2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsUtils]{Utilities for desugaring}
6 This module exports some utility functions of no great interest.
15 MatchResult(..), CanItFail(..),
16 cantFailMatchResult, alwaysFailMatchResult,
17 extractMatchResult, combineMatchResults,
18 adjustMatchResult, adjustMatchResultDs,
19 mkCoLetsMatchResult, mkCoLetMatchResult,
21 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
22 bindInMatchResult, bindOneInMatchResult,
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.
191 = EqnInfo { eqn_pats :: [Pat Id], -- The patterns for an eqn
192 eqn_rhs :: MatchResult } -- What to do after match
194 -- The semantics of (match vs (EqnInfo wrap pats rhs)) is the MatchResult
195 -- \fail. wrap (case vs of { pats -> rhs fail })
196 -- where vs are not in the domain of wrap
198 firstPat :: EquationInfo -> Pat Id
199 firstPat eqn = head (eqn_pats eqn)
201 shiftEqns :: [EquationInfo] -> [EquationInfo]
202 -- Drop the outermost layer of the first pattern in each equation
203 shiftEqns eqns = [ eqn { eqn_pats = shiftPats (eqn_pats eqn) }
206 shiftPats :: [Pat Id] -> [Pat Id]
207 shiftPats (ConPatOut _ _ _ _ (PrefixCon arg_pats) _ : pats) = map unLoc arg_pats ++ pats
208 shiftPats (pat_with_no_sub_pats : pats) = pats
213 -- A MatchResult is an expression with a hole in it
216 CanItFail -- Tells whether the failure expression is used
217 (CoreExpr -> DsM CoreExpr)
218 -- Takes a expression to plug in at the
219 -- failure point(s). The expression should
222 data CanItFail = CanFail | CantFail
224 orFail CantFail CantFail = CantFail
228 Functions on MatchResults
231 alwaysFailMatchResult :: MatchResult
232 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
234 cantFailMatchResult :: CoreExpr -> MatchResult
235 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
237 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
238 extractMatchResult (MatchResult CantFail match_fn) fail_expr
239 = match_fn (error "It can't fail!")
241 extractMatchResult (MatchResult CanFail match_fn) fail_expr
242 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
243 match_fn if_it_fails `thenDs` \ body ->
244 returnDs (mkDsLet fail_bind body)
247 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
248 combineMatchResults (MatchResult CanFail body_fn1)
249 (MatchResult can_it_fail2 body_fn2)
250 = MatchResult can_it_fail2 body_fn
252 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
253 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
254 body_fn1 duplicatable_expr `thenDs` \ body1 ->
255 returnDs (Let fail_bind body1)
257 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
260 adjustMatchResult :: (CoreExpr -> CoreExpr) -> MatchResult -> MatchResult
261 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
262 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
263 returnDs (encl_fn body))
265 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
266 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
267 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
270 bindInMatchResult :: [(Var,Var)] -> MatchResult -> MatchResult
271 bindInMatchResult binds = adjustMatchResult (\e -> foldr bind e binds)
273 bind (new,old) body = bindMR new old body
275 bindOneInMatchResult :: Var -> Var -> MatchResult -> MatchResult
276 bindOneInMatchResult new old = adjustMatchResult (bindMR new old)
278 bindMR :: Var -> Var -> CoreExpr -> CoreExpr
281 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
282 | otherwise = Let (NonRec new (Var old)) body
284 mkCoLetsMatchResult :: [CoreBind] -> MatchResult -> MatchResult
285 mkCoLetsMatchResult binds match_result
286 = adjustMatchResult (mkDsLets binds) match_result
288 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
289 mkCoLetMatchResult bind match_result
290 = adjustMatchResult (mkDsLet bind) match_result
292 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
293 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
294 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
295 returnDs (mkIfThenElse pred_expr body fail))
297 mkCoPrimCaseMatchResult :: Id -- Scrutinee
298 -> Type -- Type of the case
299 -> [(Literal, MatchResult)] -- Alternatives
301 mkCoPrimCaseMatchResult var ty match_alts
302 = MatchResult CanFail mk_case
305 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
306 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
308 sorted_alts = sortWith fst match_alts -- Right order for a Case
309 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
310 returnDs (LitAlt lit, [], body)
313 mkCoAlgCaseMatchResult :: Id -- Scrutinee
314 -> Type -- Type of exp
315 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
317 mkCoAlgCaseMatchResult var ty match_alts
318 | isNewTyCon tycon -- Newtype case; use a let
319 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
320 mkCoLetsMatchResult [NonRec arg_id1 newtype_rhs] match_result1
322 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
323 = MatchResult CanFail mk_parrCase
325 | otherwise -- Datatype case; use a case
326 = MatchResult fail_flag mk_case
328 tycon = dataConTyCon con1
329 -- [Interesting: becuase of GADTs, we can't rely on the type of
330 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
333 (con1, arg_ids1, match_result1) = head match_alts
334 arg_id1 = head arg_ids1
335 newtype_rhs = mkNewTypeBody tycon (idType arg_id1) (Var var)
337 -- Stuff for data types
338 data_cons = tyConDataCons tycon
339 match_results = [match_result | (_,_,match_result) <- match_alts]
341 fail_flag | exhaustive_case
342 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
346 wild_var = mkWildId (idType var)
347 sorted_alts = sortWith get_tag match_alts
348 get_tag (con, _, _) = dataConTag con
349 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
350 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
352 mk_alt fail (con, args, MatchResult _ body_fn)
353 = body_fn fail `thenDs` \ body ->
354 newUniqueSupply `thenDs` \ us ->
355 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
357 mk_default fail | exhaustive_case = []
358 | otherwise = [(DEFAULT, [], fail)]
360 un_mentioned_constructors
361 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
362 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
364 -- Stuff for parallel arrays
366 -- * the following is to desugar cases over fake constructors for
367 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
370 -- Concerning `isPArrFakeAlts':
372 -- * it is *not* sufficient to just check the type of the type
373 -- constructor, as we have to be careful not to confuse the real
374 -- representation of parallel arrays with the fake constructors;
375 -- moreover, a list of alternatives must not mix fake and real
376 -- constructors (this is checked earlier on)
378 -- FIXME: We actually go through the whole list and make sure that
379 -- either all or none of the constructors are fake parallel
380 -- array constructors. This is to spot equations that mix fake
381 -- constructors with the real representation defined in
382 -- `PrelPArr'. It would be nicer to spot this situation
383 -- earlier and raise a proper error message, but it can really
384 -- only happen in `PrelPArr' anyway.
386 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
387 isPArrFakeAlts ((dcon, _, _):alts) =
388 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
389 (True , True ) -> True
390 (False, False) -> False
392 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
395 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
396 unboxAlt `thenDs` \alt ->
397 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
399 elemTy = case splitTyConApp (idType var) of
400 (_, [elemTy]) -> elemTy
402 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
403 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
406 newSysLocalDs intPrimTy `thenDs` \l ->
407 dsLookupGlobalId indexPName `thenDs` \indexP ->
408 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
409 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
411 wild = mkWildId intPrimTy
412 dft = (DEFAULT, [], fail)
414 -- each alternative matches one array length (corresponding to one
415 -- fake array constructor), so the match is on a literal; each
416 -- alternative's body is extended by a local binding for each
417 -- constructor argument, which are bound to array elements starting
420 mkAlt indexP (con, args, MatchResult _ bodyFun) =
421 bodyFun fail `thenDs` \body ->
422 returnDs (LitAlt lit, [], mkDsLets binds body)
424 lit = MachInt $ toInteger (dataConSourceArity con)
425 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
427 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
431 %************************************************************************
433 \subsection{Desugarer's versions of some Core functions}
435 %************************************************************************
438 mkErrorAppDs :: Id -- The error function
439 -> Type -- Type to which it should be applied
440 -> String -- The error message string to pass
443 mkErrorAppDs err_id ty msg
444 = getSrcSpanDs `thenDs` \ src_loc ->
446 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
447 core_msg = Lit (mkStringLit full_msg)
449 returnDs (mkApps (Var err_id) [Type ty, core_msg])
453 *************************************************************
455 \subsection{Making literals}
457 %************************************************************************
460 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
461 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
462 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
463 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
464 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
466 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
467 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
470 | inIntRange i -- Small enough, so start from an Int
471 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
472 returnDs (mkSmallIntegerLit integer_dc i)
474 -- Special case for integral literals with a large magnitude:
475 -- They are transformed into an expression involving only smaller
476 -- integral literals. This improves constant folding.
478 | otherwise -- Big, so start from a string
479 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
480 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
481 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
483 lit i = mkSmallIntegerLit integer_dc i
484 plus a b = Var plus_id `App` a `App` b
485 times a b = Var times_id `App` a `App` b
487 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
488 horner :: Integer -> Integer -> CoreExpr
489 horner b i | abs q <= 1 = if r == 0 || r == i
491 else lit r `plus` lit (i-r)
492 | r == 0 = horner b q `times` lit b
493 | otherwise = lit r `plus` (horner b q `times` lit b)
495 (q,r) = i `quotRem` b
498 returnDs (horner tARGET_MAX_INT i)
500 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
502 mkStringExpr str = mkStringExprFS (mkFastString str)
506 = returnDs (mkNilExpr charTy)
510 the_char = mkCharExpr (headFS str)
512 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
514 | all safeChar int_chars
515 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
516 returnDs (App (Var unpack_id) (Lit (MachStr str)))
519 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
520 returnDs (App (Var unpack_id) (Lit (MachStr (mkFastString (intsToUtf8 int_chars)))))
523 int_chars = unpackIntFS str
524 safeChar c = c >= 1 && c <= 0xFF
528 %************************************************************************
530 \subsection[mkSelectorBind]{Make a selector bind}
532 %************************************************************************
534 This is used in various places to do with lazy patterns.
535 For each binder $b$ in the pattern, we create a binding:
537 b = case v of pat' -> b'
539 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
541 ToDo: making these bindings should really depend on whether there's
542 much work to be done per binding. If the pattern is complex, it
543 should be de-mangled once, into a tuple (and then selected from).
544 Otherwise the demangling can be in-line in the bindings (as here).
546 Boring! Boring! One error message per binder. The above ToDo is
547 even more helpful. Something very similar happens for pattern-bound
551 mkSelectorBinds :: LPat Id -- The pattern
552 -> CoreExpr -- Expression to which the pattern is bound
553 -> DsM [(Id,CoreExpr)]
555 mkSelectorBinds (L _ (VarPat v)) val_expr
556 = returnDs [(v, val_expr)]
558 mkSelectorBinds pat val_expr
559 | isSingleton binders || is_simple_lpat pat
560 = -- Given p = e, where p binds x,y
561 -- we are going to make
562 -- v = p (where v is fresh)
563 -- x = case v of p -> x
564 -- y = case v of p -> x
567 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
568 -- This does not matter after desugaring, but there's a subtle
569 -- issue with implicit parameters. Consider
571 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
572 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
573 -- does it get that type? So that when we abstract over it we get the
574 -- right top-level type (?i::Int) => ...)
576 -- So to get the type of 'v', use the pattern not the rhs. Often more
578 newSysLocalDs (hsPatType pat) `thenDs` \ val_var ->
580 -- For the error message we make one error-app, to avoid duplication.
581 -- But we need it at different types... so we use coerce for that
582 mkErrorAppDs iRREFUT_PAT_ERROR_ID
583 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
584 newSysLocalDs unitTy `thenDs` \ err_var ->
585 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
586 returnDs ( (val_var, val_expr) :
587 (err_var, err_expr) :
592 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
593 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
594 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
595 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
598 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
600 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
602 binders = collectPatBinders pat
603 local_tuple = mkTupleExpr binders
604 tuple_ty = exprType local_tuple
606 mk_bind scrut_var err_var bndr_var
607 -- (mk_bind sv err_var) generates
608 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
609 -- Remember, pat binds bv
610 = matchSimply (Var scrut_var) PatBindRhs pat
611 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
612 returnDs (bndr_var, rhs_expr)
614 error_expr = mkCoerce (idType bndr_var) (Var err_var)
616 is_simple_lpat p = is_simple_pat (unLoc p)
618 is_simple_pat (TuplePat ps Boxed) = all is_triv_lpat ps
619 is_simple_pat (ConPatOut _ _ _ _ ps _) = all is_triv_lpat (hsConArgs ps)
620 is_simple_pat (VarPat _) = True
621 is_simple_pat (ParPat p) = is_simple_lpat p
622 is_simple_pat other = False
624 is_triv_lpat p = is_triv_pat (unLoc p)
626 is_triv_pat (VarPat v) = True
627 is_triv_pat (WildPat _) = True
628 is_triv_pat (ParPat p) = is_triv_lpat p
629 is_triv_pat other = False
633 %************************************************************************
637 %************************************************************************
639 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
641 * If it has only one element, it is the identity function.
643 * If there are more elements than a big tuple can have, it nests
646 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
647 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
650 mkTupleExpr :: [Id] -> CoreExpr
651 mkTupleExpr ids = mkBigCoreTup (map Var ids)
653 -- corresponding type
654 mkTupleType :: [Id] -> Type
655 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
657 mkBigCoreTup :: [CoreExpr] -> CoreExpr
658 mkBigCoreTup = mkBigTuple mkCoreTup
660 mkBigTuple :: ([a] -> a) -> [a] -> a
661 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
663 -- Each sub-list is short enough to fit in a tuple
664 mk_big_tuple [as] = small_tuple as
665 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
667 chunkify :: [a] -> [[a]]
668 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
669 -- But there may be more than mAX_TUPLE_SIZE sub-lists
671 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
672 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
676 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
680 @mkTupleSelector@ builds a selector which scrutises the given
681 expression and extracts the one name from the list given.
682 If you want the no-shadowing rule to apply, the caller
683 is responsible for making sure that none of these names
686 If there is just one id in the ``tuple'', then the selector is
689 If it's big, it does nesting
690 mkTupleSelector [a,b,c,d] b v e
692 (p,q) -> case p of p {
694 We use 'tpl' vars for the p,q, since shadowing does not matter.
696 In fact, it's more convenient to generate it innermost first, getting
703 mkTupleSelector :: [Id] -- The tuple args
704 -> Id -- The selected one
705 -> Id -- A variable of the same type as the scrutinee
706 -> CoreExpr -- Scrutinee
709 mkTupleSelector vars the_var scrut_var scrut
710 = mk_tup_sel (chunkify vars) the_var
712 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
713 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
714 mk_tup_sel (chunkify tpl_vs) tpl_v
716 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
717 tpl_vs = mkTemplateLocals tpl_tys
718 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
722 A generalization of @mkTupleSelector@, allowing the body
723 of the case to be an arbitrary expression.
725 If the tuple is big, it is nested:
727 mkTupleCase uniqs [a,b,c,d] body v e
728 = case e of v { (p,q) ->
729 case p of p { (a,b) ->
730 case q of q { (c,d) ->
733 To avoid shadowing, we use uniqs to invent new variables p,q.
735 ToDo: eliminate cases where none of the variables are needed.
739 :: UniqSupply -- for inventing names of intermediate variables
740 -> [Id] -- the tuple args
741 -> CoreExpr -- body of the case
742 -> Id -- a variable of the same type as the scrutinee
743 -> CoreExpr -- scrutinee
746 mkTupleCase uniqs vars body scrut_var scrut
747 = mk_tuple_case uniqs (chunkify vars) body
749 mk_tuple_case us [vars] body
750 = mkSmallTupleCase vars body scrut_var scrut
751 mk_tuple_case us vars_s body
753 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
755 mk_tuple_case us' (chunkify vars') body'
756 one_tuple_case chunk_vars (us, vs, body)
758 (us1, us2) = splitUniqSupply us
759 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
760 (mkCoreTupTy (map idType chunk_vars))
761 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
762 in (us2, scrut_var:vs, body')
765 The same, but with a tuple small enough not to need nesting.
769 :: [Id] -- the tuple args
770 -> CoreExpr -- body of the case
771 -> Id -- a variable of the same type as the scrutinee
772 -> CoreExpr -- scrutinee
775 mkSmallTupleCase [var] body _scrut_var scrut
776 = bindNonRec var scrut body
777 mkSmallTupleCase vars body scrut_var scrut
778 -- One branch no refinement?
779 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
782 %************************************************************************
784 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
786 %************************************************************************
788 Call the constructor Ids when building explicit lists, so that they
789 interact well with rules.
792 mkNilExpr :: Type -> CoreExpr
793 mkNilExpr ty = mkConApp nilDataCon [Type ty]
795 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
796 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
798 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
799 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
802 -- The next three functions make tuple types, constructors and selectors,
803 -- with the rule that a 1-tuple is represented by the thing itselg
804 mkCoreTupTy :: [Type] -> Type
805 mkCoreTupTy [ty] = ty
806 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
808 mkCoreTup :: [CoreExpr] -> CoreExpr
809 -- Builds exactly the specified tuple.
810 -- No fancy business for big tuples
811 mkCoreTup [] = Var unitDataConId
813 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
814 (map (Type . exprType) cs ++ cs)
816 mkCoreSel :: [Id] -- The tuple args
817 -> Id -- The selected one
818 -> Id -- A variable of the same type as the scrutinee
819 -> CoreExpr -- Scrutinee
821 -- mkCoreSel [x,y,z] x v e
822 -- ===> case e of v { (x,y,z) -> x
823 mkCoreSel [var] should_be_the_same_var scrut_var scrut
824 = ASSERT(var == should_be_the_same_var)
827 mkCoreSel vars the_var scrut_var scrut
828 = ASSERT( notNull vars )
829 Case scrut scrut_var (idType the_var)
830 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
834 %************************************************************************
836 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
838 %************************************************************************
840 Generally, we handle pattern matching failure like this: let-bind a
841 fail-variable, and use that variable if the thing fails:
843 let fail.33 = error "Help"
854 If the case can't fail, then there'll be no mention of @fail.33@, and the
855 simplifier will later discard it.
858 If it can fail in only one way, then the simplifier will inline it.
861 Only if it is used more than once will the let-binding remain.
864 There's a problem when the result of the case expression is of
865 unboxed type. Then the type of @fail.33@ is unboxed too, and
866 there is every chance that someone will change the let into a case:
872 which is of course utterly wrong. Rather than drop the condition that
873 only boxed types can be let-bound, we just turn the fail into a function
874 for the primitive case:
876 let fail.33 :: Void -> Int#
877 fail.33 = \_ -> error "Help"
886 Now @fail.33@ is a function, so it can be let-bound.
889 mkFailurePair :: CoreExpr -- Result type of the whole case expression
890 -> DsM (CoreBind, -- Binds the newly-created fail variable
891 -- to either the expression or \ _ -> expression
892 CoreExpr) -- Either the fail variable, or fail variable
893 -- applied to unit tuple
896 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
897 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
898 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
899 App (Var fail_fun_var) (Var unitDataConId))
902 = newFailLocalDs ty `thenDs` \ fail_var ->
903 returnDs (NonRec fail_var expr, Var fail_var)