2 % (c) The AQUA Project, Glasgow University, 1998
4 \section[StdIdInfo]{Standard unfoldings}
6 This module contains definitions for the IdInfo for things that
7 have a standard form, namely:
11 * method and superclass selectors
12 * primitive operations
16 mkSpecPragmaId, mkWorkerId,
18 mkDictFunId, mkDefaultMethodId,
21 mkDataConId, mkDataConWrapId,
23 mkPrimOpId, mkCCallOpId,
25 -- And some particular Ids; see below for why they are wired in
27 unsafeCoerceId, realWorldPrimId,
28 eRROR_ID, rEC_SEL_ERROR_ID, pAT_ERROR_ID, rEC_CON_ERROR_ID,
29 rEC_UPD_ERROR_ID, iRREFUT_PAT_ERROR_ID, nON_EXHAUSTIVE_GUARDS_ERROR_ID,
30 nO_METHOD_BINDING_ERROR_ID, aBSENT_ERROR_ID, pAR_ERROR_ID
33 #include "HsVersions.h"
36 import TysPrim ( openAlphaTyVars, alphaTyVar, alphaTy,
37 intPrimTy, realWorldStatePrimTy
39 import TysWiredIn ( boolTy, charTy, mkListTy )
40 import PrelMods ( pREL_ERR, pREL_GHC )
41 import PrelRules ( primOpRule )
42 import Rules ( addRule )
43 import Type ( Type, ClassContext, mkDictTy, mkDictTys, mkTyConApp, mkTyVarTys,
44 mkFunTys, mkFunTy, mkSigmaTy, classesToPreds,
45 isUnLiftedType, mkForAllTys, mkTyVarTy, tyVarsOfType, tyVarsOfTypes,
46 splitSigmaTy, splitFunTy_maybe,
47 splitFunTys, splitForAllTys, unUsgTy,
50 import PprType ( pprParendType )
51 import Module ( Module )
52 import CoreUtils ( exprType, mkInlineMe )
53 import CoreUnfold ( mkTopUnfolding, mkCompulsoryUnfolding, mkOtherCon )
54 import Subst ( mkTopTyVarSubst, substClasses )
55 import TyCon ( TyCon, isNewTyCon, tyConTyVars, tyConDataCons, isDataTyCon,
56 tyConTheta, isProductTyCon, isUnboxedTupleTyCon )
57 import Class ( Class, classBigSig, classTyCon, classTyVars, classSelIds )
58 import Var ( Id, TyVar )
59 import VarSet ( isEmptyVarSet )
60 import Name ( mkDerivedName, mkWiredInIdName, mkLocalName,
61 mkWorkerOcc, mkSuperDictSelOcc, mkCCallName,
64 import OccName ( mkSrcVarOcc )
65 import PrimOp ( PrimOp(DataToTagOp, CCallOp),
66 primOpSig, mkPrimOpIdName,
69 import Demand ( wwStrict, wwPrim )
70 import DataCon ( DataCon, StrictnessMark(..),
71 dataConFieldLabels, dataConRepArity, dataConTyCon,
72 dataConArgTys, dataConRepType, dataConRepStrictness,
73 dataConName, dataConTheta,
74 dataConSig, dataConStrictMarks, dataConId
76 import Id ( idType, mkId,
77 mkVanillaId, mkTemplateLocals,
78 mkTemplateLocal, setInlinePragma, idCprInfo
80 import IdInfo ( IdInfo, vanillaIdInfo, mkIdInfo,
81 exactArity, setUnfoldingInfo, setCafInfo, setCprInfo,
82 setArityInfo, setInlinePragInfo, setSpecInfo,
83 mkStrictnessInfo, setStrictnessInfo,
84 IdFlavour(..), InlinePragInfo(..), CafInfo(..), StrictnessInfo(..), CprInfo(..)
86 import FieldLabel ( FieldLabel, FieldLabelTag, mkFieldLabel, fieldLabelName,
87 firstFieldLabelTag, allFieldLabelTags, fieldLabelType
91 import BasicTypes ( Arity )
93 import Maybe ( isJust )
100 %************************************************************************
102 \subsection{Wired in Ids}
104 %************************************************************************
108 = [ -- These error-y things are wired in because we don't yet have
109 -- a way to express in an interface file that the result type variable
110 -- is 'open'; that is can be unified with an unboxed type
112 -- [The interface file format now carry such information, but there's
113 -- no way yet of expressing at the definition site for these error-reporting
114 -- functions that they have an 'open' result type. -- sof 1/99]
118 , iRREFUT_PAT_ERROR_ID
119 , nON_EXHAUSTIVE_GUARDS_ERROR_ID
120 , nO_METHOD_BINDING_ERROR_ID
126 -- These two can't be defined in Haskell
133 %************************************************************************
135 \subsection{Easy ones}
137 %************************************************************************
140 mkSpecPragmaId occ uniq ty loc
141 = mkId (mkLocalName uniq occ loc) ty (mkIdInfo SpecPragmaId)
142 -- Maybe a SysLocal? But then we'd lose the location
144 mkDefaultMethodId dm_name rec_c ty
145 = mkVanillaId dm_name ty
147 mkWorkerId uniq unwrkr ty
148 = mkVanillaId (mkDerivedName mkWorkerOcc (getName unwrkr) uniq) ty
151 %************************************************************************
153 \subsection{Data constructors}
155 %************************************************************************
158 mkDataConId :: Name -> DataCon -> Id
159 -- Makes the *worker* for the data constructor; that is, the function
160 -- that takes the reprsentation arguments and builds the constructor.
161 mkDataConId work_name data_con
162 = mkId work_name (dataConRepType data_con) info
164 info = mkIdInfo (DataConId data_con)
165 `setArityInfo` exactArity arity
166 `setStrictnessInfo` strict_info
167 `setCprInfo` cpr_info
169 arity = dataConRepArity data_con
171 strict_info = StrictnessInfo (dataConRepStrictness data_con) False
173 cpr_info | isProductTyCon tycon &&
174 not (isUnboxedTupleTyCon tycon) &&
175 arity > 0 = ReturnsCPR
176 | otherwise = NoCPRInfo
178 tycon = dataConTyCon data_con
179 -- Newtypes don't have a worker at all
181 -- If we are a product with 0 args we must be void(like)
182 -- We can't create an unboxed tuple with 0 args for this
183 -- and since Void has only one, constant value it should
184 -- just mean returning a pointer to a pre-existing cell.
185 -- So we won't really gain from doing anything fancy
186 -- and we treat this case as Top.
189 The wrapper for a constructor is an ordinary top-level binding that evaluates
190 any strict args, unboxes any args that are going to be flattened, and calls
193 We're going to build a constructor that looks like:
195 data (Data a, C b) => T a b = T1 !a !Int b
198 \d1::Data a, d2::C b ->
199 \p q r -> case p of { p ->
201 Con T1 [a,b] [p,q,r]}}
205 * d2 is thrown away --- a context in a data decl is used to make sure
206 one *could* construct dictionaries at the site the constructor
207 is used, but the dictionary isn't actually used.
209 * We have to check that we can construct Data dictionaries for
210 the types a and Int. Once we've done that we can throw d1 away too.
212 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
213 all that matters is that the arguments are evaluated. "seq" is
214 very careful to preserve evaluation order, which we don't need
217 You might think that we could simply give constructors some strictness
218 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
219 But we don't do that because in the case of primops and functions strictness
220 is a *property* not a *requirement*. In the case of constructors we need to
221 do something active to evaluate the argument.
223 Making an explicit case expression allows the simplifier to eliminate
224 it in the (common) case where the constructor arg is already evaluated.
227 mkDataConWrapId data_con
230 wrap_id = mkId (dataConName data_con) wrap_ty info
231 work_id = dataConId data_con
233 info = mkIdInfo (DataConWrapId data_con)
234 `setUnfoldingInfo` mkTopUnfolding (mkInlineMe wrap_rhs)
235 `setCprInfo` cpr_info
236 -- The Cpr info can be important inside INLINE rhss, where the
237 -- wrapper constructor isn't inlined
238 `setArityInfo` exactArity arity
239 -- It's important to specify the arity, so that partial
240 -- applications are treated as values
241 `setCafInfo` NoCafRefs
242 -- The wrapper Id ends up in STG code as an argument,
243 -- sometimes before its definition, so we want to
244 -- signal that it has no CAFs
246 wrap_ty = mkForAllTys all_tyvars $
250 cpr_info = idCprInfo work_id
252 wrap_rhs | isNewTyCon tycon
253 = ASSERT( null ex_tyvars && null ex_dict_args && length orig_arg_tys == 1 )
254 -- No existentials on a newtype, but it can have a contex
255 -- e.g. newtype Eq a => T a = MkT (...)
257 mkLams tyvars $ mkLams dict_args $ Lam id_arg1 $
258 Note (Coerce result_ty (head orig_arg_tys)) (Var id_arg1)
260 {- I nuked this because map (:) xs would create a
261 new local lambda for the (:) in core-to-stg.
262 There isn't a defn for the worker!
264 | null dict_args && all not_marked_strict strict_marks
265 = Var work_id -- The common case. Not only is this efficient,
266 -- but it also ensures that the wrapper is replaced
267 -- by the worker even when there are no args.
271 -- This is really important in rule matching,
272 -- which is a bit sad. (We could match on the wrappers,
273 -- but that makes it less likely that rules will match
274 -- when we bring bits of unfoldings together
278 = mkLams all_tyvars $ mkLams dict_args $
279 mkLams ex_dict_args $ mkLams id_args $
280 foldr mk_case con_app
281 (zip (ex_dict_args++id_args) strict_marks) i3 []
283 con_app i rep_ids = mkApps (Var work_id)
284 (map varToCoreExpr (all_tyvars ++ reverse rep_ids))
286 (tyvars, theta, ex_tyvars, ex_theta, orig_arg_tys, tycon) = dataConSig data_con
287 all_tyvars = tyvars ++ ex_tyvars
289 dict_tys = mkDictTys theta
290 ex_dict_tys = mkDictTys ex_theta
291 all_arg_tys = dict_tys ++ ex_dict_tys ++ orig_arg_tys
292 result_ty = mkTyConApp tycon (mkTyVarTys tyvars)
294 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
298 (dict_args, i1) = mkLocals 1 dict_tys
299 (ex_dict_args,i2) = mkLocals i1 ex_dict_tys
300 (id_args,i3) = mkLocals i2 orig_arg_tys
302 (id_arg1:_) = id_args -- Used for newtype only
304 strict_marks = dataConStrictMarks data_con
305 not_marked_strict NotMarkedStrict = True
306 not_marked_strict other = False
310 :: (Id, StrictnessMark) -- arg, strictness
311 -> (Int -> [Id] -> CoreExpr) -- body
312 -> Int -- next rep arg id
313 -> [Id] -- rep args so far
315 mk_case (arg,strict) body i rep_args
317 NotMarkedStrict -> body i (arg:rep_args)
319 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
321 Case (Var arg) arg [(DEFAULT,[], body i (arg:rep_args))]
323 MarkedUnboxed con tys ->
324 Case (Var arg) arg [(DataAlt con, con_args,
325 body i' (reverse con_args++rep_args))]
326 where n_tys = length tys
327 (con_args,i') = mkLocals i tys
331 %************************************************************************
333 \subsection{Record selectors}
335 %************************************************************************
337 We're going to build a record selector unfolding that looks like this:
339 data T a b c = T1 { ..., op :: a, ...}
340 | T2 { ..., op :: a, ...}
343 sel = /\ a b c -> \ d -> case d of
349 mkRecordSelId tycon field_label
350 -- Assumes that all fields with the same field label
351 -- have the same type
354 sel_id = mkId (fieldLabelName field_label) selector_ty info
356 field_ty = fieldLabelType field_label
357 field_name = fieldLabelName field_label
358 data_cons = tyConDataCons tycon
359 tyvars = tyConTyVars tycon -- These scope over the types in
360 -- the FieldLabels of constructors of this type
361 tycon_theta = tyConTheta tycon -- The context on the data decl
362 -- eg data (Eq a, Ord b) => T a b = ...
364 data_ty = mkTyConApp tycon (mkTyVarTys tyvars)
365 tyvar_tys = mkTyVarTys tyvars
367 -- Very tiresomely, the selectors are (unnecessarily!) overloaded over
368 -- just the dictionaries in the types of the constructors that contain
369 -- the relevant field. Urgh.
370 -- NB: this code relies on the fact that DataCons are quantified over
371 -- the identical type variables as their parent TyCon
372 dict_tys = [mkDictTy cls tys | (cls, tys) <- tycon_theta, needed_dict (cls, tys)]
373 needed_dict pred = or [ pred `elem` (dataConTheta dc)
374 | (DataAlt dc, _, _) <- the_alts]
377 selector_ty = mkForAllTys tyvars $ mkFunTys dict_tys $
378 mkFunTy data_ty field_ty
380 info = mkIdInfo (RecordSelId field_label)
381 `setArityInfo` exactArity 1
382 `setUnfoldingInfo` unfolding
383 `setCafInfo` NoCafRefs
384 -- ToDo: consider adding further IdInfo
386 unfolding = mkTopUnfolding sel_rhs
389 (data_id:dict_ids) = mkTemplateLocals (data_ty:dict_tys)
390 alts = map mk_maybe_alt data_cons
391 the_alts = catMaybes alts
392 default_alt | all isJust alts = [] -- No default needed
393 | otherwise = [(DEFAULT, [], error_expr)]
395 sel_rhs | isNewTyCon tycon = new_sel_rhs
396 | otherwise = data_sel_rhs
398 data_sel_rhs = mkLams tyvars $ mkLams dict_ids $ Lam data_id $
399 Case (Var data_id) data_id (the_alts ++ default_alt)
401 new_sel_rhs = mkLams tyvars $ Lam data_id $
402 Note (Coerce (unUsgTy field_ty) (unUsgTy data_ty)) (Var data_id)
404 mk_maybe_alt data_con
405 = case maybe_the_arg_id of
407 Just the_arg_id -> Just (DataAlt data_con, arg_ids, Var the_arg_id)
409 arg_ids = mkTemplateLocals (dataConArgTys data_con tyvar_tys)
410 -- The first one will shadow data_id, but who cares
411 field_lbls = dataConFieldLabels data_con
412 maybe_the_arg_id = assocMaybe (field_lbls `zip` arg_ids) field_label
414 error_expr = mkApps (Var rEC_SEL_ERROR_ID) [Type (unUsgTy field_ty), mkStringLit full_msg]
415 -- preserves invariant that type args are *not* usage-annotated on top. KSW 1999-04.
416 full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
420 %************************************************************************
422 \subsection{Dictionary selectors}
424 %************************************************************************
426 Selecting a field for a dictionary. If there is just one field, then
427 there's nothing to do.
429 ToDo: unify with mkRecordSelId.
432 mkDictSelId name clas
436 sel_id = mkId name ty info
437 field_lbl = mkFieldLabel name ty tag
438 tag = assoc "MkId.mkDictSelId" (classSelIds clas `zip` allFieldLabelTags) sel_id
440 info = mkIdInfo (RecordSelId field_lbl)
441 `setArityInfo` exactArity 1
442 `setUnfoldingInfo` unfolding
443 `setCafInfo` NoCafRefs
445 -- We no longer use 'must-inline' on record selectors. They'll
446 -- inline like crazy if they scrutinise a constructor
448 unfolding = mkTopUnfolding rhs
450 tyvars = classTyVars clas
452 tycon = classTyCon clas
453 [data_con] = tyConDataCons tycon
454 tyvar_tys = mkTyVarTys tyvars
455 arg_tys = dataConArgTys data_con tyvar_tys
456 the_arg_id = arg_ids !! (tag - firstFieldLabelTag)
458 dict_ty = mkDictTy clas tyvar_tys
459 (dict_id:arg_ids) = mkTemplateLocals (dict_ty : arg_tys)
461 rhs | isNewTyCon tycon = mkLams tyvars $ Lam dict_id $
462 Note (Coerce (head arg_tys) dict_ty) (Var dict_id)
463 | otherwise = mkLams tyvars $ Lam dict_id $
464 Case (Var dict_id) dict_id
465 [(DataAlt data_con, arg_ids, Var the_arg_id)]
469 %************************************************************************
471 \subsection{Primitive operations
473 %************************************************************************
476 mkPrimOpId :: PrimOp -> Id
480 (tyvars,arg_tys,res_ty, arity, strict_info) = primOpSig prim_op
481 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
482 name = mkPrimOpIdName prim_op id
483 id = mkId name ty info
485 info = mkIdInfo (PrimOpId prim_op)
487 `setArityInfo` exactArity arity
488 `setStrictnessInfo` strict_info
490 rules = addRule id emptyCoreRules (primOpRule prim_op)
493 -- For each ccall we manufacture a separate CCallOpId, giving it
494 -- a fresh unique, a type that is correct for this particular ccall,
495 -- and a CCall structure that gives the correct details about calling
498 -- The *name* of this Id is a local name whose OccName gives the full
499 -- details of the ccall, type and all. This means that the interface
500 -- file reader can reconstruct a suitable Id
502 mkCCallOpId :: Unique -> CCall -> Type -> Id
503 mkCCallOpId uniq ccall ty
504 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
505 -- A CCallOpId should have no free type variables;
506 -- when doing substitutions won't substitute over it
509 occ_str = showSDocIface (braces (pprCCallOp ccall <+> ppr ty))
510 -- The "occurrence name" of a ccall is the full info about the
511 -- ccall; it is encoded, but may have embedded spaces etc!
513 name = mkCCallName uniq occ_str
514 prim_op = CCallOp ccall
516 info = mkIdInfo (PrimOpId prim_op)
517 `setArityInfo` exactArity arity
518 `setStrictnessInfo` strict_info
520 (_, tau) = splitForAllTys ty
521 (arg_tys, _) = splitFunTys tau
522 arity = length arg_tys
523 strict_info = mkStrictnessInfo (take arity (repeat wwPrim), False)
527 %************************************************************************
529 \subsection{DictFuns}
531 %************************************************************************
534 mkDictFunId :: Name -- Name to use for the dict fun;
541 mkDictFunId dfun_name clas inst_tyvars inst_tys inst_decl_theta
542 = mkVanillaId dfun_name dfun_ty
544 (class_tyvars, sc_theta, _, _) = classBigSig clas
545 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys) sc_theta
547 dfun_theta = classesToPreds inst_decl_theta
549 {- 1 dec 99: disable the Mark Jones optimisation for the sake
550 of compatibility with Hugs.
551 See `types/InstEnv' for a discussion related to this.
553 dfun_theta = case inst_decl_theta of
554 [] -> [] -- If inst_decl_theta is empty, then we don't
555 -- want to have any dict arguments, so that we can
556 -- expose the constant methods.
558 other -> nub (inst_decl_theta ++ filter not_const sc_theta')
559 -- Otherwise we pass the superclass dictionaries to
560 -- the dictionary function; the Mark Jones optimisation.
562 -- NOTE the "nub". I got caught by this one:
563 -- class Monad m => MonadT t m where ...
564 -- instance Monad m => MonadT (EnvT env) m where ...
565 -- Here, the inst_decl_theta has (Monad m); but so
566 -- does the sc_theta'!
568 -- NOTE the "not_const". I got caught by this one too:
569 -- class Foo a => Baz a b where ...
570 -- instance Wob b => Baz T b where..
571 -- Now sc_theta' has Foo T
573 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
575 not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
579 %************************************************************************
581 \subsection{Un-definable}
583 %************************************************************************
585 These two can't be defined in Haskell.
587 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
588 just gets expanded into a type coercion wherever it occurs. Hence we
589 add it as a built-in Id with an unfolding here.
591 The type variables we use here are "open" type variables: this means
592 they can unify with both unlifted and lifted types. Hence we provide
593 another gun with which to shoot yourself in the foot.
597 = pcMiscPrelId unsafeCoerceIdKey pREL_GHC SLIT("unsafeCoerce#") ty info
600 `setUnfoldingInfo` mkCompulsoryUnfolding rhs
603 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
604 (mkFunTy openAlphaTy openBetaTy)
605 [x] = mkTemplateLocals [openAlphaTy]
606 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
607 Note (Coerce openBetaTy openAlphaTy) (Var x)
611 @getTag#@ is another function which can't be defined in Haskell. It needs to
612 evaluate its argument and call the dataToTag# primitive.
616 = pcMiscPrelId getTagIdKey pREL_GHC SLIT("getTag#") ty info
619 `setUnfoldingInfo` mkCompulsoryUnfolding rhs
620 -- We don't provide a defn for this; you must inline it
622 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy intPrimTy)
623 [x,y] = mkTemplateLocals [alphaTy,alphaTy]
624 rhs = mkLams [alphaTyVar,x] $
625 Case (Var x) y [ (DEFAULT, [], mkApps (Var dataToTagId) [Type alphaTy, Var y]) ]
627 dataToTagId = mkPrimOpId DataToTagOp
630 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
631 nasty as-is, change it back to a literal (@Literal@).
634 realWorldPrimId -- :: State# RealWorld
635 = pcMiscPrelId realWorldPrimIdKey pREL_GHC SLIT("realWorld#")
637 (noCafIdInfo `setUnfoldingInfo` mkOtherCon [])
638 -- The mkOtherCon makes it look that realWorld# is evaluated
639 -- which in turn makes Simplify.interestingArg return True,
640 -- which in turn makes INLINE things applied to realWorld# likely
645 %************************************************************************
647 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
649 %************************************************************************
651 GHC randomly injects these into the code.
653 @patError@ is just a version of @error@ for pattern-matching
654 failures. It knows various ``codes'' which expand to longer
655 strings---this saves space!
657 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
658 well shouldn't be yanked on, but if one is, then you will get a
659 friendly message from @absentErr@ (rather than a totally random
662 @parError@ is a special version of @error@ which the compiler does
663 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
664 templates, but we don't ever expect to generate code for it.
668 = pc_bottoming_Id errorIdKey pREL_ERR SLIT("error") errorTy
670 = generic_ERROR_ID recSelErrIdKey SLIT("patError")
672 = generic_ERROR_ID patErrorIdKey SLIT("patError")
674 = generic_ERROR_ID recConErrorIdKey SLIT("recConError")
676 = generic_ERROR_ID recUpdErrorIdKey SLIT("recUpdError")
678 = generic_ERROR_ID irrefutPatErrorIdKey SLIT("irrefutPatError")
679 nON_EXHAUSTIVE_GUARDS_ERROR_ID
680 = generic_ERROR_ID nonExhaustiveGuardsErrorIdKey SLIT("nonExhaustiveGuardsError")
681 nO_METHOD_BINDING_ERROR_ID
682 = generic_ERROR_ID noMethodBindingErrorIdKey SLIT("noMethodBindingError")
685 = pc_bottoming_Id absentErrorIdKey pREL_ERR SLIT("absentErr")
686 (mkSigmaTy [openAlphaTyVar] [] openAlphaTy)
689 = pcMiscPrelId parErrorIdKey pREL_ERR SLIT("parError")
690 (mkSigmaTy [openAlphaTyVar] [] openAlphaTy) noCafIdInfo
695 %************************************************************************
697 \subsection{Utilities}
699 %************************************************************************
702 pcMiscPrelId :: Unique{-IdKey-} -> Module -> FAST_STRING -> Type -> IdInfo -> Id
703 pcMiscPrelId key mod str ty info
705 name = mkWiredInIdName key mod (mkSrcVarOcc str) imp
706 imp = mkId name ty info -- the usual case...
709 -- We lie and say the thing is imported; otherwise, we get into
710 -- a mess with dependency analysis; e.g., core2stg may heave in
711 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
712 -- being compiled, then it's just a matter of luck if the definition
713 -- will be in "the right place" to be in scope.
715 pc_bottoming_Id key mod name ty
716 = pcMiscPrelId key mod name ty bottoming_info
718 bottoming_info = noCafIdInfo
719 `setStrictnessInfo` mkStrictnessInfo ([wwStrict], True)
721 -- these "bottom" out, no matter what their arguments
723 generic_ERROR_ID u n = pc_bottoming_Id u pREL_ERR n errorTy
726 noCafIdInfo = vanillaIdInfo `setCafInfo` NoCafRefs
728 (openAlphaTyVar:openBetaTyVar:_) = openAlphaTyVars
729 openAlphaTy = mkTyVarTy openAlphaTyVar
730 openBetaTy = mkTyVarTy openBetaTyVar
733 errorTy = mkUsgTy UsMany $
734 mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkUsgTy UsOnce (mkListTy charTy)]
735 (mkUsgTy UsMany openAlphaTy))
736 -- Notice the openAlphaTyVar. It says that "error" can be applied
737 -- to unboxed as well as boxed types. This is OK because it never
738 -- returns, so the return type is irrelevant.