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.
12 -- The above warning supression flag is a temporary kludge.
13 -- While working on this module you are encouraged to remove it and fix
14 -- any warnings in the module. See
15 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
22 mkDsLet, mkDsLets, mkDsApp, mkDsApps,
24 MatchResult(..), CanItFail(..),
25 cantFailMatchResult, alwaysFailMatchResult,
26 extractMatchResult, combineMatchResults,
27 adjustMatchResult, adjustMatchResultDs,
28 mkCoLetMatchResult, mkGuardedMatchResult,
29 matchCanFail, mkEvalMatchResult,
30 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
33 mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr,
34 mkIntExpr, mkCharExpr,
35 mkStringExpr, mkStringExprFS, mkIntegerExpr,
37 mkSelectorBinds, mkTupleExpr, mkTupleSelector,
38 mkTupleType, mkTupleCase, mkBigCoreTup,
39 mkCoreTup, mkCoreTupTy, seqVar,
41 dsSyntaxTable, lookupEvidence,
43 selectSimpleMatchVarL, selectMatchVars, selectMatchVar,
44 mkTickBox, mkOptTickBox, mkBinaryTickBox
47 #include "HsVersions.h"
49 import {-# SOURCE #-} Match ( matchSimply )
50 import {-# SOURCE #-} DsExpr( dsExpr )
83 infixl 4 `mkDsApp`, `mkDsApps`
88 %************************************************************************
92 %************************************************************************
95 dsSyntaxTable :: SyntaxTable Id
96 -> DsM ([CoreBind], -- Auxiliary bindings
97 [(Name,Id)]) -- Maps the standard name to its value
99 dsSyntaxTable rebound_ids
100 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
101 return (concat binds_s, prs)
103 -- The cheapo special case can happen when we
104 -- make an intermediate HsDo when desugaring a RecStmt
105 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
106 mk_bind (std_name, expr)
107 = dsExpr expr `thenDs` \ rhs ->
108 newSysLocalDs (exprType rhs) `thenDs` \ id ->
109 return ([NonRec id rhs], (std_name, id))
111 lookupEvidence :: [(Name, Id)] -> Name -> Id
112 lookupEvidence prs std_name
113 = assocDefault (mk_panic std_name) prs std_name
115 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
119 %************************************************************************
121 \subsection{Building lets}
123 %************************************************************************
125 Use case, not let for unlifted types. The simplifier will turn some
129 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
130 mkDsLet (NonRec bndr rhs) body -- See Note [CoreSyn let/app invariant]
131 | isUnLiftedType (idType bndr) && not (exprOkForSpeculation rhs)
132 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
136 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
137 mkDsLets binds body = foldr mkDsLet body binds
140 mkDsApp :: CoreExpr -> CoreExpr -> CoreExpr
141 -- Check the invariant that the arg of an App is ok-for-speculation if unlifted
142 -- See CoreSyn Note [CoreSyn let/app invariant]
143 mkDsApp fun (Type ty) = App fun (Type ty)
144 mkDsApp fun arg = mk_val_app fun arg arg_ty res_ty
146 (arg_ty, res_ty) = splitFunTy (exprType fun)
149 mkDsApps :: CoreExpr -> [CoreExpr] -> CoreExpr
150 -- Slightly more efficient version of (foldl mkDsApp)
152 = go fun (exprType fun) args
154 go fun fun_ty [] = fun
155 go fun fun_ty (Type ty : args) = go (App fun (Type ty)) (applyTy fun_ty ty) args
156 go fun fun_ty (arg : args) = go (mk_val_app fun arg arg_ty res_ty) res_ty args
158 (arg_ty, res_ty) = splitFunTy fun_ty
160 mk_val_app fun arg arg_ty res_ty -- See Note [CoreSyn let/app invariant]
161 | not (isUnLiftedType arg_ty) || exprOkForSpeculation arg
162 = App fun arg -- The vastly common case
164 mk_val_app (Var f `App` Type ty1 `App` Type ty2 `App` arg1) arg2 _ res_ty
165 | f == seqId -- Note [Desugaring seq]
166 = Case arg1 (mkWildId ty1) res_ty [(DEFAULT,[],arg2)]
168 mk_val_app fun arg arg_ty res_ty
169 = Case arg (mkWildId arg_ty) res_ty [(DEFAULT,[],App fun (Var arg_id))]
171 arg_id = mkWildId arg_ty -- Lots of shadowing, but it doesn't matter,
172 -- because 'fun ' should not have a free wild-id
175 Note [Desugaring seq] cf Trac #1031
176 ~~~~~~~~~~~~~~~~~~~~~
177 f x y = x `seq` (y `seq` (# x,y #))
179 The [CoreSyn let/app invariant] means that, other things being equal, because
180 the argument to the outer 'seq' has an unlifted type, we'll use call-by-value thus:
182 f x y = case (y `seq` (# x,y #)) of v -> x `seq` v
184 But that is bad for two reasons:
185 (a) we now evaluate y before x, and
186 (b) we can't bind v to an unboxed pair
188 Seq is very, very special! So we recognise it right here, and desugar to
189 case x of _ -> case y of _ -> (# x,y #)
191 The special case would be valid for all calls to 'seq', but it's only *necessary*
192 for ones whose second argument has an unlifted type. So we only catch the latter
193 case here, to avoid unnecessary tests.
196 %************************************************************************
198 \subsection{ Selecting match variables}
200 %************************************************************************
202 We're about to match against some patterns. We want to make some
203 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
204 hand, which should indeed be bound to the pattern as a whole, then use it;
205 otherwise, make one up.
208 selectSimpleMatchVarL :: LPat Id -> DsM Id
209 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
211 -- (selectMatchVars ps tys) chooses variables of type tys
212 -- to use for matching ps against. If the pattern is a variable,
213 -- we try to use that, to save inventing lots of fresh variables.
215 -- OLD, but interesting note:
216 -- But even if it is a variable, its type might not match. Consider
218 -- T1 :: Int -> T Int
221 -- f :: T a -> a -> Int
222 -- f (T1 i) (x::Int) = x
223 -- f (T2 i) (y::a) = 0
224 -- Then we must not choose (x::Int) as the matching variable!
225 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
227 selectMatchVars :: [Pat Id] -> DsM [Id]
228 selectMatchVars ps = mapM selectMatchVar ps
230 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
231 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
232 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
233 selectMatchVar (VarPat var) = return var
234 selectMatchVar (AsPat var pat) = return (unLoc var)
235 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
236 -- OK, better make up one...
240 %************************************************************************
242 %* type synonym EquationInfo and access functions for its pieces *
244 %************************************************************************
245 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
247 The ``equation info'' used by @match@ is relatively complicated and
248 worthy of a type synonym and a few handy functions.
251 firstPat :: EquationInfo -> Pat Id
252 firstPat eqn = ASSERT( notNull (eqn_pats eqn) ) head (eqn_pats eqn)
254 shiftEqns :: [EquationInfo] -> [EquationInfo]
255 -- Drop the first pattern in each equation
256 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
259 Functions on MatchResults
262 matchCanFail :: MatchResult -> Bool
263 matchCanFail (MatchResult CanFail _) = True
264 matchCanFail (MatchResult CantFail _) = False
266 alwaysFailMatchResult :: MatchResult
267 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
269 cantFailMatchResult :: CoreExpr -> MatchResult
270 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
272 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
273 extractMatchResult (MatchResult CantFail match_fn) fail_expr
274 = match_fn (error "It can't fail!")
276 extractMatchResult (MatchResult CanFail match_fn) fail_expr
277 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
278 match_fn if_it_fails `thenDs` \ body ->
279 returnDs (mkDsLet fail_bind body)
282 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
283 combineMatchResults (MatchResult CanFail body_fn1)
284 (MatchResult can_it_fail2 body_fn2)
285 = MatchResult can_it_fail2 body_fn
287 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
288 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
289 body_fn1 duplicatable_expr `thenDs` \ body1 ->
290 returnDs (Let fail_bind body1)
292 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
295 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
296 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
297 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
298 returnDs (encl_fn body))
300 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
301 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
302 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
305 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
307 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
309 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
310 wrapBind new old body
312 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
313 | otherwise = Let (NonRec new (Var old)) body
315 seqVar :: Var -> CoreExpr -> CoreExpr
316 seqVar var body = Case (Var var) var (exprType body)
317 [(DEFAULT, [], body)]
319 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
320 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
322 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
323 mkEvalMatchResult var ty
324 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
326 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
327 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
328 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
329 returnDs (mkIfThenElse pred_expr body fail))
331 mkCoPrimCaseMatchResult :: Id -- Scrutinee
332 -> Type -- Type of the case
333 -> [(Literal, MatchResult)] -- Alternatives
335 mkCoPrimCaseMatchResult var ty match_alts
336 = MatchResult CanFail mk_case
339 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
340 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
342 sorted_alts = sortWith fst match_alts -- Right order for a Case
343 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
344 returnDs (LitAlt lit, [], body)
347 mkCoAlgCaseMatchResult :: Id -- Scrutinee
348 -> Type -- Type of exp
349 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
351 mkCoAlgCaseMatchResult var ty match_alts
352 | isNewTyCon tycon -- Newtype case; use a let
353 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
354 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
356 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
357 = MatchResult CanFail mk_parrCase
359 | otherwise -- Datatype case; use a case
360 = MatchResult fail_flag mk_case
362 tycon = dataConTyCon con1
363 -- [Interesting: becuase of GADTs, we can't rely on the type of
364 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
367 (con1, arg_ids1, match_result1) = ASSERT( notNull match_alts ) head match_alts
368 arg_id1 = ASSERT( notNull arg_ids1 ) head arg_ids1
370 (tc, ty_args) = splitNewTyConApp var_ty
371 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
373 -- Stuff for data types
374 data_cons = tyConDataCons tycon
375 match_results = [match_result | (_,_,match_result) <- match_alts]
377 fail_flag | exhaustive_case
378 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
382 wild_var = mkWildId (idType var)
383 sorted_alts = sortWith get_tag match_alts
384 get_tag (con, _, _) = dataConTag con
385 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
386 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
388 mk_alt fail (con, args, MatchResult _ body_fn)
389 = body_fn fail `thenDs` \ body ->
390 newUniqueSupply `thenDs` \ us ->
391 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
393 mk_default fail | exhaustive_case = []
394 | otherwise = [(DEFAULT, [], fail)]
396 un_mentioned_constructors
397 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
398 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
400 -- Stuff for parallel arrays
402 -- * the following is to desugar cases over fake constructors for
403 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
406 -- Concerning `isPArrFakeAlts':
408 -- * it is *not* sufficient to just check the type of the type
409 -- constructor, as we have to be careful not to confuse the real
410 -- representation of parallel arrays with the fake constructors;
411 -- moreover, a list of alternatives must not mix fake and real
412 -- constructors (this is checked earlier on)
414 -- FIXME: We actually go through the whole list and make sure that
415 -- either all or none of the constructors are fake parallel
416 -- array constructors. This is to spot equations that mix fake
417 -- constructors with the real representation defined in
418 -- `PrelPArr'. It would be nicer to spot this situation
419 -- earlier and raise a proper error message, but it can really
420 -- only happen in `PrelPArr' anyway.
422 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
423 isPArrFakeAlts ((dcon, _, _):alts) =
424 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
425 (True , True ) -> True
426 (False, False) -> False
428 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
431 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
432 unboxAlt `thenDs` \alt ->
433 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
435 elemTy = case splitTyConApp (idType var) of
436 (_, [elemTy]) -> elemTy
438 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
439 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
442 newSysLocalDs intPrimTy `thenDs` \l ->
443 dsLookupGlobalId indexPName `thenDs` \indexP ->
444 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
445 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
447 wild = mkWildId intPrimTy
448 dft = (DEFAULT, [], fail)
450 -- each alternative matches one array length (corresponding to one
451 -- fake array constructor), so the match is on a literal; each
452 -- alternative's body is extended by a local binding for each
453 -- constructor argument, which are bound to array elements starting
456 mkAlt indexP (con, args, MatchResult _ bodyFun) =
457 bodyFun fail `thenDs` \body ->
458 returnDs (LitAlt lit, [], mkDsLets binds body)
460 lit = MachInt $ toInteger (dataConSourceArity con)
461 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
463 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
467 %************************************************************************
469 \subsection{Desugarer's versions of some Core functions}
471 %************************************************************************
474 mkErrorAppDs :: Id -- The error function
475 -> Type -- Type to which it should be applied
476 -> String -- The error message string to pass
479 mkErrorAppDs err_id ty msg
480 = getSrcSpanDs `thenDs` \ src_loc ->
482 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
483 core_msg = Lit (mkStringLit full_msg)
484 -- mkStringLit returns a result of type String#
486 returnDs (mkApps (Var err_id) [Type ty, core_msg])
490 *************************************************************
492 \subsection{Making literals}
494 %************************************************************************
497 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
498 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
499 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
500 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
501 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
503 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
504 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
507 | inIntRange i -- Small enough, so start from an Int
508 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
509 returnDs (mkSmallIntegerLit integer_dc i)
511 -- Special case for integral literals with a large magnitude:
512 -- They are transformed into an expression involving only smaller
513 -- integral literals. This improves constant folding.
515 | otherwise -- Big, so start from a string
516 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
517 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
518 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
520 lit i = mkSmallIntegerLit integer_dc i
521 plus a b = Var plus_id `App` a `App` b
522 times a b = Var times_id `App` a `App` b
524 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
525 horner :: Integer -> Integer -> CoreExpr
526 horner b i | abs q <= 1 = if r == 0 || r == i
528 else lit r `plus` lit (i-r)
529 | r == 0 = horner b q `times` lit b
530 | otherwise = lit r `plus` (horner b q `times` lit b)
532 (q,r) = i `quotRem` b
535 returnDs (horner tARGET_MAX_INT i)
537 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
539 mkStringExpr str = mkStringExprFS (mkFastString str)
543 = returnDs (mkNilExpr charTy)
547 the_char = mkCharExpr (headFS str)
549 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
552 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
553 returnDs (App (Var unpack_id) (Lit (MachStr str)))
556 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
557 returnDs (App (Var unpack_id) (Lit (MachStr str)))
561 safeChar c = ord c >= 1 && ord c <= 0x7F
565 %************************************************************************
567 \subsection[mkSelectorBind]{Make a selector bind}
569 %************************************************************************
571 This is used in various places to do with lazy patterns.
572 For each binder $b$ in the pattern, we create a binding:
574 b = case v of pat' -> b'
576 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
578 ToDo: making these bindings should really depend on whether there's
579 much work to be done per binding. If the pattern is complex, it
580 should be de-mangled once, into a tuple (and then selected from).
581 Otherwise the demangling can be in-line in the bindings (as here).
583 Boring! Boring! One error message per binder. The above ToDo is
584 even more helpful. Something very similar happens for pattern-bound
588 mkSelectorBinds :: LPat Id -- The pattern
589 -> CoreExpr -- Expression to which the pattern is bound
590 -> DsM [(Id,CoreExpr)]
592 mkSelectorBinds (L _ (VarPat v)) val_expr
593 = returnDs [(v, val_expr)]
595 mkSelectorBinds pat val_expr
596 | isSingleton binders || is_simple_lpat pat
597 = -- Given p = e, where p binds x,y
598 -- we are going to make
599 -- v = p (where v is fresh)
600 -- x = case v of p -> x
601 -- y = case v of p -> x
604 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
605 -- This does not matter after desugaring, but there's a subtle
606 -- issue with implicit parameters. Consider
608 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
609 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
610 -- does it get that type? So that when we abstract over it we get the
611 -- right top-level type (?i::Int) => ...)
613 -- So to get the type of 'v', use the pattern not the rhs. Often more
615 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
617 -- For the error message we make one error-app, to avoid duplication.
618 -- But we need it at different types... so we use coerce for that
619 mkErrorAppDs iRREFUT_PAT_ERROR_ID
620 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
621 newSysLocalDs unitTy `thenDs` \ err_var ->
622 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
623 returnDs ( (val_var, val_expr) :
624 (err_var, err_expr) :
629 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
630 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
631 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
632 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
635 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
637 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
639 binders = collectPatBinders pat
640 local_tuple = mkTupleExpr binders
641 tuple_ty = exprType local_tuple
643 mk_bind scrut_var err_var bndr_var
644 -- (mk_bind sv err_var) generates
645 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
646 -- Remember, pat binds bv
647 = matchSimply (Var scrut_var) PatBindRhs pat
648 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
649 returnDs (bndr_var, rhs_expr)
651 error_expr = mkCoerce co (Var err_var)
652 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
654 is_simple_lpat p = is_simple_pat (unLoc p)
656 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
657 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConPatArgs ps)
658 is_simple_pat (VarPat _) = True
659 is_simple_pat (ParPat p) = is_simple_lpat p
660 is_simple_pat other = False
662 is_triv_lpat p = is_triv_pat (unLoc p)
664 is_triv_pat (VarPat v) = True
665 is_triv_pat (WildPat _) = True
666 is_triv_pat (ParPat p) = is_triv_lpat p
667 is_triv_pat other = False
671 %************************************************************************
675 %************************************************************************
677 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
679 * If it has only one element, it is the identity function.
681 * If there are more elements than a big tuple can have, it nests
684 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
685 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
688 mkTupleExpr :: [Id] -> CoreExpr
689 mkTupleExpr ids = mkBigCoreTup (map Var ids)
691 -- corresponding type
692 mkTupleType :: [Id] -> Type
693 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
695 mkBigCoreTup :: [CoreExpr] -> CoreExpr
696 mkBigCoreTup = mkBigTuple mkCoreTup
698 mkBigTuple :: ([a] -> a) -> [a] -> a
699 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
701 -- Each sub-list is short enough to fit in a tuple
702 mk_big_tuple [as] = small_tuple as
703 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
705 chunkify :: [a] -> [[a]]
706 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
707 -- But there may be more than mAX_TUPLE_SIZE sub-lists
709 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
710 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
714 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
718 @mkTupleSelector@ builds a selector which scrutises the given
719 expression and extracts the one name from the list given.
720 If you want the no-shadowing rule to apply, the caller
721 is responsible for making sure that none of these names
724 If there is just one id in the ``tuple'', then the selector is
727 If it's big, it does nesting
728 mkTupleSelector [a,b,c,d] b v e
730 (p,q) -> case p of p {
732 We use 'tpl' vars for the p,q, since shadowing does not matter.
734 In fact, it's more convenient to generate it innermost first, getting
741 mkTupleSelector :: [Id] -- The tuple args
742 -> Id -- The selected one
743 -> Id -- A variable of the same type as the scrutinee
744 -> CoreExpr -- Scrutinee
747 mkTupleSelector vars the_var scrut_var scrut
748 = mk_tup_sel (chunkify vars) the_var
750 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
751 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
752 mk_tup_sel (chunkify tpl_vs) tpl_v
754 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
755 tpl_vs = mkTemplateLocals tpl_tys
756 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
760 A generalization of @mkTupleSelector@, allowing the body
761 of the case to be an arbitrary expression.
763 If the tuple is big, it is nested:
765 mkTupleCase uniqs [a,b,c,d] body v e
766 = case e of v { (p,q) ->
767 case p of p { (a,b) ->
768 case q of q { (c,d) ->
771 To avoid shadowing, we use uniqs to invent new variables p,q.
773 ToDo: eliminate cases where none of the variables are needed.
777 :: UniqSupply -- for inventing names of intermediate variables
778 -> [Id] -- the tuple args
779 -> CoreExpr -- body of the case
780 -> Id -- a variable of the same type as the scrutinee
781 -> CoreExpr -- scrutinee
784 mkTupleCase uniqs vars body scrut_var scrut
785 = mk_tuple_case uniqs (chunkify vars) body
787 mk_tuple_case us [vars] body
788 = mkSmallTupleCase vars body scrut_var scrut
789 mk_tuple_case us vars_s body
791 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
793 mk_tuple_case us' (chunkify vars') body'
794 one_tuple_case chunk_vars (us, vs, body)
796 (us1, us2) = splitUniqSupply us
797 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
798 (mkCoreTupTy (map idType chunk_vars))
799 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
800 in (us2, scrut_var:vs, body')
803 The same, but with a tuple small enough not to need nesting.
807 :: [Id] -- the tuple args
808 -> CoreExpr -- body of the case
809 -> Id -- a variable of the same type as the scrutinee
810 -> CoreExpr -- scrutinee
813 mkSmallTupleCase [var] body _scrut_var scrut
814 = bindNonRec var scrut body
815 mkSmallTupleCase vars body scrut_var scrut
816 -- One branch no refinement?
817 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
820 %************************************************************************
822 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
824 %************************************************************************
826 Call the constructor Ids when building explicit lists, so that they
827 interact well with rules.
830 mkNilExpr :: Type -> CoreExpr
831 mkNilExpr ty = mkConApp nilDataCon [Type ty]
833 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
834 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
836 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
837 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
840 -- The next three functions make tuple types, constructors and selectors,
841 -- with the rule that a 1-tuple is represented by the thing itselg
842 mkCoreTupTy :: [Type] -> Type
843 mkCoreTupTy [ty] = ty
844 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
846 mkCoreTup :: [CoreExpr] -> CoreExpr
847 -- Builds exactly the specified tuple.
848 -- No fancy business for big tuples
849 mkCoreTup [] = Var unitDataConId
851 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
852 (map (Type . exprType) cs ++ cs)
854 mkCoreSel :: [Id] -- The tuple args
855 -> Id -- The selected one
856 -> Id -- A variable of the same type as the scrutinee
857 -> CoreExpr -- Scrutinee
859 -- mkCoreSel [x,y,z] x v e
860 -- ===> case e of v { (x,y,z) -> x
861 mkCoreSel [var] should_be_the_same_var scrut_var scrut
862 = ASSERT(var == should_be_the_same_var)
865 mkCoreSel vars the_var scrut_var scrut
866 = ASSERT( notNull vars )
867 Case scrut scrut_var (idType the_var)
868 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
871 %************************************************************************
873 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
875 %************************************************************************
877 Generally, we handle pattern matching failure like this: let-bind a
878 fail-variable, and use that variable if the thing fails:
880 let fail.33 = error "Help"
891 If the case can't fail, then there'll be no mention of @fail.33@, and the
892 simplifier will later discard it.
895 If it can fail in only one way, then the simplifier will inline it.
898 Only if it is used more than once will the let-binding remain.
901 There's a problem when the result of the case expression is of
902 unboxed type. Then the type of @fail.33@ is unboxed too, and
903 there is every chance that someone will change the let into a case:
909 which is of course utterly wrong. Rather than drop the condition that
910 only boxed types can be let-bound, we just turn the fail into a function
911 for the primitive case:
913 let fail.33 :: Void -> Int#
914 fail.33 = \_ -> error "Help"
923 Now @fail.33@ is a function, so it can be let-bound.
926 mkFailurePair :: CoreExpr -- Result type of the whole case expression
927 -> DsM (CoreBind, -- Binds the newly-created fail variable
928 -- to either the expression or \ _ -> expression
929 CoreExpr) -- Either the fail variable, or fail variable
930 -- applied to unit tuple
933 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
934 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
935 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
936 App (Var fail_fun_var) (Var unitDataConId))
939 = newFailLocalDs ty `thenDs` \ fail_var ->
940 returnDs (NonRec fail_var expr, Var fail_var)
946 mkOptTickBox :: Maybe (Int,[Id]) -> CoreExpr -> DsM CoreExpr
947 mkOptTickBox Nothing e = return e
948 mkOptTickBox (Just (ix,ids)) e = mkTickBox ix ids e
950 mkTickBox :: Int -> [Id] -> CoreExpr -> DsM CoreExpr
951 mkTickBox ix vars e = do
954 let tick | opt_Hpc = mkTickBoxOpId uq mod ix
955 | otherwise = mkBreakPointOpId uq mod ix
957 let occName = mkVarOcc "tick"
958 let name = mkInternalName uq2 occName noSrcSpan -- use mkSysLocal?
959 let var = Id.mkLocalId name realWorldStatePrimTy
962 then return (Var tick)
964 let tickVar = Var tick
965 let tickType = mkFunTys (map idType vars) realWorldStatePrimTy
966 let scrutApTy = App tickVar (Type tickType)
967 return (mkApps scrutApTy (map Var vars) :: Expr Id)
968 return $ Case scrut var ty [(DEFAULT,[],e)]
972 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
973 mkBinaryTickBox ixT ixF e = do
977 let bndr1 = mkSysLocal FSLIT("t1") uq boolTy
978 falseBox <- mkTickBox ixF [] $ Var falseDataConId
979 trueBox <- mkTickBox ixT [] $ Var trueDataConId
980 return $ Case e bndr1 boolTy
981 [ (DataAlt falseDataCon, [], falseBox)
982 , (DataAlt trueDataCon, [], trueBox)