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,
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,
32 dsReboundNames, lookupReboundName,
34 selectSimpleMatchVarL, selectMatchVars
37 #include "HsVersions.h"
39 import {-# SOURCE #-} Match ( matchSimply )
40 import {-# SOURCE #-} DsExpr( dsExpr )
43 import TcHsSyn ( hsPatType )
45 import Constants ( mAX_TUPLE_SIZE )
48 import CoreUtils ( exprType, mkIfThenElse, mkCoerce, bindNonRec )
49 import MkId ( iRREFUT_PAT_ERROR_ID, mkReboxingAlt, mkNewTypeBody )
50 import Id ( idType, Id, mkWildId, mkTemplateLocals, mkSysLocal )
53 import Literal ( Literal(..), mkStringLit, inIntRange, tARGET_MAX_INT )
54 import TyCon ( isNewTyCon, tyConDataCons )
55 import DataCon ( DataCon, dataConSourceArity, dataConTyCon, dataConTag )
56 import Type ( mkFunTy, isUnLiftedType, Type, splitTyConApp, mkTyVarTy )
57 import TcType ( tcEqType )
58 import TysPrim ( intPrimTy )
59 import TysWiredIn ( nilDataCon, consDataCon,
61 unitDataConId, unitTy,
65 import BasicTypes ( Boxity(..) )
66 import UniqSet ( mkUniqSet, minusUniqSet, isEmptyUniqSet )
67 import UniqSupply ( splitUniqSupply, uniqFromSupply, uniqsFromSupply )
68 import PrelNames ( unpackCStringName, unpackCStringUtf8Name,
69 plusIntegerName, timesIntegerName, smallIntegerDataConName,
70 lengthPName, indexPName )
72 import UnicodeUtil ( intsToUtf8 )
73 import SrcLoc ( Located(..), unLoc )
74 import Util ( isSingleton, notNull, zipEqual, sortWith )
75 import ListSetOps ( assocDefault )
81 %************************************************************************
85 %************************************************************************
88 dsReboundNames :: ReboundNames Id
89 -> DsM ([CoreBind], -- Auxiliary bindings
90 [(Name,Id)]) -- Maps the standard name to its value
92 dsReboundNames 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 lookupReboundName :: [(Name,Id)] -> Name -> CoreExpr
105 lookupReboundName prs std_name
106 = Var (assocDefault (mk_panic std_name) prs std_name)
108 mk_panic std_name = pprPanic "dsReboundNames" (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) (hsPatType 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.
152 -- But even if it is a variable, its type might not match. Consider
154 -- T1 :: Int -> T Int
157 -- f :: T a -> a -> Int
158 -- f (T1 i) (x::Int) = x
159 -- f (T2 i) (y::a) = 0
160 -- Then we must not choose (x::Int) as the matching variable!
162 selectMatchVars :: [Pat Id] -> [Type] -> DsM [Id]
163 selectMatchVars [] [] = return []
164 selectMatchVars (p:ps) (ty:tys) = do { v <- selectMatchVar p ty
165 ; vs <- selectMatchVars ps tys
168 selectMatchVar (LazyPat pat) pat_ty = selectMatchVar (unLoc pat) pat_ty
169 selectMatchVar (VarPat var) pat_ty = try_for var pat_ty
170 selectMatchVar (AsPat var pat) pat_ty = try_for (unLoc var) pat_ty
171 selectMatchVar other_pat pat_ty = newSysLocalDs pat_ty -- OK, better make up one...
174 | idType var `tcEqType` pat_ty = returnDs var
175 | otherwise = newSysLocalDs pat_ty
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 alwaysFailMatchResult :: MatchResult
202 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
204 cantFailMatchResult :: CoreExpr -> MatchResult
205 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
207 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
208 extractMatchResult (MatchResult CantFail match_fn) fail_expr
209 = match_fn (error "It can't fail!")
211 extractMatchResult (MatchResult CanFail match_fn) fail_expr
212 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
213 match_fn if_it_fails `thenDs` \ body ->
214 returnDs (mkDsLet fail_bind body)
217 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
218 combineMatchResults (MatchResult CanFail body_fn1)
219 (MatchResult can_it_fail2 body_fn2)
220 = MatchResult can_it_fail2 body_fn
222 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
223 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
224 body_fn1 duplicatable_expr `thenDs` \ body1 ->
225 returnDs (Let fail_bind body1)
227 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
230 adjustMatchResult :: (CoreExpr -> CoreExpr) -> MatchResult -> MatchResult
231 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
232 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
233 returnDs (encl_fn body))
235 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
236 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
237 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
240 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
242 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
244 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
245 wrapBind new old body
247 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
248 | otherwise = Let (NonRec new (Var old)) body
250 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
251 mkCoLetMatchResult bind match_result
252 = adjustMatchResult (mkDsLet bind) match_result
254 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
255 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
256 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
257 returnDs (mkIfThenElse pred_expr body fail))
259 mkCoPrimCaseMatchResult :: Id -- Scrutinee
260 -> Type -- Type of the case
261 -> [(Literal, MatchResult)] -- Alternatives
263 mkCoPrimCaseMatchResult var ty match_alts
264 = MatchResult CanFail mk_case
267 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
268 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
270 sorted_alts = sortWith fst match_alts -- Right order for a Case
271 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
272 returnDs (LitAlt lit, [], body)
275 mkCoAlgCaseMatchResult :: Id -- Scrutinee
276 -> Type -- Type of exp
277 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
279 mkCoAlgCaseMatchResult var ty match_alts
280 | isNewTyCon tycon -- Newtype case; use a let
281 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
282 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
284 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
285 = MatchResult CanFail mk_parrCase
287 | otherwise -- Datatype case; use a case
288 = MatchResult fail_flag mk_case
290 tycon = dataConTyCon con1
291 -- [Interesting: becuase of GADTs, we can't rely on the type of
292 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
295 (con1, arg_ids1, match_result1) = head match_alts
296 arg_id1 = head arg_ids1
297 newtype_rhs = mkNewTypeBody tycon (idType arg_id1) (Var var)
299 -- Stuff for data types
300 data_cons = tyConDataCons tycon
301 match_results = [match_result | (_,_,match_result) <- match_alts]
303 fail_flag | exhaustive_case
304 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
308 wild_var = mkWildId (idType var)
309 sorted_alts = sortWith get_tag match_alts
310 get_tag (con, _, _) = dataConTag con
311 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
312 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
314 mk_alt fail (con, args, MatchResult _ body_fn)
315 = body_fn fail `thenDs` \ body ->
316 newUniqueSupply `thenDs` \ us ->
317 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
319 mk_default fail | exhaustive_case = []
320 | otherwise = [(DEFAULT, [], fail)]
322 un_mentioned_constructors
323 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
324 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
326 -- Stuff for parallel arrays
328 -- * the following is to desugar cases over fake constructors for
329 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
332 -- Concerning `isPArrFakeAlts':
334 -- * it is *not* sufficient to just check the type of the type
335 -- constructor, as we have to be careful not to confuse the real
336 -- representation of parallel arrays with the fake constructors;
337 -- moreover, a list of alternatives must not mix fake and real
338 -- constructors (this is checked earlier on)
340 -- FIXME: We actually go through the whole list and make sure that
341 -- either all or none of the constructors are fake parallel
342 -- array constructors. This is to spot equations that mix fake
343 -- constructors with the real representation defined in
344 -- `PrelPArr'. It would be nicer to spot this situation
345 -- earlier and raise a proper error message, but it can really
346 -- only happen in `PrelPArr' anyway.
348 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
349 isPArrFakeAlts ((dcon, _, _):alts) =
350 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
351 (True , True ) -> True
352 (False, False) -> False
354 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
357 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
358 unboxAlt `thenDs` \alt ->
359 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
361 elemTy = case splitTyConApp (idType var) of
362 (_, [elemTy]) -> elemTy
364 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
365 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
368 newSysLocalDs intPrimTy `thenDs` \l ->
369 dsLookupGlobalId indexPName `thenDs` \indexP ->
370 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
371 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
373 wild = mkWildId intPrimTy
374 dft = (DEFAULT, [], fail)
376 -- each alternative matches one array length (corresponding to one
377 -- fake array constructor), so the match is on a literal; each
378 -- alternative's body is extended by a local binding for each
379 -- constructor argument, which are bound to array elements starting
382 mkAlt indexP (con, args, MatchResult _ bodyFun) =
383 bodyFun fail `thenDs` \body ->
384 returnDs (LitAlt lit, [], mkDsLets binds body)
386 lit = MachInt $ toInteger (dataConSourceArity con)
387 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
389 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
393 %************************************************************************
395 \subsection{Desugarer's versions of some Core functions}
397 %************************************************************************
400 mkErrorAppDs :: Id -- The error function
401 -> Type -- Type to which it should be applied
402 -> String -- The error message string to pass
405 mkErrorAppDs err_id ty msg
406 = getSrcSpanDs `thenDs` \ src_loc ->
408 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
409 core_msg = Lit (mkStringLit full_msg)
411 returnDs (mkApps (Var err_id) [Type ty, core_msg])
415 *************************************************************
417 \subsection{Making literals}
419 %************************************************************************
422 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
423 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
424 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
425 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
426 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
428 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
429 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
432 | inIntRange i -- Small enough, so start from an Int
433 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
434 returnDs (mkSmallIntegerLit integer_dc i)
436 -- Special case for integral literals with a large magnitude:
437 -- They are transformed into an expression involving only smaller
438 -- integral literals. This improves constant folding.
440 | otherwise -- Big, so start from a string
441 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
442 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
443 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
445 lit i = mkSmallIntegerLit integer_dc i
446 plus a b = Var plus_id `App` a `App` b
447 times a b = Var times_id `App` a `App` b
449 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
450 horner :: Integer -> Integer -> CoreExpr
451 horner b i | abs q <= 1 = if r == 0 || r == i
453 else lit r `plus` lit (i-r)
454 | r == 0 = horner b q `times` lit b
455 | otherwise = lit r `plus` (horner b q `times` lit b)
457 (q,r) = i `quotRem` b
460 returnDs (horner tARGET_MAX_INT i)
462 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
464 mkStringExpr str = mkStringExprFS (mkFastString str)
468 = returnDs (mkNilExpr charTy)
472 the_char = mkCharExpr (headFS str)
474 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
476 | all safeChar int_chars
477 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
478 returnDs (App (Var unpack_id) (Lit (MachStr str)))
481 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
482 returnDs (App (Var unpack_id) (Lit (MachStr (mkFastString (intsToUtf8 int_chars)))))
485 int_chars = unpackIntFS str
486 safeChar c = c >= 1 && c <= 0xFF
490 %************************************************************************
492 \subsection[mkSelectorBind]{Make a selector bind}
494 %************************************************************************
496 This is used in various places to do with lazy patterns.
497 For each binder $b$ in the pattern, we create a binding:
499 b = case v of pat' -> b'
501 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
503 ToDo: making these bindings should really depend on whether there's
504 much work to be done per binding. If the pattern is complex, it
505 should be de-mangled once, into a tuple (and then selected from).
506 Otherwise the demangling can be in-line in the bindings (as here).
508 Boring! Boring! One error message per binder. The above ToDo is
509 even more helpful. Something very similar happens for pattern-bound
513 mkSelectorBinds :: LPat Id -- The pattern
514 -> CoreExpr -- Expression to which the pattern is bound
515 -> DsM [(Id,CoreExpr)]
517 mkSelectorBinds (L _ (VarPat v)) val_expr
518 = returnDs [(v, val_expr)]
520 mkSelectorBinds pat val_expr
521 | isSingleton binders || is_simple_lpat pat
522 = -- Given p = e, where p binds x,y
523 -- we are going to make
524 -- v = p (where v is fresh)
525 -- x = case v of p -> x
526 -- y = case v of p -> x
529 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
530 -- This does not matter after desugaring, but there's a subtle
531 -- issue with implicit parameters. Consider
533 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
534 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
535 -- does it get that type? So that when we abstract over it we get the
536 -- right top-level type (?i::Int) => ...)
538 -- So to get the type of 'v', use the pattern not the rhs. Often more
540 newSysLocalDs (hsPatType pat) `thenDs` \ val_var ->
542 -- For the error message we make one error-app, to avoid duplication.
543 -- But we need it at different types... so we use coerce for that
544 mkErrorAppDs iRREFUT_PAT_ERROR_ID
545 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
546 newSysLocalDs unitTy `thenDs` \ err_var ->
547 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
548 returnDs ( (val_var, val_expr) :
549 (err_var, err_expr) :
554 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
555 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
556 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
557 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
560 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
562 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
564 binders = collectPatBinders pat
565 local_tuple = mkTupleExpr binders
566 tuple_ty = exprType local_tuple
568 mk_bind scrut_var err_var bndr_var
569 -- (mk_bind sv err_var) generates
570 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
571 -- Remember, pat binds bv
572 = matchSimply (Var scrut_var) PatBindRhs pat
573 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
574 returnDs (bndr_var, rhs_expr)
576 error_expr = mkCoerce (idType bndr_var) (Var err_var)
578 is_simple_lpat p = is_simple_pat (unLoc p)
580 is_simple_pat (TuplePat ps Boxed) = all is_triv_lpat ps
581 is_simple_pat (ConPatOut _ _ _ _ ps _) = all is_triv_lpat (hsConArgs ps)
582 is_simple_pat (VarPat _) = True
583 is_simple_pat (ParPat p) = is_simple_lpat p
584 is_simple_pat other = False
586 is_triv_lpat p = is_triv_pat (unLoc p)
588 is_triv_pat (VarPat v) = True
589 is_triv_pat (WildPat _) = True
590 is_triv_pat (ParPat p) = is_triv_lpat p
591 is_triv_pat other = False
595 %************************************************************************
599 %************************************************************************
601 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
603 * If it has only one element, it is the identity function.
605 * If there are more elements than a big tuple can have, it nests
608 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
609 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
612 mkTupleExpr :: [Id] -> CoreExpr
613 mkTupleExpr ids = mkBigCoreTup (map Var ids)
615 -- corresponding type
616 mkTupleType :: [Id] -> Type
617 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
619 mkBigCoreTup :: [CoreExpr] -> CoreExpr
620 mkBigCoreTup = mkBigTuple mkCoreTup
622 mkBigTuple :: ([a] -> a) -> [a] -> a
623 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
625 -- Each sub-list is short enough to fit in a tuple
626 mk_big_tuple [as] = small_tuple as
627 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
629 chunkify :: [a] -> [[a]]
630 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
631 -- But there may be more than mAX_TUPLE_SIZE sub-lists
633 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
634 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
638 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
642 @mkTupleSelector@ builds a selector which scrutises the given
643 expression and extracts the one name from the list given.
644 If you want the no-shadowing rule to apply, the caller
645 is responsible for making sure that none of these names
648 If there is just one id in the ``tuple'', then the selector is
651 If it's big, it does nesting
652 mkTupleSelector [a,b,c,d] b v e
654 (p,q) -> case p of p {
656 We use 'tpl' vars for the p,q, since shadowing does not matter.
658 In fact, it's more convenient to generate it innermost first, getting
665 mkTupleSelector :: [Id] -- The tuple args
666 -> Id -- The selected one
667 -> Id -- A variable of the same type as the scrutinee
668 -> CoreExpr -- Scrutinee
671 mkTupleSelector vars the_var scrut_var scrut
672 = mk_tup_sel (chunkify vars) the_var
674 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
675 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
676 mk_tup_sel (chunkify tpl_vs) tpl_v
678 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
679 tpl_vs = mkTemplateLocals tpl_tys
680 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
684 A generalization of @mkTupleSelector@, allowing the body
685 of the case to be an arbitrary expression.
687 If the tuple is big, it is nested:
689 mkTupleCase uniqs [a,b,c,d] body v e
690 = case e of v { (p,q) ->
691 case p of p { (a,b) ->
692 case q of q { (c,d) ->
695 To avoid shadowing, we use uniqs to invent new variables p,q.
697 ToDo: eliminate cases where none of the variables are needed.
701 :: UniqSupply -- for inventing names of intermediate variables
702 -> [Id] -- the tuple args
703 -> CoreExpr -- body of the case
704 -> Id -- a variable of the same type as the scrutinee
705 -> CoreExpr -- scrutinee
708 mkTupleCase uniqs vars body scrut_var scrut
709 = mk_tuple_case uniqs (chunkify vars) body
711 mk_tuple_case us [vars] body
712 = mkSmallTupleCase vars body scrut_var scrut
713 mk_tuple_case us vars_s body
715 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
717 mk_tuple_case us' (chunkify vars') body'
718 one_tuple_case chunk_vars (us, vs, body)
720 (us1, us2) = splitUniqSupply us
721 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
722 (mkCoreTupTy (map idType chunk_vars))
723 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
724 in (us2, scrut_var:vs, body')
727 The same, but with a tuple small enough not to need nesting.
731 :: [Id] -- the tuple args
732 -> CoreExpr -- body of the case
733 -> Id -- a variable of the same type as the scrutinee
734 -> CoreExpr -- scrutinee
737 mkSmallTupleCase [var] body _scrut_var scrut
738 = bindNonRec var scrut body
739 mkSmallTupleCase vars body scrut_var scrut
740 -- One branch no refinement?
741 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
744 %************************************************************************
746 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
748 %************************************************************************
750 Call the constructor Ids when building explicit lists, so that they
751 interact well with rules.
754 mkNilExpr :: Type -> CoreExpr
755 mkNilExpr ty = mkConApp nilDataCon [Type ty]
757 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
758 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
760 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
761 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
764 -- The next three functions make tuple types, constructors and selectors,
765 -- with the rule that a 1-tuple is represented by the thing itselg
766 mkCoreTupTy :: [Type] -> Type
767 mkCoreTupTy [ty] = ty
768 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
770 mkCoreTup :: [CoreExpr] -> CoreExpr
771 -- Builds exactly the specified tuple.
772 -- No fancy business for big tuples
773 mkCoreTup [] = Var unitDataConId
775 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
776 (map (Type . exprType) cs ++ cs)
778 mkCoreSel :: [Id] -- The tuple args
779 -> Id -- The selected one
780 -> Id -- A variable of the same type as the scrutinee
781 -> CoreExpr -- Scrutinee
783 -- mkCoreSel [x,y,z] x v e
784 -- ===> case e of v { (x,y,z) -> x
785 mkCoreSel [var] should_be_the_same_var scrut_var scrut
786 = ASSERT(var == should_be_the_same_var)
789 mkCoreSel vars the_var scrut_var scrut
790 = ASSERT( notNull vars )
791 Case scrut scrut_var (idType the_var)
792 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
796 %************************************************************************
798 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
800 %************************************************************************
802 Generally, we handle pattern matching failure like this: let-bind a
803 fail-variable, and use that variable if the thing fails:
805 let fail.33 = error "Help"
816 If the case can't fail, then there'll be no mention of @fail.33@, and the
817 simplifier will later discard it.
820 If it can fail in only one way, then the simplifier will inline it.
823 Only if it is used more than once will the let-binding remain.
826 There's a problem when the result of the case expression is of
827 unboxed type. Then the type of @fail.33@ is unboxed too, and
828 there is every chance that someone will change the let into a case:
834 which is of course utterly wrong. Rather than drop the condition that
835 only boxed types can be let-bound, we just turn the fail into a function
836 for the primitive case:
838 let fail.33 :: Void -> Int#
839 fail.33 = \_ -> error "Help"
848 Now @fail.33@ is a function, so it can be let-bound.
851 mkFailurePair :: CoreExpr -- Result type of the whole case expression
852 -> DsM (CoreBind, -- Binds the newly-created fail variable
853 -- to either the expression or \ _ -> expression
854 CoreExpr) -- Either the fail variable, or fail variable
855 -- applied to unit tuple
858 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
859 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
860 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
861 App (Var fail_fun_var) (Var unitDataConId))
864 = newFailLocalDs ty `thenDs` \ fail_var ->
865 returnDs (NonRec fail_var expr, Var fail_var)