2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utilities for desugaring
8 This module exports some utility functions of no great interest.
15 mkDsLet, mkDsLets, mkDsApp, mkDsApps,
17 MatchResult(..), CanItFail(..),
18 cantFailMatchResult, alwaysFailMatchResult,
19 extractMatchResult, combineMatchResults,
20 adjustMatchResult, adjustMatchResultDs,
21 mkCoLetMatchResult, mkGuardedMatchResult,
22 matchCanFail, mkEvalMatchResult,
23 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
26 mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr,
27 mkIntExpr, mkCharExpr,
28 mkStringExpr, mkStringExprFS, mkIntegerExpr,
30 mkSelectorBinds, mkTupleExpr, mkTupleSelector,
31 mkTupleType, mkTupleCase, mkBigCoreTup,
32 mkCoreTup, mkCoreTupTy, seqVar,
34 dsSyntaxTable, lookupEvidence,
36 selectSimpleMatchVarL, selectMatchVars, selectMatchVar,
37 mkTickBox, mkOptTickBox, mkBinaryTickBox
40 #include "HsVersions.h"
42 import {-# SOURCE #-} Match ( matchSimply )
43 import {-# SOURCE #-} DsExpr( dsExpr )
74 infixl 4 `mkDsApp`, `mkDsApps`
79 %************************************************************************
83 %************************************************************************
86 dsSyntaxTable :: SyntaxTable Id
87 -> DsM ([CoreBind], -- Auxiliary bindings
88 [(Name,Id)]) -- Maps the standard name to its value
90 dsSyntaxTable rebound_ids
91 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
92 return (concat binds_s, prs)
94 -- The cheapo special case can happen when we
95 -- make an intermediate HsDo when desugaring a RecStmt
96 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
97 mk_bind (std_name, expr)
98 = dsExpr expr `thenDs` \ rhs ->
99 newSysLocalDs (exprType rhs) `thenDs` \ id ->
100 return ([NonRec id rhs], (std_name, id))
102 lookupEvidence :: [(Name, Id)] -> Name -> Id
103 lookupEvidence prs std_name
104 = assocDefault (mk_panic std_name) prs std_name
106 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
110 %************************************************************************
112 \subsection{Building lets}
114 %************************************************************************
116 Use case, not let for unlifted types. The simplifier will turn some
120 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
121 mkDsLet (NonRec bndr rhs) body -- See Note [CoreSyn let/app invariant]
122 | isUnLiftedType (idType bndr) && not (exprOkForSpeculation rhs)
123 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
127 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
128 mkDsLets binds body = foldr mkDsLet body binds
131 mkDsApp :: CoreExpr -> CoreExpr -> CoreExpr
132 -- Check the invariant that the arg of an App is ok-for-speculation if unlifted
133 -- See CoreSyn Note [CoreSyn let/app invariant]
134 mkDsApp fun (Type ty) = App fun (Type ty)
135 mkDsApp fun arg = mk_val_app fun arg arg_ty res_ty
137 (arg_ty, res_ty) = splitFunTy (exprType fun)
140 mkDsApps :: CoreExpr -> [CoreExpr] -> CoreExpr
141 -- Slightly more efficient version of (foldl mkDsApp)
143 = go fun (exprType fun) args
145 go fun fun_ty [] = fun
146 go fun fun_ty (Type ty : args) = go (App fun (Type ty)) (applyTy fun_ty ty) args
147 go fun fun_ty (arg : args) = go (mk_val_app fun arg arg_ty res_ty) res_ty args
149 (arg_ty, res_ty) = splitFunTy fun_ty
151 mk_val_app fun arg arg_ty res_ty -- See Note [CoreSyn let/app invariant]
152 | not (isUnLiftedType arg_ty) || exprOkForSpeculation arg
153 = App fun arg -- The vastly common case
155 mk_val_app (Var f `App` Type ty1 `App` Type ty2 `App` arg1) arg2 _ res_ty
156 | f == seqId -- Note [Desugaring seq]
157 = Case arg1 (mkWildId ty1) res_ty [(DEFAULT,[],arg2)]
159 mk_val_app fun arg arg_ty res_ty
160 = Case arg (mkWildId arg_ty) res_ty [(DEFAULT,[],App fun (Var arg_id))]
162 arg_id = mkWildId arg_ty -- Lots of shadowing, but it doesn't matter,
163 -- because 'fun ' should not have a free wild-id
166 Note [Desugaring seq] cf Trac #1031
167 ~~~~~~~~~~~~~~~~~~~~~
168 f x y = x `seq` (y `seq` (# x,y #))
170 The [CoreSyn let/app invariant] means that, other things being equal, because
171 the argument to the outer 'seq' has an unlifted type, we'll use call-by-value thus:
173 f x y = case (y `seq` (# x,y #)) of v -> x `seq` v
175 But that is bad for two reasons:
176 (a) we now evaluate y before x, and
177 (b) we can't bind v to an unboxed pair
179 Seq is very, very special! So we recognise it right here, and desugar to
180 case x of _ -> case y of _ -> (# x,y #)
182 The special case would be valid for all calls to 'seq', but it's only *necessary*
183 for ones whose second argument has an unlifted type. So we only catch the latter
184 case here, to avoid unnecessary tests.
187 %************************************************************************
189 \subsection{ Selecting match variables}
191 %************************************************************************
193 We're about to match against some patterns. We want to make some
194 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
195 hand, which should indeed be bound to the pattern as a whole, then use it;
196 otherwise, make one up.
199 selectSimpleMatchVarL :: LPat Id -> DsM Id
200 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
202 -- (selectMatchVars ps tys) chooses variables of type tys
203 -- to use for matching ps against. If the pattern is a variable,
204 -- we try to use that, to save inventing lots of fresh variables.
206 -- OLD, but interesting note:
207 -- But even if it is a variable, its type might not match. Consider
209 -- T1 :: Int -> T Int
212 -- f :: T a -> a -> Int
213 -- f (T1 i) (x::Int) = x
214 -- f (T2 i) (y::a) = 0
215 -- Then we must not choose (x::Int) as the matching variable!
216 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
218 selectMatchVars :: [Pat Id] -> DsM [Id]
219 selectMatchVars ps = mapM selectMatchVar ps
221 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
222 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
223 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
224 selectMatchVar (VarPat var) = return var
225 selectMatchVar (AsPat var pat) = return (unLoc var)
226 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
227 -- OK, better make up one...
231 %************************************************************************
233 %* type synonym EquationInfo and access functions for its pieces *
235 %************************************************************************
236 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
238 The ``equation info'' used by @match@ is relatively complicated and
239 worthy of a type synonym and a few handy functions.
242 firstPat :: EquationInfo -> Pat Id
243 firstPat eqn = head (eqn_pats eqn)
245 shiftEqns :: [EquationInfo] -> [EquationInfo]
246 -- Drop the first pattern in each equation
247 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
250 Functions on MatchResults
253 matchCanFail :: MatchResult -> Bool
254 matchCanFail (MatchResult CanFail _) = True
255 matchCanFail (MatchResult CantFail _) = False
257 alwaysFailMatchResult :: MatchResult
258 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
260 cantFailMatchResult :: CoreExpr -> MatchResult
261 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
263 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
264 extractMatchResult (MatchResult CantFail match_fn) fail_expr
265 = match_fn (error "It can't fail!")
267 extractMatchResult (MatchResult CanFail match_fn) fail_expr
268 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
269 match_fn if_it_fails `thenDs` \ body ->
270 returnDs (mkDsLet fail_bind body)
273 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
274 combineMatchResults (MatchResult CanFail body_fn1)
275 (MatchResult can_it_fail2 body_fn2)
276 = MatchResult can_it_fail2 body_fn
278 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
279 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
280 body_fn1 duplicatable_expr `thenDs` \ body1 ->
281 returnDs (Let fail_bind body1)
283 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
286 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
287 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
288 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
289 returnDs (encl_fn body))
291 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
292 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
293 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
296 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
298 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
300 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
301 wrapBind new old body
303 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
304 | otherwise = Let (NonRec new (Var old)) body
306 seqVar :: Var -> CoreExpr -> CoreExpr
307 seqVar var body = Case (Var var) var (exprType body)
308 [(DEFAULT, [], body)]
310 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
311 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
313 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
314 mkEvalMatchResult var ty
315 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
317 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
318 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
319 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
320 returnDs (mkIfThenElse pred_expr body fail))
322 mkCoPrimCaseMatchResult :: Id -- Scrutinee
323 -> Type -- Type of the case
324 -> [(Literal, MatchResult)] -- Alternatives
326 mkCoPrimCaseMatchResult var ty match_alts
327 = MatchResult CanFail mk_case
330 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
331 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
333 sorted_alts = sortWith fst match_alts -- Right order for a Case
334 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
335 returnDs (LitAlt lit, [], body)
338 mkCoAlgCaseMatchResult :: Id -- Scrutinee
339 -> Type -- Type of exp
340 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
342 mkCoAlgCaseMatchResult var ty match_alts
343 | isNewTyCon tycon -- Newtype case; use a let
344 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
345 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
347 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
348 = MatchResult CanFail mk_parrCase
350 | otherwise -- Datatype case; use a case
351 = MatchResult fail_flag mk_case
353 tycon = dataConTyCon con1
354 -- [Interesting: becuase of GADTs, we can't rely on the type of
355 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
358 (con1, arg_ids1, match_result1) = head match_alts
359 arg_id1 = head arg_ids1
361 (tc, ty_args) = splitNewTyConApp var_ty
362 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
364 -- Stuff for data types
365 data_cons = tyConDataCons tycon
366 match_results = [match_result | (_,_,match_result) <- match_alts]
368 fail_flag | exhaustive_case
369 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
373 wild_var = mkWildId (idType var)
374 sorted_alts = sortWith get_tag match_alts
375 get_tag (con, _, _) = dataConTag con
376 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
377 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
379 mk_alt fail (con, args, MatchResult _ body_fn)
380 = body_fn fail `thenDs` \ body ->
381 newUniqueSupply `thenDs` \ us ->
382 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
384 mk_default fail | exhaustive_case = []
385 | otherwise = [(DEFAULT, [], fail)]
387 un_mentioned_constructors
388 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
389 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
391 -- Stuff for parallel arrays
393 -- * the following is to desugar cases over fake constructors for
394 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
397 -- Concerning `isPArrFakeAlts':
399 -- * it is *not* sufficient to just check the type of the type
400 -- constructor, as we have to be careful not to confuse the real
401 -- representation of parallel arrays with the fake constructors;
402 -- moreover, a list of alternatives must not mix fake and real
403 -- constructors (this is checked earlier on)
405 -- FIXME: We actually go through the whole list and make sure that
406 -- either all or none of the constructors are fake parallel
407 -- array constructors. This is to spot equations that mix fake
408 -- constructors with the real representation defined in
409 -- `PrelPArr'. It would be nicer to spot this situation
410 -- earlier and raise a proper error message, but it can really
411 -- only happen in `PrelPArr' anyway.
413 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
414 isPArrFakeAlts ((dcon, _, _):alts) =
415 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
416 (True , True ) -> True
417 (False, False) -> False
419 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
422 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
423 unboxAlt `thenDs` \alt ->
424 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
426 elemTy = case splitTyConApp (idType var) of
427 (_, [elemTy]) -> elemTy
429 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
430 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
433 newSysLocalDs intPrimTy `thenDs` \l ->
434 dsLookupGlobalId indexPName `thenDs` \indexP ->
435 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
436 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
438 wild = mkWildId intPrimTy
439 dft = (DEFAULT, [], fail)
441 -- each alternative matches one array length (corresponding to one
442 -- fake array constructor), so the match is on a literal; each
443 -- alternative's body is extended by a local binding for each
444 -- constructor argument, which are bound to array elements starting
447 mkAlt indexP (con, args, MatchResult _ bodyFun) =
448 bodyFun fail `thenDs` \body ->
449 returnDs (LitAlt lit, [], mkDsLets binds body)
451 lit = MachInt $ toInteger (dataConSourceArity con)
452 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
454 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
458 %************************************************************************
460 \subsection{Desugarer's versions of some Core functions}
462 %************************************************************************
465 mkErrorAppDs :: Id -- The error function
466 -> Type -- Type to which it should be applied
467 -> String -- The error message string to pass
470 mkErrorAppDs err_id ty msg
471 = getSrcSpanDs `thenDs` \ src_loc ->
473 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
474 core_msg = Lit (mkStringLit full_msg)
475 -- mkStringLit returns a result of type String#
477 returnDs (mkApps (Var err_id) [Type ty, core_msg])
481 *************************************************************
483 \subsection{Making literals}
485 %************************************************************************
488 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
489 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
490 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
491 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
492 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
494 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
495 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
498 | inIntRange i -- Small enough, so start from an Int
499 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
500 returnDs (mkSmallIntegerLit integer_dc i)
502 -- Special case for integral literals with a large magnitude:
503 -- They are transformed into an expression involving only smaller
504 -- integral literals. This improves constant folding.
506 | otherwise -- Big, so start from a string
507 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
508 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
509 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
511 lit i = mkSmallIntegerLit integer_dc i
512 plus a b = Var plus_id `App` a `App` b
513 times a b = Var times_id `App` a `App` b
515 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
516 horner :: Integer -> Integer -> CoreExpr
517 horner b i | abs q <= 1 = if r == 0 || r == i
519 else lit r `plus` lit (i-r)
520 | r == 0 = horner b q `times` lit b
521 | otherwise = lit r `plus` (horner b q `times` lit b)
523 (q,r) = i `quotRem` b
526 returnDs (horner tARGET_MAX_INT i)
528 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
530 mkStringExpr str = mkStringExprFS (mkFastString str)
534 = returnDs (mkNilExpr charTy)
538 the_char = mkCharExpr (headFS str)
540 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
543 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
544 returnDs (App (Var unpack_id) (Lit (MachStr str)))
547 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
548 returnDs (App (Var unpack_id) (Lit (MachStr str)))
552 safeChar c = ord c >= 1 && ord c <= 0x7F
556 %************************************************************************
558 \subsection[mkSelectorBind]{Make a selector bind}
560 %************************************************************************
562 This is used in various places to do with lazy patterns.
563 For each binder $b$ in the pattern, we create a binding:
565 b = case v of pat' -> b'
567 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
569 ToDo: making these bindings should really depend on whether there's
570 much work to be done per binding. If the pattern is complex, it
571 should be de-mangled once, into a tuple (and then selected from).
572 Otherwise the demangling can be in-line in the bindings (as here).
574 Boring! Boring! One error message per binder. The above ToDo is
575 even more helpful. Something very similar happens for pattern-bound
579 mkSelectorBinds :: LPat Id -- The pattern
580 -> CoreExpr -- Expression to which the pattern is bound
581 -> DsM [(Id,CoreExpr)]
583 mkSelectorBinds (L _ (VarPat v)) val_expr
584 = returnDs [(v, val_expr)]
586 mkSelectorBinds pat val_expr
587 | isSingleton binders || is_simple_lpat pat
588 = -- Given p = e, where p binds x,y
589 -- we are going to make
590 -- v = p (where v is fresh)
591 -- x = case v of p -> x
592 -- y = case v of p -> x
595 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
596 -- This does not matter after desugaring, but there's a subtle
597 -- issue with implicit parameters. Consider
599 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
600 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
601 -- does it get that type? So that when we abstract over it we get the
602 -- right top-level type (?i::Int) => ...)
604 -- So to get the type of 'v', use the pattern not the rhs. Often more
606 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
608 -- For the error message we make one error-app, to avoid duplication.
609 -- But we need it at different types... so we use coerce for that
610 mkErrorAppDs iRREFUT_PAT_ERROR_ID
611 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
612 newSysLocalDs unitTy `thenDs` \ err_var ->
613 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
614 returnDs ( (val_var, val_expr) :
615 (err_var, err_expr) :
620 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
621 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
622 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
623 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
626 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
628 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
630 binders = collectPatBinders pat
631 local_tuple = mkTupleExpr binders
632 tuple_ty = exprType local_tuple
634 mk_bind scrut_var err_var bndr_var
635 -- (mk_bind sv err_var) generates
636 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
637 -- Remember, pat binds bv
638 = matchSimply (Var scrut_var) PatBindRhs pat
639 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
640 returnDs (bndr_var, rhs_expr)
642 error_expr = mkCoerce co (Var err_var)
643 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
645 is_simple_lpat p = is_simple_pat (unLoc p)
647 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
648 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConArgs ps)
649 is_simple_pat (VarPat _) = True
650 is_simple_pat (ParPat p) = is_simple_lpat p
651 is_simple_pat other = False
653 is_triv_lpat p = is_triv_pat (unLoc p)
655 is_triv_pat (VarPat v) = True
656 is_triv_pat (WildPat _) = True
657 is_triv_pat (ParPat p) = is_triv_lpat p
658 is_triv_pat other = False
662 %************************************************************************
666 %************************************************************************
668 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
670 * If it has only one element, it is the identity function.
672 * If there are more elements than a big tuple can have, it nests
675 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
676 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
679 mkTupleExpr :: [Id] -> CoreExpr
680 mkTupleExpr ids = mkBigCoreTup (map Var ids)
682 -- corresponding type
683 mkTupleType :: [Id] -> Type
684 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
686 mkBigCoreTup :: [CoreExpr] -> CoreExpr
687 mkBigCoreTup = mkBigTuple mkCoreTup
689 mkBigTuple :: ([a] -> a) -> [a] -> a
690 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
692 -- Each sub-list is short enough to fit in a tuple
693 mk_big_tuple [as] = small_tuple as
694 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
696 chunkify :: [a] -> [[a]]
697 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
698 -- But there may be more than mAX_TUPLE_SIZE sub-lists
700 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
701 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
705 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
709 @mkTupleSelector@ builds a selector which scrutises the given
710 expression and extracts the one name from the list given.
711 If you want the no-shadowing rule to apply, the caller
712 is responsible for making sure that none of these names
715 If there is just one id in the ``tuple'', then the selector is
718 If it's big, it does nesting
719 mkTupleSelector [a,b,c,d] b v e
721 (p,q) -> case p of p {
723 We use 'tpl' vars for the p,q, since shadowing does not matter.
725 In fact, it's more convenient to generate it innermost first, getting
732 mkTupleSelector :: [Id] -- The tuple args
733 -> Id -- The selected one
734 -> Id -- A variable of the same type as the scrutinee
735 -> CoreExpr -- Scrutinee
738 mkTupleSelector vars the_var scrut_var scrut
739 = mk_tup_sel (chunkify vars) the_var
741 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
742 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
743 mk_tup_sel (chunkify tpl_vs) tpl_v
745 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
746 tpl_vs = mkTemplateLocals tpl_tys
747 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
751 A generalization of @mkTupleSelector@, allowing the body
752 of the case to be an arbitrary expression.
754 If the tuple is big, it is nested:
756 mkTupleCase uniqs [a,b,c,d] body v e
757 = case e of v { (p,q) ->
758 case p of p { (a,b) ->
759 case q of q { (c,d) ->
762 To avoid shadowing, we use uniqs to invent new variables p,q.
764 ToDo: eliminate cases where none of the variables are needed.
768 :: UniqSupply -- for inventing names of intermediate variables
769 -> [Id] -- the tuple args
770 -> CoreExpr -- body of the case
771 -> Id -- a variable of the same type as the scrutinee
772 -> CoreExpr -- scrutinee
775 mkTupleCase uniqs vars body scrut_var scrut
776 = mk_tuple_case uniqs (chunkify vars) body
778 mk_tuple_case us [vars] body
779 = mkSmallTupleCase vars body scrut_var scrut
780 mk_tuple_case us vars_s body
782 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
784 mk_tuple_case us' (chunkify vars') body'
785 one_tuple_case chunk_vars (us, vs, body)
787 (us1, us2) = splitUniqSupply us
788 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
789 (mkCoreTupTy (map idType chunk_vars))
790 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
791 in (us2, scrut_var:vs, body')
794 The same, but with a tuple small enough not to need nesting.
798 :: [Id] -- the tuple args
799 -> CoreExpr -- body of the case
800 -> Id -- a variable of the same type as the scrutinee
801 -> CoreExpr -- scrutinee
804 mkSmallTupleCase [var] body _scrut_var scrut
805 = bindNonRec var scrut body
806 mkSmallTupleCase vars body scrut_var scrut
807 -- One branch no refinement?
808 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
811 %************************************************************************
813 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
815 %************************************************************************
817 Call the constructor Ids when building explicit lists, so that they
818 interact well with rules.
821 mkNilExpr :: Type -> CoreExpr
822 mkNilExpr ty = mkConApp nilDataCon [Type ty]
824 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
825 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
827 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
828 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
831 -- The next three functions make tuple types, constructors and selectors,
832 -- with the rule that a 1-tuple is represented by the thing itselg
833 mkCoreTupTy :: [Type] -> Type
834 mkCoreTupTy [ty] = ty
835 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
837 mkCoreTup :: [CoreExpr] -> CoreExpr
838 -- Builds exactly the specified tuple.
839 -- No fancy business for big tuples
840 mkCoreTup [] = Var unitDataConId
842 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
843 (map (Type . exprType) cs ++ cs)
845 mkCoreSel :: [Id] -- The tuple args
846 -> Id -- The selected one
847 -> Id -- A variable of the same type as the scrutinee
848 -> CoreExpr -- Scrutinee
850 -- mkCoreSel [x,y,z] x v e
851 -- ===> case e of v { (x,y,z) -> x
852 mkCoreSel [var] should_be_the_same_var scrut_var scrut
853 = ASSERT(var == should_be_the_same_var)
856 mkCoreSel vars the_var scrut_var scrut
857 = ASSERT( notNull vars )
858 Case scrut scrut_var (idType the_var)
859 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
862 %************************************************************************
864 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
866 %************************************************************************
868 Generally, we handle pattern matching failure like this: let-bind a
869 fail-variable, and use that variable if the thing fails:
871 let fail.33 = error "Help"
882 If the case can't fail, then there'll be no mention of @fail.33@, and the
883 simplifier will later discard it.
886 If it can fail in only one way, then the simplifier will inline it.
889 Only if it is used more than once will the let-binding remain.
892 There's a problem when the result of the case expression is of
893 unboxed type. Then the type of @fail.33@ is unboxed too, and
894 there is every chance that someone will change the let into a case:
900 which is of course utterly wrong. Rather than drop the condition that
901 only boxed types can be let-bound, we just turn the fail into a function
902 for the primitive case:
904 let fail.33 :: Void -> Int#
905 fail.33 = \_ -> error "Help"
914 Now @fail.33@ is a function, so it can be let-bound.
917 mkFailurePair :: CoreExpr -- Result type of the whole case expression
918 -> DsM (CoreBind, -- Binds the newly-created fail variable
919 -- to either the expression or \ _ -> expression
920 CoreExpr) -- Either the fail variable, or fail variable
921 -- applied to unit tuple
924 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
925 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
926 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
927 App (Var fail_fun_var) (Var unitDataConId))
930 = newFailLocalDs ty `thenDs` \ fail_var ->
931 returnDs (NonRec fail_var expr, Var fail_var)
937 mkOptTickBox :: Maybe Int -> CoreExpr -> DsM CoreExpr
938 mkOptTickBox Nothing e = return e
939 mkOptTickBox (Just ix) e = mkTickBox ix e
941 mkTickBox :: Int -> CoreExpr -> DsM CoreExpr
945 let tick = mkTickBoxOpId uq mod ix
947 let occName = mkVarOcc "tick"
948 let name = mkInternalName uq2 occName noSrcLoc -- use mkSysLocal?
949 let var = Id.mkLocalId name realWorldStatePrimTy
950 return $ Case (Var tick)
957 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
958 mkBinaryTickBox ixT ixF e = do
962 let bndr1 = mkSysLocal FSLIT("t1") uq boolTy
963 falseBox <- mkTickBox ixF $ Var falseDataConId
964 trueBox <- mkTickBox ixT $ Var trueDataConId
965 return $ Case e bndr1 boolTy
966 [ (DataAlt falseDataCon, [], falseBox)
967 , (DataAlt trueDataCon, [], trueBox)