occur_check_tv (tyVarSetToList (tyVarsOfType ty)) `thenTc_`
+ returnTc ()
+
+ occur_check_tv tv2@(TyVar uniq2 _ _ box2)
| uniq1 == uniq2 -- Same tyvar; fail
- = failTc (unifyOccurCheck tv1 ps_ty2)
+ = failWithTc (unifyOccurCheck tv1 ps_ty2)
| otherwise -- A different tyvar
= tcReadTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
case maybe_ty2 of
BoundTo ty2' -> occur_check ty2'
- UnBound -> returnTc ()
+ other -> returnTc ()
+\end{code}
- occur_check (AppTy fun arg) = occur_check fun `thenTc_` occur_check arg
- occur_check (FunTy fun arg _) = occur_check fun `thenTc_` occur_check arg
- occur_check (TyConTy _ _) = returnTc ()
- occur_check (SynTy _ _ ty2) = occur_check ty2
- occur_check other = panic "Unexpected Dict or ForAll in occurCheck"
+%************************************************************************
+%* *
+\subsection[Unify-fun]{@unifyFunTy@}
+%* *
+%************************************************************************
+
+@unifyFunTy@ is used to avoid the fruitless creation of type variables.
+
+\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}
-Notes on synonyms
-~~~~~~~~~~~~~~~~~
-If you are tempted to make a short cut on synonyms, as in this
-pseudocode...
+\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{verbatim}
-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.
- unifyTauTypeLists args1 args2
- else
- -- Never mind. Just expand them and try again
- uTys ty1 ty2
-\end{verbatim}
+\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}
-then THINK AGAIN. Here is the whole story, as detected and reported
-by Chris Okasaki \tr{<Chris_Okasaki@loch.mess.cs.cmu.edu>}:
-\begin{quotation}
-Here's a test program that should detect the problem:
+%************************************************************************
+%* *
+\subsection{Unification wih a explicit substitution}
+%* *
+%************************************************************************
-\begin{verbatim}
- type Bogus a = Int
- x = (1 :: Bogus Char) :: Bogus Bool
-\end{verbatim}
+Unify types with an explicit substitution and no monad.
-The problem with [the attempted shortcut code] is that
-\begin{verbatim}
- con1 == con2
-\end{verbatim}
-is not a sufficient condition to be able to use the shortcut!
-You also need to know that the type synonym actually USES all
-its arguments. For example, consider the following type synonym
-which does not use all its arguments.
-\begin{verbatim}
- type Bogus a = Int
-\end{verbatim}
+\begin{code}
+type Subst = TyVarEnv Type -- Not necessarily idempotent
-If you ever tried unifying, say, \tr{Bogus Char} with \tr{Bogus Bool},
-the unifier would blithely try to unify \tr{Char} with \tr{Bool} and
-would fail, even though the expanded forms (both \tr{Int}) should
-match.
+unifyTysX :: Type -> Type -> Maybe Subst
+unifyTysX ty1 ty2 = uTysX ty1 ty2 (\s -> Just s) emptyTyVarEnv
-Similarly, unifying \tr{Bogus Char} with \tr{Bogus t} would
-unnecessarily bind \tr{t} to \tr{Char}.
+unifyTyListsX :: [Type] -> [Type] -> Maybe Subst
+unifyTyListsX tys1 tys2 = uTyListsX tys1 tys2 (\s -> Just s) emptyTyVarEnv
-... You could explicitly test for the problem synonyms and mark them
-somehow as needing expansion, perhaps also issuing a warning to the
-user.
-\end{quotation}
+uTysX :: Type -> Type
+ -> (Subst -> Maybe Subst)
+ -> Subst
+ -> Maybe Subst
+
+uTysX ty1 (SynTy _ ty2) k subst = uTysX ty1 ty2 k subst
+
+ -- 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
+
+ -- Functions; just check the two parts
+uTysX (FunTy fun1 arg1) (FunTy fun2 arg2) k subst
+ = uTysX fun1 fun2 (uTysX arg1 arg2 k) subst
+
+ -- 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 sty
- = ppAboves [
- ppCat [ppStr "Expected:", ppr sty ty1],
- ppCat [ppStr " Actual:", ppr sty ty2]
- ]
-
-unifyMisMatch ty1 ty2 sty
- = ppHang (ppStr "Couldn't match the type")
- 4 (ppSep [ppr sty ty1, ppStr "against", ppr sty ty2])
-
-unifyKindErr tyvar ty sty
- = ppHang (ppStr "Kind mis-match between")
- 4 (ppSep [ppr sty tyvar, ppStr "and", ppr sty ty])
-
-unifyOccurCheck tyvar ty sty
- = ppHang (ppStr "Occur check: cannot construct the infinite type")
- 4 (ppSep [ppr sty tyvar, ppStr "=", ppr sty ty])
+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