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
39 #include "HsVersions.h"
41 import {-# SOURCE #-} Match ( matchSimply )
42 import {-# SOURCE #-} DsExpr( dsExpr )
80 %************************************************************************
84 %************************************************************************
87 dsSyntaxTable :: SyntaxTable Id
88 -> DsM ([CoreBind], -- Auxiliary bindings
89 [(Name,Id)]) -- Maps the standard name to its value
91 dsSyntaxTable rebound_ids
92 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
93 return (concat binds_s, prs)
95 -- The cheapo special case can happen when we
96 -- make an intermediate HsDo when desugaring a RecStmt
97 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
98 mk_bind (std_name, expr)
99 = dsExpr expr `thenDs` \ rhs ->
100 newSysLocalDs (exprType rhs) `thenDs` \ id ->
101 return ([NonRec id rhs], (std_name, id))
103 lookupEvidence :: [(Name, Id)] -> Name -> Id
104 lookupEvidence prs std_name
105 = assocDefault (mk_panic std_name) prs std_name
107 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
111 %************************************************************************
113 \subsection{Building lets}
115 %************************************************************************
117 Use case, not let for unlifted types. The simplifier will turn some
121 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
122 mkDsLet (NonRec bndr rhs) body
123 | isUnLiftedType (idType bndr)
124 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
128 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
129 mkDsLets binds body = foldr mkDsLet body binds
133 %************************************************************************
135 \subsection{ Selecting match variables}
137 %************************************************************************
139 We're about to match against some patterns. We want to make some
140 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
141 hand, which should indeed be bound to the pattern as a whole, then use it;
142 otherwise, make one up.
145 selectSimpleMatchVarL :: LPat Id -> DsM Id
146 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
148 -- (selectMatchVars ps tys) chooses variables of type tys
149 -- to use for matching ps against. If the pattern is a variable,
150 -- we try to use that, to save inventing lots of fresh variables.
152 -- OLD, but interesting note:
153 -- But even if it is a variable, its type might not match. Consider
155 -- T1 :: Int -> T Int
158 -- f :: T a -> a -> Int
159 -- f (T1 i) (x::Int) = x
160 -- f (T2 i) (y::a) = 0
161 -- Then we must not choose (x::Int) as the matching variable!
162 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
164 selectMatchVars :: [Pat Id] -> DsM [Id]
165 selectMatchVars ps = mapM selectMatchVar ps
167 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
168 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
169 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
170 selectMatchVar (VarPat var) = return var
171 selectMatchVar (AsPat var pat) = return (unLoc var)
172 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
173 -- OK, better make up one...
177 %************************************************************************
179 %* type synonym EquationInfo and access functions for its pieces *
181 %************************************************************************
182 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
184 The ``equation info'' used by @match@ is relatively complicated and
185 worthy of a type synonym and a few handy functions.
188 firstPat :: EquationInfo -> Pat Id
189 firstPat eqn = head (eqn_pats eqn)
191 shiftEqns :: [EquationInfo] -> [EquationInfo]
192 -- Drop the first pattern in each equation
193 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
196 Functions on MatchResults
199 matchCanFail :: MatchResult -> Bool
200 matchCanFail (MatchResult CanFail _) = True
201 matchCanFail (MatchResult CantFail _) = False
203 alwaysFailMatchResult :: MatchResult
204 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
206 cantFailMatchResult :: CoreExpr -> MatchResult
207 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
209 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
210 extractMatchResult (MatchResult CantFail match_fn) fail_expr
211 = match_fn (error "It can't fail!")
213 extractMatchResult (MatchResult CanFail match_fn) fail_expr
214 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
215 match_fn if_it_fails `thenDs` \ body ->
216 returnDs (mkDsLet fail_bind body)
219 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
220 combineMatchResults (MatchResult CanFail body_fn1)
221 (MatchResult can_it_fail2 body_fn2)
222 = MatchResult can_it_fail2 body_fn
224 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
225 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
226 body_fn1 duplicatable_expr `thenDs` \ body1 ->
227 returnDs (Let fail_bind body1)
229 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
232 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
233 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
234 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
235 returnDs (encl_fn body))
237 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
238 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
239 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
242 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
244 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
246 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
247 wrapBind new old body
249 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
250 | otherwise = Let (NonRec new (Var old)) body
252 seqVar :: Var -> CoreExpr -> CoreExpr
253 seqVar var body = Case (Var var) var (exprType body)
254 [(DEFAULT, [], body)]
256 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
257 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
259 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
260 mkEvalMatchResult var ty
261 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
263 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
264 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
265 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
266 returnDs (mkIfThenElse pred_expr body fail))
268 mkCoPrimCaseMatchResult :: Id -- Scrutinee
269 -> Type -- Type of the case
270 -> [(Literal, MatchResult)] -- Alternatives
272 mkCoPrimCaseMatchResult var ty match_alts
273 = MatchResult CanFail mk_case
276 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
277 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
279 sorted_alts = sortWith fst match_alts -- Right order for a Case
280 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
281 returnDs (LitAlt lit, [], body)
284 mkCoAlgCaseMatchResult :: Id -- Scrutinee
285 -> Type -- Type of exp
286 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
288 mkCoAlgCaseMatchResult var ty match_alts
289 | isNewTyCon tycon -- Newtype case; use a let
290 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
291 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
293 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
294 = MatchResult CanFail mk_parrCase
296 | otherwise -- Datatype case; use a case
297 = MatchResult fail_flag mk_case
299 tycon = dataConTyCon con1
300 -- [Interesting: becuase of GADTs, we can't rely on the type of
301 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
304 (con1, arg_ids1, match_result1) = head match_alts
305 arg_id1 = head arg_ids1
307 (tc, ty_args) = splitNewTyConApp var_ty
308 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
310 -- Stuff for data types
311 data_cons = tyConDataCons tycon
312 match_results = [match_result | (_,_,match_result) <- match_alts]
314 fail_flag | exhaustive_case
315 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
319 wild_var = mkWildId (idType var)
320 sorted_alts = sortWith get_tag match_alts
321 get_tag (con, _, _) = dataConTag con
322 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
323 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
325 mk_alt fail (con, args, MatchResult _ body_fn)
326 = body_fn fail `thenDs` \ body ->
327 newUniqueSupply `thenDs` \ us ->
328 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
330 mk_default fail | exhaustive_case = []
331 | otherwise = [(DEFAULT, [], fail)]
333 un_mentioned_constructors
334 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
335 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
337 -- Stuff for parallel arrays
339 -- * the following is to desugar cases over fake constructors for
340 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
343 -- Concerning `isPArrFakeAlts':
345 -- * it is *not* sufficient to just check the type of the type
346 -- constructor, as we have to be careful not to confuse the real
347 -- representation of parallel arrays with the fake constructors;
348 -- moreover, a list of alternatives must not mix fake and real
349 -- constructors (this is checked earlier on)
351 -- FIXME: We actually go through the whole list and make sure that
352 -- either all or none of the constructors are fake parallel
353 -- array constructors. This is to spot equations that mix fake
354 -- constructors with the real representation defined in
355 -- `PrelPArr'. It would be nicer to spot this situation
356 -- earlier and raise a proper error message, but it can really
357 -- only happen in `PrelPArr' anyway.
359 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
360 isPArrFakeAlts ((dcon, _, _):alts) =
361 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
362 (True , True ) -> True
363 (False, False) -> False
365 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
368 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
369 unboxAlt `thenDs` \alt ->
370 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
372 elemTy = case splitTyConApp (idType var) of
373 (_, [elemTy]) -> elemTy
375 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
376 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
379 newSysLocalDs intPrimTy `thenDs` \l ->
380 dsLookupGlobalId indexPName `thenDs` \indexP ->
381 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
382 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
384 wild = mkWildId intPrimTy
385 dft = (DEFAULT, [], fail)
387 -- each alternative matches one array length (corresponding to one
388 -- fake array constructor), so the match is on a literal; each
389 -- alternative's body is extended by a local binding for each
390 -- constructor argument, which are bound to array elements starting
393 mkAlt indexP (con, args, MatchResult _ bodyFun) =
394 bodyFun fail `thenDs` \body ->
395 returnDs (LitAlt lit, [], mkDsLets binds body)
397 lit = MachInt $ toInteger (dataConSourceArity con)
398 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
400 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
404 %************************************************************************
406 \subsection{Desugarer's versions of some Core functions}
408 %************************************************************************
411 mkErrorAppDs :: Id -- The error function
412 -> Type -- Type to which it should be applied
413 -> String -- The error message string to pass
416 mkErrorAppDs err_id ty msg
417 = getSrcSpanDs `thenDs` \ src_loc ->
419 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
420 core_msg = Lit (mkStringLit full_msg)
421 -- mkStringLit returns a result of type String#
423 returnDs (mkApps (Var err_id) [Type ty, core_msg])
427 *************************************************************
429 \subsection{Making literals}
431 %************************************************************************
434 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
435 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
436 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
437 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
438 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
440 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
441 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
444 | inIntRange i -- Small enough, so start from an Int
445 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
446 returnDs (mkSmallIntegerLit integer_dc i)
448 -- Special case for integral literals with a large magnitude:
449 -- They are transformed into an expression involving only smaller
450 -- integral literals. This improves constant folding.
452 | otherwise -- Big, so start from a string
453 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
454 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
455 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
457 lit i = mkSmallIntegerLit integer_dc i
458 plus a b = Var plus_id `App` a `App` b
459 times a b = Var times_id `App` a `App` b
461 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
462 horner :: Integer -> Integer -> CoreExpr
463 horner b i | abs q <= 1 = if r == 0 || r == i
465 else lit r `plus` lit (i-r)
466 | r == 0 = horner b q `times` lit b
467 | otherwise = lit r `plus` (horner b q `times` lit b)
469 (q,r) = i `quotRem` b
472 returnDs (horner tARGET_MAX_INT i)
474 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
476 mkStringExpr str = mkStringExprFS (mkFastString str)
480 = returnDs (mkNilExpr charTy)
484 the_char = mkCharExpr (headFS str)
486 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
489 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
490 returnDs (App (Var unpack_id) (Lit (MachStr str)))
493 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
494 returnDs (App (Var unpack_id) (Lit (MachStr str)))
498 safeChar c = ord c >= 1 && ord c <= 0x7F
502 %************************************************************************
504 \subsection[mkSelectorBind]{Make a selector bind}
506 %************************************************************************
508 This is used in various places to do with lazy patterns.
509 For each binder $b$ in the pattern, we create a binding:
511 b = case v of pat' -> b'
513 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
515 ToDo: making these bindings should really depend on whether there's
516 much work to be done per binding. If the pattern is complex, it
517 should be de-mangled once, into a tuple (and then selected from).
518 Otherwise the demangling can be in-line in the bindings (as here).
520 Boring! Boring! One error message per binder. The above ToDo is
521 even more helpful. Something very similar happens for pattern-bound
525 mkSelectorBinds :: LPat Id -- The pattern
526 -> CoreExpr -- Expression to which the pattern is bound
527 -> DsM [(Id,CoreExpr)]
529 mkSelectorBinds (L _ (VarPat v)) val_expr
530 = returnDs [(v, val_expr)]
532 mkSelectorBinds pat val_expr
533 | isSingleton binders || is_simple_lpat pat
534 = -- Given p = e, where p binds x,y
535 -- we are going to make
536 -- v = p (where v is fresh)
537 -- x = case v of p -> x
538 -- y = case v of p -> x
541 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
542 -- This does not matter after desugaring, but there's a subtle
543 -- issue with implicit parameters. Consider
545 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
546 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
547 -- does it get that type? So that when we abstract over it we get the
548 -- right top-level type (?i::Int) => ...)
550 -- So to get the type of 'v', use the pattern not the rhs. Often more
552 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
554 -- For the error message we make one error-app, to avoid duplication.
555 -- But we need it at different types... so we use coerce for that
556 mkErrorAppDs iRREFUT_PAT_ERROR_ID
557 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
558 newSysLocalDs unitTy `thenDs` \ err_var ->
559 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
560 returnDs ( (val_var, val_expr) :
561 (err_var, err_expr) :
566 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
567 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
568 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
569 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
572 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
574 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
576 binders = collectPatBinders pat
577 local_tuple = mkTupleExpr binders
578 tuple_ty = exprType local_tuple
580 mk_bind scrut_var err_var bndr_var
581 -- (mk_bind sv err_var) generates
582 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
583 -- Remember, pat binds bv
584 = matchSimply (Var scrut_var) PatBindRhs pat
585 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
586 returnDs (bndr_var, rhs_expr)
588 error_expr = mkCoerce co (Var err_var)
589 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
591 is_simple_lpat p = is_simple_pat (unLoc p)
593 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
594 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConArgs ps)
595 is_simple_pat (VarPat _) = True
596 is_simple_pat (ParPat p) = is_simple_lpat p
597 is_simple_pat other = False
599 is_triv_lpat p = is_triv_pat (unLoc p)
601 is_triv_pat (VarPat v) = True
602 is_triv_pat (WildPat _) = True
603 is_triv_pat (ParPat p) = is_triv_lpat p
604 is_triv_pat other = False
608 %************************************************************************
612 %************************************************************************
614 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
616 * If it has only one element, it is the identity function.
618 * If there are more elements than a big tuple can have, it nests
621 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
622 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
625 mkTupleExpr :: [Id] -> CoreExpr
626 mkTupleExpr ids = mkBigCoreTup (map Var ids)
628 -- corresponding type
629 mkTupleType :: [Id] -> Type
630 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
632 mkBigCoreTup :: [CoreExpr] -> CoreExpr
633 mkBigCoreTup = mkBigTuple mkCoreTup
635 mkBigTuple :: ([a] -> a) -> [a] -> a
636 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
638 -- Each sub-list is short enough to fit in a tuple
639 mk_big_tuple [as] = small_tuple as
640 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
642 chunkify :: [a] -> [[a]]
643 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
644 -- But there may be more than mAX_TUPLE_SIZE sub-lists
646 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
647 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
651 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
655 @mkTupleSelector@ builds a selector which scrutises the given
656 expression and extracts the one name from the list given.
657 If you want the no-shadowing rule to apply, the caller
658 is responsible for making sure that none of these names
661 If there is just one id in the ``tuple'', then the selector is
664 If it's big, it does nesting
665 mkTupleSelector [a,b,c,d] b v e
667 (p,q) -> case p of p {
669 We use 'tpl' vars for the p,q, since shadowing does not matter.
671 In fact, it's more convenient to generate it innermost first, getting
678 mkTupleSelector :: [Id] -- The tuple args
679 -> Id -- The selected one
680 -> Id -- A variable of the same type as the scrutinee
681 -> CoreExpr -- Scrutinee
684 mkTupleSelector vars the_var scrut_var scrut
685 = mk_tup_sel (chunkify vars) the_var
687 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
688 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
689 mk_tup_sel (chunkify tpl_vs) tpl_v
691 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
692 tpl_vs = mkTemplateLocals tpl_tys
693 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
697 A generalization of @mkTupleSelector@, allowing the body
698 of the case to be an arbitrary expression.
700 If the tuple is big, it is nested:
702 mkTupleCase uniqs [a,b,c,d] body v e
703 = case e of v { (p,q) ->
704 case p of p { (a,b) ->
705 case q of q { (c,d) ->
708 To avoid shadowing, we use uniqs to invent new variables p,q.
710 ToDo: eliminate cases where none of the variables are needed.
714 :: UniqSupply -- for inventing names of intermediate variables
715 -> [Id] -- the tuple args
716 -> CoreExpr -- body of the case
717 -> Id -- a variable of the same type as the scrutinee
718 -> CoreExpr -- scrutinee
721 mkTupleCase uniqs vars body scrut_var scrut
722 = mk_tuple_case uniqs (chunkify vars) body
724 mk_tuple_case us [vars] body
725 = mkSmallTupleCase vars body scrut_var scrut
726 mk_tuple_case us vars_s body
728 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
730 mk_tuple_case us' (chunkify vars') body'
731 one_tuple_case chunk_vars (us, vs, body)
733 (us1, us2) = splitUniqSupply us
734 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
735 (mkCoreTupTy (map idType chunk_vars))
736 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
737 in (us2, scrut_var:vs, body')
740 The same, but with a tuple small enough not to need nesting.
744 :: [Id] -- the tuple args
745 -> CoreExpr -- body of the case
746 -> Id -- a variable of the same type as the scrutinee
747 -> CoreExpr -- scrutinee
750 mkSmallTupleCase [var] body _scrut_var scrut
751 = bindNonRec var scrut body
752 mkSmallTupleCase vars body scrut_var scrut
753 -- One branch no refinement?
754 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
757 %************************************************************************
759 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
761 %************************************************************************
763 Call the constructor Ids when building explicit lists, so that they
764 interact well with rules.
767 mkNilExpr :: Type -> CoreExpr
768 mkNilExpr ty = mkConApp nilDataCon [Type ty]
770 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
771 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
773 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
774 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
777 -- The next three functions make tuple types, constructors and selectors,
778 -- with the rule that a 1-tuple is represented by the thing itselg
779 mkCoreTupTy :: [Type] -> Type
780 mkCoreTupTy [ty] = ty
781 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
783 mkCoreTup :: [CoreExpr] -> CoreExpr
784 -- Builds exactly the specified tuple.
785 -- No fancy business for big tuples
786 mkCoreTup [] = Var unitDataConId
788 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
789 (map (Type . exprType) cs ++ cs)
791 mkCoreSel :: [Id] -- The tuple args
792 -> Id -- The selected one
793 -> Id -- A variable of the same type as the scrutinee
794 -> CoreExpr -- Scrutinee
796 -- mkCoreSel [x,y,z] x v e
797 -- ===> case e of v { (x,y,z) -> x
798 mkCoreSel [var] should_be_the_same_var scrut_var scrut
799 = ASSERT(var == should_be_the_same_var)
802 mkCoreSel vars the_var scrut_var scrut
803 = ASSERT( notNull vars )
804 Case scrut scrut_var (idType the_var)
805 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
809 %************************************************************************
811 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
813 %************************************************************************
815 Generally, we handle pattern matching failure like this: let-bind a
816 fail-variable, and use that variable if the thing fails:
818 let fail.33 = error "Help"
829 If the case can't fail, then there'll be no mention of @fail.33@, and the
830 simplifier will later discard it.
833 If it can fail in only one way, then the simplifier will inline it.
836 Only if it is used more than once will the let-binding remain.
839 There's a problem when the result of the case expression is of
840 unboxed type. Then the type of @fail.33@ is unboxed too, and
841 there is every chance that someone will change the let into a case:
847 which is of course utterly wrong. Rather than drop the condition that
848 only boxed types can be let-bound, we just turn the fail into a function
849 for the primitive case:
851 let fail.33 :: Void -> Int#
852 fail.33 = \_ -> error "Help"
861 Now @fail.33@ is a function, so it can be let-bound.
864 mkFailurePair :: CoreExpr -- Result type of the whole case expression
865 -> DsM (CoreBind, -- Binds the newly-created fail variable
866 -- to either the expression or \ _ -> expression
867 CoreExpr) -- Either the fail variable, or fail variable
868 -- applied to unit tuple
871 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
872 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
873 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
874 App (Var fail_fun_var) (Var unitDataConId))
877 = newFailLocalDs ty `thenDs` \ fail_var ->
878 returnDs (NonRec fail_var expr, Var fail_var)