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.
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 )
81 %************************************************************************
85 %************************************************************************
88 dsSyntaxTable :: SyntaxTable Id
89 -> DsM ([CoreBind], -- Auxiliary bindings
90 [(Name,Id)]) -- Maps the standard name to its value
92 dsSyntaxTable rebound_ids
93 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
94 return (concat binds_s, prs)
96 -- The cheapo special case can happen when we
97 -- make an intermediate HsDo when desugaring a RecStmt
98 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
99 mk_bind (std_name, expr)
100 = dsExpr expr `thenDs` \ rhs ->
101 newSysLocalDs (exprType rhs) `thenDs` \ id ->
102 return ([NonRec id rhs], (std_name, id))
104 lookupEvidence :: [(Name, Id)] -> Name -> Id
105 lookupEvidence prs std_name
106 = assocDefault (mk_panic std_name) prs std_name
108 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
112 %************************************************************************
114 \subsection{Building lets}
116 %************************************************************************
118 Use case, not let for unlifted types. The simplifier will turn some
122 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
123 mkDsLet (NonRec bndr rhs) body
124 | isUnLiftedType (idType bndr)
125 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
129 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
130 mkDsLets binds body = foldr mkDsLet body binds
134 %************************************************************************
136 \subsection{ Selecting match variables}
138 %************************************************************************
140 We're about to match against some patterns. We want to make some
141 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
142 hand, which should indeed be bound to the pattern as a whole, then use it;
143 otherwise, make one up.
146 selectSimpleMatchVarL :: LPat Id -> DsM Id
147 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
149 -- (selectMatchVars ps tys) chooses variables of type tys
150 -- to use for matching ps against. If the pattern is a variable,
151 -- we try to use that, to save inventing lots of fresh variables.
153 -- OLD, but interesting note:
154 -- But even if it is a variable, its type might not match. Consider
156 -- T1 :: Int -> T Int
159 -- f :: T a -> a -> Int
160 -- f (T1 i) (x::Int) = x
161 -- f (T2 i) (y::a) = 0
162 -- Then we must not choose (x::Int) as the matching variable!
163 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
165 selectMatchVars :: [Pat Id] -> DsM [Id]
166 selectMatchVars ps = mapM selectMatchVar ps
168 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
169 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
170 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
171 selectMatchVar (VarPat var) = return var
172 selectMatchVar (AsPat var pat) = return (unLoc var)
173 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
174 -- OK, better make up one...
178 %************************************************************************
180 %* type synonym EquationInfo and access functions for its pieces *
182 %************************************************************************
183 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
185 The ``equation info'' used by @match@ is relatively complicated and
186 worthy of a type synonym and a few handy functions.
189 firstPat :: EquationInfo -> Pat Id
190 firstPat eqn = head (eqn_pats eqn)
192 shiftEqns :: [EquationInfo] -> [EquationInfo]
193 -- Drop the first pattern in each equation
194 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
197 Functions on MatchResults
200 matchCanFail :: MatchResult -> Bool
201 matchCanFail (MatchResult CanFail _) = True
202 matchCanFail (MatchResult CantFail _) = False
204 alwaysFailMatchResult :: MatchResult
205 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
207 cantFailMatchResult :: CoreExpr -> MatchResult
208 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
210 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
211 extractMatchResult (MatchResult CantFail match_fn) fail_expr
212 = match_fn (error "It can't fail!")
214 extractMatchResult (MatchResult CanFail match_fn) fail_expr
215 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
216 match_fn if_it_fails `thenDs` \ body ->
217 returnDs (mkDsLet fail_bind body)
220 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
221 combineMatchResults (MatchResult CanFail body_fn1)
222 (MatchResult can_it_fail2 body_fn2)
223 = MatchResult can_it_fail2 body_fn
225 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
226 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
227 body_fn1 duplicatable_expr `thenDs` \ body1 ->
228 returnDs (Let fail_bind body1)
230 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
233 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
234 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
235 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
236 returnDs (encl_fn body))
238 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
239 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
240 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
243 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
245 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
247 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
248 wrapBind new old body
250 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
251 | otherwise = Let (NonRec new (Var old)) body
253 seqVar :: Var -> CoreExpr -> CoreExpr
254 seqVar var body = Case (Var var) var (exprType body)
255 [(DEFAULT, [], body)]
257 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
258 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
260 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
261 mkEvalMatchResult var ty
262 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
264 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
265 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
266 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
267 returnDs (mkIfThenElse pred_expr body fail))
269 mkCoPrimCaseMatchResult :: Id -- Scrutinee
270 -> Type -- Type of the case
271 -> [(Literal, MatchResult)] -- Alternatives
273 mkCoPrimCaseMatchResult var ty match_alts
274 = MatchResult CanFail mk_case
277 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
278 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
280 sorted_alts = sortWith fst match_alts -- Right order for a Case
281 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
282 returnDs (LitAlt lit, [], body)
285 mkCoAlgCaseMatchResult :: Id -- Scrutinee
286 -> Type -- Type of exp
287 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
289 mkCoAlgCaseMatchResult var ty match_alts
290 | isNewTyCon tycon -- Newtype case; use a let
291 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
292 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
294 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
295 = MatchResult CanFail mk_parrCase
297 | otherwise -- Datatype case; use a case
298 = MatchResult fail_flag mk_case
300 tycon = dataConTyCon con1
301 -- [Interesting: becuase of GADTs, we can't rely on the type of
302 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
305 (con1, arg_ids1, match_result1) = head match_alts
306 arg_id1 = head arg_ids1
308 (tc, ty_args) = splitNewTyConApp var_ty
309 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
311 -- Stuff for data types
312 data_cons = tyConDataCons tycon
313 match_results = [match_result | (_,_,match_result) <- match_alts]
315 fail_flag | exhaustive_case
316 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
320 wild_var = mkWildId (idType var)
321 sorted_alts = sortWith get_tag match_alts
322 get_tag (con, _, _) = dataConTag con
323 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
324 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
326 mk_alt fail (con, args, MatchResult _ body_fn)
327 = body_fn fail `thenDs` \ body ->
328 newUniqueSupply `thenDs` \ us ->
329 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
331 mk_default fail | exhaustive_case = []
332 | otherwise = [(DEFAULT, [], fail)]
334 un_mentioned_constructors
335 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
336 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
338 -- Stuff for parallel arrays
340 -- * the following is to desugar cases over fake constructors for
341 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
344 -- Concerning `isPArrFakeAlts':
346 -- * it is *not* sufficient to just check the type of the type
347 -- constructor, as we have to be careful not to confuse the real
348 -- representation of parallel arrays with the fake constructors;
349 -- moreover, a list of alternatives must not mix fake and real
350 -- constructors (this is checked earlier on)
352 -- FIXME: We actually go through the whole list and make sure that
353 -- either all or none of the constructors are fake parallel
354 -- array constructors. This is to spot equations that mix fake
355 -- constructors with the real representation defined in
356 -- `PrelPArr'. It would be nicer to spot this situation
357 -- earlier and raise a proper error message, but it can really
358 -- only happen in `PrelPArr' anyway.
360 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
361 isPArrFakeAlts ((dcon, _, _):alts) =
362 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
363 (True , True ) -> True
364 (False, False) -> False
366 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
369 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
370 unboxAlt `thenDs` \alt ->
371 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
373 elemTy = case splitTyConApp (idType var) of
374 (_, [elemTy]) -> elemTy
376 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
377 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
380 newSysLocalDs intPrimTy `thenDs` \l ->
381 dsLookupGlobalId indexPName `thenDs` \indexP ->
382 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
383 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
385 wild = mkWildId intPrimTy
386 dft = (DEFAULT, [], fail)
388 -- each alternative matches one array length (corresponding to one
389 -- fake array constructor), so the match is on a literal; each
390 -- alternative's body is extended by a local binding for each
391 -- constructor argument, which are bound to array elements starting
394 mkAlt indexP (con, args, MatchResult _ bodyFun) =
395 bodyFun fail `thenDs` \body ->
396 returnDs (LitAlt lit, [], mkDsLets binds body)
398 lit = MachInt $ toInteger (dataConSourceArity con)
399 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
401 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
405 %************************************************************************
407 \subsection{Desugarer's versions of some Core functions}
409 %************************************************************************
412 mkErrorAppDs :: Id -- The error function
413 -> Type -- Type to which it should be applied
414 -> String -- The error message string to pass
417 mkErrorAppDs err_id ty msg
418 = getSrcSpanDs `thenDs` \ src_loc ->
420 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
421 core_msg = Lit (mkStringLit full_msg)
422 -- mkStringLit returns a result of type String#
424 returnDs (mkApps (Var err_id) [Type ty, core_msg])
428 *************************************************************
430 \subsection{Making literals}
432 %************************************************************************
435 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
436 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
437 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
438 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
439 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
441 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
442 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
445 | inIntRange i -- Small enough, so start from an Int
446 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
447 returnDs (mkSmallIntegerLit integer_dc i)
449 -- Special case for integral literals with a large magnitude:
450 -- They are transformed into an expression involving only smaller
451 -- integral literals. This improves constant folding.
453 | otherwise -- Big, so start from a string
454 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
455 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
456 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
458 lit i = mkSmallIntegerLit integer_dc i
459 plus a b = Var plus_id `App` a `App` b
460 times a b = Var times_id `App` a `App` b
462 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
463 horner :: Integer -> Integer -> CoreExpr
464 horner b i | abs q <= 1 = if r == 0 || r == i
466 else lit r `plus` lit (i-r)
467 | r == 0 = horner b q `times` lit b
468 | otherwise = lit r `plus` (horner b q `times` lit b)
470 (q,r) = i `quotRem` b
473 returnDs (horner tARGET_MAX_INT i)
475 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
477 mkStringExpr str = mkStringExprFS (mkFastString str)
481 = returnDs (mkNilExpr charTy)
485 the_char = mkCharExpr (headFS str)
487 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
490 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
491 returnDs (App (Var unpack_id) (Lit (MachStr str)))
494 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
495 returnDs (App (Var unpack_id) (Lit (MachStr str)))
499 safeChar c = ord c >= 1 && ord c <= 0x7F
503 %************************************************************************
505 \subsection[mkSelectorBind]{Make a selector bind}
507 %************************************************************************
509 This is used in various places to do with lazy patterns.
510 For each binder $b$ in the pattern, we create a binding:
512 b = case v of pat' -> b'
514 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
516 ToDo: making these bindings should really depend on whether there's
517 much work to be done per binding. If the pattern is complex, it
518 should be de-mangled once, into a tuple (and then selected from).
519 Otherwise the demangling can be in-line in the bindings (as here).
521 Boring! Boring! One error message per binder. The above ToDo is
522 even more helpful. Something very similar happens for pattern-bound
526 mkSelectorBinds :: LPat Id -- The pattern
527 -> CoreExpr -- Expression to which the pattern is bound
528 -> DsM [(Id,CoreExpr)]
530 mkSelectorBinds (L _ (VarPat v)) val_expr
531 = returnDs [(v, val_expr)]
533 mkSelectorBinds pat val_expr
534 | isSingleton binders || is_simple_lpat pat
535 = -- Given p = e, where p binds x,y
536 -- we are going to make
537 -- v = p (where v is fresh)
538 -- x = case v of p -> x
539 -- y = case v of p -> x
542 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
543 -- This does not matter after desugaring, but there's a subtle
544 -- issue with implicit parameters. Consider
546 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
547 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
548 -- does it get that type? So that when we abstract over it we get the
549 -- right top-level type (?i::Int) => ...)
551 -- So to get the type of 'v', use the pattern not the rhs. Often more
553 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
555 -- For the error message we make one error-app, to avoid duplication.
556 -- But we need it at different types... so we use coerce for that
557 mkErrorAppDs iRREFUT_PAT_ERROR_ID
558 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
559 newSysLocalDs unitTy `thenDs` \ err_var ->
560 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
561 returnDs ( (val_var, val_expr) :
562 (err_var, err_expr) :
567 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
568 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
569 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
570 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
573 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
575 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
577 binders = collectPatBinders pat
578 local_tuple = mkTupleExpr binders
579 tuple_ty = exprType local_tuple
581 mk_bind scrut_var err_var bndr_var
582 -- (mk_bind sv err_var) generates
583 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
584 -- Remember, pat binds bv
585 = matchSimply (Var scrut_var) PatBindRhs pat
586 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
587 returnDs (bndr_var, rhs_expr)
589 error_expr = mkCoerce co (Var err_var)
590 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
592 is_simple_lpat p = is_simple_pat (unLoc p)
594 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
595 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConArgs ps)
596 is_simple_pat (VarPat _) = True
597 is_simple_pat (ParPat p) = is_simple_lpat p
598 is_simple_pat other = False
600 is_triv_lpat p = is_triv_pat (unLoc p)
602 is_triv_pat (VarPat v) = True
603 is_triv_pat (WildPat _) = True
604 is_triv_pat (ParPat p) = is_triv_lpat p
605 is_triv_pat other = False
609 %************************************************************************
613 %************************************************************************
615 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
617 * If it has only one element, it is the identity function.
619 * If there are more elements than a big tuple can have, it nests
622 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
623 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
626 mkTupleExpr :: [Id] -> CoreExpr
627 mkTupleExpr ids = mkBigCoreTup (map Var ids)
629 -- corresponding type
630 mkTupleType :: [Id] -> Type
631 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
633 mkBigCoreTup :: [CoreExpr] -> CoreExpr
634 mkBigCoreTup = mkBigTuple mkCoreTup
636 mkBigTuple :: ([a] -> a) -> [a] -> a
637 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
639 -- Each sub-list is short enough to fit in a tuple
640 mk_big_tuple [as] = small_tuple as
641 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
643 chunkify :: [a] -> [[a]]
644 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
645 -- But there may be more than mAX_TUPLE_SIZE sub-lists
647 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
648 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
652 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
656 @mkTupleSelector@ builds a selector which scrutises the given
657 expression and extracts the one name from the list given.
658 If you want the no-shadowing rule to apply, the caller
659 is responsible for making sure that none of these names
662 If there is just one id in the ``tuple'', then the selector is
665 If it's big, it does nesting
666 mkTupleSelector [a,b,c,d] b v e
668 (p,q) -> case p of p {
670 We use 'tpl' vars for the p,q, since shadowing does not matter.
672 In fact, it's more convenient to generate it innermost first, getting
679 mkTupleSelector :: [Id] -- The tuple args
680 -> Id -- The selected one
681 -> Id -- A variable of the same type as the scrutinee
682 -> CoreExpr -- Scrutinee
685 mkTupleSelector vars the_var scrut_var scrut
686 = mk_tup_sel (chunkify vars) the_var
688 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
689 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
690 mk_tup_sel (chunkify tpl_vs) tpl_v
692 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
693 tpl_vs = mkTemplateLocals tpl_tys
694 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
698 A generalization of @mkTupleSelector@, allowing the body
699 of the case to be an arbitrary expression.
701 If the tuple is big, it is nested:
703 mkTupleCase uniqs [a,b,c,d] body v e
704 = case e of v { (p,q) ->
705 case p of p { (a,b) ->
706 case q of q { (c,d) ->
709 To avoid shadowing, we use uniqs to invent new variables p,q.
711 ToDo: eliminate cases where none of the variables are needed.
715 :: UniqSupply -- for inventing names of intermediate variables
716 -> [Id] -- the tuple args
717 -> CoreExpr -- body of the case
718 -> Id -- a variable of the same type as the scrutinee
719 -> CoreExpr -- scrutinee
722 mkTupleCase uniqs vars body scrut_var scrut
723 = mk_tuple_case uniqs (chunkify vars) body
725 mk_tuple_case us [vars] body
726 = mkSmallTupleCase vars body scrut_var scrut
727 mk_tuple_case us vars_s body
729 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
731 mk_tuple_case us' (chunkify vars') body'
732 one_tuple_case chunk_vars (us, vs, body)
734 (us1, us2) = splitUniqSupply us
735 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
736 (mkCoreTupTy (map idType chunk_vars))
737 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
738 in (us2, scrut_var:vs, body')
741 The same, but with a tuple small enough not to need nesting.
745 :: [Id] -- the tuple args
746 -> CoreExpr -- body of the case
747 -> Id -- a variable of the same type as the scrutinee
748 -> CoreExpr -- scrutinee
751 mkSmallTupleCase [var] body _scrut_var scrut
752 = bindNonRec var scrut body
753 mkSmallTupleCase vars body scrut_var scrut
754 -- One branch no refinement?
755 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
758 %************************************************************************
760 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
762 %************************************************************************
764 Call the constructor Ids when building explicit lists, so that they
765 interact well with rules.
768 mkNilExpr :: Type -> CoreExpr
769 mkNilExpr ty = mkConApp nilDataCon [Type ty]
771 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
772 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
774 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
775 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
778 -- The next three functions make tuple types, constructors and selectors,
779 -- with the rule that a 1-tuple is represented by the thing itselg
780 mkCoreTupTy :: [Type] -> Type
781 mkCoreTupTy [ty] = ty
782 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
784 mkCoreTup :: [CoreExpr] -> CoreExpr
785 -- Builds exactly the specified tuple.
786 -- No fancy business for big tuples
787 mkCoreTup [] = Var unitDataConId
789 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
790 (map (Type . exprType) cs ++ cs)
792 mkCoreSel :: [Id] -- The tuple args
793 -> Id -- The selected one
794 -> Id -- A variable of the same type as the scrutinee
795 -> CoreExpr -- Scrutinee
797 -- mkCoreSel [x,y,z] x v e
798 -- ===> case e of v { (x,y,z) -> x
799 mkCoreSel [var] should_be_the_same_var scrut_var scrut
800 = ASSERT(var == should_be_the_same_var)
803 mkCoreSel vars the_var scrut_var scrut
804 = ASSERT( notNull vars )
805 Case scrut scrut_var (idType the_var)
806 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
810 %************************************************************************
812 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
814 %************************************************************************
816 Generally, we handle pattern matching failure like this: let-bind a
817 fail-variable, and use that variable if the thing fails:
819 let fail.33 = error "Help"
830 If the case can't fail, then there'll be no mention of @fail.33@, and the
831 simplifier will later discard it.
834 If it can fail in only one way, then the simplifier will inline it.
837 Only if it is used more than once will the let-binding remain.
840 There's a problem when the result of the case expression is of
841 unboxed type. Then the type of @fail.33@ is unboxed too, and
842 there is every chance that someone will change the let into a case:
848 which is of course utterly wrong. Rather than drop the condition that
849 only boxed types can be let-bound, we just turn the fail into a function
850 for the primitive case:
852 let fail.33 :: Void -> Int#
853 fail.33 = \_ -> error "Help"
862 Now @fail.33@ is a function, so it can be let-bound.
865 mkFailurePair :: CoreExpr -- Result type of the whole case expression
866 -> DsM (CoreBind, -- Binds the newly-created fail variable
867 -- to either the expression or \ _ -> expression
868 CoreExpr) -- Either the fail variable, or fail variable
869 -- applied to unit tuple
872 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
873 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
874 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
875 App (Var fail_fun_var) (Var unitDataConId))
878 = newFailLocalDs ty `thenDs` \ fail_var ->
879 returnDs (NonRec fail_var expr, Var fail_var)
885 mkOptTickBox :: Maybe Int -> CoreExpr -> DsM CoreExpr
886 mkOptTickBox Nothing e = return e
887 mkOptTickBox (Just ix) e = mkTickBox ix e
889 mkTickBox :: Int -> CoreExpr -> DsM CoreExpr
892 return $ Note (TickBox mod ix) e
894 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
895 mkBinaryTickBox ixT ixF e = do
897 return $ Note (BinaryTickBox mod ixT ixF) e