2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsUtils]{Utilities for desugaring}
6 This module exports some utility functions of no great interest.
15 MatchResult(..), CanItFail(..),
16 cantFailMatchResult, alwaysFailMatchResult,
17 extractMatchResult, combineMatchResults,
18 adjustMatchResult, adjustMatchResultDs,
19 mkCoLetMatchResult, mkGuardedMatchResult,
20 matchCanFail, mkEvalMatchResult,
21 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
24 mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr,
25 mkIntExpr, mkCharExpr,
26 mkStringExpr, mkStringExprFS, mkIntegerExpr,
28 mkSelectorBinds, mkTupleExpr, mkTupleSelector,
29 mkTupleType, mkTupleCase, mkBigCoreTup,
30 mkCoreTup, mkCoreTupTy, seqVar,
32 dsSyntaxTable, lookupEvidence,
34 selectSimpleMatchVarL, selectMatchVars, selectMatchVar
37 #include "HsVersions.h"
39 import {-# SOURCE #-} Match ( matchSimply )
40 import {-# SOURCE #-} DsExpr( dsExpr )
43 import TcHsSyn ( hsLPatType, hsPatType )
45 import Constants ( mAX_TUPLE_SIZE )
48 import CoreUtils ( exprType, mkIfThenElse, mkCoerce, bindNonRec )
49 import MkId ( iRREFUT_PAT_ERROR_ID, mkReboxingAlt, unwrapNewTypeBody )
50 import Id ( idType, Id, mkWildId, mkTemplateLocals, mkSysLocal )
53 import Literal ( Literal(..), mkStringLit, inIntRange, tARGET_MAX_INT )
54 import TyCon ( isNewTyCon, tyConDataCons, tyConArity )
55 import DataCon ( DataCon, dataConSourceArity, dataConTyCon, dataConTag, dataConRepArgTys )
56 import Type ( mkFunTy, isUnLiftedType, Type, splitTyConApp, mkTyVarTy,
58 import Coercion ( Coercion, mkUnsafeCoercion )
59 import TcType ( tcEqType )
60 import TysPrim ( intPrimTy )
61 import TysWiredIn ( nilDataCon, consDataCon,
63 unitDataConId, unitTy,
67 import BasicTypes ( Boxity(..) )
68 import UniqSet ( mkUniqSet, minusUniqSet, isEmptyUniqSet )
69 import UniqSupply ( splitUniqSupply, uniqFromSupply, uniqsFromSupply )
70 import PrelNames ( unpackCStringName, unpackCStringUtf8Name,
71 plusIntegerName, timesIntegerName, smallIntegerDataConName,
72 lengthPName, indexPName )
74 import SrcLoc ( Located(..), unLoc )
75 import Util ( isSingleton, zipEqual, sortWith )
76 import ListSetOps ( assocDefault )
78 import Data.Char ( ord )
81 import Util ( notNull ) -- Used in an assertion
87 %************************************************************************
91 %************************************************************************
94 dsSyntaxTable :: SyntaxTable Id
95 -> DsM ([CoreBind], -- Auxiliary bindings
96 [(Name,Id)]) -- Maps the standard name to its value
98 dsSyntaxTable rebound_ids
99 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
100 return (concat binds_s, prs)
102 -- The cheapo special case can happen when we
103 -- make an intermediate HsDo when desugaring a RecStmt
104 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
105 mk_bind (std_name, expr)
106 = dsExpr expr `thenDs` \ rhs ->
107 newSysLocalDs (exprType rhs) `thenDs` \ id ->
108 return ([NonRec id rhs], (std_name, id))
110 lookupEvidence :: [(Name, Id)] -> Name -> Id
111 lookupEvidence prs std_name
112 = assocDefault (mk_panic std_name) prs std_name
114 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
118 %************************************************************************
120 \subsection{Building lets}
122 %************************************************************************
124 Use case, not let for unlifted types. The simplifier will turn some
128 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
129 mkDsLet (NonRec bndr rhs) body
130 | isUnLiftedType (idType bndr)
131 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
135 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
136 mkDsLets binds body = foldr mkDsLet body binds
140 %************************************************************************
142 \subsection{ Selecting match variables}
144 %************************************************************************
146 We're about to match against some patterns. We want to make some
147 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
148 hand, which should indeed be bound to the pattern as a whole, then use it;
149 otherwise, make one up.
152 selectSimpleMatchVarL :: LPat Id -> DsM Id
153 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
155 -- (selectMatchVars ps tys) chooses variables of type tys
156 -- to use for matching ps against. If the pattern is a variable,
157 -- we try to use that, to save inventing lots of fresh variables.
159 -- OLD, but interesting note:
160 -- But even if it is a variable, its type might not match. Consider
162 -- T1 :: Int -> T Int
165 -- f :: T a -> a -> Int
166 -- f (T1 i) (x::Int) = x
167 -- f (T2 i) (y::a) = 0
168 -- Then we must not choose (x::Int) as the matching variable!
169 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
171 selectMatchVars :: [Pat Id] -> DsM [Id]
172 selectMatchVars ps = mapM selectMatchVar ps
174 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
175 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
176 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
177 selectMatchVar (VarPat var) = return var
178 selectMatchVar (AsPat var pat) = return (unLoc var)
179 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
180 -- OK, better make up one...
184 %************************************************************************
186 %* type synonym EquationInfo and access functions for its pieces *
188 %************************************************************************
189 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
191 The ``equation info'' used by @match@ is relatively complicated and
192 worthy of a type synonym and a few handy functions.
195 firstPat :: EquationInfo -> Pat Id
196 firstPat eqn = head (eqn_pats eqn)
198 shiftEqns :: [EquationInfo] -> [EquationInfo]
199 -- Drop the first pattern in each equation
200 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
203 Functions on MatchResults
206 matchCanFail :: MatchResult -> Bool
207 matchCanFail (MatchResult CanFail _) = True
208 matchCanFail (MatchResult CantFail _) = False
210 alwaysFailMatchResult :: MatchResult
211 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
213 cantFailMatchResult :: CoreExpr -> MatchResult
214 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
216 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
217 extractMatchResult (MatchResult CantFail match_fn) fail_expr
218 = match_fn (error "It can't fail!")
220 extractMatchResult (MatchResult CanFail match_fn) fail_expr
221 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
222 match_fn if_it_fails `thenDs` \ body ->
223 returnDs (mkDsLet fail_bind body)
226 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
227 combineMatchResults (MatchResult CanFail body_fn1)
228 (MatchResult can_it_fail2 body_fn2)
229 = MatchResult can_it_fail2 body_fn
231 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
232 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
233 body_fn1 duplicatable_expr `thenDs` \ body1 ->
234 returnDs (Let fail_bind body1)
236 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
239 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
240 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
241 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
242 returnDs (encl_fn body))
244 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
245 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
246 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
249 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
251 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
253 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
254 wrapBind new old body
256 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
257 | otherwise = Let (NonRec new (Var old)) body
259 seqVar :: Var -> CoreExpr -> CoreExpr
260 seqVar var body = Case (Var var) var (exprType body)
261 [(DEFAULT, [], body)]
263 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
264 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
266 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
267 mkEvalMatchResult var ty
268 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
270 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
271 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
272 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
273 returnDs (mkIfThenElse pred_expr body fail))
275 mkCoPrimCaseMatchResult :: Id -- Scrutinee
276 -> Type -- Type of the case
277 -> [(Literal, MatchResult)] -- Alternatives
279 mkCoPrimCaseMatchResult var ty match_alts
280 = MatchResult CanFail mk_case
283 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
284 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
286 sorted_alts = sortWith fst match_alts -- Right order for a Case
287 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
288 returnDs (LitAlt lit, [], body)
291 mkCoAlgCaseMatchResult :: Id -- Scrutinee
292 -> Type -- Type of exp
293 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
295 mkCoAlgCaseMatchResult var ty match_alts
296 | isNewTyCon tycon -- Newtype case; use a let
297 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
298 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
300 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
301 = MatchResult CanFail mk_parrCase
303 | otherwise -- Datatype case; use a case
304 = MatchResult fail_flag mk_case
306 tycon = dataConTyCon con1
307 -- [Interesting: becuase of GADTs, we can't rely on the type of
308 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
311 (con1, arg_ids1, match_result1) = head match_alts
312 arg_id1 = head arg_ids1
314 (tc, ty_args) = splitNewTyConApp var_ty
315 newtype_rhs = unwrapNewTypeBody tycon ty_args (Var var)
317 -- Stuff for data types
318 data_cons = tyConDataCons tycon
319 match_results = [match_result | (_,_,match_result) <- match_alts]
321 fail_flag | exhaustive_case
322 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
326 wild_var = mkWildId (idType var)
327 sorted_alts = sortWith get_tag match_alts
328 get_tag (con, _, _) = dataConTag con
329 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
330 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
332 mk_alt fail (con, args, MatchResult _ body_fn)
333 = body_fn fail `thenDs` \ body ->
334 newUniqueSupply `thenDs` \ us ->
335 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
337 mk_default fail | exhaustive_case = []
338 | otherwise = [(DEFAULT, [], fail)]
340 un_mentioned_constructors
341 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
342 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
344 -- Stuff for parallel arrays
346 -- * the following is to desugar cases over fake constructors for
347 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
350 -- Concerning `isPArrFakeAlts':
352 -- * it is *not* sufficient to just check the type of the type
353 -- constructor, as we have to be careful not to confuse the real
354 -- representation of parallel arrays with the fake constructors;
355 -- moreover, a list of alternatives must not mix fake and real
356 -- constructors (this is checked earlier on)
358 -- FIXME: We actually go through the whole list and make sure that
359 -- either all or none of the constructors are fake parallel
360 -- array constructors. This is to spot equations that mix fake
361 -- constructors with the real representation defined in
362 -- `PrelPArr'. It would be nicer to spot this situation
363 -- earlier and raise a proper error message, but it can really
364 -- only happen in `PrelPArr' anyway.
366 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
367 isPArrFakeAlts ((dcon, _, _):alts) =
368 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
369 (True , True ) -> True
370 (False, False) -> False
372 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
375 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
376 unboxAlt `thenDs` \alt ->
377 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
379 elemTy = case splitTyConApp (idType var) of
380 (_, [elemTy]) -> elemTy
382 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
383 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
386 newSysLocalDs intPrimTy `thenDs` \l ->
387 dsLookupGlobalId indexPName `thenDs` \indexP ->
388 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
389 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
391 wild = mkWildId intPrimTy
392 dft = (DEFAULT, [], fail)
394 -- each alternative matches one array length (corresponding to one
395 -- fake array constructor), so the match is on a literal; each
396 -- alternative's body is extended by a local binding for each
397 -- constructor argument, which are bound to array elements starting
400 mkAlt indexP (con, args, MatchResult _ bodyFun) =
401 bodyFun fail `thenDs` \body ->
402 returnDs (LitAlt lit, [], mkDsLets binds body)
404 lit = MachInt $ toInteger (dataConSourceArity con)
405 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
407 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
411 %************************************************************************
413 \subsection{Desugarer's versions of some Core functions}
415 %************************************************************************
418 mkErrorAppDs :: Id -- The error function
419 -> Type -- Type to which it should be applied
420 -> String -- The error message string to pass
423 mkErrorAppDs err_id ty msg
424 = getSrcSpanDs `thenDs` \ src_loc ->
426 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
427 core_msg = Lit (mkStringLit full_msg)
428 -- mkStringLit returns a result of type String#
430 returnDs (mkApps (Var err_id) [Type ty, core_msg])
434 *************************************************************
436 \subsection{Making literals}
438 %************************************************************************
441 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
442 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
443 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
444 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
445 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
447 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
448 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
451 | inIntRange i -- Small enough, so start from an Int
452 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
453 returnDs (mkSmallIntegerLit integer_dc i)
455 -- Special case for integral literals with a large magnitude:
456 -- They are transformed into an expression involving only smaller
457 -- integral literals. This improves constant folding.
459 | otherwise -- Big, so start from a string
460 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
461 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
462 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
464 lit i = mkSmallIntegerLit integer_dc i
465 plus a b = Var plus_id `App` a `App` b
466 times a b = Var times_id `App` a `App` b
468 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
469 horner :: Integer -> Integer -> CoreExpr
470 horner b i | abs q <= 1 = if r == 0 || r == i
472 else lit r `plus` lit (i-r)
473 | r == 0 = horner b q `times` lit b
474 | otherwise = lit r `plus` (horner b q `times` lit b)
476 (q,r) = i `quotRem` b
479 returnDs (horner tARGET_MAX_INT i)
481 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
483 mkStringExpr str = mkStringExprFS (mkFastString str)
487 = returnDs (mkNilExpr charTy)
491 the_char = mkCharExpr (headFS str)
493 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
496 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
497 returnDs (App (Var unpack_id) (Lit (MachStr str)))
500 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
501 returnDs (App (Var unpack_id) (Lit (MachStr str)))
505 safeChar c = ord c >= 1 && ord c <= 0x7F
509 %************************************************************************
511 \subsection[mkSelectorBind]{Make a selector bind}
513 %************************************************************************
515 This is used in various places to do with lazy patterns.
516 For each binder $b$ in the pattern, we create a binding:
518 b = case v of pat' -> b'
520 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
522 ToDo: making these bindings should really depend on whether there's
523 much work to be done per binding. If the pattern is complex, it
524 should be de-mangled once, into a tuple (and then selected from).
525 Otherwise the demangling can be in-line in the bindings (as here).
527 Boring! Boring! One error message per binder. The above ToDo is
528 even more helpful. Something very similar happens for pattern-bound
532 mkSelectorBinds :: LPat Id -- The pattern
533 -> CoreExpr -- Expression to which the pattern is bound
534 -> DsM [(Id,CoreExpr)]
536 mkSelectorBinds (L _ (VarPat v)) val_expr
537 = returnDs [(v, val_expr)]
539 mkSelectorBinds pat val_expr
540 | isSingleton binders || is_simple_lpat pat
541 = -- Given p = e, where p binds x,y
542 -- we are going to make
543 -- v = p (where v is fresh)
544 -- x = case v of p -> x
545 -- y = case v of p -> x
548 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
549 -- This does not matter after desugaring, but there's a subtle
550 -- issue with implicit parameters. Consider
552 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
553 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
554 -- does it get that type? So that when we abstract over it we get the
555 -- right top-level type (?i::Int) => ...)
557 -- So to get the type of 'v', use the pattern not the rhs. Often more
559 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
561 -- For the error message we make one error-app, to avoid duplication.
562 -- But we need it at different types... so we use coerce for that
563 mkErrorAppDs iRREFUT_PAT_ERROR_ID
564 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
565 newSysLocalDs unitTy `thenDs` \ err_var ->
566 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
567 returnDs ( (val_var, val_expr) :
568 (err_var, err_expr) :
573 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
574 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
575 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
576 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
579 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
581 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
583 binders = collectPatBinders pat
584 local_tuple = mkTupleExpr binders
585 tuple_ty = exprType local_tuple
587 mk_bind scrut_var err_var bndr_var
588 -- (mk_bind sv err_var) generates
589 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
590 -- Remember, pat binds bv
591 = matchSimply (Var scrut_var) PatBindRhs pat
592 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
593 returnDs (bndr_var, rhs_expr)
595 error_expr = mkCoerce co (Var err_var)
596 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
598 is_simple_lpat p = is_simple_pat (unLoc p)
600 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
601 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConArgs ps)
602 is_simple_pat (VarPat _) = True
603 is_simple_pat (ParPat p) = is_simple_lpat p
604 is_simple_pat other = False
606 is_triv_lpat p = is_triv_pat (unLoc p)
608 is_triv_pat (VarPat v) = True
609 is_triv_pat (WildPat _) = True
610 is_triv_pat (ParPat p) = is_triv_lpat p
611 is_triv_pat other = False
615 %************************************************************************
619 %************************************************************************
621 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
623 * If it has only one element, it is the identity function.
625 * If there are more elements than a big tuple can have, it nests
628 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
629 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
632 mkTupleExpr :: [Id] -> CoreExpr
633 mkTupleExpr ids = mkBigCoreTup (map Var ids)
635 -- corresponding type
636 mkTupleType :: [Id] -> Type
637 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
639 mkBigCoreTup :: [CoreExpr] -> CoreExpr
640 mkBigCoreTup = mkBigTuple mkCoreTup
642 mkBigTuple :: ([a] -> a) -> [a] -> a
643 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
645 -- Each sub-list is short enough to fit in a tuple
646 mk_big_tuple [as] = small_tuple as
647 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
649 chunkify :: [a] -> [[a]]
650 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
651 -- But there may be more than mAX_TUPLE_SIZE sub-lists
653 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
654 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
658 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
662 @mkTupleSelector@ builds a selector which scrutises the given
663 expression and extracts the one name from the list given.
664 If you want the no-shadowing rule to apply, the caller
665 is responsible for making sure that none of these names
668 If there is just one id in the ``tuple'', then the selector is
671 If it's big, it does nesting
672 mkTupleSelector [a,b,c,d] b v e
674 (p,q) -> case p of p {
676 We use 'tpl' vars for the p,q, since shadowing does not matter.
678 In fact, it's more convenient to generate it innermost first, getting
685 mkTupleSelector :: [Id] -- The tuple args
686 -> Id -- The selected one
687 -> Id -- A variable of the same type as the scrutinee
688 -> CoreExpr -- Scrutinee
691 mkTupleSelector vars the_var scrut_var scrut
692 = mk_tup_sel (chunkify vars) the_var
694 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
695 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
696 mk_tup_sel (chunkify tpl_vs) tpl_v
698 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
699 tpl_vs = mkTemplateLocals tpl_tys
700 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
704 A generalization of @mkTupleSelector@, allowing the body
705 of the case to be an arbitrary expression.
707 If the tuple is big, it is nested:
709 mkTupleCase uniqs [a,b,c,d] body v e
710 = case e of v { (p,q) ->
711 case p of p { (a,b) ->
712 case q of q { (c,d) ->
715 To avoid shadowing, we use uniqs to invent new variables p,q.
717 ToDo: eliminate cases where none of the variables are needed.
721 :: UniqSupply -- for inventing names of intermediate variables
722 -> [Id] -- the tuple args
723 -> CoreExpr -- body of the case
724 -> Id -- a variable of the same type as the scrutinee
725 -> CoreExpr -- scrutinee
728 mkTupleCase uniqs vars body scrut_var scrut
729 = mk_tuple_case uniqs (chunkify vars) body
731 mk_tuple_case us [vars] body
732 = mkSmallTupleCase vars body scrut_var scrut
733 mk_tuple_case us vars_s body
735 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
737 mk_tuple_case us' (chunkify vars') body'
738 one_tuple_case chunk_vars (us, vs, body)
740 (us1, us2) = splitUniqSupply us
741 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
742 (mkCoreTupTy (map idType chunk_vars))
743 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
744 in (us2, scrut_var:vs, body')
747 The same, but with a tuple small enough not to need nesting.
751 :: [Id] -- the tuple args
752 -> CoreExpr -- body of the case
753 -> Id -- a variable of the same type as the scrutinee
754 -> CoreExpr -- scrutinee
757 mkSmallTupleCase [var] body _scrut_var scrut
758 = bindNonRec var scrut body
759 mkSmallTupleCase vars body scrut_var scrut
760 -- One branch no refinement?
761 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
764 %************************************************************************
766 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
768 %************************************************************************
770 Call the constructor Ids when building explicit lists, so that they
771 interact well with rules.
774 mkNilExpr :: Type -> CoreExpr
775 mkNilExpr ty = mkConApp nilDataCon [Type ty]
777 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
778 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
780 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
781 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
784 -- The next three functions make tuple types, constructors and selectors,
785 -- with the rule that a 1-tuple is represented by the thing itselg
786 mkCoreTupTy :: [Type] -> Type
787 mkCoreTupTy [ty] = ty
788 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
790 mkCoreTup :: [CoreExpr] -> CoreExpr
791 -- Builds exactly the specified tuple.
792 -- No fancy business for big tuples
793 mkCoreTup [] = Var unitDataConId
795 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
796 (map (Type . exprType) cs ++ cs)
798 mkCoreSel :: [Id] -- The tuple args
799 -> Id -- The selected one
800 -> Id -- A variable of the same type as the scrutinee
801 -> CoreExpr -- Scrutinee
803 -- mkCoreSel [x,y,z] x v e
804 -- ===> case e of v { (x,y,z) -> x
805 mkCoreSel [var] should_be_the_same_var scrut_var scrut
806 = ASSERT(var == should_be_the_same_var)
809 mkCoreSel vars the_var scrut_var scrut
810 = ASSERT( notNull vars )
811 Case scrut scrut_var (idType the_var)
812 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
816 %************************************************************************
818 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
820 %************************************************************************
822 Generally, we handle pattern matching failure like this: let-bind a
823 fail-variable, and use that variable if the thing fails:
825 let fail.33 = error "Help"
836 If the case can't fail, then there'll be no mention of @fail.33@, and the
837 simplifier will later discard it.
840 If it can fail in only one way, then the simplifier will inline it.
843 Only if it is used more than once will the let-binding remain.
846 There's a problem when the result of the case expression is of
847 unboxed type. Then the type of @fail.33@ is unboxed too, and
848 there is every chance that someone will change the let into a case:
854 which is of course utterly wrong. Rather than drop the condition that
855 only boxed types can be let-bound, we just turn the fail into a function
856 for the primitive case:
858 let fail.33 :: Void -> Int#
859 fail.33 = \_ -> error "Help"
868 Now @fail.33@ is a function, so it can be let-bound.
871 mkFailurePair :: CoreExpr -- Result type of the whole case expression
872 -> DsM (CoreBind, -- Binds the newly-created fail variable
873 -- to either the expression or \ _ -> expression
874 CoreExpr) -- Either the fail variable, or fail variable
875 -- applied to unit tuple
878 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
879 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
880 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
881 App (Var fail_fun_var) (Var unitDataConId))
884 = newFailLocalDs ty `thenDs` \ fail_var ->
885 returnDs (NonRec fail_var expr, Var fail_var)