%
+% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
-\section[TcDeriv]{Deriving}
Handles @deriving@ clauses on @data@ declarations.
#include "HsVersions.h"
import HsSyn
-import DynFlags ( DynFlag(..) )
+import DynFlags
-import Generics ( mkTyConGenericBinds )
+import Generics
import TcRnMonad
-import TcMType ( checkValidInstance )
-import TcEnv ( newDFunName, pprInstInfoDetails,
- InstInfo(..), InstBindings(..), simpleInstInfoClsTy,
- tcLookupClass, tcLookupTyCon, tcExtendTyVarEnv
- )
-import TcGenDeriv -- Deriv stuff
-import InstEnv ( Instance, OverlapFlag, mkLocalInstance, instanceHead, extendInstEnvList )
-import Inst ( getOverlapFlag )
-import TcHsType ( tcHsDeriv )
-import TcSimplify ( tcSimplifyDeriv )
-
-import RnBinds ( rnMethodBinds, rnTopBinds )
-import RnEnv ( bindLocalNames )
-import HscTypes ( FixityEnv )
-
-import Class ( className, classArity, classKey, classTyVars, classSCTheta, Class )
-import Type ( zipOpenTvSubst, substTheta, pprThetaArrow, pprClassPred, mkTyVarTy )
-import ErrUtils ( dumpIfSet_dyn )
-import MkId ( mkDictFunId )
-import DataCon ( isNullarySrcDataCon, isVanillaDataCon, dataConOrigArgTys, dataConInstOrigArgTys )
-import Maybes ( catMaybes )
-import RdrName ( RdrName )
-import Name ( Name, getSrcLoc )
-import NameSet ( duDefs )
-import Type ( splitKindFunTys )
-import TyCon ( tyConTyVars, tyConDataCons, tyConArity, tyConHasGenerics,
- tyConStupidTheta, isProductTyCon, isDataTyCon, newTyConRhs,
- isEnumerationTyCon, isRecursiveTyCon, TyCon
- )
-import TcType ( TcType, ThetaType, mkTyVarTys, mkTyConApp, tcTyConAppTyCon,
- isUnLiftedType, mkClassPred, tyVarsOfType,
- isSubArgTypeKind, tcEqTypes, tcSplitAppTys, mkAppTys )
-import Var ( TyVar, tyVarKind, varName )
-import VarSet ( mkVarSet, subVarSet )
+import TcEnv
+import TcClassDcl( tcAddDeclCtxt ) -- Small helper
+import TcGenDeriv -- Deriv stuff
+import InstEnv
+import Inst
+import TcHsType
+import TcMType
+import TcSimplify
+
+import RnBinds
+import RnEnv
+import HscTypes
+
+import Class
+import Type
+import ErrUtils
+import MkId
+import DataCon
+import Maybes
+import RdrName
+import Name
+import NameSet
+import TyCon
+import TcType
+import Var
+import VarSet
import PrelNames
-import SrcLoc ( srcLocSpan, Located(..) )
-import Util ( zipWithEqual, sortLe, notNull )
-import ListSetOps ( removeDups, assocMaybe )
+import SrcLoc
+import Util
+import ListSetOps
import Outputable
import Bag
\end{code}
So, here are the synonyms for the ``equation'' structures:
\begin{code}
-type DerivEqn = (Name, Class, TyCon, [TyVar], DerivRhs)
- -- The Name is the name for the DFun we'll build
- -- The tyvars bind all the variables in the RHS
-
-pprDerivEqn (n,c,tc,tvs,rhs)
- = parens (hsep [ppr n, ppr c, ppr tc, ppr tvs] <+> equals <+> ppr rhs)
-
type DerivRhs = ThetaType
type DerivSoln = DerivRhs
+type DerivEqn = (SrcSpan, InstOrigin, Name, [TyVar], Class, Type, DerivRhs)
+ -- (span, orig, df, tvs, C, ty, rhs)
+ -- implies a dfun declaration of the form
+ -- df :: forall tvs. rhs => C ty
+ -- The Name is the name for the DFun we'll build
+ -- The tyvars bind all the variables in the RHS
+ -- For family indexes, the tycon is the *family* tycon
+ -- (not the representation tycon)
+
+pprDerivEqn :: DerivEqn -> SDoc
+pprDerivEqn (l, _, n, tvs, c, ty, rhs)
+ = parens (hsep [ppr l, ppr n, ppr tvs, ppr c, ppr ty]
+ <+> equals <+> ppr rhs)
\end{code}
\begin{code}
tcDeriving :: [LTyClDecl Name] -- All type constructors
+ -> [LDerivDecl Name] -- All stand-alone deriving declarations
-> TcM ([InstInfo], -- The generated "instance decls"
HsValBinds Name) -- Extra generated top-level bindings
-tcDeriving tycl_decls
+tcDeriving tycl_decls deriv_decls
= recoverM (returnM ([], emptyValBindsOut)) $
do { -- Fish the "deriving"-related information out of the TcEnv
-- and make the necessary "equations".
- overlap_flag <- getOverlapFlag
- ; (ordinary_eqns, newtype_inst_info) <- makeDerivEqns overlap_flag tycl_decls
+ ; (ordinary_eqns, newtype_inst_info) <- makeDerivEqns tycl_decls deriv_decls
; (ordinary_inst_info, deriv_binds)
<- extendLocalInstEnv (map iSpec newtype_inst_info) $
- deriveOrdinaryStuff overlap_flag ordinary_eqns
+ deriveOrdinaryStuff ordinary_eqns
-- Add the newtype-derived instances to the inst env
-- before tacking the "ordinary" ones
= vcat (map pprInstInfoDetails inst_infos) $$ ppr extra_binds
-----------------------------------------
-deriveOrdinaryStuff overlap_flag [] -- Short cut
+deriveOrdinaryStuff [] -- Short cut
= returnM ([], emptyLHsBinds)
-deriveOrdinaryStuff overlap_flag eqns
+deriveOrdinaryStuff eqns
= do { -- Take the equation list and solve it, to deliver a list of
-- solutions, a.k.a. the contexts for the instance decls
-- required for the corresponding equations.
- inst_specs <- solveDerivEqns overlap_flag eqns
+ overlap_flag <- getOverlapFlag
+ ; inst_specs <- solveDerivEqns overlap_flag eqns
-- Generate the InstInfo for each dfun,
-- plus any auxiliary bindings it needs
; extra_binds <- genTaggeryBinds inst_infos
-- Done
- ; returnM (inst_infos, unionManyBags (extra_binds : aux_binds_s))
+ ; returnM (map fst inst_infos,
+ unionManyBags (extra_binds : aux_binds_s))
}
-----------------------------------------
[See Appendix~E in the Haskell~1.2 report.] This code here deals w/
all those.
+Note [Newtype deriving superclasses]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The 'tys' here come from the partial application in the deriving
+clause. The last arg is the new instance type.
+
+We must pass the superclasses; the newtype might be an instance
+of them in a different way than the representation type
+E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
+Then the Show instance is not done via isomorphism; it shows
+ Foo 3 as "Foo 3"
+The Num instance is derived via isomorphism, but the Show superclass
+dictionary must the Show instance for Foo, *not* the Show dictionary
+gotten from the Num dictionary. So we must build a whole new dictionary
+not just use the Num one. The instance we want is something like:
+ instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
+ (+) = ((+)@a)
+ ...etc...
+There may be a coercion needed which we get from the tycon for the newtype
+when the dict is constructed in TcInstDcls.tcInstDecl2
+
+
\begin{code}
-makeDerivEqns :: OverlapFlag
- -> [LTyClDecl Name]
+makeDerivEqns :: [LTyClDecl Name]
+ -> [LDerivDecl Name]
-> TcM ([DerivEqn], -- Ordinary derivings
[InstInfo]) -- Special newtype derivings
-makeDerivEqns overlap_flag tycl_decls
- = mapAndUnzipM mk_eqn derive_these `thenM` \ (maybe_ordinaries, maybe_newtypes) ->
- returnM (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
- where
- ------------------------------------------------------------------
- derive_these :: [(NewOrData, Name, LHsType Name)]
- -- Find the (nd, TyCon, Pred) pairs that must be `derived'
- derive_these = [ (nd, tycon, pred)
- | L _ (TyData { tcdND = nd, tcdLName = L _ tycon,
- tcdDerivs = Just preds }) <- tycl_decls,
- pred <- preds ]
-
- ------------------------------------------------------------------
- mk_eqn :: (NewOrData, Name, LHsType Name) -> TcM (Maybe DerivEqn, Maybe InstInfo)
- -- We swizzle the tyvars and datacons out of the tycon
- -- to make the rest of the equation
- --
- -- The "deriv_ty" is a LHsType to take account of the fact that for newtype derivign
- -- we allow deriving (forall a. C [a]).
-
- mk_eqn (new_or_data, tycon_name, hs_deriv_ty)
- = tcLookupTyCon tycon_name `thenM` \ tycon ->
- setSrcSpan (srcLocSpan (getSrcLoc tycon)) $
- addErrCtxt (derivCtxt tycon) $
- tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
- -- the type variables for the type constructor
- tcHsDeriv hs_deriv_ty `thenM` \ (deriv_tvs, clas, tys) ->
- doptM Opt_GlasgowExts `thenM` \ gla_exts ->
- mk_eqn_help gla_exts new_or_data tycon deriv_tvs clas tys
-
- ------------------------------------------------------------------
- -- data/newtype T a = ... deriving( C t1 t2 )
- -- leads to a call to mk_eqn_help with
- -- tycon = T, deriv_tvs = ftv(t1,t2), clas = C, tys = [t1,t2]
-
- mk_eqn_help gla_exts DataType tycon deriv_tvs clas tys
- | Just err <- checkSideConditions gla_exts tycon deriv_tvs clas tys
- = bale_out (derivingThingErr clas tys tycon (tyConTyVars tycon) err)
- | otherwise
- = do { eqn <- mkDataTypeEqn tycon clas
- ; returnM (Just eqn, Nothing) }
-
- mk_eqn_help gla_exts NewType tycon deriv_tvs clas tys
- | can_derive_via_isomorphism && (gla_exts || std_class_via_iso clas)
- = -- Go ahead and use the isomorphism
- traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) `thenM_`
- new_dfun_name clas tycon `thenM` \ dfun_name ->
- returnM (Nothing, Just (InstInfo { iSpec = mk_inst_spec dfun_name,
- iBinds = NewTypeDerived rep_tys }))
- | std_class gla_exts clas
- = mk_eqn_help gla_exts DataType tycon deriv_tvs clas tys -- Go via bale-out route
-
- | otherwise -- Non-standard instance
- = bale_out (if gla_exts then
- cant_derive_err -- Too hard
- else
- non_std_err) -- Just complain about being a non-std instance
- where
- -- Here is the plan for newtype derivings. We see
- -- newtype T a1...an = T (t ak...an) deriving (.., C s1 .. sm, ...)
- -- where t is a type,
- -- ak...an is a suffix of a1..an
- -- ak...an do not occur free in t,
- -- (C s1 ... sm) is a *partial applications* of class C
- -- with the last parameter missing
- --
- -- We generate the instances
- -- instance C s1 .. sm (t ak...ap) => C s1 .. sm (T a1...ap)
- -- where T a1...ap is the partial application of the LHS of the correct kind
- -- and p >= k
- --
- -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
- -- instance Monad (ST s) => Monad (T s) where
- -- fail = coerce ... (fail @ ST s)
- -- (Actually we don't need the coerce, because non-rec newtypes are transparent
-
- clas_tyvars = classTyVars clas
- kind = tyVarKind (last clas_tyvars)
- -- Kind of the thing we want to instance
- -- e.g. argument kind of Monad, *->*
-
- (arg_kinds, _) = splitKindFunTys kind
- n_args_to_drop = length arg_kinds
- -- Want to drop 1 arg from (T s a) and (ST s a)
- -- to get instance Monad (ST s) => Monad (T s)
+makeDerivEqns tycl_decls deriv_decls
+ = do { eqns1 <- mapM deriveTyData $
+ [ (p,d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- tycl_decls
+ , p <- preds ]
+ ; eqns2 <- mapM deriveStandalone deriv_decls
+ ; return ([eqn | (Just eqn, _) <- eqns1 ++ eqns2],
+ [inst | (_, Just inst) <- eqns1 ++ eqns2]) }
- -- Note [newtype representation]
- -- Need newTyConRhs *not* newTyConRep to get the representation
- -- type, because the latter looks through all intermediate newtypes
- -- For example
- -- newtype B = MkB Int
- -- newtype A = MkA B deriving( Num )
- -- We want the Num instance of B, *not* the Num instance of Int,
- -- when making the Num instance of A!
- (tc_tvs, rep_ty) = newTyConRhs tycon
- (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
-
- n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
- tyvars_to_drop = drop n_tyvars_to_keep tc_tvs
- tyvars_to_keep = take n_tyvars_to_keep tc_tvs
-
- n_args_to_keep = length rep_ty_args - n_args_to_drop
- args_to_drop = drop n_args_to_keep rep_ty_args
- args_to_keep = take n_args_to_keep rep_ty_args
-
- rep_fn' = mkAppTys rep_fn args_to_keep
- rep_tys = tys ++ [rep_fn']
- rep_pred = mkClassPred clas rep_tys
- -- rep_pred is the representation dictionary, from where
- -- we are gong to get all the methods for the newtype dictionary
-
- inst_tys = (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)])
- -- The 'tys' here come from the partial application
- -- in the deriving clause. The last arg is the new
- -- instance type.
-
- -- We must pass the superclasses; the newtype might be an instance
- -- of them in a different way than the representation type
- -- E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
- -- Then the Show instance is not done via isomorphism; it shows
- -- Foo 3 as "Foo 3"
- -- The Num instance is derived via isomorphism, but the Show superclass
- -- dictionary must the Show instance for Foo, *not* the Show dictionary
- -- gotten from the Num dictionary. So we must build a whole new dictionary
- -- not just use the Num one. The instance we want is something like:
- -- instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
- -- (+) = ((+)@a)
- -- ...etc...
- -- There's no 'corece' needed because after the type checker newtypes
- -- are transparent.
-
- sc_theta = substTheta (zipOpenTvSubst clas_tyvars inst_tys)
- (classSCTheta clas)
-
- -- If there are no tyvars, there's no need
- -- to abstract over the dictionaries we need
- dict_tvs = deriv_tvs ++ tc_tvs
- dict_args | null dict_tvs = []
- | otherwise = rep_pred : sc_theta
-
- -- Finally! Here's where we build the dictionary Id
- mk_inst_spec dfun_name
- = mkLocalInstance dfun overlap_flag
- where
- dfun = mkDictFunId dfun_name dict_tvs dict_args clas inst_tys
-
- -------------------------------------------------------------------
- -- Figuring out whether we can only do this newtype-deriving thing
-
- right_arity = length tys + 1 == classArity clas
-
- -- Never derive Read,Show,Typeable,Data this way
- non_iso_classes = [readClassKey, showClassKey, typeableClassKey, dataClassKey]
- can_derive_via_isomorphism
- = not (getUnique clas `elem` non_iso_classes)
- && right_arity -- Well kinded;
- -- eg not: newtype T ... deriving( ST )
- -- because ST needs *2* type params
- && n_tyvars_to_keep >= 0 -- Type constructor has right kind:
- -- eg not: newtype T = T Int deriving( Monad )
- && n_args_to_keep >= 0 -- Rep type has right kind:
- -- eg not: newtype T a = T Int deriving( Monad )
- && eta_ok -- Eta reduction works
- && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
- -- newtype A = MkA [A]
- -- Don't want
- -- instance Eq [A] => Eq A !!
- -- Here's a recursive newtype that's actually OK
- -- newtype S1 = S1 [T1 ()]
- -- newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
- -- It's currently rejected. Oh well.
- -- In fact we generate an instance decl that has method of form
- -- meth @ instTy = meth @ repTy
- -- (no coerce's). We'd need a coerce if we wanted to handle
- -- recursive newtypes too
-
- -- Check that eta reduction is OK
- -- (a) the dropped-off args are identical
- -- (b) the remaining type args mention
- -- only the remaining type variables
- eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
- && (tyVarsOfType rep_fn' `subVarSet` mkVarSet tyvars_to_keep)
-
- cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
- (vcat [ptext SLIT("even with cunning newtype deriving:"),
- if isRecursiveTyCon tycon then
- ptext SLIT("the newtype is recursive")
- else empty,
- if not right_arity then
- quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("does not have arity 1")
- else empty,
- if not (n_tyvars_to_keep >= 0) then
- ptext SLIT("the type constructor has wrong kind")
- else if not (n_args_to_keep >= 0) then
- ptext SLIT("the representation type has wrong kind")
- else if not eta_ok then
- ptext SLIT("the eta-reduction property does not hold")
- else empty
- ])
+------------------------------------------------------------------
+deriveStandalone :: LDerivDecl Name -> TcM (Maybe DerivEqn, Maybe InstInfo)
+-- Standalone deriving declarations
+-- e.g. derive instance Show T
+-- Rather like tcLocalInstDecl
+deriveStandalone (L loc (DerivDecl deriv_ty))
+ = setSrcSpan loc $
+ addErrCtxt (standaloneCtxt deriv_ty) $
+ do { (tvs, theta, tau) <- tcHsInstHead deriv_ty
+ ; (cls, inst_tys) <- checkValidInstHead tau
+ ; let cls_tys = take (length inst_tys - 1) inst_tys
+ inst_ty = last inst_tys
+
+ ; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty }
- non_std_err = derivingThingErr clas tys tycon tyvars_to_keep
- (vcat [non_std_why clas,
- ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")])
+------------------------------------------------------------------
+deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM (Maybe DerivEqn, Maybe InstInfo)
+deriveTyData (deriv_pred, L loc decl@(TyData { tcdLName = L _ tycon_name,
+ tcdTyVars = tv_names,
+ tcdTyPats = ty_pats }))
+ = setSrcSpan loc $
+ tcAddDeclCtxt decl $
+ do { let hs_ty_args = ty_pats `orElse` map (nlHsTyVar . hsLTyVarName) tv_names
+ hs_app = nlHsTyConApp tycon_name hs_ty_args
+ -- We get kinding info for the tyvars by typechecking (T a b)
+ -- Hence forming a tycon application and then dis-assembling it
+ ; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app
+ ; tcExtendTyVarEnv tvs $ -- Deriving preds may (now) mention
+ -- the type variables for the type constructor
+ do { (deriv_tvs, cls, cls_tys) <- tcHsDeriv deriv_pred
+ -- The "deriv_pred" is a LHsType to take account of the fact that for
+ -- newtype deriving we allow deriving (forall a. C [a]).
+ ; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys tc_app } }
- bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing)
+------------------------------------------------------------------
+mkEqnHelp orig tvs cls cls_tys tc_app
+ | Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app
+ = do { -- Make tc_app saturated, because that's what the
+ -- mkDataTypeEqn things expect
+ -- It might not be saturated in the standalone deriving case
+ -- derive instance Monad (T a)
+ let extra_tvs = dropList tc_args (tyConTyVars tycon)
+ full_tc_args = tc_args ++ mkTyVarTys extra_tvs
+ full_tvs = tvs ++ extra_tvs
+
+ ; (rep_tc, rep_tc_args) <- tcLookupFamInst tycon full_tc_args
+
+ ; gla_exts <- doptM Opt_GlasgowExts
+ ; overlap_flag <- getOverlapFlag
+ ; if isDataTyCon tycon then
+ mkDataTypeEqn orig gla_exts full_tvs cls cls_tys
+ tycon full_tc_args rep_tc rep_tc_args
+ else
+ mkNewTypeEqn orig gla_exts overlap_flag full_tvs cls cls_tys
+ tycon full_tc_args rep_tc rep_tc_args }
+ | otherwise
+ = baleOut (derivingThingErr cls cls_tys tc_app
+ (ptext SLIT("Last argument of the instance must be a type application")))
-std_class gla_exts clas
- = key `elem` derivableClassKeys
- || (gla_exts && (key == typeableClassKey || key == dataClassKey))
- where
- key = classKey clas
-
-std_class_via_iso clas -- These standard classes can be derived for a newtype
- -- using the isomorphism trick *even if no -fglasgow-exts*
- = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
- -- Not Read/Show because they respect the type
- -- Not Enum, becuase newtypes are never in Enum
+baleOut err = addErrTc err >> returnM (Nothing, Nothing)
+\end{code}
-new_dfun_name clas tycon -- Just a simple wrapper
- = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
- -- The type passed to newDFunName is only used to generate
- -- a suitable string; hence the empty type arg list
+%************************************************************************
+%* *
+ Deriving data types
+%* *
+%************************************************************************
-------------------------------------------------------------------
-mkDataTypeEqn :: TyCon -> Class -> TcM DerivEqn
-mkDataTypeEqn tycon clas
- | clas `hasKey` typeableClassKey
+\begin{code}
+mkDataTypeEqn orig gla_exts tvs cls cls_tys tycon tc_args rep_tc rep_tc_args
+ | Just err <- checkSideConditions gla_exts cls cls_tys tycon tc_args
+ = baleOut (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) err)
+
+ | otherwise
+ = ASSERT( null cls_tys )
+ do { loc <- getSrcSpanM
+ ; eqn <- mk_data_eqn loc orig tvs cls tycon tc_args rep_tc rep_tc_args
+ ; return (Just eqn, Nothing) }
+
+mk_data_eqn :: SrcSpan -> InstOrigin -> [TyVar] -> Class
+ -> TyCon -> [TcType] -> TyCon -> [TcType] -> TcM DerivEqn
+mk_data_eqn loc orig tvs cls tycon tc_args rep_tc rep_tc_args
+ | cls `hasKey` typeableClassKey
= -- The Typeable class is special in several ways
-- data T a b = ... deriving( Typeable )
-- gives
-- Typeable; it depends on the arity of the type
do { real_clas <- tcLookupClass (typeableClassNames !! tyConArity tycon)
; dfun_name <- new_dfun_name real_clas tycon
- ; return (dfun_name, real_clas, tycon, [], []) }
+ ; return (loc, orig, dfun_name, [], real_clas, mkTyConApp tycon [], []) }
| otherwise
- = do { dfun_name <- new_dfun_name clas tycon
- ; return (dfun_name, clas, tycon, tyvars, constraints) }
- where
- tyvars = tyConTyVars tycon
- constraints = extra_constraints ++ ordinary_constraints
- extra_constraints = tyConStupidTheta tycon
- -- "extra_constraints": see note [Data decl contexts] above
-
- ordinary_constraints
- = [ mkClassPred clas [arg_ty]
- | data_con <- tyConDataCons tycon,
- arg_ty <- dataConInstOrigArgTys data_con (map mkTyVarTy (tyConTyVars tycon)),
- not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
- ]
-
+ = do { dfun_name <- new_dfun_name cls tycon
+ ; let ordinary_constraints
+ = [ mkClassPred cls [arg_ty]
+ | data_con <- tyConDataCons rep_tc,
+ arg_ty <- dataConInstOrigArgTys data_con rep_tc_args,
+ not (isUnLiftedType arg_ty) ] -- No constraints for unlifted types?
+
+ tiresome_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args
+ stupid_constraints = substTheta tiresome_subst (tyConStupidTheta rep_tc)
+ -- see note [Data decl contexts] above
+
+ ; return (loc, orig, dfun_name, tvs, cls, mkTyConApp tycon tc_args,
+ stupid_constraints ++ ordinary_constraints)
+ }
------------------------------------------------------------------
-- Check side conditions that dis-allow derivability for particular classes
-- This is *apart* from the newtype-deriving mechanism
-checkSideConditions :: Bool -> TyCon -> [TyVar] -> Class -> [TcType] -> Maybe SDoc
-checkSideConditions gla_exts tycon deriv_tvs clas tys
- | notNull deriv_tvs || notNull tys
+checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> [TcType] -> Maybe SDoc
+checkSideConditions gla_exts cls cls_tys tycon tc_tys
+ | notNull cls_tys
= Just ty_args_why -- e.g. deriving( Foo s )
| otherwise
- = case [cond | (key,cond) <- sideConditions, key == getUnique clas] of
- [] -> Just (non_std_why clas)
+ = case [cond | (key,cond) <- sideConditions, key == getUnique cls] of
+ [] -> Just (non_std_why cls)
[cond] -> cond (gla_exts, tycon)
- other -> pprPanic "checkSideConditions" (ppr clas)
+ other -> pprPanic "checkSideConditions" (ppr cls)
where
- ty_args_why = quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("is not a class")
+ ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("is not a class")
-non_std_why clas = quotes (ppr clas) <+> ptext SLIT("is not a derivable class")
+non_std_why cls = quotes (ppr cls) <+> ptext SLIT("is not a derivable class")
sideConditions :: [(Unique, Condition)]
sideConditions
-- Currently: (a) args all of kind *
-- (b) 7 or fewer args
cond_typeableOK (gla_exts, tycon)
- | tyConArity tycon > 7 = Just too_many
- | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tycon)) = Just bad_kind
- | otherwise = Nothing
+ | tyConArity tycon > 7 = Just too_many
+ | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tycon))
+ = Just bad_kind
+ | isFamInstTyCon tycon = Just fam_inst -- no Typable for family insts
+ | otherwise = Nothing
where
too_many = quotes (ppr tycon) <+> ptext SLIT("has too many arguments")
- bad_kind = quotes (ppr tycon) <+> ptext SLIT("has arguments of kind other than `*'")
+ bad_kind = quotes (ppr tycon) <+>
+ ptext SLIT("has arguments of kind other than `*'")
+ fam_inst = quotes (ppr tycon) <+> ptext SLIT("is a type family")
cond_glaExts :: Condition
cond_glaExts (gla_exts, tycon) | gla_exts = Nothing
| otherwise = Just why
where
why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class")
+
+std_class gla_exts clas
+ = key `elem` derivableClassKeys
+ || (gla_exts && (key == typeableClassKey || key == dataClassKey))
+ where
+ key = classKey clas
+
+std_class_via_iso clas -- These standard classes can be derived for a newtype
+ -- using the isomorphism trick *even if no -fglasgow-exts*
+ = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
+ -- Not Read/Show because they respect the type
+ -- Not Enum, becuase newtypes are never in Enum
+
+
+new_dfun_name clas tycon -- Just a simple wrapper
+ = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
+ -- The type passed to newDFunName is only used to generate
+ -- a suitable string; hence the empty type arg list
\end{code}
+
+%************************************************************************
+%* *
+ Deriving newtypes
+%* *
+%************************************************************************
+
+\begin{code}
+mkNewTypeEqn orig gla_exts overlap_flag tvs cls cls_tys
+ tycon tc_args
+ rep_tycon rep_tc_args
+ | can_derive_via_isomorphism && (gla_exts || std_class_via_iso cls)
+ = do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys)
+ ; -- Go ahead and use the isomorphism
+ dfun_name <- new_dfun_name cls tycon
+ ; return (Nothing, Just (InstInfo { iSpec = mk_inst_spec dfun_name,
+ iBinds = NewTypeDerived ntd_info })) }
+ | std_class gla_exts cls
+ = mkDataTypeEqn orig gla_exts tvs cls cls_tys tycon tc_args rep_tycon rep_tc_args -- Go via bale-out route
+
+ -- Otherwise its a non-standard instance
+ | gla_exts = baleOut cant_derive_err -- Too hard
+ | otherwise = baleOut non_std_err -- Just complain about being a non-std instance
+ where
+ -- Here is the plan for newtype derivings. We see
+ -- newtype T a1...an = MkT (t ak+1...an) deriving (.., C s1 .. sm, ...)
+ -- where t is a type,
+ -- ak+1...an is a suffix of a1..an, and are all tyars
+ -- ak+1...an do not occur free in t, nor in the s1..sm
+ -- (C s1 ... sm) is a *partial applications* of class C
+ -- with the last parameter missing
+ -- (T a1 .. ak) matches the kind of C's last argument
+ -- (and hence so does t)
+ --
+ -- We generate the instance
+ -- instance forall ({a1..ak} u fvs(s1..sm)).
+ -- C s1 .. sm t => C s1 .. sm (T a1...ak)
+ -- where T a1...ap is the partial application of
+ -- the LHS of the correct kind and p >= k
+ --
+ -- NB: the variables below are:
+ -- tc_tvs = [a1, ..., an]
+ -- tyvars_to_keep = [a1, ..., ak]
+ -- rep_ty = t ak .. an
+ -- deriv_tvs = fvs(s1..sm) \ tc_tvs
+ -- tys = [s1, ..., sm]
+ -- rep_fn' = t
+ --
+ -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
+ -- We generate the instance
+ -- instance Monad (ST s) => Monad (T s) where
+
+ cls_tyvars = classTyVars cls
+ kind = tyVarKind (last cls_tyvars)
+ -- Kind of the thing we want to instance
+ -- e.g. argument kind of Monad, *->*
+
+ (arg_kinds, _) = splitKindFunTys kind
+ n_args_to_drop = length arg_kinds
+ -- Want to drop 1 arg from (T s a) and (ST s a)
+ -- to get instance Monad (ST s) => Monad (T s)
+
+ -- Note [newtype representation]
+ -- Need newTyConRhs *not* newTyConRep to get the representation
+ -- type, because the latter looks through all intermediate newtypes
+ -- For example
+ -- newtype B = MkB Int
+ -- newtype A = MkA B deriving( Num )
+ -- We want the Num instance of B, *not* the Num instance of Int,
+ -- when making the Num instance of A!
+ rep_ty = newTyConInstRhs rep_tycon rep_tc_args
+ (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
+
+ n_tyargs_to_keep = tyConArity tycon - n_args_to_drop
+ dropped_tc_args = drop n_tyargs_to_keep tc_args
+ dropped_tvs = tyVarsOfTypes dropped_tc_args
+
+ n_args_to_keep = length rep_ty_args - n_args_to_drop
+ args_to_drop = drop n_args_to_keep rep_ty_args
+ args_to_keep = take n_args_to_keep rep_ty_args
+
+ rep_fn' = mkAppTys rep_fn args_to_keep
+ rep_tys = cls_tys ++ [rep_fn']
+ rep_pred = mkClassPred cls rep_tys
+ -- rep_pred is the representation dictionary, from where
+ -- we are gong to get all the methods for the newtype
+ -- dictionary
+
+ tc_app = mkTyConApp tycon (take n_tyargs_to_keep tc_args)
+
+ -- Next we figure out what superclass dictionaries to use
+ -- See Note [Newtype deriving superclasses] above
+
+ inst_tys = cls_tys ++ [tc_app]
+ sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys)
+ (classSCTheta cls)
+
+ -- If there are no tyvars, there's no need
+ -- to abstract over the dictionaries we need
+ -- Example: newtype T = MkT Int deriving( C )
+ -- We get the derived instance
+ -- instance C T
+ -- rather than
+ -- instance C Int => C T
+ dict_tvs = filterOut (`elemVarSet` dropped_tvs) tvs
+ all_preds = rep_pred : sc_theta -- NB: rep_pred comes first
+ (dict_args, ntd_info) | null dict_tvs = ([], Just all_preds)
+ | otherwise = (all_preds, Nothing)
+
+ -- Finally! Here's where we build the dictionary Id
+ mk_inst_spec dfun_name = mkLocalInstance dfun overlap_flag
+ where
+ dfun = mkDictFunId dfun_name dict_tvs dict_args cls inst_tys
+
+ -------------------------------------------------------------------
+ -- Figuring out whether we can only do this newtype-deriving thing
+
+ right_arity = length cls_tys + 1 == classArity cls
+
+ -- Never derive Read,Show,Typeable,Data this way
+ non_iso_classes = [readClassKey, showClassKey, typeableClassKey, dataClassKey]
+ can_derive_via_isomorphism
+ = not (getUnique cls `elem` non_iso_classes)
+ && right_arity -- Well kinded;
+ -- eg not: newtype T ... deriving( ST )
+ -- because ST needs *2* type params
+ && n_tyargs_to_keep >= 0 -- Type constructor has right kind:
+ -- eg not: newtype T = T Int deriving( Monad )
+ && n_args_to_keep >= 0 -- Rep type has right kind:
+ -- eg not: newtype T a = T Int deriving( Monad )
+ && eta_ok -- Eta reduction works
+ && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
+ -- newtype A = MkA [A]
+ -- Don't want
+ -- instance Eq [A] => Eq A !!
+ -- Here's a recursive newtype that's actually OK
+ -- newtype S1 = S1 [T1 ()]
+ -- newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
+ -- It's currently rejected. Oh well.
+ -- In fact we generate an instance decl that has method of form
+ -- meth @ instTy = meth @ repTy
+ -- (no coerce's). We'd need a coerce if we wanted to handle
+ -- recursive newtypes too
+
+ -- Check that eta reduction is OK
+ eta_ok = (args_to_drop `tcEqTypes` dropped_tc_args)
+ -- (a) the dropped-off args are identical in the source and rep type
+ -- newtype T a b = MkT (S [a] b) deriving( Monad )
+ -- Here the 'b' must be the same in the rep type (S [a] b)
+
+ && (tyVarsOfType rep_fn' `disjointVarSet` dropped_tvs)
+ -- (b) the remaining type args do not mention any of the dropped
+ -- type variables
+
+ && (tyVarsOfTypes cls_tys `disjointVarSet` dropped_tvs)
+ -- (c) the type class args do not mention any of the dropped type
+ -- variables
+
+ && all isTyVarTy dropped_tc_args
+ -- (d) in case of newtype family instances, the eta-dropped
+ -- arguments must be type variables (not more complex indexes)
+
+ cant_derive_err = derivingThingErr cls cls_tys tc_app
+ (vcat [ptext SLIT("even with cunning newtype deriving:"),
+ if isRecursiveTyCon tycon then
+ ptext SLIT("the newtype is recursive")
+ else empty,
+ if not right_arity then
+ quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("does not have arity 1")
+ else empty,
+ if not (n_tyargs_to_keep >= 0) then
+ ptext SLIT("the type constructor has wrong kind")
+ else if not (n_args_to_keep >= 0) then
+ ptext SLIT("the representation type has wrong kind")
+ else if not eta_ok then
+ ptext SLIT("the eta-reduction property does not hold")
+ else empty
+ ])
+
+ non_std_err = derivingThingErr cls cls_tys tc_app
+ (vcat [non_std_why cls,
+ ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")])
+\end{code}
+
+
%************************************************************************
%* *
\subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
-- This bunch is Absolutely minimal...
solveDerivEqns overlap_flag orig_eqns
- = iterateDeriv 1 initial_solutions
+ = do { traceTc (text "solveDerivEqns" <+> vcat (map pprDerivEqn orig_eqns))
+ ; iterateDeriv 1 initial_solutions }
where
-- The initial solutions for the equations claim that each
-- instance has an empty context; this solution is certainly
iterateDeriv (n+1) new_solns
------------------------------------------------------------------
- gen_soln (_, clas, tc,tyvars,deriv_rhs)
- = setSrcSpan (srcLocSpan (getSrcLoc tc)) $
- do { let inst_tys = [mkTyConApp tc (mkTyVarTys tyvars)]
- ; theta <- addErrCtxt (derivInstCtxt1 clas inst_tys) $
- tcSimplifyDeriv tc tyvars deriv_rhs
- ; addErrCtxt (derivInstCtxt2 theta clas inst_tys) $
- checkValidInstance tyvars theta clas inst_tys
- ; return (sortLe (<=) theta) } -- Canonicalise before returning the soluction
- where
-
+ gen_soln :: DerivEqn -> TcM [PredType]
+ gen_soln (loc, orig, _, tyvars, clas, inst_ty, deriv_rhs)
+ = setSrcSpan loc $
+ do { theta <- tcSimplifyDeriv orig tyvars deriv_rhs
+ ; addErrCtxt (derivInstCtxt theta clas [inst_ty]) $
+ do { checkNoErrs (checkValidInstance tyvars theta clas [inst_ty])
+ -- See Note [Deriving context]
+ -- If this fails, don't continue
+
+ -- Check for a bizarre corner case, when the derived instance decl should
+ -- have form instance C a b => D (T a) where ...
+ -- Note that 'b' isn't a parameter of T. This gives rise to all sorts
+ -- of problems; in particular, it's hard to compare solutions for
+ -- equality when finding the fixpoint. So I just rule it out for now.
+ ; let tv_set = mkVarSet tyvars
+ weird_preds = [pred | pred <- theta, not (tyVarsOfPred pred `subVarSet` tv_set)]
+ ; mapM_ (addErrTc . badDerivedPred) weird_preds
+
+ -- Claim: the result instance declaration is guaranteed valid
+ -- Hence no need to call:
+ -- checkValidInstance tyvars theta clas inst_tys
+ ; return (sortLe (<=) theta) } } -- Canonicalise before returning the solution
------------------------------------------------------------------
- mk_inst_spec (dfun_name, clas, tycon, tyvars, _) theta
+ mk_inst_spec :: DerivEqn -> DerivSoln -> Instance
+ mk_inst_spec (loc, orig, dfun_name, tyvars, clas, inst_ty, _) theta
= mkLocalInstance dfun overlap_flag
where
- dfun = mkDictFunId dfun_name tyvars theta clas
- [mkTyConApp tycon (mkTyVarTys tyvars)]
+ dfun = mkDictFunId dfun_name tyvars theta clas [inst_ty]
extendLocalInstEnv :: [Instance] -> TcM a -> TcM a
-- Add new locally-defined instances; don't bother to check
\end{itemize}
\begin{code}
--- Generate the InstInfo for the required instance,
+-- Generate the InstInfo for the required instance paired with the
+-- *representation* tycon for that instance,
-- plus any auxiliary bindings required
-genInst :: Instance -> TcM (InstInfo, LHsBinds RdrName)
+--
+-- Representation tycons differ from the tycon in the instance signature in
+-- case of instances for indexed families.
+--
+genInst :: Instance -> TcM ((InstInfo, TyCon), LHsBinds RdrName)
genInst spec
= do { fix_env <- getFixityEnv
; let
(tyvars,_,clas,[ty]) = instanceHead spec
clas_nm = className clas
- tycon = tcTyConAppTyCon ty
- (meth_binds, aux_binds) = genDerivBinds clas fix_env tycon
+ (visible_tycon, tyArgs) = tcSplitTyConApp ty
+
+ -- In case of a family instance, we need to use the representation
+ -- tycon (after all, it has the data constructors)
+ ; (tycon, _) <- tcLookupFamInst visible_tycon tyArgs
+ ; let (meth_binds, aux_binds) = genDerivBinds clas fix_env tycon
-- Bring the right type variables into
-- scope, and rename the method binds
-- It's a bit yukky that we return *renamed* InstInfo, but
-- *non-renamed* auxiliary bindings
; (rn_meth_binds, _fvs) <- discardWarnings $
- bindLocalNames (map varName tyvars) $
+ bindLocalNames (map Var.varName tyvars) $
rnMethodBinds clas_nm (\n -> []) [] meth_binds
-- Build the InstInfo
- ; return (InstInfo { iSpec = spec,
- iBinds = VanillaInst rn_meth_binds [] },
+ ; return ((InstInfo { iSpec = spec,
+ iBinds = VanillaInst rn_meth_binds [] }, tycon),
aux_binds)
- }
+ }
genDerivBinds clas fix_env tycon
| className clas `elem` typeableClassNames
If we have a @tag2con@ function, we also generate a @maxtag@ constant.
\begin{code}
-genTaggeryBinds :: [InstInfo] -> TcM (LHsBinds RdrName)
+genTaggeryBinds :: [(InstInfo, TyCon)] -> TcM (LHsBinds RdrName)
genTaggeryBinds infos
= do { names_so_far <- foldlM do_con2tag [] tycons_of_interest
; nm_alist_etc <- foldlM do_tag2con names_so_far tycons_of_interest
; return (listToBag (map gen_tag_n_con_monobind nm_alist_etc)) }
where
- all_CTs = [ (cls, tcTyConAppTyCon ty)
- | info <- infos,
- let (cls,ty) = simpleInstInfoClsTy info ]
+ all_CTs = [ (fst (simpleInstInfoClsTy info), tc)
+ | (info, tc) <- infos]
all_tycons = map snd all_CTs
(tycons_of_interest, _) = removeDups compare all_tycons
\end{code}
\begin{code}
-derivingThingErr clas tys tycon tyvars why
- = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
+derivingThingErr clas tys ty why
+ = sep [hsep [ptext SLIT("Can't make a derived instance of"),
+ quotes (ppr pred)],
nest 2 (parens why)]
where
- pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
+ pred = mkClassPred clas (tys ++ [ty])
-derivCtxt :: TyCon -> SDoc
-derivCtxt tycon
- = ptext SLIT("When deriving instances for") <+> quotes (ppr tycon)
+standaloneCtxt :: LHsType Name -> SDoc
+standaloneCtxt ty = ptext SLIT("In the stand-alone deriving instance for") <+> quotes (ppr ty)
-derivInstCtxt1 clas inst_tys
- = ptext SLIT("When deriving the instance for") <+> quotes (pprClassPred clas inst_tys)
+derivInstCtxt theta clas inst_tys
+ = hang (ptext SLIT("In the derived instance:"))
+ 2 (pprThetaArrow theta <+> pprClassPred clas inst_tys)
+-- Used for the ...Thetas variants; all top level
-derivInstCtxt2 theta clas inst_tys
- = vcat [ptext SLIT("In the derived instance declaration"),
- nest 2 (ptext SLIT("instance") <+> sep [pprThetaArrow theta,
- pprClassPred clas inst_tys])]
+badDerivedPred pred
+ = vcat [ptext SLIT("Can't derive instances where the instance context mentions"),
+ ptext SLIT("type variables that are not data type parameters"),
+ nest 2 (ptext SLIT("Offending constraint:") <+> ppr pred)]
\end{code}
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