%
+% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
-\section[TcInstDecls]{Typechecking instance declarations}
+
+TcInstDecls: Typechecking instance declarations
\begin{code}
module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where
-#include "HsVersions.h"
-
import HsSyn
-import TcBinds ( mkPragFun, tcPrags, badBootDeclErr )
-import TcClassDcl ( tcMethodBind, mkMethodBind, badMethodErr,
- tcClassDecl2, getGenericInstances )
-import TcRnMonad
-import TcMType ( tcSkolSigType, checkValidInstance, checkValidInstHead )
-import TcType ( mkClassPred, tcSplitSigmaTy, tcSplitDFunHead,
- SkolemInfo(InstSkol), tcSplitDFunTy, mkFunTy )
-import Inst ( newDictBndr, newDictBndrs, instToId, showLIE,
- getOverlapFlag, tcExtendLocalInstEnv )
-import InstEnv ( mkLocalInstance, instanceDFunId )
-import TcDeriv ( tcDeriving )
-import TcEnv ( InstInfo(..), InstBindings(..),
- newDFunName, tcExtendIdEnv
- )
-import TcHsType ( kcHsSigType, tcHsKindedType )
-import TcUnify ( checkSigTyVars )
-import TcSimplify ( tcSimplifySuperClasses )
-import Type ( zipOpenTvSubst, substTheta, mkTyConApp, mkTyVarTy )
-import Coercion ( mkAppCoercion, mkAppsCoercion, mkSymCoercion )
-import TyCon ( TyCon, newTyConCo )
-import DataCon ( classDataCon, dataConTyCon, dataConInstArgTys )
-import Class ( classBigSig )
-import Var ( TyVar, Id, idName, idType )
-import Id ( mkSysLocal )
-import UniqSupply ( uniqsFromSupply, splitUniqSupply )
-import MkId ( mkDictFunId )
-import Name ( Name, getSrcLoc )
-import Maybe ( catMaybes )
-import SrcLoc ( srcLocSpan, unLoc, noLoc, Located(..), srcSpanStart )
-import ListSetOps ( minusList )
+import TcBinds
+import TcTyClsDecls
+import TcClassDcl
+import TcRnMonad
+import TcMType
+import TcType
+import Inst
+import InstEnv
+import FamInst
+import FamInstEnv
+import TcDeriv
+import TcEnv
+import RnEnv ( lookupImportedName )
+import TcHsType
+import TcUnify
+import TcSimplify
+import Type
+import Coercion
+import TyCon
+import TypeRep
+import DataCon
+import Class
+import Var
+import Id
+import MkId
+import Name
+import NameSet
+import DynFlags
+import SrcLoc
+import Util
import Outputable
import Bag
-import BasicTypes ( Activation( AlwaysActive ), InlineSpec(..) )
+import BasicTypes
+import HscTypes
import FastString
+
+import Data.Maybe
+import Control.Monad
+import Data.List
+
+#include "HsVersions.h"
\end{code}
Typechecking instance declarations is done in two passes. The first
all the instance and value decls. Indeed that's the reason we need
two passes over the instance decls.
-Here is the overall algorithm.
-Assume that we have an instance declaration
-
- instance c => k (t tvs) where b
-
-\begin{enumerate}
-\item
-$LIE_c$ is the LIE for the context of class $c$
-\item
-$betas_bar$ is the free variables in the class method type, excluding the
- class variable
-\item
-$LIE_cop$ is the LIE constraining a particular class method
-\item
-$tau_cop$ is the tau type of a class method
-\item
-$LIE_i$ is the LIE for the context of instance $i$
-\item
-$X$ is the instance constructor tycon
-\item
-$gammas_bar$ is the set of type variables of the instance
-\item
-$LIE_iop$ is the LIE for a particular class method instance
-\item
-$tau_iop$ is the tau type for this instance of a class method
-\item
-$alpha$ is the class variable
-\item
-$LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
-\item
-$tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
-\end{enumerate}
-
-ToDo: Update the list above with names actually in the code.
-
-\begin{enumerate}
-\item
-First, make the LIEs for the class and instance contexts, which means
-instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
-and make LIElistI and LIEI.
-\item
-Then process each method in turn.
-\item
-order the instance methods according to the ordering of the class methods
-\item
-express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
-\item
-Create final dictionary function from bindings generated already
-\begin{pseudocode}
-df = lambda inst_tyvars
- lambda LIEI
- let Bop1
- Bop2
- ...
- Bopn
- and dbinds_super
- in <op1,op2,...,opn,sd1,...,sdm>
-\end{pseudocode}
-Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
-and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
-\end{enumerate}
+
+Note [How instance declarations are translated]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Here is how we translation instance declarations into Core
+
+Running example:
+ class C a where
+ op1, op2 :: Ix b => a -> b -> b
+ op2 = <dm-rhs>
+
+ instance C a => C [a]
+ {-# INLINE [2] op1 #-}
+ op1 = <rhs>
+===>
+ -- Method selectors
+ op1,op2 :: forall a. C a => forall b. Ix b => a -> b -> b
+ op1 = ...
+ op2 = ...
+
+ -- Default methods get the 'self' dictionary as argument
+ -- so they can call other methods at the same type
+ -- Default methods get the same type as their method selector
+ $dmop2 :: forall a. C a => forall b. Ix b => a -> b -> b
+ $dmop2 = /\a. \(d:C a). /\b. \(d2: Ix b). <dm-rhs>
+ -- NB: type variables 'a' and 'b' are *both* in scope in <dm-rhs>
+ -- Note [Tricky type variable scoping]
+
+ -- A top-level definition for each instance method
+ -- Here op1_i, op2_i are the "instance method Ids"
+ {-# INLINE [2] op1_i #-} -- From the instance decl bindings
+ op1_i, op2_i :: forall a. C a => forall b. Ix b => [a] -> b -> b
+ op1_i = /\a. \(d:C a).
+ let this :: C [a]
+ this = df_i a d
+ -- Note [Subtle interaction of recursion and overlap]
+
+ local_op1 :: forall b. Ix b => [a] -> b -> b
+ local_op1 = <rhs>
+ -- Source code; run the type checker on this
+ -- NB: Type variable 'a' (but not 'b') is in scope in <rhs>
+ -- Note [Tricky type variable scoping]
+
+ in local_op1 a d
+
+ op2_i = /\a \d:C a. $dmop2 [a] (df_i a d)
+
+ -- The dictionary function itself
+ {-# INLINE df_i #-} -- Always inline dictionary functions
+ df_i :: forall a. C a -> C [a]
+ df_i = /\a. \d:C a. letrec d' = MkC (op1_i a d)
+ ($dmop2 [a] d')
+ in d'
+ -- But see Note [Default methods in instances]
+ -- We can't apply the type checker to the default-method call
+
+* The dictionary function itself is inlined as vigorously as we
+ possibly can, so that we expose that dictionary constructor to
+ selectors as much as poss. That is why the op_i stuff is in
+ *separate* bindings, so that the df_i binding is small enough
+ to inline. See Note [Inline dfuns unconditionally].
+
+* Note that df_i may be mutually recursive with both op1_i and op2_i.
+ It's crucial that df_i is not chosen as the loop breaker, even
+ though op1_i has a (user-specified) INLINE pragma.
+ Not even once! Else op1_i, op2_i may be inlined into df_i.
+
+* Instead the idea is to inline df_i into op1_i, which may then select
+ methods from the MkC record, and thereby break the recursion with
+ df_i, leaving a *self*-recurisve op1_i. (If op1_i doesn't call op at
+ the same type, it won't mention df_i, so there won't be recursion in
+ the first place.)
+
+* If op1_i is marked INLINE by the user there's a danger that we won't
+ inline df_i in it, and that in turn means that (since it'll be a
+ loop-breaker because df_i isn't), op1_i will ironically never be
+ inlined. We need to fix this somehow -- perhaps allowing inlining
+ of INLINE funcitons inside other INLINE functions.
+
+Note [Subtle interaction of recursion and overlap]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider this
+ class C a where { op1,op2 :: a -> a }
+ instance C a => C [a] where
+ op1 x = op2 x ++ op2 x
+ op2 x = ...
+ intance C [Int] where
+ ...
+
+When type-checking the C [a] instance, we need a C [a] dictionary (for
+the call of op2). If we look up in the instance environment, we find
+an overlap. And in *general* the right thing is to complain (see Note
+[Overlapping instances] in InstEnv). But in *this* case it's wrong to
+complain, because we just want to delegate to the op2 of this same
+instance.
+
+Why is this justified? Because we generate a (C [a]) constraint in
+a context in which 'a' cannot be instantiated to anything that matches
+other overlapping instances, or else we would not be excecuting this
+version of op1 in the first place.
+
+It might even be a bit disguised:
+
+ nullFail :: C [a] => [a] -> [a]
+ nullFail x = op2 x ++ op2 x
+
+ instance C a => C [a] where
+ op1 x = nullFail x
+
+Precisely this is used in package 'regex-base', module Context.hs.
+See the overlapping instances for RegexContext, and the fact that they
+call 'nullFail' just like the example above. The DoCon package also
+does the same thing; it shows up in module Fraction.hs
+
+Conclusion: when typechecking the methods in a C [a] instance, we want
+to have C [a] available. That is why we have the strange local
+definition for 'this' in the definition of op1_i in the example above.
+We can typecheck the defintion of local_op1, and when doing tcSimplifyCheck
+we supply 'this' as a given dictionary. Only needed, though, if there
+are some type variales involved; otherwise there can be no overlap and
+none of this arises.
+
+Note [Tricky type variable scoping]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In our example
+ class C a where
+ op1, op2 :: Ix b => a -> b -> b
+ op2 = <dm-rhs>
+
+ instance C a => C [a]
+ {-# INLINE [2] op1 #-}
+ op1 = <rhs>
+
+note that 'a' and 'b' are *both* in scope in <dm-rhs>, but only 'a' is
+in scope in <rhs>. In particular, we must make sure that 'b' is in
+scope when typechecking <dm-rhs>. This is achieved by subFunTys,
+which brings appropriate tyvars into scope. This happens for both
+<dm-rhs> and for <rhs>, but that doesn't matter: the *renamer* will have
+complained if 'b' is mentioned in <rhs>.
+
+Note [Inline dfuns unconditionally]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The code above unconditionally inlines dict funs. Here's why.
+Consider this program:
+
+ test :: Int -> Int -> Bool
+ test x y = (x,y) == (y,x) || test y x
+ -- Recursive to avoid making it inline.
+
+This needs the (Eq (Int,Int)) instance. If we inline that dfun
+the code we end up with is good:
+
+ Test.$wtest =
+ \r -> case ==# [ww ww1] of wild {
+ PrelBase.False -> Test.$wtest ww1 ww;
+ PrelBase.True ->
+ case ==# [ww1 ww] of wild1 {
+ PrelBase.False -> Test.$wtest ww1 ww;
+ PrelBase.True -> PrelBase.True [];
+ };
+ };
+ Test.test = \r [w w1]
+ case w of w2 {
+ PrelBase.I# ww ->
+ case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
+ };
+
+If we don't inline the dfun, the code is not nearly as good:
+
+ (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
+ PrelBase.:DEq tpl1 tpl2 -> tpl2;
+ };
+
+ Test.$wtest =
+ \r [ww ww1]
+ let { y = PrelBase.I#! [ww1]; } in
+ let { x = PrelBase.I#! [ww]; } in
+ let { sat_slx = PrelTup.(,)! [y x]; } in
+ let { sat_sly = PrelTup.(,)! [x y];
+ } in
+ case == sat_sly sat_slx of wild {
+ PrelBase.False -> Test.$wtest ww1 ww;
+ PrelBase.True -> PrelBase.True [];
+ };
+
+ Test.test =
+ \r [w w1]
+ case w of w2 {
+ PrelBase.I# ww ->
+ case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
+ };
+
+Why didn't GHC inline $fEq in those days? Because it looked big:
+
+ PrelTup.zdfEqZ1T{-rcX-}
+ = \ @ a{-reT-} :: * @ b{-reS-} :: *
+ zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
+ zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
+ let {
+ zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
+ zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
+ let {
+ zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
+ zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
+ let {
+ zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
+ zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
+ ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
+ case ds{-rf5-}
+ of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
+ case ds1{-rf4-}
+ of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
+ PrelBase.zaza{-r4e-}
+ (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
+ (zeze{-rf0-} a2{-reZ-} b2{-reY-})
+ }
+ } } in
+ let {
+ a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
+ a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
+ b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
+ PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
+ } in
+ PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
+
+and it's not as bad as it seems, because it's further dramatically
+simplified: only zeze2 is extracted and its body is simplified.
%************************************************************************
-%* *
+%* *
\subsection{Extracting instance decls}
-%* *
+%* *
%************************************************************************
Gather up the instance declarations from their various sources
\begin{code}
-tcInstDecls1 -- Deal with both source-code and imported instance decls
- :: [LTyClDecl Name] -- For deriving stuff
- -> [LInstDecl Name] -- Source code instance decls
- -> TcM (TcGblEnv, -- The full inst env
- [InstInfo], -- Source-code instance decls to process;
- -- contains all dfuns for this module
- HsValBinds Name) -- Supporting bindings for derived instances
-
-tcInstDecls1 tycl_decls inst_decls
+tcInstDecls1 -- Deal with both source-code and imported instance decls
+ :: [LTyClDecl Name] -- For deriving stuff
+ -> [LInstDecl Name] -- Source code instance decls
+ -> [LDerivDecl Name] -- Source code stand-alone deriving decls
+ -> TcM (TcGblEnv, -- The full inst env
+ [InstInfo Name], -- Source-code instance decls to process;
+ -- contains all dfuns for this module
+ HsValBinds Name) -- Supporting bindings for derived instances
+
+tcInstDecls1 tycl_decls inst_decls deriv_decls
= checkNoErrs $
- -- Stop if addInstInfos etc discovers any errors
- -- (they recover, so that we get more than one error each round)
-
- -- (1) Do the ordinary instance declarations
- mappM tcLocalInstDecl1 inst_decls `thenM` \ local_inst_infos ->
-
- let
- local_inst_info = catMaybes local_inst_infos
- clas_decls = filter (isClassDecl.unLoc) tycl_decls
- in
- -- (2) Instances from generic class declarations
- getGenericInstances clas_decls `thenM` \ generic_inst_info ->
-
- -- Next, construct the instance environment so far, consisting of
- -- a) local instance decls
- -- b) generic instances
- addInsts local_inst_info $
- addInsts generic_inst_info $
-
- -- (3) Compute instances from "deriving" clauses;
- -- This stuff computes a context for the derived instance decl, so it
- -- needs to know about all the instances possible; hence inst_env4
- tcDeriving tycl_decls `thenM` \ (deriv_inst_info, deriv_binds) ->
- addInsts deriv_inst_info $
-
- getGblEnv `thenM` \ gbl_env ->
- returnM (gbl_env,
- generic_inst_info ++ deriv_inst_info ++ local_inst_info,
- deriv_binds)
-
-addInsts :: [InstInfo] -> TcM a -> TcM a
+ do { -- Stop if addInstInfos etc discovers any errors
+ -- (they recover, so that we get more than one error each
+ -- round)
+
+ -- (1) Do class and family instance declarations
+ ; let { idxty_decls = filter (isFamInstDecl . unLoc) tycl_decls }
+ ; local_info_tycons <- mapAndRecoverM tcLocalInstDecl1 inst_decls
+ ; idx_tycons <- mapAndRecoverM tcIdxTyInstDeclTL idxty_decls
+
+ ; let { (local_info,
+ at_tycons_s) = unzip local_info_tycons
+ ; at_idx_tycon = concat at_tycons_s ++ idx_tycons
+ ; clas_decls = filter (isClassDecl.unLoc) tycl_decls
+ ; implicit_things = concatMap implicitTyThings at_idx_tycon
+ }
+
+ -- (2) Add the tycons of indexed types and their implicit
+ -- tythings to the global environment
+ ; tcExtendGlobalEnv (at_idx_tycon ++ implicit_things) $ do {
+
+ -- (3) Instances from generic class declarations
+ ; generic_inst_info <- getGenericInstances clas_decls
+
+ -- Next, construct the instance environment so far, consisting
+ -- of
+ -- a) local instance decls
+ -- b) generic instances
+ -- c) local family instance decls
+ ; addInsts local_info $ do {
+ ; addInsts generic_inst_info $ do {
+ ; addFamInsts at_idx_tycon $ do {
+
+ -- (4) Compute instances from "deriving" clauses;
+ -- This stuff computes a context for the derived instance
+ -- decl, so it needs to know about all the instances possible
+ -- NB: class instance declarations can contain derivings as
+ -- part of associated data type declarations
+ failIfErrsM -- If the addInsts stuff gave any errors, don't
+ -- try the deriving stuff, becuase that may give
+ -- more errors still
+ ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls inst_decls
+ deriv_decls
+ ; addInsts deriv_inst_info $ do {
+
+ ; gbl_env <- getGblEnv
+ ; return (gbl_env,
+ generic_inst_info ++ deriv_inst_info ++ local_info,
+ deriv_binds)
+ }}}}}}
+ where
+ -- Make sure that toplevel type instance are not for associated types.
+ -- !!!TODO: Need to perform this check for the TyThing of type functions,
+ -- too.
+ tcIdxTyInstDeclTL ldecl@(L loc decl) =
+ do { tything <- tcFamInstDecl ldecl
+ ; setSrcSpan loc $
+ when (isAssocFamily tything) $
+ addErr $ assocInClassErr (tcdName decl)
+ ; return tything
+ }
+ isAssocFamily (ATyCon tycon) =
+ case tyConFamInst_maybe tycon of
+ Nothing -> panic "isAssocFamily: no family?!?"
+ Just (fam, _) -> isTyConAssoc fam
+ isAssocFamily _ = panic "isAssocFamily: no tycon?!?"
+
+assocInClassErr :: Name -> SDoc
+assocInClassErr name =
+ ptext (sLit "Associated type") <+> quotes (ppr name) <+>
+ ptext (sLit "must be inside a class instance")
+
+addInsts :: [InstInfo Name] -> TcM a -> TcM a
addInsts infos thing_inside
= tcExtendLocalInstEnv (map iSpec infos) thing_inside
-\end{code}
+
+addFamInsts :: [TyThing] -> TcM a -> TcM a
+addFamInsts tycons thing_inside
+ = tcExtendLocalFamInstEnv (map mkLocalFamInstTyThing tycons) thing_inside
+ where
+ mkLocalFamInstTyThing (ATyCon tycon) = mkLocalFamInst tycon
+ mkLocalFamInstTyThing tything = pprPanic "TcInstDcls.addFamInsts"
+ (ppr tything)
+\end{code}
\begin{code}
-tcLocalInstDecl1 :: LInstDecl Name
- -> TcM (Maybe InstInfo) -- Nothing if there was an error
- -- A source-file instance declaration
- -- Type-check all the stuff before the "where"
- --
- -- We check for respectable instance type, and context
-tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
- -- !!!TODO: Handle the `ats' parameter!!! -=chak
- = -- Prime error recovery, set source location
- recoverM (returnM Nothing) $
- setSrcSpan loc $
- addErrCtxt (instDeclCtxt1 poly_ty) $
-
- do { is_boot <- tcIsHsBoot
- ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
- badBootDeclErr
-
- -- Typecheck the instance type itself. We can't use
- -- tcHsSigType, because it's not a valid user type.
- ; kinded_ty <- kcHsSigType poly_ty
- ; poly_ty' <- tcHsKindedType kinded_ty
- ; let (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
-
- ; (clas, inst_tys) <- checkValidInstHead tau
- ; checkValidInstance tyvars theta clas inst_tys
-
- ; dfun_name <- newDFunName clas inst_tys (srcSpanStart loc)
- ; overlap_flag <- getOverlapFlag
- ; let dfun = mkDictFunId dfun_name tyvars theta clas inst_tys
- ispec = mkLocalInstance dfun overlap_flag
-
- ; return (Just (InstInfo { iSpec = ispec, iBinds = VanillaInst binds uprags })) }
+tcLocalInstDecl1 :: LInstDecl Name
+ -> TcM (InstInfo Name, [TyThing])
+ -- A source-file instance declaration
+ -- Type-check all the stuff before the "where"
+ --
+ -- We check for respectable instance type, and context
+tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats))
+ = setSrcSpan loc $
+ addErrCtxt (instDeclCtxt1 poly_ty) $
+
+ do { is_boot <- tcIsHsBoot
+ ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
+ badBootDeclErr
+
+ ; (tyvars, theta, tau) <- tcHsInstHead poly_ty
+
+ -- Now, check the validity of the instance.
+ ; (clas, inst_tys) <- checkValidInstHead tau
+ ; checkValidInstance tyvars theta clas inst_tys
+
+ -- Next, process any associated types.
+ ; idx_tycons <- recoverM (return []) $
+ do { idx_tycons <- checkNoErrs $ mapAndRecoverM tcFamInstDecl ats
+ ; checkValidAndMissingATs clas (tyvars, inst_tys)
+ (zip ats idx_tycons)
+ ; return idx_tycons }
+
+ -- Finally, construct the Core representation of the instance.
+ -- (This no longer includes the associated types.)
+ ; dfun_name <- newDFunName clas inst_tys (getLoc poly_ty)
+ -- Dfun location is that of instance *header*
+ ; overlap_flag <- getOverlapFlag
+ ; let (eq_theta,dict_theta) = partition isEqPred theta
+ theta' = eq_theta ++ dict_theta
+ dfun = mkDictFunId dfun_name tyvars theta' clas inst_tys
+ ispec = mkLocalInstance dfun overlap_flag
+
+ ; return (InstInfo { iSpec = ispec,
+ iBinds = VanillaInst binds uprags },
+ idx_tycons)
+ }
+ where
+ -- We pass in the source form and the type checked form of the ATs. We
+ -- really need the source form only to be able to produce more informative
+ -- error messages.
+ checkValidAndMissingATs :: Class
+ -> ([TyVar], [TcType]) -- instance types
+ -> [(LTyClDecl Name, -- source form of AT
+ TyThing)] -- Core form of AT
+ -> TcM ()
+ checkValidAndMissingATs clas inst_tys ats
+ = do { -- Issue a warning for each class AT that is not defined in this
+ -- instance.
+ ; let class_ats = map tyConName (classATs clas)
+ defined_ats = listToNameSet . map (tcdName.unLoc.fst) $ ats
+ omitted = filterOut (`elemNameSet` defined_ats) class_ats
+ ; warn <- doptM Opt_WarnMissingMethods
+ ; mapM_ (warnTc warn . omittedATWarn) omitted
+
+ -- Ensure that all AT indexes that correspond to class parameters
+ -- coincide with the types in the instance head. All remaining
+ -- AT arguments must be variables. Also raise an error for any
+ -- type instances that are not associated with this class.
+ ; mapM_ (checkIndexes clas inst_tys) ats
+ }
+
+ checkIndexes clas inst_tys (hsAT, ATyCon tycon) =
+-- !!!TODO: check that this does the Right Thing for indexed synonyms, too!
+ checkIndexes' clas inst_tys hsAT
+ (tyConTyVars tycon,
+ snd . fromJust . tyConFamInst_maybe $ tycon)
+ checkIndexes _ _ _ = panic "checkIndexes"
+
+ checkIndexes' clas (instTvs, instTys) hsAT (atTvs, atTys)
+ = let atName = tcdName . unLoc $ hsAT
+ in
+ setSrcSpan (getLoc hsAT) $
+ addErrCtxt (atInstCtxt atName) $
+ case find ((atName ==) . tyConName) (classATs clas) of
+ Nothing -> addErrTc $ badATErr clas atName -- not in this class
+ Just atDecl ->
+ case assocTyConArgPoss_maybe atDecl of
+ Nothing -> panic "checkIndexes': AT has no args poss?!?"
+ Just poss ->
+
+ -- The following is tricky! We need to deal with three
+ -- complications: (1) The AT possibly only uses a subset of
+ -- the class parameters as indexes and those it uses may be in
+ -- a different order; (2) the AT may have extra arguments,
+ -- which must be type variables; and (3) variables in AT and
+ -- instance head will be different `Name's even if their
+ -- source lexemes are identical.
+ --
+ -- Re (1), `poss' contains a permutation vector to extract the
+ -- class parameters in the right order.
+ --
+ -- Re (2), we wrap the (permuted) class parameters in a Maybe
+ -- type and use Nothing for any extra AT arguments. (First
+ -- equation of `checkIndex' below.)
+ --
+ -- Re (3), we replace any type variable in the AT parameters
+ -- that has the same source lexeme as some variable in the
+ -- instance types with the instance type variable sharing its
+ -- source lexeme.
+ --
+ let relevantInstTys = map (instTys !!) poss
+ instArgs = map Just relevantInstTys ++
+ repeat Nothing -- extra arguments
+ renaming = substSameTyVar atTvs instTvs
+ in
+ zipWithM_ checkIndex (substTys renaming atTys) instArgs
+
+ checkIndex ty Nothing
+ | isTyVarTy ty = return ()
+ | otherwise = addErrTc $ mustBeVarArgErr ty
+ checkIndex ty (Just instTy)
+ | ty `tcEqType` instTy = return ()
+ | otherwise = addErrTc $ wrongATArgErr ty instTy
+
+ listToNameSet = addListToNameSet emptyNameSet
+
+ substSameTyVar [] _ = emptyTvSubst
+ substSameTyVar (tv:tvs) replacingTvs =
+ let replacement = case find (tv `sameLexeme`) replacingTvs of
+ Nothing -> mkTyVarTy tv
+ Just rtv -> mkTyVarTy rtv
+ --
+ tv1 `sameLexeme` tv2 =
+ nameOccName (tyVarName tv1) == nameOccName (tyVarName tv2)
+ in
+ extendTvSubst (substSameTyVar tvs replacingTvs) tv replacement
\end{code}
%************************************************************************
-%* *
-\subsection{Type-checking instance declarations, pass 2}
-%* *
+%* *
+ Type-checking instance declarations, pass 2
+%* *
%************************************************************************
\begin{code}
-tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo]
- -> TcM (LHsBinds Id, TcLclEnv)
--- (a) From each class declaration,
--- generate any default-method bindings
+tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo Name]
+ -> TcM (LHsBinds Id, TcLclEnv)
+-- (a) From each class declaration,
+-- generate any default-method bindings
-- (b) From each instance decl
--- generate the dfun binding
+-- generate the dfun binding
tcInstDecls2 tycl_decls inst_decls
- = do { -- (a) Default methods from class decls
- (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
- filter (isClassDecl.unLoc) tycl_decls
- ; tcExtendIdEnv (concat dm_ids_s) $ do
-
- -- (b) instance declarations
- ; inst_binds_s <- mappM tcInstDecl2 inst_decls
-
- -- Done
- ; let binds = unionManyBags dm_binds_s `unionBags`
- unionManyBags inst_binds_s
- ; tcl_env <- getLclEnv -- Default method Ids in here
- ; returnM (binds, tcl_env) }
+ = do { -- (a) Default methods from class decls
+ (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
+ filter (isClassDecl.unLoc) tycl_decls
+ ; tcExtendIdEnv (concat dm_ids_s) $ do
+
+ -- (b) instance declarations
+ ; inst_binds_s <- mapM tcInstDecl2 inst_decls
+
+ -- Done
+ ; let binds = unionManyBags dm_binds_s `unionBags`
+ unionManyBags inst_binds_s
+ ; tcl_env <- getLclEnv -- Default method Ids in here
+ ; return (binds, tcl_env) }
\end{code}
-======= New documentation starts here (Sept 92) ==============
-
-The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
-the dictionary function for this instance declaration. For example
-\begin{verbatim}
- instance Foo a => Foo [a] where
- op1 x = ...
- op2 y = ...
-\end{verbatim}
-might generate something like
-\begin{verbatim}
- dfun.Foo.List dFoo_a = let op1 x = ...
- op2 y = ...
- in
- Dict [op1, op2]
-\end{verbatim}
-
-HOWEVER, if the instance decl has no context, then it returns a
-bigger @HsBinds@ with declarations for each method. For example
-\begin{verbatim}
- instance Foo [a] where
- op1 x = ...
- op2 y = ...
-\end{verbatim}
-might produce
-\begin{verbatim}
- dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
- const.Foo.op1.List a x = ...
- const.Foo.op2.List a y = ...
-\end{verbatim}
-This group may be mutually recursive, because (for example) there may
-be no method supplied for op2 in which case we'll get
-\begin{verbatim}
- const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
-\end{verbatim}
-that is, the default method applied to the dictionary at this type.
-
-What we actually produce in either case is:
-
- AbsBinds [a] [dfun_theta_dicts]
- [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
- { d = (sd1,sd2, ..., op1, op2, ...)
- op1 = ...
- op2 = ...
- }
-
-The "maybe" says that we only ask AbsBinds to make global constant methods
-if the dfun_theta is empty.
-
-
-For an instance declaration, say,
-
- instance (C1 a, C2 b) => C (T a b) where
- ...
-
-where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
-function whose type is
-
- (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
-
-Notice that we pass it the superclass dictionaries at the instance type; this
-is the ``Mark Jones optimisation''. The stuff before the "=>" here
-is the @dfun_theta@ below.
-
-First comes the easy case of a non-local instance decl.
-
\begin{code}
-tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
+tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id)
-- Returns a binding for the dfun
------------------------
--- Derived newtype instances
+-- Derived newtype instances; surprisingly tricky!
--
--- We need to make a copy of the dictionary we are deriving from
--- because we may need to change some of the superclass dictionaries
--- see Note [Newtype deriving superclasses] in TcDeriv.lhs
+-- class Show a => Foo a b where ...
+-- newtype N a = MkN (Tree [a]) deriving( Foo Int )
--
--- In the case of a newtype, things are rather easy
--- class Show a => Foo a b where ...
--- newtype T a = MkT (Tree [a]) deriving( Foo Int )
-- The newtype gives an FC axiom looking like
--- axiom CoT a :: T a :=: Tree [a]
+-- axiom CoN a :: N a ~ Tree [a]
+-- (see Note [Newtype coercions] in TyCon for this unusual form of axiom)
--
--- So all need is to generate a binding looking like
--- dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
--- dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
--- case df `cast` (Foo Int (sym (CoT a))) of
--- Foo _ op1 .. opn -> Foo ds op1 .. opn
-
-tcInstDecl2 (InstInfo { iSpec = ispec,
- iBinds = NewTypeDerived tycon rep_tys })
- = do { let dfun_id = instanceDFunId ispec
- rigid_info = InstSkol dfun_id
- origin = SigOrigin rigid_info
- inst_ty = idType dfun_id
- ; inst_loc <- getInstLoc origin
- ; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
- ; dicts <- newDictBndrs inst_loc theta
- ; uniqs <- newUniqueSupply
- ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head
- ; this_dict <- newDictBndr inst_loc (mkClassPred cls rep_tys)
- ; let (rep_dict_id:sc_dict_ids)
- | null dicts = [instToId this_dict]
- | otherwise = map instToId dicts
-
- -- (Here, we are relying on the order of dictionary
- -- arguments built by NewTypeDerived in TcDeriv.)
-
- wrap_fn = mkCoTyLams tvs <.> mkCoLams (rep_dict_id:sc_dict_ids)
-
- coerced_rep_dict = mkHsCoerce (co_fn tvs cls_tycon) (HsVar rep_dict_id)
-
- body | null sc_dict_ids = coerced_rep_dict
- | otherwise = HsCase (noLoc coerced_rep_dict) $
- MatchGroup [the_match] (mkFunTy in_dict_ty inst_head)
- in_dict_ty = mkTyConApp cls_tycon cls_inst_tys
-
- the_match = mkSimpleMatch [noLoc the_pat] the_rhs
- the_rhs = mkHsConApp cls_data_con cls_inst_tys (map HsVar (sc_dict_ids ++ op_ids))
-
- (uniqs1, uniqs2) = splitUniqSupply uniqs
-
- op_ids = zipWith (mkSysLocal FSLIT("op"))
- (uniqsFromSupply uniqs1) op_tys
-
- dict_ids = zipWith (mkSysLocal FSLIT("dict"))
- (uniqsFromSupply uniqs2) (map idType sc_dict_ids)
-
- the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
- pat_dicts = dict_ids,
- pat_binds = emptyLHsBinds,
- pat_args = PrefixCon (map nlVarPat op_ids),
- pat_ty = in_dict_ty}
-
- cls_data_con = classDataCon cls
- cls_tycon = dataConTyCon cls_data_con
- cls_arg_tys = dataConInstArgTys cls_data_con cls_inst_tys
-
- n_dict_args = if length dicts == 0 then 0 else length dicts - 1
- op_tys = drop n_dict_args cls_arg_tys
-
- dict = mkHsCoerce wrap_fn body
- ; return (unitBag (noLoc $ VarBind dfun_id (noLoc dict))) }
+-- So all need is to generate a binding looking like:
+-- dfunFooT :: forall a. (Foo Int (Tree [a], Show (N a)) => Foo Int (N a)
+-- dfunFooT = /\a. \(ds:Show (N a)) (df:Foo (Tree [a])).
+-- case df `cast` (Foo Int (sym (CoN a))) of
+-- Foo _ op1 .. opn -> Foo ds op1 .. opn
+--
+-- If there are no superclasses, matters are simpler, because we don't need the case
+-- see Note [Newtype deriving superclasses] in TcDeriv.lhs
+
+tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived })
+ = do { let dfun_id = instanceDFunId ispec
+ rigid_info = InstSkol
+ origin = SigOrigin rigid_info
+ inst_ty = idType dfun_id
+ ; (inst_tvs', theta, inst_head_ty) <- tcSkolSigType rigid_info inst_ty
+ -- inst_head_ty is a PredType
+
+ ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head_ty
+ (class_tyvars, sc_theta, _, _) = classBigSig cls
+ cls_tycon = classTyCon cls
+ sc_theta' = substTheta (zipOpenTvSubst class_tyvars cls_inst_tys) sc_theta
+
+ Just (initial_cls_inst_tys, last_ty) = snocView cls_inst_tys
+ (nt_tycon, tc_args) = tcSplitTyConApp last_ty -- Can't fail
+ rep_ty = newTyConInstRhs nt_tycon tc_args
+
+ rep_pred = mkClassPred cls (initial_cls_inst_tys ++ [rep_ty])
+ -- In our example, rep_pred is (Foo Int (Tree [a]))
+ the_coercion = make_coercion cls_tycon initial_cls_inst_tys nt_tycon tc_args
+ -- Coercion of kind (Foo Int (Tree [a]) ~ Foo Int (N a)
+
+ ; sc_loc <- getInstLoc InstScOrigin
+ ; sc_dicts <- newDictBndrs sc_loc sc_theta'
+ ; inst_loc <- getInstLoc origin
+ ; dfun_dicts <- newDictBndrs inst_loc theta
+ ; this_dict <- newDictBndr inst_loc (mkClassPred cls cls_inst_tys)
+ ; rep_dict <- newDictBndr inst_loc rep_pred
+
+ -- Figure out bindings for the superclass context from dfun_dicts
+ -- Don't include this_dict in the 'givens', else
+ -- sc_dicts get bound by just selecting from this_dict!!
+ ; sc_binds <- addErrCtxt superClassCtxt $
+ tcSimplifySuperClasses inst_loc this_dict dfun_dicts
+ (rep_dict:sc_dicts)
+
+ -- It's possible that the superclass stuff might unified something
+ -- in the envt with one of the clas_tyvars
+ ; checkSigTyVars inst_tvs'
+
+ ; let coerced_rep_dict = wrapId the_coercion (instToId rep_dict)
+
+ ; body <- make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict
+ ; let dict_bind = noLoc $ VarBind (instToId this_dict) (noLoc body)
+
+ ; return (unitBag $ noLoc $
+ AbsBinds inst_tvs' (map instToVar dfun_dicts)
+ [(inst_tvs', dfun_id, instToId this_dict, [])]
+ (dict_bind `consBag` sc_binds)) }
where
- co_fn :: [TyVar] -> TyCon -> ExprCoFn
- co_fn tvs cls_tycon | Just co_con <- newTyConCo tycon
- = ExprCoFn (mkAppCoercion -- (mkAppsCoercion
- (mkTyConApp cls_tycon [])
- -- rep_tys)
- (mkSymCoercion (mkTyConApp co_con (map mkTyVarTy tvs))))
- | otherwise
- = idCoercion
+ -----------------------
+ -- make_coercion
+ -- The inst_head looks like (C s1 .. sm (T a1 .. ak))
+ -- But we want the coercion (C s1 .. sm (sym (CoT a1 .. ak)))
+ -- with kind (C s1 .. sm (T a1 .. ak) ~ C s1 .. sm <rep_ty>)
+ -- where rep_ty is the (eta-reduced) type rep of T
+ -- So we just replace T with CoT, and insert a 'sym'
+ -- NB: we know that k will be >= arity of CoT, because the latter fully eta-reduced
+
+ make_coercion cls_tycon initial_cls_inst_tys nt_tycon tc_args
+ | Just co_con <- newTyConCo_maybe nt_tycon
+ , let co = mkSymCoercion (mkTyConApp co_con tc_args)
+ = WpCast (mkTyConApp cls_tycon (initial_cls_inst_tys ++ [co]))
+ | otherwise -- The newtype is transparent; no need for a cast
+ = idHsWrapper
+
+ -----------------------
+ -- (make_body C tys scs coreced_rep_dict)
+ -- returns
+ -- (case coerced_rep_dict of { C _ ops -> C scs ops })
+ -- But if there are no superclasses, it returns just coerced_rep_dict
+ -- See Note [Newtype deriving superclasses] in TcDeriv.lhs
+
+ make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict
+ | null sc_dicts -- Case (a)
+ = return coerced_rep_dict
+ | otherwise -- Case (b)
+ = do { op_ids <- newSysLocalIds (fsLit "op") op_tys
+ ; dummy_sc_dict_ids <- newSysLocalIds (fsLit "sc") (map idType sc_dict_ids)
+ ; let the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
+ pat_dicts = dummy_sc_dict_ids,
+ pat_binds = emptyLHsBinds,
+ pat_args = PrefixCon (map nlVarPat op_ids),
+ pat_ty = pat_ty}
+ the_match = mkSimpleMatch [noLoc the_pat] the_rhs
+ the_rhs = mkHsConApp cls_data_con cls_inst_tys $
+ map HsVar (sc_dict_ids ++ op_ids)
+
+ -- Warning: this HsCase scrutinises a value with a PredTy, which is
+ -- never otherwise seen in Haskell source code. It'd be
+ -- nicer to generate Core directly!
+ ; return (HsCase (noLoc coerced_rep_dict) $
+ MatchGroup [the_match] (mkFunTy pat_ty pat_ty)) }
+ where
+ sc_dict_ids = map instToId sc_dicts
+ pat_ty = mkTyConApp cls_tycon cls_inst_tys
+ cls_data_con = head (tyConDataCons cls_tycon)
+ cls_arg_tys = dataConInstArgTys cls_data_con cls_inst_tys
+ op_tys = dropList sc_dict_ids cls_arg_tys
------------------------
-- Ordinary instances
tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
- = let
- dfun_id = instanceDFunId ispec
- rigid_info = InstSkol dfun_id
- inst_ty = idType dfun_id
+ = let
+ dfun_id = instanceDFunId ispec
+ rigid_info = InstSkol
+ inst_ty = idType dfun_id
+ loc = getSrcSpan dfun_id
in
- -- Prime error recovery
- recoverM (returnM emptyLHsBinds) $
- setSrcSpan (srcLocSpan (getSrcLoc dfun_id)) $
- addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
-
- -- Instantiate the instance decl with skolem constants
- tcSkolSigType rigid_info inst_ty `thenM` \ (inst_tyvars', dfun_theta', inst_head') ->
- -- These inst_tyvars' scope over the 'where' part
- -- Those tyvars are inside the dfun_id's type, which is a bit
- -- bizarre, but OK so long as you realise it!
+ -- Prime error recovery
+ recoverM (return emptyLHsBinds) $
+ setSrcSpan loc $
+ addErrCtxt (instDeclCtxt2 (idType dfun_id)) $ do
+
+ -- Instantiate the instance decl with skolem constants
+ (inst_tyvars', dfun_theta', inst_head') <- tcSkolSigType rigid_info inst_ty
+ -- These inst_tyvars' scope over the 'where' part
+ -- Those tyvars are inside the dfun_id's type, which is a bit
+ -- bizarre, but OK so long as you realise it!
let
- (clas, inst_tys') = tcSplitDFunHead inst_head'
+ (clas, inst_tys') = tcSplitDFunHead inst_head'
(class_tyvars, sc_theta, _, op_items) = classBigSig clas
-- Instantiate the super-class context with inst_tys
- sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
- origin = SigOrigin rigid_info
- in
- -- Create dictionary Ids from the specified instance contexts.
- getInstLoc InstScOrigin `thenM` \ sc_loc ->
- newDictBndrs sc_loc sc_theta' `thenM` \ sc_dicts ->
- getInstLoc origin `thenM` \ inst_loc ->
- newDictBndrs inst_loc dfun_theta' `thenM` \ dfun_arg_dicts ->
- newDictBndr inst_loc (mkClassPred clas inst_tys') `thenM` \ this_dict ->
- -- Default-method Ids may be mentioned in synthesised RHSs,
- -- but they'll already be in the environment.
-
- -- Typecheck the methods
- let -- These insts are in scope; quite a few, eh?
- avail_insts = [this_dict] ++ dfun_arg_dicts ++ sc_dicts
- in
- tcMethods origin clas inst_tyvars'
- dfun_theta' inst_tys' avail_insts
- op_items monobinds uprags `thenM` \ (meth_ids, meth_binds) ->
-
- -- Figure out bindings for the superclass context
- -- Don't include this_dict in the 'givens', else
- -- sc_dicts get bound by just selecting from this_dict!!
- addErrCtxt superClassCtxt
- (tcSimplifySuperClasses inst_tyvars'
- dfun_arg_dicts
- sc_dicts) `thenM` \ sc_binds ->
-
- -- It's possible that the superclass stuff might unified one
- -- of the inst_tyavars' with something in the envt
- checkSigTyVars inst_tyvars' `thenM_`
-
- -- Deal with 'SPECIALISE instance' pragmas
- tcPrags dfun_id (filter isSpecInstLSig uprags) `thenM` \ prags ->
-
- -- Create the result bindings
+ sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
+ origin = SigOrigin rigid_info
+
+ -- Create dictionary Ids from the specified instance contexts.
+ sc_loc <- getInstLoc InstScOrigin
+ sc_dicts <- newDictOccs sc_loc sc_theta' -- These are wanted
+ inst_loc <- getInstLoc origin
+ dfun_dicts <- newDictBndrs inst_loc dfun_theta' -- Includes equalities
+ this_dict <- newDictBndr inst_loc (mkClassPred clas inst_tys')
+ -- Default-method Ids may be mentioned in synthesised RHSs,
+ -- but they'll already be in the environment.
+
+ -- Typecheck the methods
+ let this_dict_id = instToId this_dict
+ dfun_lam_vars = map instToVar dfun_dicts -- Includes equalities
+ prag_fn = mkPragFun uprags
+ tc_meth = tcInstanceMethod loc clas inst_tyvars'
+ dfun_dicts
+ dfun_theta' inst_tys'
+ this_dict dfun_id
+ prag_fn monobinds
+ (meth_exprs, meth_binds) <- tcExtendTyVarEnv inst_tyvars' $
+ mapAndUnzipM tc_meth op_items
+
+ -- Figure out bindings for the superclass context
+ -- Don't include this_dict in the 'givens', else
+ -- sc_dicts get bound by just selecting from this_dict!!
+ sc_binds <- addErrCtxt superClassCtxt $
+ tcSimplifySuperClasses inst_loc this_dict dfun_dicts sc_dicts
+ -- Note [Recursive superclasses]
+
+ -- It's possible that the superclass stuff might unified something
+ -- in the envt with one of the inst_tyvars'
+ checkSigTyVars inst_tyvars'
+
+ -- Deal with 'SPECIALISE instance' pragmas
+ prags <- tcPrags dfun_id (filter isSpecInstLSig uprags)
+
+ -- Create the result bindings
let
dict_constr = classDataCon clas
- scs_and_meths = map instToId sc_dicts ++ meth_ids
- this_dict_id = instToId this_dict
- inline_prag | null dfun_arg_dicts = []
- | otherwise = [InlinePrag (Inline AlwaysActive True)]
- -- Always inline the dfun; this is an experimental decision
- -- because it makes a big performance difference sometimes.
- -- Often it means we can do the method selection, and then
- -- inline the method as well. Marcin's idea; see comments below.
- --
- -- BUT: don't inline it if it's a constant dictionary;
- -- we'll get all the benefit without inlining, and we get
- -- a **lot** of code duplication if we inline it
- --
- -- See Note [Inline dfuns] below
-
- dict_rhs
- = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
- -- We don't produce a binding for the dict_constr; instead we
- -- rely on the simplifier to unfold this saturated application
- -- We do this rather than generate an HsCon directly, because
- -- it means that the special cases (e.g. dictionary with only one
- -- member) are dealt with by the common MkId.mkDataConWrapId code rather
- -- than needing to be repeated here.
-
- dict_bind = noLoc (VarBind this_dict_id dict_rhs)
- all_binds = dict_bind `consBag` (sc_binds `unionBags` meth_binds)
-
- main_bind = noLoc $ AbsBinds
- inst_tyvars'
- (map instToId dfun_arg_dicts)
- [(inst_tyvars', dfun_id, this_dict_id,
- inline_prag ++ prags)]
- all_binds
- in
- showLIE (text "instance") `thenM_`
- returnM (unitBag main_bind)
+ inline_prag | null dfun_dicts = []
+ | otherwise = [L loc (InlinePrag (Inline AlwaysActive True))]
+ -- Always inline the dfun; this is an experimental decision
+ -- because it makes a big performance difference sometimes.
+ -- Often it means we can do the method selection, and then
+ -- inline the method as well. Marcin's idea; see comments below.
+ --
+ -- BUT: don't inline it if it's a constant dictionary;
+ -- we'll get all the benefit without inlining, and we get
+ -- a **lot** of code duplication if we inline it
+ --
+ -- See Note [Inline dfuns] below
+
+ sc_dict_vars = map instToVar sc_dicts
+ dict_bind = L loc (VarBind this_dict_id dict_rhs)
+ dict_rhs = foldl (\ f a -> L loc (HsApp f (L loc a))) inst_constr meth_exprs
+ inst_constr = L loc $ wrapId (mkWpApps sc_dict_vars <.> mkWpTyApps inst_tys')
+ (dataConWrapId dict_constr)
+ -- We don't produce a binding for the dict_constr; instead we
+ -- rely on the simplifier to unfold this saturated application
+ -- We do this rather than generate an HsCon directly, because
+ -- it means that the special cases (e.g. dictionary with only one
+ -- member) are dealt with by the common MkId.mkDataConWrapId code rather
+ -- than needing to be repeated here.
+
+
+ main_bind = noLoc $ AbsBinds
+ inst_tyvars'
+ dfun_lam_vars
+ [(inst_tyvars', dfun_id, this_dict_id, inline_prag ++ prags)]
+ (dict_bind `consBag` sc_binds)
+
+ showLIE (text "instance")
+ return (main_bind `consBag` unionManyBags meth_binds)
+\end{code}
+Note [Recursive superclasses]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+See Trac #1470 for why we would *like* to add "this_dict" to the
+available instances here. But we can't do so because then the superclases
+get satisfied by selection from this_dict, and that leads to an immediate
+loop. What we need is to add this_dict to Avails without adding its
+superclasses, and we currently have no way to do that.
-tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
- avail_insts op_items monobinds uprags
- = -- Check that all the method bindings come from this class
- let
- sel_names = [idName sel_id | (sel_id, _) <- op_items]
- bad_bndrs = collectHsBindBinders monobinds `minusList` sel_names
- in
- mappM (addErrTc . badMethodErr clas) bad_bndrs `thenM_`
- -- Make the method bindings
- let
- mk_method_bind = mkMethodBind origin clas inst_tys' monobinds
- in
- mapAndUnzipM mk_method_bind op_items `thenM` \ (meth_insts, meth_infos) ->
-
- -- And type check them
- -- It's really worth making meth_insts available to the tcMethodBind
- -- Consider instance Monad (ST s) where
- -- {-# INLINE (>>) #-}
- -- (>>) = ...(>>=)...
- -- If we don't include meth_insts, we end up with bindings like this:
- -- rec { dict = MkD then bind ...
- -- then = inline_me (... (GHC.Base.>>= dict) ...)
- -- bind = ... }
- -- The trouble is that (a) 'then' and 'dict' are mutually recursive,
- -- and (b) the inline_me prevents us inlining the >>= selector, which
- -- would unravel the loop. Result: (>>) ends up as a loop breaker, and
- -- is not inlined across modules. Rather ironic since this does not
- -- happen without the INLINE pragma!
- --
- -- Solution: make meth_insts available, so that 'then' refers directly
- -- to the local 'bind' rather than going via the dictionary.
- --
- -- BUT WATCH OUT! If the method type mentions the class variable, then
- -- this optimisation is not right. Consider
- -- class C a where
- -- op :: Eq a => a
- --
- -- instance C Int where
- -- op = op
- -- The occurrence of 'op' on the rhs gives rise to a constraint
- -- op at Int
- -- The trouble is that the 'meth_inst' for op, which is 'available', also
- -- looks like 'op at Int'. But they are not the same.
- let
- prag_fn = mkPragFun uprags
- all_insts = avail_insts ++ catMaybes meth_insts
- sig_fn n = Just [] -- No scoped type variables, but every method has
- -- a type signature, in effect, so that we check
- -- the method has the right type
- tc_method_bind = tcMethodBind inst_tyvars' dfun_theta' all_insts sig_fn prag_fn
- meth_ids = [meth_id | (_,meth_id,_) <- meth_infos]
- in
+%************************************************************************
+%* *
+ Type-checking an instance method
+%* *
+%************************************************************************
- mapM tc_method_bind meth_infos `thenM` \ meth_binds_s ->
-
- returnM (meth_ids, unionManyBags meth_binds_s)
-\end{code}
+tcInstanceMethod
+- Make the method bindings, as a [(NonRec, HsBinds)], one per method
+- Remembering to use fresh Name (the instance method Name) as the binder
+- Bring the instance method Ids into scope, for the benefit of tcInstSig
+- Use sig_fn mapping instance method Name -> instance tyvars
+- Ditto prag_fn
+- Use tcValBinds to do the checking
+\begin{code}
+tcInstanceMethod :: SrcSpan -> Class -> [TcTyVar] -> [Inst]
+ -> TcThetaType -> [TcType]
+ -> Inst -> Id
+ -> TcPragFun -> LHsBinds Name
+ -> (Id, DefMeth)
+ -> TcM (HsExpr Id, LHsBinds Id)
+ -- The returned inst_meth_ids all have types starting
+ -- forall tvs. theta => ...
+
+tcInstanceMethod loc clas tyvars dfun_dicts theta inst_tys
+ this_dict dfun_id prag_fn binds_in (sel_id, dm_info)
+ = do { cloned_this <- cloneDict this_dict
+ -- Need to clone the dict in case it is floated out, and
+ -- then clashes with its friends
+ ; uniq1 <- newUnique
+ ; let local_meth_name = mkInternalName uniq1 sel_occ loc -- Same OccName
+ this_dict_bind = L loc $ VarBind (instToId cloned_this) $
+ L loc $ wrapId meth_wrapper dfun_id
+ mb_this_bind | null tyvars = Nothing
+ | otherwise = Just (cloned_this, this_dict_bind)
+ -- Only need the this_dict stuff if there are type variables
+ -- involved; otherwise overlap is not possible
+ -- See Note [Subtle interaction of recursion and overlap]
+
+ tc_body rn_bind = do { (meth_id, tc_binds) <- tcInstanceMethodBody
+ InstSkol clas tyvars dfun_dicts theta inst_tys
+ mb_this_bind sel_id
+ local_meth_name
+ meth_sig_fn meth_prag_fn rn_bind
+ ; return (wrapId meth_wrapper meth_id, tc_binds) }
+
+ ; case (findMethodBind sel_name local_meth_name binds_in, dm_info) of
+ -- There is a user-supplied method binding, so use it
+ (Just user_bind, _) -> tc_body user_bind
+
+ -- The user didn't supply a method binding, so we have to make
+ -- up a default binding, in a way depending on the default-method info
+
+ (Nothing, GenDefMeth) -> do -- Derivable type classes stuff
+ { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id local_meth_name
+ ; tc_body meth_bind }
+
+ (Nothing, NoDefMeth) -> do -- No default method in the class
+ { warn <- doptM Opt_WarnMissingMethods
+ ; warnTc (warn -- Warn only if -fwarn-missing-methods
+ && reportIfUnused (getOccName sel_id))
+ -- Don't warn about _foo methods
+ omitted_meth_warn
+ ; return (error_rhs, emptyBag) }
+
+ (Nothing, DefMeth) -> do -- An polymorphic default method
+ { -- Build the typechecked version directly,
+ -- without calling typecheck_method;
+ -- see Note [Default methods in instances]
+ dm_name <- lookupImportedName (mkDefMethRdrName sel_name)
+ -- Might not be imported, but will be an OrigName
+ ; dm_id <- tcLookupId dm_name
+ ; return (wrapId dm_wrapper dm_id, emptyBag) } }
+ where
+ sel_name = idName sel_id
+ sel_occ = nameOccName sel_name
+ this_dict_id = instToId this_dict
- ------------------------------
- [Inline dfuns] Inlining dfuns unconditionally
- ------------------------------
+ meth_prag_fn _ = prag_fn sel_name
+ meth_sig_fn _ = Just [] -- The 'Just' says "yes, there's a type sig"
+ -- But there are no scoped type variables from local_method_id
+ -- Only the ones from the instance decl itself, which are already
+ -- in scope. Example:
+ -- class C a where { op :: forall b. Eq b => ... }
+ -- instance C [c] where { op = <rhs> }
+ -- In <rhs>, 'c' is scope but 'b' is not!
-The code above unconditionally inlines dict funs. Here's why.
-Consider this program:
+ error_rhs = HsApp error_fun error_msg
+ error_fun = L loc $ wrapId (WpTyApp meth_tau) nO_METHOD_BINDING_ERROR_ID
+ error_msg = L loc (HsLit (HsStringPrim (mkFastString error_string)))
+ meth_tau = funResultTy (applyTys (idType sel_id) inst_tys)
+ error_string = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
- test :: Int -> Int -> Bool
- test x y = (x,y) == (y,x) || test y x
- -- Recursive to avoid making it inline.
+ dm_wrapper = WpApp this_dict_id <.> mkWpTyApps inst_tys
-This needs the (Eq (Int,Int)) instance. If we inline that dfun
-the code we end up with is good:
+ omitted_meth_warn :: SDoc
+ omitted_meth_warn = ptext (sLit "No explicit method nor default method for")
+ <+> quotes (ppr sel_id)
- Test.$wtest =
- \r -> case ==# [ww ww1] of wild {
- PrelBase.False -> Test.$wtest ww1 ww;
- PrelBase.True ->
- case ==# [ww1 ww] of wild1 {
- PrelBase.False -> Test.$wtest ww1 ww;
- PrelBase.True -> PrelBase.True [];
- };
- };
- Test.test = \r [w w1]
- case w of w2 {
- PrelBase.I# ww ->
- case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
- };
+ dfun_lam_vars = map instToVar dfun_dicts
+ meth_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys tyvars)
-If we don't inline the dfun, the code is not nearly as good:
- (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
- PrelBase.:DEq tpl1 tpl2 -> tpl2;
- };
-
- Test.$wtest =
- \r [ww ww1]
- let { y = PrelBase.I#! [ww1]; } in
- let { x = PrelBase.I#! [ww]; } in
- let { sat_slx = PrelTup.(,)! [y x]; } in
- let { sat_sly = PrelTup.(,)! [x y];
- } in
- case == sat_sly sat_slx of wild {
- PrelBase.False -> Test.$wtest ww1 ww;
- PrelBase.True -> PrelBase.True [];
- };
-
- Test.test =
- \r [w w1]
- case w of w2 {
- PrelBase.I# ww ->
- case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
- };
+wrapId :: HsWrapper -> id -> HsExpr id
+wrapId wrapper id = mkHsWrap wrapper (HsVar id)
+\end{code}
-Why doesn't GHC inline $fEq? Because it looks big:
+Note [Default methods in instances]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider this
- PrelTup.zdfEqZ1T{-rcX-}
- = \ @ a{-reT-} :: * @ b{-reS-} :: *
- zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
- zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
- let {
- zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
- zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
- let {
- zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
- zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
- let {
- zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
- zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
- ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
- case ds{-rf5-}
- of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
- case ds1{-rf4-}
- of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
- PrelBase.zaza{-r4e-}
- (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
- (zeze{-rf0-} a2{-reZ-} b2{-reY-})
- }
- } } in
- let {
- a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
- a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
- b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
- PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
- } in
- PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
+ class Baz v x where
+ foo :: x -> x
+ foo y = y
-and it's not as bad as it seems, because it's further dramatically
-simplified: only zeze2 is extracted and its body is simplified.
+ instance Baz Int Int
+
+From the class decl we get
+
+ $dmfoo :: forall v x. Baz v x => x -> x
+
+Notice that the type is ambiguous. That's fine, though. The instance decl generates
+
+ $dBazIntInt = MkBaz ($dmfoo Int Int $dBazIntInt)
+
+BUT this does mean we must generate the dictionary translation directly, rather
+than generating source-code and type-checking it. That was the bug ing
+Trac #1061. In any case it's less work to generate the translated version!
%************************************************************************
-%* *
+%* *
\subsection{Error messages}
-%* *
+%* *
%************************************************************************
\begin{code}
-instDeclCtxt1 hs_inst_ty
+instDeclCtxt1 :: LHsType Name -> SDoc
+instDeclCtxt1 hs_inst_ty
= inst_decl_ctxt (case unLoc hs_inst_ty of
- HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
- HsPredTy pred -> ppr pred
- other -> ppr hs_inst_ty) -- Don't expect this
+ HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
+ HsPredTy pred -> ppr pred
+ _ -> ppr hs_inst_ty) -- Don't expect this
+instDeclCtxt2 :: Type -> SDoc
instDeclCtxt2 dfun_ty
= inst_decl_ctxt (ppr (mkClassPred cls tys))
where
(_,_,cls,tys) = tcSplitDFunTy dfun_ty
-inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
-
-superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")
+inst_decl_ctxt :: SDoc -> SDoc
+inst_decl_ctxt doc = ptext (sLit "In the instance declaration for") <+> quotes doc
+
+superClassCtxt :: SDoc
+superClassCtxt = ptext (sLit "When checking the super-classes of an instance declaration")
+
+atInstCtxt :: Name -> SDoc
+atInstCtxt name = ptext (sLit "In the associated type instance for") <+>
+ quotes (ppr name)
+
+mustBeVarArgErr :: Type -> SDoc
+mustBeVarArgErr ty =
+ sep [ ptext (sLit "Arguments that do not correspond to a class parameter") <+>
+ ptext (sLit "must be variables")
+ , ptext (sLit "Instead of a variable, found") <+> ppr ty
+ ]
+
+wrongATArgErr :: Type -> Type -> SDoc
+wrongATArgErr ty instTy =
+ sep [ ptext (sLit "Type indexes must match class instance head")
+ , ptext (sLit "Found") <+> ppr ty <+> ptext (sLit "but expected") <+>
+ ppr instTy
+ ]
\end{code}
projects / ghc-hetmet.git / blobdiff