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 )
82 %************************************************************************
86 %************************************************************************
89 dsSyntaxTable :: SyntaxTable Id
90 -> DsM ([CoreBind], -- Auxiliary bindings
91 [(Name,Id)]) -- Maps the standard name to its value
93 dsSyntaxTable rebound_ids
94 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
95 return (concat binds_s, prs)
97 -- The cheapo special case can happen when we
98 -- make an intermediate HsDo when desugaring a RecStmt
99 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
100 mk_bind (std_name, expr)
101 = dsExpr expr `thenDs` \ rhs ->
102 newSysLocalDs (exprType rhs) `thenDs` \ id ->
103 return ([NonRec id rhs], (std_name, id))
105 lookupEvidence :: [(Name, Id)] -> Name -> Id
106 lookupEvidence prs std_name
107 = assocDefault (mk_panic std_name) prs std_name
109 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
113 %************************************************************************
115 \subsection{Building lets}
117 %************************************************************************
119 Use case, not let for unlifted types. The simplifier will turn some
123 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
124 mkDsLet (NonRec bndr rhs) body
125 | isUnLiftedType (idType bndr)
126 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
130 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
131 mkDsLets binds body = foldr mkDsLet body binds
135 %************************************************************************
137 \subsection{ Selecting match variables}
139 %************************************************************************
141 We're about to match against some patterns. We want to make some
142 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
143 hand, which should indeed be bound to the pattern as a whole, then use it;
144 otherwise, make one up.
147 selectSimpleMatchVarL :: LPat Id -> DsM Id
148 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
150 -- (selectMatchVars ps tys) chooses variables of type tys
151 -- to use for matching ps against. If the pattern is a variable,
152 -- we try to use that, to save inventing lots of fresh variables.
154 -- OLD, but interesting note:
155 -- But even if it is a variable, its type might not match. Consider
157 -- T1 :: Int -> T Int
160 -- f :: T a -> a -> Int
161 -- f (T1 i) (x::Int) = x
162 -- f (T2 i) (y::a) = 0
163 -- Then we must not choose (x::Int) as the matching variable!
164 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
166 selectMatchVars :: [Pat Id] -> DsM [Id]
167 selectMatchVars ps = mapM selectMatchVar ps
169 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
170 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
171 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
172 selectMatchVar (VarPat var) = return var
173 selectMatchVar (AsPat var pat) = return (unLoc var)
174 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
175 -- OK, better make up one...
179 %************************************************************************
181 %* type synonym EquationInfo and access functions for its pieces *
183 %************************************************************************
184 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
186 The ``equation info'' used by @match@ is relatively complicated and
187 worthy of a type synonym and a few handy functions.
190 firstPat :: EquationInfo -> Pat Id
191 firstPat eqn = head (eqn_pats eqn)
193 shiftEqns :: [EquationInfo] -> [EquationInfo]
194 -- Drop the first pattern in each equation
195 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
198 Functions on MatchResults
201 matchCanFail :: MatchResult -> Bool
202 matchCanFail (MatchResult CanFail _) = True
203 matchCanFail (MatchResult CantFail _) = False
205 alwaysFailMatchResult :: MatchResult
206 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
208 cantFailMatchResult :: CoreExpr -> MatchResult
209 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
211 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
212 extractMatchResult (MatchResult CantFail match_fn) fail_expr
213 = match_fn (error "It can't fail!")
215 extractMatchResult (MatchResult CanFail match_fn) fail_expr
216 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
217 match_fn if_it_fails `thenDs` \ body ->
218 returnDs (mkDsLet fail_bind body)
221 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
222 combineMatchResults (MatchResult CanFail body_fn1)
223 (MatchResult can_it_fail2 body_fn2)
224 = MatchResult can_it_fail2 body_fn
226 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
227 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
228 body_fn1 duplicatable_expr `thenDs` \ body1 ->
229 returnDs (Let fail_bind body1)
231 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
234 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
235 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
236 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
237 returnDs (encl_fn body))
239 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
240 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
241 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
244 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
246 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
248 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
249 wrapBind new old body
251 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
252 | otherwise = Let (NonRec new (Var old)) body
254 seqVar :: Var -> CoreExpr -> CoreExpr
255 seqVar var body = Case (Var var) var (exprType body)
256 [(DEFAULT, [], body)]
258 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
259 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
261 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
262 mkEvalMatchResult var ty
263 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
265 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
266 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
267 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
268 returnDs (mkIfThenElse pred_expr body fail))
270 mkCoPrimCaseMatchResult :: Id -- Scrutinee
271 -> Type -- Type of the case
272 -> [(Literal, MatchResult)] -- Alternatives
274 mkCoPrimCaseMatchResult var ty match_alts
275 = MatchResult CanFail mk_case
278 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
279 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
281 sorted_alts = sortWith fst match_alts -- Right order for a Case
282 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
283 returnDs (LitAlt lit, [], body)
286 mkCoAlgCaseMatchResult :: Id -- Scrutinee
287 -> Type -- Type of exp
288 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
290 mkCoAlgCaseMatchResult var ty match_alts
291 | isNewTyCon tycon -- Newtype case; use a let
292 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
293 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
295 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
296 = MatchResult CanFail mk_parrCase
298 | otherwise -- Datatype case; use a case
299 = MatchResult fail_flag mk_case
301 tycon = dataConTyCon con1
302 -- [Interesting: becuase of GADTs, we can't rely on the type of
303 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
306 (con1, arg_ids1, match_result1) = head match_alts
307 arg_id1 = head arg_ids1
309 (tc, ty_args) = splitNewTyConApp var_ty
310 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
312 -- Stuff for data types
313 data_cons = tyConDataCons tycon
314 match_results = [match_result | (_,_,match_result) <- match_alts]
316 fail_flag | exhaustive_case
317 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
321 wild_var = mkWildId (idType var)
322 sorted_alts = sortWith get_tag match_alts
323 get_tag (con, _, _) = dataConTag con
324 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
325 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
327 mk_alt fail (con, args, MatchResult _ body_fn)
328 = body_fn fail `thenDs` \ body ->
329 newUniqueSupply `thenDs` \ us ->
330 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
332 mk_default fail | exhaustive_case = []
333 | otherwise = [(DEFAULT, [], fail)]
335 un_mentioned_constructors
336 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
337 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
339 -- Stuff for parallel arrays
341 -- * the following is to desugar cases over fake constructors for
342 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
345 -- Concerning `isPArrFakeAlts':
347 -- * it is *not* sufficient to just check the type of the type
348 -- constructor, as we have to be careful not to confuse the real
349 -- representation of parallel arrays with the fake constructors;
350 -- moreover, a list of alternatives must not mix fake and real
351 -- constructors (this is checked earlier on)
353 -- FIXME: We actually go through the whole list and make sure that
354 -- either all or none of the constructors are fake parallel
355 -- array constructors. This is to spot equations that mix fake
356 -- constructors with the real representation defined in
357 -- `PrelPArr'. It would be nicer to spot this situation
358 -- earlier and raise a proper error message, but it can really
359 -- only happen in `PrelPArr' anyway.
361 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
362 isPArrFakeAlts ((dcon, _, _):alts) =
363 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
364 (True , True ) -> True
365 (False, False) -> False
367 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
370 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
371 unboxAlt `thenDs` \alt ->
372 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
374 elemTy = case splitTyConApp (idType var) of
375 (_, [elemTy]) -> elemTy
377 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
378 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
381 newSysLocalDs intPrimTy `thenDs` \l ->
382 dsLookupGlobalId indexPName `thenDs` \indexP ->
383 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
384 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
386 wild = mkWildId intPrimTy
387 dft = (DEFAULT, [], fail)
389 -- each alternative matches one array length (corresponding to one
390 -- fake array constructor), so the match is on a literal; each
391 -- alternative's body is extended by a local binding for each
392 -- constructor argument, which are bound to array elements starting
395 mkAlt indexP (con, args, MatchResult _ bodyFun) =
396 bodyFun fail `thenDs` \body ->
397 returnDs (LitAlt lit, [], mkDsLets binds body)
399 lit = MachInt $ toInteger (dataConSourceArity con)
400 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
402 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
406 %************************************************************************
408 \subsection{Desugarer's versions of some Core functions}
410 %************************************************************************
413 mkErrorAppDs :: Id -- The error function
414 -> Type -- Type to which it should be applied
415 -> String -- The error message string to pass
418 mkErrorAppDs err_id ty msg
419 = getSrcSpanDs `thenDs` \ src_loc ->
421 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
422 core_msg = Lit (mkStringLit full_msg)
423 -- mkStringLit returns a result of type String#
425 returnDs (mkApps (Var err_id) [Type ty, core_msg])
429 *************************************************************
431 \subsection{Making literals}
433 %************************************************************************
436 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
437 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
438 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
439 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
440 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
442 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
443 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
446 | inIntRange i -- Small enough, so start from an Int
447 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
448 returnDs (mkSmallIntegerLit integer_dc i)
450 -- Special case for integral literals with a large magnitude:
451 -- They are transformed into an expression involving only smaller
452 -- integral literals. This improves constant folding.
454 | otherwise -- Big, so start from a string
455 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
456 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
457 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
459 lit i = mkSmallIntegerLit integer_dc i
460 plus a b = Var plus_id `App` a `App` b
461 times a b = Var times_id `App` a `App` b
463 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
464 horner :: Integer -> Integer -> CoreExpr
465 horner b i | abs q <= 1 = if r == 0 || r == i
467 else lit r `plus` lit (i-r)
468 | r == 0 = horner b q `times` lit b
469 | otherwise = lit r `plus` (horner b q `times` lit b)
471 (q,r) = i `quotRem` b
474 returnDs (horner tARGET_MAX_INT i)
476 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
478 mkStringExpr str = mkStringExprFS (mkFastString str)
482 = returnDs (mkNilExpr charTy)
486 the_char = mkCharExpr (headFS str)
488 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
491 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
492 returnDs (App (Var unpack_id) (Lit (MachStr str)))
495 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
496 returnDs (App (Var unpack_id) (Lit (MachStr str)))
500 safeChar c = ord c >= 1 && ord c <= 0x7F
504 %************************************************************************
506 \subsection[mkSelectorBind]{Make a selector bind}
508 %************************************************************************
510 This is used in various places to do with lazy patterns.
511 For each binder $b$ in the pattern, we create a binding:
513 b = case v of pat' -> b'
515 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
517 ToDo: making these bindings should really depend on whether there's
518 much work to be done per binding. If the pattern is complex, it
519 should be de-mangled once, into a tuple (and then selected from).
520 Otherwise the demangling can be in-line in the bindings (as here).
522 Boring! Boring! One error message per binder. The above ToDo is
523 even more helpful. Something very similar happens for pattern-bound
527 mkSelectorBinds :: LPat Id -- The pattern
528 -> CoreExpr -- Expression to which the pattern is bound
529 -> DsM [(Id,CoreExpr)]
531 mkSelectorBinds (L _ (VarPat v)) val_expr
532 = returnDs [(v, val_expr)]
534 mkSelectorBinds pat val_expr
535 | isSingleton binders || is_simple_lpat pat
536 = -- Given p = e, where p binds x,y
537 -- we are going to make
538 -- v = p (where v is fresh)
539 -- x = case v of p -> x
540 -- y = case v of p -> x
543 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
544 -- This does not matter after desugaring, but there's a subtle
545 -- issue with implicit parameters. Consider
547 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
548 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
549 -- does it get that type? So that when we abstract over it we get the
550 -- right top-level type (?i::Int) => ...)
552 -- So to get the type of 'v', use the pattern not the rhs. Often more
554 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
556 -- For the error message we make one error-app, to avoid duplication.
557 -- But we need it at different types... so we use coerce for that
558 mkErrorAppDs iRREFUT_PAT_ERROR_ID
559 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
560 newSysLocalDs unitTy `thenDs` \ err_var ->
561 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
562 returnDs ( (val_var, val_expr) :
563 (err_var, err_expr) :
568 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
569 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
570 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
571 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
574 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
576 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
578 binders = collectPatBinders pat
579 local_tuple = mkTupleExpr binders
580 tuple_ty = exprType local_tuple
582 mk_bind scrut_var err_var bndr_var
583 -- (mk_bind sv err_var) generates
584 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
585 -- Remember, pat binds bv
586 = matchSimply (Var scrut_var) PatBindRhs pat
587 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
588 returnDs (bndr_var, rhs_expr)
590 error_expr = mkCoerce co (Var err_var)
591 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
593 is_simple_lpat p = is_simple_pat (unLoc p)
595 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
596 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConArgs ps)
597 is_simple_pat (VarPat _) = True
598 is_simple_pat (ParPat p) = is_simple_lpat p
599 is_simple_pat other = False
601 is_triv_lpat p = is_triv_pat (unLoc p)
603 is_triv_pat (VarPat v) = True
604 is_triv_pat (WildPat _) = True
605 is_triv_pat (ParPat p) = is_triv_lpat p
606 is_triv_pat other = False
610 %************************************************************************
614 %************************************************************************
616 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
618 * If it has only one element, it is the identity function.
620 * If there are more elements than a big tuple can have, it nests
623 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
624 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
627 mkTupleExpr :: [Id] -> CoreExpr
628 mkTupleExpr ids = mkBigCoreTup (map Var ids)
630 -- corresponding type
631 mkTupleType :: [Id] -> Type
632 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
634 mkBigCoreTup :: [CoreExpr] -> CoreExpr
635 mkBigCoreTup = mkBigTuple mkCoreTup
637 mkBigTuple :: ([a] -> a) -> [a] -> a
638 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
640 -- Each sub-list is short enough to fit in a tuple
641 mk_big_tuple [as] = small_tuple as
642 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
644 chunkify :: [a] -> [[a]]
645 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
646 -- But there may be more than mAX_TUPLE_SIZE sub-lists
648 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
649 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
653 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
657 @mkTupleSelector@ builds a selector which scrutises the given
658 expression and extracts the one name from the list given.
659 If you want the no-shadowing rule to apply, the caller
660 is responsible for making sure that none of these names
663 If there is just one id in the ``tuple'', then the selector is
666 If it's big, it does nesting
667 mkTupleSelector [a,b,c,d] b v e
669 (p,q) -> case p of p {
671 We use 'tpl' vars for the p,q, since shadowing does not matter.
673 In fact, it's more convenient to generate it innermost first, getting
680 mkTupleSelector :: [Id] -- The tuple args
681 -> Id -- The selected one
682 -> Id -- A variable of the same type as the scrutinee
683 -> CoreExpr -- Scrutinee
686 mkTupleSelector vars the_var scrut_var scrut
687 = mk_tup_sel (chunkify vars) the_var
689 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
690 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
691 mk_tup_sel (chunkify tpl_vs) tpl_v
693 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
694 tpl_vs = mkTemplateLocals tpl_tys
695 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
699 A generalization of @mkTupleSelector@, allowing the body
700 of the case to be an arbitrary expression.
702 If the tuple is big, it is nested:
704 mkTupleCase uniqs [a,b,c,d] body v e
705 = case e of v { (p,q) ->
706 case p of p { (a,b) ->
707 case q of q { (c,d) ->
710 To avoid shadowing, we use uniqs to invent new variables p,q.
712 ToDo: eliminate cases where none of the variables are needed.
716 :: UniqSupply -- for inventing names of intermediate variables
717 -> [Id] -- the tuple args
718 -> CoreExpr -- body of the case
719 -> Id -- a variable of the same type as the scrutinee
720 -> CoreExpr -- scrutinee
723 mkTupleCase uniqs vars body scrut_var scrut
724 = mk_tuple_case uniqs (chunkify vars) body
726 mk_tuple_case us [vars] body
727 = mkSmallTupleCase vars body scrut_var scrut
728 mk_tuple_case us vars_s body
730 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
732 mk_tuple_case us' (chunkify vars') body'
733 one_tuple_case chunk_vars (us, vs, body)
735 (us1, us2) = splitUniqSupply us
736 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
737 (mkCoreTupTy (map idType chunk_vars))
738 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
739 in (us2, scrut_var:vs, body')
742 The same, but with a tuple small enough not to need nesting.
746 :: [Id] -- the tuple args
747 -> CoreExpr -- body of the case
748 -> Id -- a variable of the same type as the scrutinee
749 -> CoreExpr -- scrutinee
752 mkSmallTupleCase [var] body _scrut_var scrut
753 = bindNonRec var scrut body
754 mkSmallTupleCase vars body scrut_var scrut
755 -- One branch no refinement?
756 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
759 %************************************************************************
761 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
763 %************************************************************************
765 Call the constructor Ids when building explicit lists, so that they
766 interact well with rules.
769 mkNilExpr :: Type -> CoreExpr
770 mkNilExpr ty = mkConApp nilDataCon [Type ty]
772 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
773 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
775 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
776 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
779 -- The next three functions make tuple types, constructors and selectors,
780 -- with the rule that a 1-tuple is represented by the thing itselg
781 mkCoreTupTy :: [Type] -> Type
782 mkCoreTupTy [ty] = ty
783 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
785 mkCoreTup :: [CoreExpr] -> CoreExpr
786 -- Builds exactly the specified tuple.
787 -- No fancy business for big tuples
788 mkCoreTup [] = Var unitDataConId
790 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
791 (map (Type . exprType) cs ++ cs)
793 mkCoreSel :: [Id] -- The tuple args
794 -> Id -- The selected one
795 -> Id -- A variable of the same type as the scrutinee
796 -> CoreExpr -- Scrutinee
798 -- mkCoreSel [x,y,z] x v e
799 -- ===> case e of v { (x,y,z) -> x
800 mkCoreSel [var] should_be_the_same_var scrut_var scrut
801 = ASSERT(var == should_be_the_same_var)
804 mkCoreSel vars the_var scrut_var scrut
805 = ASSERT( notNull vars )
806 Case scrut scrut_var (idType the_var)
807 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
811 %************************************************************************
813 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
815 %************************************************************************
817 Generally, we handle pattern matching failure like this: let-bind a
818 fail-variable, and use that variable if the thing fails:
820 let fail.33 = error "Help"
831 If the case can't fail, then there'll be no mention of @fail.33@, and the
832 simplifier will later discard it.
835 If it can fail in only one way, then the simplifier will inline it.
838 Only if it is used more than once will the let-binding remain.
841 There's a problem when the result of the case expression is of
842 unboxed type. Then the type of @fail.33@ is unboxed too, and
843 there is every chance that someone will change the let into a case:
849 which is of course utterly wrong. Rather than drop the condition that
850 only boxed types can be let-bound, we just turn the fail into a function
851 for the primitive case:
853 let fail.33 :: Void -> Int#
854 fail.33 = \_ -> error "Help"
863 Now @fail.33@ is a function, so it can be let-bound.
866 mkFailurePair :: CoreExpr -- Result type of the whole case expression
867 -> DsM (CoreBind, -- Binds the newly-created fail variable
868 -- to either the expression or \ _ -> expression
869 CoreExpr) -- Either the fail variable, or fail variable
870 -- applied to unit tuple
873 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
874 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
875 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
876 App (Var fail_fun_var) (Var unitDataConId))
879 = newFailLocalDs ty `thenDs` \ fail_var ->
880 returnDs (NonRec fail_var expr, Var fail_var)
886 mkOptTickBox :: Maybe Int -> CoreExpr -> DsM CoreExpr
887 mkOptTickBox Nothing e = return e
888 mkOptTickBox (Just ix) e = mkTickBox ix e
890 mkTickBox :: Int -> CoreExpr -> DsM CoreExpr
894 let tick = mkTickBoxOpId uq mod ix
896 let occName = mkVarOcc "tick"
897 let name = mkInternalName uq2 occName noSrcLoc -- use mkSysLocal?
898 let var = Id.mkLocalId name realWorldStatePrimTy
899 return $ Case (Var tick)
906 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
907 mkBinaryTickBox ixT ixF e = do
911 let bndr1 = mkSysLocal FSLIT("t1") uq boolTy
912 falseBox <- mkTickBox ixF $ Var falseDataConId
913 trueBox <- mkTickBox ixT $ Var trueDataConId
914 return $ Case e bndr1 boolTy
915 [ (DataAlt falseDataCon, [], falseBox)
916 , (DataAlt trueDataCon, [], trueBox)