%
+% (c) The University of Glasgow 2006
% (c) The AQUA Project, Glasgow University, 1998
%
-\section[StdIdInfo]{Standard unfoldings}
This module contains definitions for the IdInfo for things that
have a standard form, namely:
- * data constructors
- * record selectors
- * method and superclass selectors
- * primitive operations
+- data constructors
+- record selectors
+- method and superclass selectors
+- primitive operations
\begin{code}
module MkId (
- mkDictFunId, mkDefaultMethodId,
- mkDictSelId,
+ mkDictFunId, mkDefaultMethodId,
+ mkDictSelId,
- mkDataConIds,
- mkRecordSelId,
- mkPrimOpId, mkFCallId,
+ mkDataConIds,
+ mkPrimOpId, mkFCallId, mkTickBoxOpId, mkBreakPointOpId,
- mkReboxingAlt, wrapNewTypeBody, unwrapNewTypeBody,
+ mkReboxingAlt, wrapNewTypeBody, unwrapNewTypeBody,
+ wrapFamInstBody, unwrapFamInstScrut,
+ mkUnpackCase, mkProductBox,
- -- And some particular Ids; see below for why they are wired in
- wiredInIds, ghcPrimIds,
- unsafeCoerceId, realWorldPrimId, voidArgId, nullAddrId, seqId,
- lazyId, lazyIdUnfolding, lazyIdKey,
-
- mkRuntimeErrorApp,
- rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID, rUNTIME_ERROR_ID,
- nON_EXHAUSTIVE_GUARDS_ERROR_ID, nO_METHOD_BINDING_ERROR_ID,
- pAT_ERROR_ID, eRROR_ID,
-
- unsafeCoerceName
+ -- And some particular Ids; see below for why they are wired in
+ wiredInIds, ghcPrimIds,
+ unsafeCoerceName, unsafeCoerceId, realWorldPrimId,
+ voidArgId, nullAddrId, seqId, lazyId, lazyIdKey
) where
#include "HsVersions.h"
-
-import BasicTypes ( Arity, StrictnessMark(..), isMarkedUnboxed, isMarkedStrict )
-import Rules ( mkSpecInfo )
-import TysPrim ( openAlphaTyVars, alphaTyVar, alphaTy,
- realWorldStatePrimTy, addrPrimTy
- )
-import TysWiredIn ( charTy, mkListTy )
-import PrelRules ( primOpRules )
-import Type ( TyThing(..), mkForAllTy, tyVarsOfTypes )
-import Coercion ( mkSymCoercion, mkUnsafeCoercion )
-import TcType ( Type, ThetaType, mkDictTy, mkPredTys, mkPredTy,
- mkTyConApp, mkTyVarTys, mkClassPred,
- mkFunTys, mkFunTy, mkSigmaTy, tcSplitSigmaTy,
- isUnLiftedType, mkForAllTys, mkTyVarTy, tyVarsOfType,
- tcSplitFunTys, tcSplitForAllTys, dataConsStupidTheta
- )
-import CoreUtils ( exprType )
-import CoreUnfold ( mkTopUnfolding, mkCompulsoryUnfolding )
-import Literal ( nullAddrLit, mkStringLit )
-import TyCon ( TyCon, isNewTyCon, tyConDataCons, FieldLabel,
- tyConStupidTheta, isProductTyCon, isDataTyCon, isRecursiveTyCon,
- newTyConCo, tyConArity )
-import Class ( Class, classTyCon, classSelIds )
-import Var ( Id, TyVar, Var )
-import VarSet ( isEmptyVarSet, subVarSet, varSetElems )
-import Name ( mkFCallName, mkWiredInName, Name, BuiltInSyntax(..) )
-import OccName ( mkOccNameFS, varName )
-import PrimOp ( PrimOp, primOpSig, primOpOcc, primOpTag )
-import ForeignCall ( ForeignCall )
-import DataCon ( DataCon, DataConIds(..), dataConTyCon, dataConUnivTyVars,
- dataConFieldLabels, dataConRepArity, dataConResTys,
- dataConRepArgTys, dataConRepType,
- dataConSig, dataConStrictMarks, dataConExStricts,
- splitProductType, isVanillaDataCon, dataConFieldType,
- dataConInstOrigArgTys
- )
-import Id ( idType, mkGlobalId, mkVanillaGlobal, mkSysLocal,
- mkTemplateLocals, mkTemplateLocalsNum, mkExportedLocalId,
- mkTemplateLocal, idName
- )
-import IdInfo ( IdInfo, noCafIdInfo, setUnfoldingInfo,
- setArityInfo, setSpecInfo, setCafInfo,
- setAllStrictnessInfo, vanillaIdInfo,
- GlobalIdDetails(..), CafInfo(..)
- )
-import NewDemand ( mkStrictSig, DmdResult(..),
- mkTopDmdType, topDmd, evalDmd, lazyDmd, retCPR,
- Demand(..), Demands(..) )
-import DmdAnal ( dmdAnalTopRhs )
+import Rules
+import TysPrim
+import PrelRules
+import Type
+import Coercion
+import TcType
+import MkCore
+import CoreUtils ( exprType, mkCoerce )
+import CoreUnfold
+import Literal
+import TyCon
+import Class
+import VarSet
+import Name
+import PrimOp
+import ForeignCall
+import DataCon
+import Id
+import Var ( Var, TyVar, mkCoVar, mkExportedLocalVar )
+import IdInfo
+import Demand
import CoreSyn
-import Unique ( mkBuiltinUnique, mkPrimOpIdUnique )
-import Maybes
+import Unique
import PrelNames
-import Util ( dropList, isSingleton )
+import BasicTypes hiding ( SuccessFlag(..) )
+import Util
import Outputable
import FastString
-import ListSetOps ( assoc )
-\end{code}
+import ListSetOps
+import Module
+\end{code}
%************************************************************************
-%* *
+%* *
\subsection{Wired in Ids}
-%* *
+%* *
%************************************************************************
+Note [Wired-in Ids]
+~~~~~~~~~~~~~~~~~~~
+There are several reasons why an Id might appear in the wiredInIds:
+
+(1) The ghcPrimIds are wired in because they can't be defined in
+ Haskell at all, although the can be defined in Core. They have
+ compulsory unfoldings, so they are always inlined and they have
+ no definition site. Their home module is GHC.Prim, so they
+ also have a description in primops.txt.pp, where they are called
+ 'pseudoops'.
+
+(2) The 'error' function, eRROR_ID, is wired in because we don't yet have
+ a way to express in an interface file that the result type variable
+ is 'open'; that is can be unified with an unboxed type
+
+ [The interface file format now carry such information, but there's
+ no way yet of expressing at the definition site for these
+ error-reporting functions that they have an 'open'
+ result type. -- sof 1/99]
+
+(3) Other error functions (rUNTIME_ERROR_ID) are wired in (a) because
+ the desugarer generates code that mentiones them directly, and
+ (b) for the same reason as eRROR_ID
+
+(4) lazyId is wired in because the wired-in version overrides the
+ strictness of the version defined in GHC.Base
+
+In cases (2-4), the function has a definition in a library module, and
+can be called; but the wired-in version means that the details are
+never read from that module's interface file; instead, the full definition
+is right here.
+
\begin{code}
+wiredInIds :: [Id]
wiredInIds
- = [ -- These error-y things are wired in because we don't yet have
- -- a way to express in an interface file that the result type variable
- -- is 'open'; that is can be unified with an unboxed type
- --
- -- [The interface file format now carry such information, but there's
- -- no way yet of expressing at the definition site for these
- -- error-reporting functions that they have an 'open'
- -- result type. -- sof 1/99]
-
- eRROR_ID, -- This one isn't used anywhere else in the compiler
- -- But we still need it in wiredInIds so that when GHC
- -- compiles a program that mentions 'error' we don't
- -- import its type from the interface file; we just get
- -- the Id defined here. Which has an 'open-tyvar' type.
-
- rUNTIME_ERROR_ID,
- iRREFUT_PAT_ERROR_ID,
- nON_EXHAUSTIVE_GUARDS_ERROR_ID,
- nO_METHOD_BINDING_ERROR_ID,
- pAT_ERROR_ID,
- rEC_CON_ERROR_ID,
-
- lazyId
- ] ++ ghcPrimIds
+ = [lazyId]
+ ++ errorIds -- Defined in MkCore
+ ++ ghcPrimIds
-- These Ids are exported from GHC.Prim
+ghcPrimIds :: [Id]
ghcPrimIds
- = [ -- These can't be defined in Haskell, but they have
- -- perfectly reasonable unfoldings in Core
+ = [ -- These can't be defined in Haskell, but they have
+ -- perfectly reasonable unfoldings in Core
realWorldPrimId,
unsafeCoerceId,
nullAddrId,
\end{code}
%************************************************************************
-%* *
+%* *
\subsection{Data constructors}
-%* *
+%* *
%************************************************************************
The wrapper for a constructor is an ordinary top-level binding that evaluates
We're going to build a constructor that looks like:
- data (Data a, C b) => T a b = T1 !a !Int b
+ data (Data a, C b) => T a b = T1 !a !Int b
- T1 = /\ a b ->
- \d1::Data a, d2::C b ->
- \p q r -> case p of { p ->
- case q of { q ->
- Con T1 [a,b] [p,q,r]}}
+ T1 = /\ a b ->
+ \d1::Data a, d2::C b ->
+ \p q r -> case p of { p ->
+ case q of { q ->
+ Con T1 [a,b] [p,q,r]}}
Notice that
Making an explicit case expression allows the simplifier to eliminate
it in the (common) case where the constructor arg is already evaluated.
+Note [Wrappers for data instance tycons]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In the case of data instances, the wrapper also applies the coercion turning
+the representation type into the family instance type to cast the result of
+the wrapper. For example, consider the declarations
+
+ data family Map k :: * -> *
+ data instance Map (a, b) v = MapPair (Map a (Pair b v))
+
+The tycon to which the datacon MapPair belongs gets a unique internal
+name of the form :R123Map, and we call it the representation tycon.
+In contrast, Map is the family tycon (accessible via
+tyConFamInst_maybe). A coercion allows you to move between
+representation and family type. It is accessible from :R123Map via
+tyConFamilyCoercion_maybe and has kind
+
+ Co123Map a b v :: {Map (a, b) v ~ :R123Map a b v}
+
+The wrapper and worker of MapPair get the types
+
+ -- Wrapper
+ $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
+ $WMapPair a b v = MapPair a b v `cast` sym (Co123Map a b v)
+
+ -- Worker
+ MapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
+
+This coercion is conditionally applied by wrapFamInstBody.
+
+It's a bit more complicated if the data instance is a GADT as well!
+
+ data instance T [a] where
+ T1 :: forall b. b -> T [Maybe b]
+
+Hence we translate to
+
+ -- Wrapper
+ $WT1 :: forall b. b -> T [Maybe b]
+ $WT1 b v = T1 (Maybe b) b (Maybe b) v
+ `cast` sym (Co7T (Maybe b))
+
+ -- Worker
+ T1 :: forall c b. (c ~ Maybe b) => b -> :R7T c
+
+ -- Coercion from family type to representation type
+ Co7T a :: T [a] ~ :R7T a
\begin{code}
mkDataConIds :: Name -> Name -> DataCon -> DataConIds
mkDataConIds wrap_name wkr_name data_con
- | isNewTyCon tycon
- = NewDC nt_wrap_id
+ | isNewTyCon tycon -- Newtype, only has a worker
+ = DCIds Nothing nt_work_id
- | any isMarkedStrict all_strict_marks -- Algebraic, needs wrapper
- = AlgDC (Just alg_wrap_id) wrk_id
+ | any isBanged all_strict_marks -- Algebraic, needs wrapper
+ || not (null eq_spec) -- NB: LoadIface.ifaceDeclSubBndrs
+ || isFamInstTyCon tycon -- depends on this test
+ = DCIds (Just alg_wrap_id) wrk_id
- | otherwise -- Algebraic, no wrapper
- = AlgDC Nothing wrk_id
+ | otherwise -- Algebraic, no wrapper
+ = DCIds Nothing wrk_id
where
- (tvs, theta, orig_arg_tys) = dataConSig data_con
- tycon = dataConTyCon data_con
-
- dict_tys = mkPredTys theta
- all_arg_tys = dict_tys ++ orig_arg_tys
- tycon_args = dataConUnivTyVars data_con
- result_ty_args = (mkTyVarTys tycon_args)
- result_ty = mkTyConApp tycon result_ty_args
-
- wrap_ty = mkForAllTys tvs (mkFunTys all_arg_tys result_ty)
- -- We used to include the stupid theta in the wrapper's args
- -- but now we don't. Instead the type checker just injects these
- -- extra constraints where necessary.
-
- ----------- Worker (algebraic data types only) --------------
- -- The *worker* for the data constructor is the function that
- -- takes the representation arguments and builds the constructor.
+ (univ_tvs, ex_tvs, eq_spec,
+ eq_theta, dict_theta, orig_arg_tys, res_ty) = dataConFullSig data_con
+ tycon = dataConTyCon data_con -- The representation TyCon (not family)
+
+ ----------- Worker (algebraic data types only) --------------
+ -- The *worker* for the data constructor is the function that
+ -- takes the representation arguments and builds the constructor.
wrk_id = mkGlobalId (DataConWorkId data_con) wkr_name
- (dataConRepType data_con) wkr_info
+ (dataConRepType data_con) wkr_info
wkr_arity = dataConRepArity data_con
wkr_info = noCafIdInfo
- `setArityInfo` wkr_arity
- `setAllStrictnessInfo` Just wkr_sig
- `setUnfoldingInfo` evaldUnfolding -- Record that it's evaluated,
- -- even if arity = 0
+ `setArityInfo` wkr_arity
+ `setStrictnessInfo` Just wkr_sig
+ `setUnfoldingInfo` evaldUnfolding -- Record that it's evaluated,
+ -- even if arity = 0
wkr_sig = mkStrictSig (mkTopDmdType (replicate wkr_arity topDmd) cpr_info)
- -- Notice that we do *not* say the worker is strict
- -- even if the data constructor is declared strict
- -- e.g. data T = MkT !(Int,Int)
- -- Why? Because the *wrapper* is strict (and its unfolding has case
- -- expresssions that do the evals) but the *worker* itself is not.
- -- If we pretend it is strict then when we see
- -- case x of y -> $wMkT y
- -- the simplifier thinks that y is "sure to be evaluated" (because
- -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
- --
- -- When the simplifer sees a pattern
- -- case e of MkT x -> ...
- -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
- -- but that's fine... dataConRepStrictness comes from the data con
- -- not from the worker Id.
+ -- Note [Data-con worker strictness]
+ -- Notice that we do *not* say the worker is strict
+ -- even if the data constructor is declared strict
+ -- e.g. data T = MkT !(Int,Int)
+ -- Why? Because the *wrapper* is strict (and its unfolding has case
+ -- expresssions that do the evals) but the *worker* itself is not.
+ -- If we pretend it is strict then when we see
+ -- case x of y -> $wMkT y
+ -- the simplifier thinks that y is "sure to be evaluated" (because
+ -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
+ --
+ -- When the simplifer sees a pattern
+ -- case e of MkT x -> ...
+ -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
+ -- but that's fine... dataConRepStrictness comes from the data con
+ -- not from the worker Id.
cpr_info | isProductTyCon tycon &&
- isDataTyCon tycon &&
- wkr_arity > 0 &&
- wkr_arity <= mAX_CPR_SIZE = retCPR
- | otherwise = TopRes
- -- RetCPR is only true for products that are real data types;
- -- that is, not unboxed tuples or [non-recursive] newtypes
-
- ----------- Wrappers for newtypes --------------
- nt_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty nt_wrap_info
- nt_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
- `setArityInfo` 1 -- Arity 1
- `setUnfoldingInfo` newtype_unf
- newtype_unf = ASSERT( isVanillaDataCon data_con &&
- isSingleton orig_arg_tys )
- -- No existentials on a newtype, but it can have a context
- -- e.g. newtype Eq a => T a = MkT (...)
- mkCompulsoryUnfolding $
- mkLams tvs $ Lam id_arg1 $
- wrapNewTypeBody tycon result_ty_args
- (Var id_arg1)
-
- id_arg1 = mkTemplateLocal 1 (head orig_arg_tys)
-
- ----------- Wrappers for algebraic data types --------------
+ isDataTyCon tycon &&
+ wkr_arity > 0 &&
+ wkr_arity <= mAX_CPR_SIZE = retCPR
+ | otherwise = TopRes
+ -- RetCPR is only true for products that are real data types;
+ -- that is, not unboxed tuples or [non-recursive] newtypes
+
+ ----------- Workers for newtypes --------------
+ nt_work_id = mkGlobalId (DataConWrapId data_con) wkr_name wrap_ty nt_work_info
+ nt_work_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
+ `setArityInfo` 1 -- Arity 1
+ `setUnfoldingInfo` newtype_unf
+ id_arg1 = mkTemplateLocal 1 (head orig_arg_tys)
+ newtype_unf = ASSERT2( isVanillaDataCon data_con &&
+ isSingleton orig_arg_tys, ppr data_con )
+ -- Note [Newtype datacons]
+ mkCompulsoryUnfolding $
+ mkLams wrap_tvs $ Lam id_arg1 $
+ wrapNewTypeBody tycon res_ty_args (Var id_arg1)
+
+
+ ----------- Wrapper --------------
+ -- We used to include the stupid theta in the wrapper's args
+ -- but now we don't. Instead the type checker just injects these
+ -- extra constraints where necessary.
+ wrap_tvs = (univ_tvs `minusList` map fst eq_spec) ++ ex_tvs
+ res_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
+ eq_tys = mkPredTys eq_theta
+ dict_tys = mkPredTys dict_theta
+ wrap_ty = mkForAllTys wrap_tvs $ mkFunTys eq_tys $ mkFunTys dict_tys $
+ mkFunTys orig_arg_tys $ res_ty
+ -- NB: watch out here if you allow user-written equality
+ -- constraints in data constructor signatures
+
+ ----------- Wrappers for algebraic data types --------------
alg_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty alg_wrap_info
- alg_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
- `setArityInfo` alg_arity
- -- It's important to specify the arity, so that partial
- -- applications are treated as values
- `setUnfoldingInfo` alg_unf
- `setAllStrictnessInfo` Just wrap_sig
+ alg_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
+ `setArityInfo` wrap_arity
+ -- It's important to specify the arity, so that partial
+ -- applications are treated as values
+ `setUnfoldingInfo` wrap_unf
+ `setStrictnessInfo` Just wrap_sig
all_strict_marks = dataConExStricts data_con ++ dataConStrictMarks data_con
wrap_sig = mkStrictSig (mkTopDmdType arg_dmds cpr_info)
arg_dmds = map mk_dmd all_strict_marks
- mk_dmd str | isMarkedStrict str = evalDmd
- | otherwise = lazyDmd
- -- The Cpr info can be important inside INLINE rhss, where the
- -- wrapper constructor isn't inlined.
- -- And the argument strictness can be important too; we
- -- may not inline a contructor when it is partially applied.
- -- For example:
- -- data W = C !Int !Int !Int
- -- ...(let w = C x in ...(w p q)...)...
- -- we want to see that w is strict in its two arguments
-
- alg_unf = mkTopUnfolding $ Note InlineMe $
- mkLams tvs $
- mkLams dict_args $ mkLams id_args $
- foldr mk_case con_app
- (zip (dict_args ++ id_args) all_strict_marks)
- i3 []
-
- con_app i rep_ids = mkApps (Var wrk_id)
- (map varToCoreExpr (tvs ++ reverse rep_ids))
+ mk_dmd str | isBanged str = evalDmd
+ | otherwise = lazyDmd
+ -- The Cpr info can be important inside INLINE rhss, where the
+ -- wrapper constructor isn't inlined.
+ -- And the argument strictness can be important too; we
+ -- may not inline a contructor when it is partially applied.
+ -- For example:
+ -- data W = C !Int !Int !Int
+ -- ...(let w = C x in ...(w p q)...)...
+ -- we want to see that w is strict in its two arguments
+
+ wrap_unf = mkInlineRule wrap_rhs (Just (length dict_args + length id_args))
+ wrap_rhs = mkLams wrap_tvs $
+ mkLams eq_args $
+ mkLams dict_args $ mkLams id_args $
+ foldr mk_case con_app
+ (zip (dict_args ++ id_args) all_strict_marks)
+ i3 []
+
+ con_app _ rep_ids = wrapFamInstBody tycon res_ty_args $
+ Var wrk_id `mkTyApps` res_ty_args
+ `mkVarApps` ex_tvs
+ -- Equality evidence:
+ `mkTyApps` map snd eq_spec
+ `mkVarApps` eq_args
+ `mkVarApps` reverse rep_ids
(dict_args,i2) = mkLocals 1 dict_tys
(id_args,i3) = mkLocals i2 orig_arg_tys
- alg_arity = i3-1
+ wrap_arity = i3-1
+ (eq_args,_) = mkCoVarLocals i3 eq_tys
+
+ mkCoVarLocals i [] = ([],i)
+ mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
+ y = mkCoVar (mkSysTvName (mkBuiltinUnique i)
+ (fsLit "dc_co")) x
+ in (y:ys,j)
mk_case
- :: (Id, StrictnessMark) -- Arg, strictness
- -> (Int -> [Id] -> CoreExpr) -- Body
- -> Int -- Next rep arg id
- -> [Id] -- Rep args so far, reversed
- -> CoreExpr
+ :: (Id, HsBang) -- Arg, strictness
+ -> (Int -> [Id] -> CoreExpr) -- Body
+ -> Int -- Next rep arg id
+ -> [Id] -- Rep args so far, reversed
+ -> CoreExpr
mk_case (arg,strict) body i rep_args
- = case strict of
- NotMarkedStrict -> body i (arg:rep_args)
- MarkedStrict
- | isUnLiftedType (idType arg) -> body i (arg:rep_args)
- | otherwise ->
- Case (Var arg) arg result_ty [(DEFAULT,[], body i (arg:rep_args))]
-
- MarkedUnboxed
- ->case splitProductType "do_unbox" (idType arg) of
- (tycon, tycon_args, con, tys) ->
- Case (Var arg) arg result_ty
- [(DataAlt con,
- con_args,
- body i' (reverse con_args ++ rep_args))]
- where
- (con_args, i') = mkLocals i tys
+ = case strict of
+ HsNoBang -> body i (arg:rep_args)
+ HsUnpack -> unboxProduct i (Var arg) (idType arg) the_body
+ where
+ the_body i con_args = body i (reverse con_args ++ rep_args)
+ _other -- HsUnpackFailed and HsStrict
+ | isUnLiftedType (idType arg) -> body i (arg:rep_args)
+ | otherwise -> Case (Var arg) arg res_ty
+ [(DEFAULT,[], body i (arg:rep_args))]
mAX_CPR_SIZE :: Arity
mAX_CPR_SIZE = 10
-- We do not treat very big tuples as CPR-ish:
--- a) for a start we get into trouble because there aren't
--- "enough" unboxed tuple types (a tiresome restriction,
--- but hard to fix),
--- b) more importantly, big unboxed tuples get returned mainly
--- on the stack, and are often then allocated in the heap
--- by the caller. So doing CPR for them may in fact make
--- things worse.
-
+-- a) for a start we get into trouble because there aren't
+-- "enough" unboxed tuple types (a tiresome restriction,
+-- but hard to fix),
+-- b) more importantly, big unboxed tuples get returned mainly
+-- on the stack, and are often then allocated in the heap
+-- by the caller. So doing CPR for them may in fact make
+-- things worse.
+
+mkLocals :: Int -> [Type] -> ([Id], Int)
mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
- where
- n = length tys
+ where
+ n = length tys
\end{code}
+Note [Newtype datacons]
+~~~~~~~~~~~~~~~~~~~~~~~
+The "data constructor" for a newtype should always be vanilla. At one
+point this wasn't true, because the newtype arising from
+ class C a => D a
+looked like
+ newtype T:D a = D:D (C a)
+so the data constructor for T:C had a single argument, namely the
+predicate (C a). But now we treat that as an ordinary argument, not
+part of the theta-type, so all is well.
+
%************************************************************************
-%* *
-\subsection{Record selectors}
-%* *
+%* *
+\subsection{Dictionary selectors}
+%* *
%************************************************************************
-We're going to build a record selector unfolding that looks like this:
-
- data T a b c = T1 { ..., op :: a, ...}
- | T2 { ..., op :: a, ...}
- | T3
-
- sel = /\ a b c -> \ d -> case d of
- T1 ... x ... -> x
- T2 ... x ... -> x
- other -> error "..."
-
-Similarly for newtypes
-
- newtype N a = MkN { unN :: a->a }
-
- unN :: N a -> a -> a
- unN n = coerce (a->a) n
-
-We need to take a little care if the field has a polymorphic type:
-
- data R = R { f :: forall a. a->a }
-
-Then we want
-
- f :: forall a. R -> a -> a
- f = /\ a \ r = case r of
- R f -> f a
+Selecting a field for a dictionary. If there is just one field, then
+there's nothing to do.
-(not f :: R -> forall a. a->a, which gives the type inference mechanism
-problems at call sites)
+Dictionary selectors may get nested forall-types. Thus:
-Similarly for (recursive) newtypes
+ class Foo a where
+ op :: forall b. Ord b => a -> b -> b
- newtype N = MkN { unN :: forall a. a->a }
+Then the top-level type for op is
- unN :: forall b. N -> b -> b
- unN = /\b -> \n:N -> (coerce (forall a. a->a) n)
+ op :: forall a. Foo a =>
+ forall b. Ord b =>
+ a -> b -> b
+This is unlike ordinary record selectors, which have all the for-alls
+at the outside. When dealing with classes it's very convenient to
+recover the original type signature from the class op selector.
-Note [Naughty record selectors]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-A "naughty" field is one for which we can't define a record
-selector, because an existential type variable would escape. For example:
- data T = forall a. MkT { x,y::a }
-We obviously can't define
- x (MkT v _) = v
-Nevertheless we *do* put a RecordSelId into the type environment
-so that if the user tries to use 'x' as a selector we can bleat
-helpfully, rather than saying unhelpfully that 'x' is not in scope.
-Hence the sel_naughty flag, to identify record selectors that don't really exist.
+\begin{code}
+mkDictSelId :: Bool -- True <=> don't include the unfolding
+ -- Little point on imports without -O, because the
+ -- dictionary itself won't be visible
+ -> Name -- Name of one of the *value* selectors
+ -- (dictionary superclass or method)
+ -> Class -> Id
+mkDictSelId no_unf name clas
+ = mkGlobalId (ClassOpId clas) name sel_ty info
+ where
+ sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
+ -- We can't just say (exprType rhs), because that would give a type
+ -- C a -> C a
+ -- for a single-op class (after all, the selector is the identity)
+ -- But it's type must expose the representation of the dictionary
+ -- to get (say) C a -> (a -> a)
+
+ base_info = noCafIdInfo
+ `setArityInfo` 1
+ `setStrictnessInfo` Just strict_sig
+ `setUnfoldingInfo` (if no_unf then noUnfolding
+ else mkImplicitUnfolding rhs)
+ -- In module where class op is defined, we must add
+ -- the unfolding, even though it'll never be inlined
+ -- becuase we use that to generate a top-level binding
+ -- for the ClassOp
+
+ info = base_info `setSpecInfo` mkSpecInfo [rule]
+ `setInlinePragInfo` neverInlinePragma
+ -- Add a magic BuiltinRule, and never inline it
+ -- so that the rule is always available to fire.
+ -- See Note [ClassOp/DFun selection] in TcInstDcls
+
+ n_ty_args = length tyvars
+
+ -- This is the built-in rule that goes
+ -- op (dfT d1 d2) ---> opT d1 d2
+ rule = BuiltinRule { ru_name = fsLit "Class op " `appendFS`
+ occNameFS (getOccName name)
+ , ru_fn = name
+ , ru_nargs = n_ty_args + 1
+ , ru_try = dictSelRule val_index n_ty_args n_eq_args }
+
+ -- The strictness signature is of the form U(AAAVAAAA) -> T
+ -- where the V depends on which item we are selecting
+ -- It's worth giving one, so that absence info etc is generated
+ -- even if the selector isn't inlined
+ strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
+ arg_dmd | new_tycon = evalDmd
+ | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
+ | id <- arg_ids ])
+
+ tycon = classTyCon clas
+ new_tycon = isNewTyCon tycon
+ [data_con] = tyConDataCons tycon
+ tyvars = dataConUnivTyVars data_con
+ arg_tys = dataConRepArgTys data_con -- Includes the dictionary superclasses
+ eq_theta = dataConEqTheta data_con
+ n_eq_args = length eq_theta
+
+ -- 'index' is a 0-index into the *value* arguments of the dictionary
+ val_index = assoc "MkId.mkDictSelId" sel_index_prs name
+ sel_index_prs = map idName (classAllSelIds clas) `zip` [0..]
+
+ the_arg_id = arg_ids !! val_index
+ pred = mkClassPred clas (mkTyVarTys tyvars)
+ dict_id = mkTemplateLocal 1 $ mkPredTy pred
+ arg_ids = mkTemplateLocalsNum 2 arg_tys
+ eq_ids = map mkWildEvBinder eq_theta
+
+ rhs = mkLams tyvars (Lam dict_id rhs_body)
+ rhs_body | new_tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
+ | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
+ [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]
+
+dictSelRule :: Int -> Arity -> Arity
+ -> IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
+-- Oh, very clever
+-- sel_i t1..tk (df s1..sn d1..dm) = op_i_helper s1..sn d1..dm
+-- sel_i t1..tk (D t1..tk op1 ... opm) = opi
+--
+-- NB: the data constructor has the same number of type and
+-- coercion args as the selector
+--
+-- This only works for *value* superclasses
+-- There are no selector functions for equality superclasses
+dictSelRule val_index n_ty_args n_eq_args id_unf args
+ | (dict_arg : _) <- drop n_ty_args args
+ , Just (_, _, con_args) <- exprIsConApp_maybe id_unf dict_arg
+ , let val_args = drop n_eq_args con_args
+ = Just (val_args !! val_index)
+ | otherwise
+ = Nothing
+\end{code}
-In general, a field is naughty if its type mentions a type variable that
-isn't in the result type of the constructor.
-Note [GADT record selectors]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-For GADTs, we require that all constructors with a common field 'f' have the same
-result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
-E.g.
- data T where
- T1 { f :: a } :: T [a]
- T2 { f :: a, y :: b } :: T [a]
-and now the selector takes that type as its argument:
- f :: forall a. T [a] -> a
- f t = case t of
- T1 { f = v } -> v
- T2 { f = v } -> v
-Note the forall'd tyvars of the selector are just the free tyvars
-of the result type; there may be other tyvars in the constructor's
-type (e.g. 'b' in T2).
+%************************************************************************
+%* *
+ Boxing and unboxing
+%* *
+%************************************************************************
\begin{code}
+-- unbox a product type...
+-- we will recurse into newtypes, casting along the way, and unbox at the
+-- first product data constructor we find. e.g.
+--
+-- data PairInt = PairInt Int Int
+-- newtype S = MkS PairInt
+-- newtype T = MkT S
+--
+-- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
+-- ids, we get (modulo int passing)
+--
+-- case (e `cast` CoT) `cast` CoS of
+-- PairInt a b -> body [a,b]
+--
+-- The Ints passed around are just for creating fresh locals
+unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
+unboxProduct i arg arg_ty body
+ = result
+ where
+ result = mkUnpackCase the_id arg con_args boxing_con rhs
+ (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
+ ([the_id], i') = mkLocals i [arg_ty]
+ (con_args, i'') = mkLocals i' tys
+ rhs = body i'' con_args
+
+mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
+-- (mkUnpackCase x e args Con body)
+-- returns
+-- case (e `cast` ...) of bndr { Con args -> body }
+--
+-- the type of the bndr passed in is irrelevent
+mkUnpackCase bndr arg unpk_args boxing_con body
+ = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
+ where
+ (cast_arg, bndr_ty) = go (idType bndr) arg
+ go ty arg
+ | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
+ , isNewTyCon tycon && not (isRecursiveTyCon tycon)
+ = go (newTyConInstRhs tycon tycon_args)
+ (unwrapNewTypeBody tycon tycon_args arg)
+ | otherwise = (arg, ty)
+
+-- ...and the dual
+reboxProduct :: [Unique] -- uniques to create new local binders
+ -> Type -- type of product to box
+ -> ([Unique], -- remaining uniques
+ CoreExpr, -- boxed product
+ [Id]) -- Ids being boxed into product
+reboxProduct us ty
+ = let
+ (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
+
+ us' = dropList con_arg_tys us
+
+ arg_ids = zipWith (mkSysLocal (fsLit "rb")) us con_arg_tys
+
+ bind_rhs = mkProductBox arg_ids ty
--- Steps for handling "naughty" vs "non-naughty" selectors:
--- 1. Determine naughtiness by comparing field type vs result type
--- 2. Install naughty ones with selector_ty of type _|_ and fill in mzero for info
--- 3. If it's not naughty, do the normal plan.
+ in
+ (us', bind_rhs, arg_ids)
-mkRecordSelId :: TyCon -> FieldLabel -> Id
-mkRecordSelId tycon field_label
- -- Assumes that all fields with the same field label have the same type
- | is_naughty = naughty_id
- | otherwise = sel_id
- where
- is_naughty = not (tyVarsOfType field_ty `subVarSet` res_tv_set)
- sel_id_details = RecordSelId tycon field_label is_naughty
-
- -- Escapist case here for naughty construcotrs
- -- We give it no IdInfo, and a type of forall a.a (never looked at)
- naughty_id = mkGlobalId sel_id_details field_label forall_a_a noCafIdInfo
- forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
-
- -- Normal case starts here
- sel_id = mkGlobalId sel_id_details field_label selector_ty info
- data_cons = tyConDataCons tycon
- data_cons_w_field = filter has_field data_cons -- Can't be empty!
- has_field con = field_label `elem` dataConFieldLabels con
-
- con1 = head data_cons_w_field
- res_tys = dataConResTys con1
- res_tv_set = tyVarsOfTypes res_tys
- res_tvs = varSetElems res_tv_set
- data_ty = mkTyConApp tycon res_tys
- field_ty = dataConFieldType con1 field_label
-
- -- *Very* tiresomely, the selectors are (unnecessarily!) overloaded over
- -- just the dictionaries in the types of the constructors that contain
- -- the relevant field. [The Report says that pattern matching on a
- -- constructor gives the same constraints as applying it.] Urgh.
- --
- -- However, not all data cons have all constraints (because of
- -- BuildTyCl.mkDataConStupidTheta). So we need to find all the data cons
- -- involved in the pattern match and take the union of their constraints.
- stupid_dict_tys = mkPredTys (dataConsStupidTheta data_cons_w_field)
- n_stupid_dicts = length stupid_dict_tys
-
- (field_tyvars,field_theta,field_tau) = tcSplitSigmaTy field_ty
- field_dict_tys = mkPredTys field_theta
- n_field_dict_tys = length field_dict_tys
- -- If the field has a universally quantified type we have to
- -- be a bit careful. Suppose we have
- -- data R = R { op :: forall a. Foo a => a -> a }
- -- Then we can't give op the type
- -- op :: R -> forall a. Foo a => a -> a
- -- because the typechecker doesn't understand foralls to the
- -- right of an arrow. The "right" type to give it is
- -- op :: forall a. Foo a => R -> a -> a
- -- But then we must generate the right unfolding too:
- -- op = /\a -> \dfoo -> \ r ->
- -- case r of
- -- R op -> op a dfoo
- -- Note that this is exactly the type we'd infer from a user defn
- -- op (R op) = op
-
- selector_ty :: Type
- selector_ty = mkForAllTys res_tvs $ mkForAllTys field_tyvars $
- mkFunTys stupid_dict_tys $ mkFunTys field_dict_tys $
- mkFunTy data_ty field_tau
-
- arity = 1 + n_stupid_dicts + n_field_dict_tys
-
- (strict_sig, rhs_w_str) = dmdAnalTopRhs sel_rhs
- -- Use the demand analyser to work out strictness.
- -- With all this unpackery it's not easy!
+mkProductBox :: [Id] -> Type -> CoreExpr
+mkProductBox arg_ids ty
+ = result_expr
+ where
+ (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
- info = noCafIdInfo
- `setCafInfo` caf_info
- `setArityInfo` arity
- `setUnfoldingInfo` mkTopUnfolding rhs_w_str
- `setAllStrictnessInfo` Just strict_sig
-
- -- Allocate Ids. We do it a funny way round because field_dict_tys is
- -- almost always empty. Also note that we use max_dict_tys
- -- rather than n_dict_tys, because the latter gives an infinite loop:
- -- n_dict tys depends on the_alts, which depens on arg_ids, which depends
- -- on arity, which depends on n_dict tys. Sigh! Mega sigh!
- stupid_dict_ids = mkTemplateLocalsNum 1 stupid_dict_tys
- max_stupid_dicts = length (tyConStupidTheta tycon)
- field_dict_base = max_stupid_dicts + 1
- field_dict_ids = mkTemplateLocalsNum field_dict_base field_dict_tys
- dict_id_base = field_dict_base + n_field_dict_tys
- data_id = mkTemplateLocal dict_id_base data_ty
- arg_base = dict_id_base + 1
-
- the_alts :: [CoreAlt]
- the_alts = map mk_alt data_cons_w_field -- Already sorted by data-con
- no_default = length data_cons == length data_cons_w_field -- No default needed
-
- default_alt | no_default = []
- | otherwise = [(DEFAULT, [], error_expr)]
-
- -- The default branch may have CAF refs, because it calls recSelError etc.
- caf_info | no_default = NoCafRefs
- | otherwise = MayHaveCafRefs
-
- sel_rhs = mkLams res_tvs $ mkLams field_tyvars $
- mkLams stupid_dict_ids $ mkLams field_dict_ids $
- Lam data_id $ mk_result sel_body
-
- -- NB: A newtype always has a vanilla DataCon; no existentials etc
- -- res_tys will simply be the dataConUnivTyVars
- sel_body | isNewTyCon tycon = unwrapNewTypeBody tycon res_tys (Var data_id)
- | otherwise = Case (Var data_id) data_id field_ty (default_alt ++ the_alts)
-
- mk_result poly_result = mkVarApps (mkVarApps poly_result field_tyvars) field_dict_ids
- -- We pull the field lambdas to the top, so we need to
- -- apply them in the body. For example:
- -- data T = MkT { foo :: forall a. a->a }
- --
- -- foo :: forall a. T -> a -> a
- -- foo = /\a. \t:T. case t of { MkT f -> f a }
-
- mk_alt data_con
- = -- In the non-vanilla case, the pattern must bind type variables and
- -- the context stuff; hence the arg_prefix binding below
- mkReboxingAlt uniqs data_con (arg_prefix ++ arg_ids) (Var the_arg_id)
- where
- (arg_prefix, arg_ids)
- | isVanillaDataCon data_con -- Instantiate from commmon base
- = ([], mkTemplateLocalsNum arg_base (dataConInstOrigArgTys data_con res_tys))
- | otherwise -- The case pattern binds type variables, which are used
- -- in the types of the arguments of the pattern
- = (dc_tvs ++ mkTemplateLocalsNum arg_base (mkPredTys dc_theta),
- mkTemplateLocalsNum arg_base' dc_arg_tys)
-
- (dc_tvs, dc_theta, dc_arg_tys) = dataConSig data_con
- arg_base' = arg_base + length dc_theta
-
- unpack_base = arg_base' + length dc_arg_tys
- uniqs = map mkBuiltinUnique [unpack_base..]
-
- the_arg_id = assoc "mkRecordSelId:mk_alt" (field_lbls `zip` arg_ids) field_label
- field_lbls = dataConFieldLabels data_con
-
- error_expr = mkRuntimeErrorApp rEC_SEL_ERROR_ID field_tau full_msg
- full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
+ result_expr
+ | isNewTyCon tycon && not (isRecursiveTyCon tycon)
+ = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
+ | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
+
+ wrap expr = wrapNewTypeBody tycon tycon_args expr
-- (mkReboxingAlt us con xs rhs) basically constructs the case
--- alternative (con, xs, rhs)
+-- alternative (con, xs, rhs)
-- but it does the reboxing necessary to construct the *source*
-- arguments, xs, from the representation arguments ys.
-- For example:
--- data T = MkT !(Int,Int) Bool
+-- data T = MkT !(Int,Int) Bool
--
-- mkReboxingAlt MkT [x,b] r
--- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
+-- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
--
-- mkDataAlt should really be in DataCon, but it can't because
-- it manipulates CoreSyn.
mkReboxingAlt
- :: [Unique] -- Uniques for the new Ids
+ :: [Unique] -- Uniques for the new Ids
-> DataCon
- -> [Var] -- Source-level args, including existential dicts
- -> CoreExpr -- RHS
+ -> [Var] -- Source-level args, including existential dicts
+ -> CoreExpr -- RHS
-> CoreAlt
mkReboxingAlt us con args rhs
| otherwise
= let
- (binds, args') = go args stricts us
+ (binds, args') = go args stricts us
in
(DataAlt con, args', mkLets binds rhs)
where
stricts = dataConExStricts con ++ dataConStrictMarks con
- go [] stricts us = ([], [])
+ go [] _stricts _us = ([], [])
- -- Type variable case
+ -- Type variable case
go (arg:args) stricts us
- | isTyVar arg
+ | isTyCoVar arg
= let (binds, args') = go args stricts us
- in (binds, arg:args')
+ in (binds, arg:args')
- -- Term variable case
+ -- Term variable case
go (arg:args) (str:stricts) us
| isMarkedUnboxed str
- = let
- ty = idType arg
-
- (tycon, tycon_args, pack_con, con_arg_tys)
- = splitProductType "mkReboxingAlt" ty
-
- unpacked_args = zipWith (mkSysLocal FSLIT("rb")) us con_arg_tys
- (binds, args') = go args stricts (dropList con_arg_tys us)
- con_app | isNewTyCon tycon = ASSERT( isSingleton unpacked_args )
- wrapNewTypeBody tycon tycon_args (Var (head unpacked_args))
- -- ToDo: is this right? Jun06
- | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var unpacked_args)
- in
- (NonRec arg con_app : binds, unpacked_args ++ args')
-
+ =
+ let (binds, unpacked_args') = go args stricts us'
+ (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
+ in
+ (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
| otherwise
= let (binds, args') = go args stricts us
in (binds, arg:args')
+ go (_ : _) [] _ = panic "mkReboxingAlt"
\end{code}
%************************************************************************
-%* *
-\subsection{Dictionary selectors}
-%* *
+%* *
+ Wrapping and unwrapping newtypes and type families
+%* *
%************************************************************************
-Selecting a field for a dictionary. If there is just one field, then
-there's nothing to do.
-
-Dictionary selectors may get nested forall-types. Thus:
-
- class Foo a where
- op :: forall b. Ord b => a -> b -> b
-
-Then the top-level type for op is
-
- op :: forall a. Foo a =>
- forall b. Ord b =>
- a -> b -> b
-
-This is unlike ordinary record selectors, which have all the for-alls
-at the outside. When dealing with classes it's very convenient to
-recover the original type signature from the class op selector.
-
\begin{code}
-mkDictSelId :: Name -> Class -> Id
-mkDictSelId name clas
- = mkGlobalId (ClassOpId clas) name sel_ty info
- where
- sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
- -- We can't just say (exprType rhs), because that would give a type
- -- C a -> C a
- -- for a single-op class (after all, the selector is the identity)
- -- But it's type must expose the representation of the dictionary
- -- to gat (say) C a -> (a -> a)
-
- info = noCafIdInfo
- `setArityInfo` 1
- `setUnfoldingInfo` mkTopUnfolding rhs
- `setAllStrictnessInfo` Just strict_sig
-
- -- We no longer use 'must-inline' on record selectors. They'll
- -- inline like crazy if they scrutinise a constructor
-
- -- The strictness signature is of the form U(AAAVAAAA) -> T
- -- where the V depends on which item we are selecting
- -- It's worth giving one, so that absence info etc is generated
- -- even if the selector isn't inlined
- strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
- arg_dmd | isNewTyCon tycon = evalDmd
- | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
- | id <- arg_ids ])
-
- tycon = classTyCon clas
- [data_con] = tyConDataCons tycon
- tyvars = dataConUnivTyVars data_con
- arg_tys = ASSERT( isVanillaDataCon data_con ) dataConRepArgTys data_con
- the_arg_id = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` arg_ids) name
-
- pred = mkClassPred clas (mkTyVarTys tyvars)
- (dict_id:arg_ids) = mkTemplateLocals (mkPredTy pred : arg_tys)
-
- rhs = mkLams tyvars (Lam dict_id rhs_body)
- rhs_body | isNewTyCon tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
- | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
- [(DataAlt data_con, arg_ids, Var the_arg_id)]
-
wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
-- The wrapper for the data constructor for a newtype looks like this:
--- newtype T a = MkT (a,Int)
--- MkT :: forall a. (a,Int) -> T a
--- MkT = /\a. \(x:(a,Int)). x `cast` CoT a
+-- newtype T a = MkT (a,Int)
+-- MkT :: forall a. (a,Int) -> T a
+-- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
-- where CoT is the coercion TyCon assoicated with the newtype
--
-- The call (wrapNewTypeBody T [a] e) returns the
-- body of the wrapper, namely
--- e `cast` CoT [a]
+-- e `cast` (CoT [a])
--
--- If a coercion constructor is prodivided in the newtype, then we use
+-- If a coercion constructor is provided in the newtype, then we use
-- it, otherwise the wrap/unwrap are both no-ops
--
+-- If the we are dealing with a newtype *instance*, we have a second coercion
+-- identifying the family instance with the constructor of the newtype
+-- instance. This coercion is applied in any case (ie, composed with the
+-- coercion constructor of the newtype or applied by itself).
+
wrapNewTypeBody tycon args result_expr
- | Just co_con <- newTyConCo tycon
- = Cast result_expr (mkTyConApp co_con args)
- | otherwise
- = result_expr
+ = wrapFamInstBody tycon args inner
+ where
+ inner
+ | Just co_con <- newTyConCo_maybe tycon
+ = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
+ | otherwise
+ = result_expr
+
+-- When unwrapping, we do *not* apply any family coercion, because this will
+-- be done via a CoPat by the type checker. We have to do it this way as
+-- computing the right type arguments for the coercion requires more than just
+-- a spliting operation (cf, TcPat.tcConPat).
unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
unwrapNewTypeBody tycon args result_expr
- | Just co_con <- newTyConCo tycon
- = Cast result_expr (mkSymCoercion (mkTyConApp co_con args))
+ | Just co_con <- newTyConCo_maybe tycon
+ = mkCoerce (mkTyConApp co_con args) result_expr
| otherwise
= result_expr
+-- If the type constructor is a representation type of a data instance, wrap
+-- the expression into a cast adjusting the expression type, which is an
+-- instance of the representation type, to the corresponding instance of the
+-- family instance type.
+-- See Note [Wrappers for data instance tycons]
+wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
+wrapFamInstBody tycon args body
+ | Just co_con <- tyConFamilyCoercion_maybe tycon
+ = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
+ | otherwise
+ = body
+unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
+unwrapFamInstScrut tycon args scrut
+ | Just co_con <- tyConFamilyCoercion_maybe tycon
+ = mkCoerce (mkTyConApp co_con args) scrut
+ | otherwise
+ = scrut
\end{code}
%************************************************************************
-%* *
-\subsection{Primitive operations
-%* *
+%* *
+\subsection{Primitive operations}
+%* *
%************************************************************************
\begin{code}
(tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
- (mkPrimOpIdUnique (primOpTag prim_op))
- Nothing (AnId id) UserSyntax
+ (mkPrimOpIdUnique (primOpTag prim_op))
+ (AnId id) UserSyntax
id = mkGlobalId (PrimOpId prim_op) name ty info
-
+
info = noCafIdInfo
- `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
- `setArityInfo` arity
- `setAllStrictnessInfo` Just strict_sig
+ `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
+ `setArityInfo` arity
+ `setStrictnessInfo` Just strict_sig
-- For each ccall we manufacture a separate CCallOpId, giving it
-- a fresh unique, a type that is correct for this particular ccall,
mkFCallId :: Unique -> ForeignCall -> Type -> Id
mkFCallId uniq fcall ty
= ASSERT( isEmptyVarSet (tyVarsOfType ty) )
- -- A CCallOpId should have no free type variables;
- -- when doing substitutions won't substitute over it
+ -- A CCallOpId should have no free type variables;
+ -- when doing substitutions won't substitute over it
mkGlobalId (FCallId fcall) name ty info
where
occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
- -- The "occurrence name" of a ccall is the full info about the
- -- ccall; it is encoded, but may have embedded spaces etc!
+ -- The "occurrence name" of a ccall is the full info about the
+ -- ccall; it is encoded, but may have embedded spaces etc!
name = mkFCallName uniq occ_str
info = noCafIdInfo
- `setArityInfo` arity
- `setAllStrictnessInfo` Just strict_sig
+ `setArityInfo` arity
+ `setStrictnessInfo` Just strict_sig
- (_, tau) = tcSplitForAllTys ty
+ (_, tau) = tcSplitForAllTys ty
(arg_tys, _) = tcSplitFunTys tau
- arity = length arg_tys
+ arity = length arg_tys
strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
+
+-- Tick boxes and breakpoints are both represented as TickBoxOpIds,
+-- except for the type:
+--
+-- a plain HPC tick box has type (State# RealWorld)
+-- a breakpoint Id has type forall a.a
+--
+-- The breakpoint Id will be applied to a list of arbitrary free variables,
+-- which is why it needs a polymorphic type.
+
+mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
+mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy
+
+mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
+mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
+ where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy
+
+mkTickBox' :: Unique -> Module -> TickBoxId -> Type -> Id
+mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
+ where
+ tickbox = TickBox mod ix
+ occ_str = showSDoc (braces (ppr tickbox))
+ name = mkTickBoxOpName uniq occ_str
+ info = noCafIdInfo
\end{code}
%************************************************************************
-%* *
+%* *
\subsection{DictFuns and default methods}
-%* *
+%* *
%************************************************************************
Important notes about dict funs and default methods
that they aren't discarded by the occurrence analyser.
\begin{code}
-mkDefaultMethodId dm_name ty = mkExportedLocalId dm_name ty
-
-mkDictFunId :: Name -- Name to use for the dict fun;
- -> [TyVar]
- -> ThetaType
- -> Class
- -> [Type]
- -> Id
+mkDefaultMethodId :: Id -- Selector Id
+ -> Name -- Default method name
+ -> Id -- Default method Id
+mkDefaultMethodId sel_id dm_name = mkExportedLocalId dm_name (idType sel_id)
+
+mkDictFunId :: Name -- Name to use for the dict fun;
+ -> [TyVar]
+ -> ThetaType
+ -> Class
+ -> [Type]
+ -> Id
mkDictFunId dfun_name inst_tyvars dfun_theta clas inst_tys
- = mkExportedLocalId dfun_name dfun_ty
+ = mkExportedLocalVar (DFunId is_nt) dfun_name dfun_ty vanillaIdInfo
where
+ is_nt = isNewTyCon (classTyCon clas)
dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
-
-{- 1 dec 99: disable the Mark Jones optimisation for the sake
- of compatibility with Hugs.
- See `types/InstEnv' for a discussion related to this.
-
- (class_tyvars, sc_theta, _, _) = classBigSig clas
- not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
- sc_theta' = substClasses (zipTopTvSubst class_tyvars inst_tys) sc_theta
- dfun_theta = case inst_decl_theta of
- [] -> [] -- If inst_decl_theta is empty, then we don't
- -- want to have any dict arguments, so that we can
- -- expose the constant methods.
-
- other -> nub (inst_decl_theta ++ filter not_const sc_theta')
- -- Otherwise we pass the superclass dictionaries to
- -- the dictionary function; the Mark Jones optimisation.
- --
- -- NOTE the "nub". I got caught by this one:
- -- class Monad m => MonadT t m where ...
- -- instance Monad m => MonadT (EnvT env) m where ...
- -- Here, the inst_decl_theta has (Monad m); but so
- -- does the sc_theta'!
- --
- -- NOTE the "not_const". I got caught by this one too:
- -- class Foo a => Baz a b where ...
- -- instance Wob b => Baz T b where..
- -- Now sc_theta' has Foo T
--}
\end{code}
%************************************************************************
-%* *
+%* *
\subsection{Un-definable}
-%* *
+%* *
%************************************************************************
These Ids can't be defined in Haskell. They could be defined in
another gun with which to shoot yourself in the foot.
\begin{code}
-mkWiredInIdName mod fs uniq id
- = mkWiredInName mod (mkOccNameFS varName fs) uniq Nothing (AnId id) UserSyntax
-
-unsafeCoerceName = mkWiredInIdName gHC_PRIM FSLIT("unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
-nullAddrName = mkWiredInIdName gHC_PRIM FSLIT("nullAddr#") nullAddrIdKey nullAddrId
-seqName = mkWiredInIdName gHC_PRIM FSLIT("seq") seqIdKey seqId
-realWorldName = mkWiredInIdName gHC_PRIM FSLIT("realWorld#") realWorldPrimIdKey realWorldPrimId
-lazyIdName = mkWiredInIdName gHC_BASE FSLIT("lazy") lazyIdKey lazyId
-
-errorName = mkWiredInIdName gHC_ERR FSLIT("error") errorIdKey eRROR_ID
-recSelErrorName = mkWiredInIdName gHC_ERR FSLIT("recSelError") recSelErrorIdKey rEC_SEL_ERROR_ID
-runtimeErrorName = mkWiredInIdName gHC_ERR FSLIT("runtimeError") runtimeErrorIdKey rUNTIME_ERROR_ID
-irrefutPatErrorName = mkWiredInIdName gHC_ERR FSLIT("irrefutPatError") irrefutPatErrorIdKey iRREFUT_PAT_ERROR_ID
-recConErrorName = mkWiredInIdName gHC_ERR FSLIT("recConError") recConErrorIdKey rEC_CON_ERROR_ID
-patErrorName = mkWiredInIdName gHC_ERR FSLIT("patError") patErrorIdKey pAT_ERROR_ID
-noMethodBindingErrorName = mkWiredInIdName gHC_ERR FSLIT("noMethodBindingError")
- noMethodBindingErrorIdKey nO_METHOD_BINDING_ERROR_ID
-nonExhaustiveGuardsErrorName
- = mkWiredInIdName gHC_ERR FSLIT("nonExhaustiveGuardsError")
- nonExhaustiveGuardsErrorIdKey nON_EXHAUSTIVE_GUARDS_ERROR_ID
+lazyIdName, unsafeCoerceName, nullAddrName, seqName, realWorldName :: Name
+unsafeCoerceName = mkWiredInIdName gHC_PRIM (fsLit "unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
+nullAddrName = mkWiredInIdName gHC_PRIM (fsLit "nullAddr#") nullAddrIdKey nullAddrId
+seqName = mkWiredInIdName gHC_PRIM (fsLit "seq") seqIdKey seqId
+realWorldName = mkWiredInIdName gHC_PRIM (fsLit "realWorld#") realWorldPrimIdKey realWorldPrimId
+lazyIdName = mkWiredInIdName gHC_BASE (fsLit "lazy") lazyIdKey lazyId
\end{code}
\begin{code}
+------------------------------------------------
-- unsafeCoerce# :: forall a b. a -> b
+unsafeCoerceId :: Id
unsafeCoerceId
= pcMiscPrelId unsafeCoerceName ty info
where
info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
-
+
- ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
- (mkFunTy openAlphaTy openBetaTy)
- [x] = mkTemplateLocals [openAlphaTy]
- rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
--- Note (Coerce openBetaTy openAlphaTy) (Var x)
- Cast (Var x) (mkUnsafeCoercion openAlphaTy openBetaTy)
+ ty = mkForAllTys [argAlphaTyVar,openBetaTyVar]
+ (mkFunTy argAlphaTy openBetaTy)
+ [x] = mkTemplateLocals [argAlphaTy]
+ rhs = mkLams [argAlphaTyVar,openBetaTyVar,x] $
+ Cast (Var x) (mkUnsafeCoercion argAlphaTy openBetaTy)
+------------------------------------------------
+nullAddrId :: Id
-- nullAddr# :: Addr#
-- The reason is is here is because we don't provide
-- a way to write this literal in Haskell.
-nullAddrId
- = pcMiscPrelId nullAddrName addrPrimTy info
+nullAddrId = pcMiscPrelId nullAddrName addrPrimTy info
where
info = noCafIdInfo `setUnfoldingInfo`
- mkCompulsoryUnfolding (Lit nullAddrLit)
+ mkCompulsoryUnfolding (Lit nullAddrLit)
-seqId
- = pcMiscPrelId seqName ty info
+------------------------------------------------
+seqId :: Id -- See Note [seqId magic]
+seqId = pcMiscPrelId seqName ty info
where
info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
-
-
- ty = mkForAllTys [alphaTyVar,openBetaTyVar]
- (mkFunTy alphaTy (mkFunTy openBetaTy openBetaTy))
- [x,y] = mkTemplateLocals [alphaTy, openBetaTy]
- rhs = mkLams [alphaTyVar,openBetaTyVar,x,y] (Case (Var x) x openBetaTy [(DEFAULT, [], Var y)])
-
--- lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
--- Used to lazify pseq: pseq a b = a `seq` lazy b
---
--- Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
--- not from GHC.Base.hi. This is important, because the strictness
--- analyser will spot it as strict!
---
--- Also no unfolding in lazyId: it gets "inlined" by a HACK in the worker/wrapper pass
--- (see WorkWrap.wwExpr)
--- We could use inline phases to do this, but that would be vulnerable to changes in
--- phase numbering....we must inline precisely after strictness analysis.
-lazyId
- = pcMiscPrelId lazyIdName ty info
+ `setSpecInfo` mkSpecInfo [seq_cast_rule]
+
+
+ ty = mkForAllTys [alphaTyVar,argBetaTyVar]
+ (mkFunTy alphaTy (mkFunTy argBetaTy argBetaTy))
+ [x,y] = mkTemplateLocals [alphaTy, argBetaTy]
+ rhs = mkLams [alphaTyVar,argBetaTyVar,x,y] (Case (Var x) x argBetaTy [(DEFAULT, [], Var y)])
+
+ -- See Note [Built-in RULES for seq]
+ seq_cast_rule = BuiltinRule { ru_name = fsLit "seq of cast"
+ , ru_fn = seqName
+ , ru_nargs = 4
+ , ru_try = match_seq_of_cast
+ }
+
+match_seq_of_cast :: IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
+ -- See Note [Built-in RULES for seq]
+match_seq_of_cast _ [Type _, Type res_ty, Cast scrut co, expr]
+ = Just (Var seqId `mkApps` [Type (fst (coercionKind co)), Type res_ty,
+ scrut, expr])
+match_seq_of_cast _ _ = Nothing
+
+------------------------------------------------
+lazyId :: Id -- See Note [lazyId magic]
+lazyId = pcMiscPrelId lazyIdName ty info
where
info = noCafIdInfo
ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
-
-lazyIdUnfolding :: CoreExpr -- Used to expand 'lazyId' after strictness anal
-lazyIdUnfolding = mkLams [openAlphaTyVar,x] (Var x)
- where
- [x] = mkTemplateLocals [openAlphaTy]
\end{code}
-@realWorld#@ used to be a magic literal, \tr{void#}. If things get
-nasty as-is, change it back to a literal (@Literal@).
+Note [seqId magic]
+~~~~~~~~~~~~~~~~~~
+'GHC.Prim.seq' is special in several ways.
-voidArgId is a Local Id used simply as an argument in functions
-where we just want an arg to avoid having a thunk of unlifted type.
-E.g.
- x = \ void :: State# RealWorld -> (# p, q #)
+a) Its second arg can have an unboxed type
+ x `seq` (v +# w)
-This comes up in strictness analysis
+b) Its fixity is set in LoadIface.ghcPrimIface
-\begin{code}
-realWorldPrimId -- :: State# RealWorld
- = pcMiscPrelId realWorldName realWorldStatePrimTy
- (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
- -- The evaldUnfolding makes it look that realWorld# is evaluated
- -- which in turn makes Simplify.interestingArg return True,
- -- which in turn makes INLINE things applied to realWorld# likely
- -- to be inlined
-
-voidArgId -- :: State# RealWorld
- = mkSysLocal FSLIT("void") voidArgIdKey realWorldStatePrimTy
-\end{code}
+c) It has quite a bit of desugaring magic.
+ See DsUtils.lhs Note [Desugaring seq (1)] and (2) and (3)
+d) There is some special rule handing: Note [User-defined RULES for seq]
-%************************************************************************
-%* *
-\subsection[PrelVals-error-related]{@error@ and friends; @trace@}
-%* *
-%************************************************************************
+e) See Note [Typing rule for seq] in TcExpr.
-GHC randomly injects these into the code.
+Note [User-defined RULES for seq]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Roman found situations where he had
+ case (f n) of _ -> e
+where he knew that f (which was strict in n) would terminate if n did.
+Notice that the result of (f n) is discarded. So it makes sense to
+transform to
+ case n of _ -> e
-@patError@ is just a version of @error@ for pattern-matching
-failures. It knows various ``codes'' which expand to longer
-strings---this saves space!
+Rather than attempt some general analysis to support this, I've added
+enough support that you can do this using a rewrite rule:
-@absentErr@ is a thing we put in for ``absent'' arguments. They jolly
-well shouldn't be yanked on, but if one is, then you will get a
-friendly message from @absentErr@ (rather than a totally random
-crash).
+ RULE "f/seq" forall n. seq (f n) e = seq n e
-@parError@ is a special version of @error@ which the compiler does
-not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
-templates, but we don't ever expect to generate code for it.
+You write that rule. When GHC sees a case expression that discards
+its result, it mentally transforms it to a call to 'seq' and looks for
+a RULE. (This is done in Simplify.rebuildCase.) As usual, the
+correctness of the rule is up to you.
-\begin{code}
-mkRuntimeErrorApp
- :: Id -- Should be of type (forall a. Addr# -> a)
- -- where Addr# points to a UTF8 encoded string
- -> Type -- The type to instantiate 'a'
- -> String -- The string to print
- -> CoreExpr
-
-mkRuntimeErrorApp err_id res_ty err_msg
- = mkApps (Var err_id) [Type res_ty, err_string]
- where
- err_string = Lit (mkStringLit err_msg)
-
-rEC_SEL_ERROR_ID = mkRuntimeErrorId recSelErrorName
-rUNTIME_ERROR_ID = mkRuntimeErrorId runtimeErrorName
-iRREFUT_PAT_ERROR_ID = mkRuntimeErrorId irrefutPatErrorName
-rEC_CON_ERROR_ID = mkRuntimeErrorId recConErrorName
-pAT_ERROR_ID = mkRuntimeErrorId patErrorName
-nO_METHOD_BINDING_ERROR_ID = mkRuntimeErrorId noMethodBindingErrorName
-nON_EXHAUSTIVE_GUARDS_ERROR_ID = mkRuntimeErrorId nonExhaustiveGuardsErrorName
-
--- The runtime error Ids take a UTF8-encoded string as argument
-mkRuntimeErrorId name = pc_bottoming_Id name runtimeErrorTy
-runtimeErrorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy)
-\end{code}
+To make this work, we need to be careful that the magical desugaring
+done in Note [seqId magic] item (c) is *not* done on the LHS of a rule.
+Or rather, we arrange to un-do it, in DsBinds.decomposeRuleLhs.
-\begin{code}
-eRROR_ID = pc_bottoming_Id errorName errorTy
+Note [Built-in RULES for seq]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We also have the following built-in rule for seq
-errorTy :: Type
-errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy] openAlphaTy)
- -- Notice the openAlphaTyVar. It says that "error" can be applied
- -- to unboxed as well as boxed types. This is OK because it never
- -- returns, so the return type is irrelevant.
-\end{code}
+ seq (x `cast` co) y = seq x y
+This eliminates unnecessary casts and also allows other seq rules to
+match more often. Notably,
+
+ seq (f x `cast` co) y --> seq (f x) y
+
+and now a user-defined rule for seq (see Note [User-defined RULES for seq])
+may fire.
+
+
+Note [lazyId magic]
+~~~~~~~~~~~~~~~~~~~
+ lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
+
+Used to lazify pseq: pseq a b = a `seq` lazy b
+
+Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
+not from GHC.Base.hi. This is important, because the strictness
+analyser will spot it as strict!
+
+Also no unfolding in lazyId: it gets "inlined" by a HACK in CorePrep.
+It's very important to do this inlining *after* unfoldings are exposed
+in the interface file. Otherwise, the unfolding for (say) pseq in the
+interface file will not mention 'lazy', so if we inline 'pseq' we'll totally
+miss the very thing that 'lazy' was there for in the first place.
+See Trac #3259 for a real world example.
+
+lazyId is defined in GHC.Base, so we don't *have* to inline it. If it
+appears un-applied, we'll end up just calling it.
+
+-------------------------------------------------------------
+@realWorld#@ used to be a magic literal, \tr{void#}. If things get
+nasty as-is, change it back to a literal (@Literal@).
+
+voidArgId is a Local Id used simply as an argument in functions
+where we just want an arg to avoid having a thunk of unlifted type.
+E.g.
+ x = \ void :: State# RealWorld -> (# p, q #)
+
+This comes up in strictness analysis
+
+\begin{code}
+realWorldPrimId :: Id
+realWorldPrimId -- :: State# RealWorld
+ = pcMiscPrelId realWorldName realWorldStatePrimTy
+ (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
+ -- The evaldUnfolding makes it look that realWorld# is evaluated
+ -- which in turn makes Simplify.interestingArg return True,
+ -- which in turn makes INLINE things applied to realWorld# likely
+ -- to be inlined
+
+voidArgId :: Id
+voidArgId -- :: State# RealWorld
+ = mkSysLocal (fsLit "void") voidArgIdKey realWorldStatePrimTy
+\end{code}
-%************************************************************************
-%* *
-\subsection{Utilities}
-%* *
-%************************************************************************
\begin{code}
pcMiscPrelId :: Name -> Type -> IdInfo -> Id
pcMiscPrelId name ty info
- = mkVanillaGlobal name ty info
+ = mkVanillaGlobalWithInfo name ty info
-- We lie and say the thing is imported; otherwise, we get into
-- a mess with dependency analysis; e.g., core2stg may heave in
-- random calls to GHCbase.unpackPS__. If GHCbase is the module
-- being compiled, then it's just a matter of luck if the definition
-- will be in "the right place" to be in scope.
-
-pc_bottoming_Id name ty
- = pcMiscPrelId name ty bottoming_info
- where
- bottoming_info = vanillaIdInfo `setAllStrictnessInfo` Just strict_sig
- -- Do *not* mark them as NoCafRefs, because they can indeed have
- -- CAF refs. For example, pAT_ERROR_ID calls GHC.Err.untangle,
- -- which has some CAFs
- -- In due course we may arrange that these error-y things are
- -- regarded by the GC as permanently live, in which case we
- -- can give them NoCaf info. As it is, any function that calls
- -- any pc_bottoming_Id will itself have CafRefs, which bloats
- -- SRTs.
-
- strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
- -- These "bottom" out, no matter what their arguments
-
-(openAlphaTyVar:openBetaTyVar:_) = openAlphaTyVars
-openAlphaTy = mkTyVarTy openAlphaTyVar
-openBetaTy = mkTyVarTy openBetaTyVar
\end{code}
-
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