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 mkCoLetMatchResult, mkGuardedMatchResult,
20 matchCanFail, mkEvalMatchResult,
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, seqVar,
32 dsSyntaxTable, lookupEvidence,
34 selectSimpleMatchVarL, selectMatchVars, selectMatchVar
37 #include "HsVersions.h"
39 import {-# SOURCE #-} Match ( matchSimply )
40 import {-# SOURCE #-} DsExpr( dsExpr )
43 import TcHsSyn ( hsLPatType, hsPatType )
45 import Constants ( mAX_TUPLE_SIZE )
48 import CoreUtils ( exprType, mkIfThenElse, mkCoerce, bindNonRec )
49 import MkId ( iRREFUT_PAT_ERROR_ID, mkReboxingAlt, unwrapNewTypeBody )
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,
58 import Coercion ( mkUnsafeCoercion )
59 import TysPrim ( intPrimTy )
60 import TysWiredIn ( nilDataCon, consDataCon,
62 unitDataConId, unitTy,
66 import BasicTypes ( Boxity(..) )
67 import UniqSet ( mkUniqSet, minusUniqSet, isEmptyUniqSet )
68 import UniqSupply ( splitUniqSupply, uniqFromSupply, uniqsFromSupply )
69 import PrelNames ( unpackCStringName, unpackCStringUtf8Name,
70 plusIntegerName, timesIntegerName, smallIntegerDataConName,
71 lengthPName, indexPName )
73 import SrcLoc ( Located(..), unLoc )
74 import Util ( isSingleton, zipEqual, sortWith )
75 import ListSetOps ( assocDefault )
77 import Data.Char ( ord )
80 import Util ( notNull ) -- Used in an assertion
86 %************************************************************************
90 %************************************************************************
93 dsSyntaxTable :: SyntaxTable Id
94 -> DsM ([CoreBind], -- Auxiliary bindings
95 [(Name,Id)]) -- Maps the standard name to its value
97 dsSyntaxTable rebound_ids
98 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
99 return (concat binds_s, prs)
101 -- The cheapo special case can happen when we
102 -- make an intermediate HsDo when desugaring a RecStmt
103 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
104 mk_bind (std_name, expr)
105 = dsExpr expr `thenDs` \ rhs ->
106 newSysLocalDs (exprType rhs) `thenDs` \ id ->
107 return ([NonRec id rhs], (std_name, id))
109 lookupEvidence :: [(Name, Id)] -> Name -> Id
110 lookupEvidence prs std_name
111 = assocDefault (mk_panic std_name) prs std_name
113 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
117 %************************************************************************
119 \subsection{Building lets}
121 %************************************************************************
123 Use case, not let for unlifted types. The simplifier will turn some
127 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
128 mkDsLet (NonRec bndr rhs) body
129 | isUnLiftedType (idType bndr)
130 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
134 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
135 mkDsLets binds body = foldr mkDsLet body binds
139 %************************************************************************
141 \subsection{ Selecting match variables}
143 %************************************************************************
145 We're about to match against some patterns. We want to make some
146 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
147 hand, which should indeed be bound to the pattern as a whole, then use it;
148 otherwise, make one up.
151 selectSimpleMatchVarL :: LPat Id -> DsM Id
152 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
154 -- (selectMatchVars ps tys) chooses variables of type tys
155 -- to use for matching ps against. If the pattern is a variable,
156 -- we try to use that, to save inventing lots of fresh variables.
158 -- OLD, but interesting note:
159 -- But even if it is a variable, its type might not match. Consider
161 -- T1 :: Int -> T Int
164 -- f :: T a -> a -> Int
165 -- f (T1 i) (x::Int) = x
166 -- f (T2 i) (y::a) = 0
167 -- Then we must not choose (x::Int) as the matching variable!
168 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
170 selectMatchVars :: [Pat Id] -> DsM [Id]
171 selectMatchVars ps = mapM selectMatchVar ps
173 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
174 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
175 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
176 selectMatchVar (VarPat var) = return var
177 selectMatchVar (AsPat var pat) = return (unLoc var)
178 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
179 -- OK, better make up one...
183 %************************************************************************
185 %* type synonym EquationInfo and access functions for its pieces *
187 %************************************************************************
188 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
190 The ``equation info'' used by @match@ is relatively complicated and
191 worthy of a type synonym and a few handy functions.
194 firstPat :: EquationInfo -> Pat Id
195 firstPat eqn = head (eqn_pats eqn)
197 shiftEqns :: [EquationInfo] -> [EquationInfo]
198 -- Drop the first pattern in each equation
199 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
202 Functions on MatchResults
205 matchCanFail :: MatchResult -> Bool
206 matchCanFail (MatchResult CanFail _) = True
207 matchCanFail (MatchResult CantFail _) = False
209 alwaysFailMatchResult :: MatchResult
210 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
212 cantFailMatchResult :: CoreExpr -> MatchResult
213 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
215 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
216 extractMatchResult (MatchResult CantFail match_fn) fail_expr
217 = match_fn (error "It can't fail!")
219 extractMatchResult (MatchResult CanFail match_fn) fail_expr
220 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
221 match_fn if_it_fails `thenDs` \ body ->
222 returnDs (mkDsLet fail_bind body)
225 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
226 combineMatchResults (MatchResult CanFail body_fn1)
227 (MatchResult can_it_fail2 body_fn2)
228 = MatchResult can_it_fail2 body_fn
230 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
231 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
232 body_fn1 duplicatable_expr `thenDs` \ body1 ->
233 returnDs (Let fail_bind body1)
235 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
238 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
239 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
240 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
241 returnDs (encl_fn body))
243 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
244 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
245 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
248 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
250 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
252 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
253 wrapBind new old body
255 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
256 | otherwise = Let (NonRec new (Var old)) body
258 seqVar :: Var -> CoreExpr -> CoreExpr
259 seqVar var body = Case (Var var) var (exprType body)
260 [(DEFAULT, [], body)]
262 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
263 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
265 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
266 mkEvalMatchResult var ty
267 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
269 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
270 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
271 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
272 returnDs (mkIfThenElse pred_expr body fail))
274 mkCoPrimCaseMatchResult :: Id -- Scrutinee
275 -> Type -- Type of the case
276 -> [(Literal, MatchResult)] -- Alternatives
278 mkCoPrimCaseMatchResult var ty match_alts
279 = MatchResult CanFail mk_case
282 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
283 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
285 sorted_alts = sortWith fst match_alts -- Right order for a Case
286 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
287 returnDs (LitAlt lit, [], body)
290 mkCoAlgCaseMatchResult :: Id -- Scrutinee
291 -> Type -- Type of exp
292 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
294 mkCoAlgCaseMatchResult var ty match_alts
295 | isNewTyCon tycon -- Newtype case; use a let
296 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
297 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
299 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
300 = MatchResult CanFail mk_parrCase
302 | otherwise -- Datatype case; use a case
303 = MatchResult fail_flag mk_case
305 tycon = dataConTyCon con1
306 -- [Interesting: becuase of GADTs, we can't rely on the type of
307 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
310 (con1, arg_ids1, match_result1) = head match_alts
311 arg_id1 = head arg_ids1
313 (tc, ty_args) = splitNewTyConApp var_ty
314 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
316 -- Stuff for data types
317 data_cons = tyConDataCons tycon
318 match_results = [match_result | (_,_,match_result) <- match_alts]
320 fail_flag | exhaustive_case
321 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
325 wild_var = mkWildId (idType var)
326 sorted_alts = sortWith get_tag match_alts
327 get_tag (con, _, _) = dataConTag con
328 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
329 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
331 mk_alt fail (con, args, MatchResult _ body_fn)
332 = body_fn fail `thenDs` \ body ->
333 newUniqueSupply `thenDs` \ us ->
334 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
336 mk_default fail | exhaustive_case = []
337 | otherwise = [(DEFAULT, [], fail)]
339 un_mentioned_constructors
340 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
341 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
343 -- Stuff for parallel arrays
345 -- * the following is to desugar cases over fake constructors for
346 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
349 -- Concerning `isPArrFakeAlts':
351 -- * it is *not* sufficient to just check the type of the type
352 -- constructor, as we have to be careful not to confuse the real
353 -- representation of parallel arrays with the fake constructors;
354 -- moreover, a list of alternatives must not mix fake and real
355 -- constructors (this is checked earlier on)
357 -- FIXME: We actually go through the whole list and make sure that
358 -- either all or none of the constructors are fake parallel
359 -- array constructors. This is to spot equations that mix fake
360 -- constructors with the real representation defined in
361 -- `PrelPArr'. It would be nicer to spot this situation
362 -- earlier and raise a proper error message, but it can really
363 -- only happen in `PrelPArr' anyway.
365 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
366 isPArrFakeAlts ((dcon, _, _):alts) =
367 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
368 (True , True ) -> True
369 (False, False) -> False
371 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
374 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
375 unboxAlt `thenDs` \alt ->
376 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
378 elemTy = case splitTyConApp (idType var) of
379 (_, [elemTy]) -> elemTy
381 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
382 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
385 newSysLocalDs intPrimTy `thenDs` \l ->
386 dsLookupGlobalId indexPName `thenDs` \indexP ->
387 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
388 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
390 wild = mkWildId intPrimTy
391 dft = (DEFAULT, [], fail)
393 -- each alternative matches one array length (corresponding to one
394 -- fake array constructor), so the match is on a literal; each
395 -- alternative's body is extended by a local binding for each
396 -- constructor argument, which are bound to array elements starting
399 mkAlt indexP (con, args, MatchResult _ bodyFun) =
400 bodyFun fail `thenDs` \body ->
401 returnDs (LitAlt lit, [], mkDsLets binds body)
403 lit = MachInt $ toInteger (dataConSourceArity con)
404 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
406 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
410 %************************************************************************
412 \subsection{Desugarer's versions of some Core functions}
414 %************************************************************************
417 mkErrorAppDs :: Id -- The error function
418 -> Type -- Type to which it should be applied
419 -> String -- The error message string to pass
422 mkErrorAppDs err_id ty msg
423 = getSrcSpanDs `thenDs` \ src_loc ->
425 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
426 core_msg = Lit (mkStringLit full_msg)
427 -- mkStringLit returns a result of type String#
429 returnDs (mkApps (Var err_id) [Type ty, core_msg])
433 *************************************************************
435 \subsection{Making literals}
437 %************************************************************************
440 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
441 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
442 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
443 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
444 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
446 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
447 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
450 | inIntRange i -- Small enough, so start from an Int
451 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
452 returnDs (mkSmallIntegerLit integer_dc i)
454 -- Special case for integral literals with a large magnitude:
455 -- They are transformed into an expression involving only smaller
456 -- integral literals. This improves constant folding.
458 | otherwise -- Big, so start from a string
459 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
460 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
461 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
463 lit i = mkSmallIntegerLit integer_dc i
464 plus a b = Var plus_id `App` a `App` b
465 times a b = Var times_id `App` a `App` b
467 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
468 horner :: Integer -> Integer -> CoreExpr
469 horner b i | abs q <= 1 = if r == 0 || r == i
471 else lit r `plus` lit (i-r)
472 | r == 0 = horner b q `times` lit b
473 | otherwise = lit r `plus` (horner b q `times` lit b)
475 (q,r) = i `quotRem` b
478 returnDs (horner tARGET_MAX_INT i)
480 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
482 mkStringExpr str = mkStringExprFS (mkFastString str)
486 = returnDs (mkNilExpr charTy)
490 the_char = mkCharExpr (headFS str)
492 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
495 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
496 returnDs (App (Var unpack_id) (Lit (MachStr str)))
499 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
500 returnDs (App (Var unpack_id) (Lit (MachStr str)))
504 safeChar c = ord c >= 1 && ord c <= 0x7F
508 %************************************************************************
510 \subsection[mkSelectorBind]{Make a selector bind}
512 %************************************************************************
514 This is used in various places to do with lazy patterns.
515 For each binder $b$ in the pattern, we create a binding:
517 b = case v of pat' -> b'
519 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
521 ToDo: making these bindings should really depend on whether there's
522 much work to be done per binding. If the pattern is complex, it
523 should be de-mangled once, into a tuple (and then selected from).
524 Otherwise the demangling can be in-line in the bindings (as here).
526 Boring! Boring! One error message per binder. The above ToDo is
527 even more helpful. Something very similar happens for pattern-bound
531 mkSelectorBinds :: LPat Id -- The pattern
532 -> CoreExpr -- Expression to which the pattern is bound
533 -> DsM [(Id,CoreExpr)]
535 mkSelectorBinds (L _ (VarPat v)) val_expr
536 = returnDs [(v, val_expr)]
538 mkSelectorBinds pat val_expr
539 | isSingleton binders || is_simple_lpat pat
540 = -- Given p = e, where p binds x,y
541 -- we are going to make
542 -- v = p (where v is fresh)
543 -- x = case v of p -> x
544 -- y = case v of p -> x
547 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
548 -- This does not matter after desugaring, but there's a subtle
549 -- issue with implicit parameters. Consider
551 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
552 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
553 -- does it get that type? So that when we abstract over it we get the
554 -- right top-level type (?i::Int) => ...)
556 -- So to get the type of 'v', use the pattern not the rhs. Often more
558 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
560 -- For the error message we make one error-app, to avoid duplication.
561 -- But we need it at different types... so we use coerce for that
562 mkErrorAppDs iRREFUT_PAT_ERROR_ID
563 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
564 newSysLocalDs unitTy `thenDs` \ err_var ->
565 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
566 returnDs ( (val_var, val_expr) :
567 (err_var, err_expr) :
572 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
573 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
574 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
575 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
578 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
580 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
582 binders = collectPatBinders pat
583 local_tuple = mkTupleExpr binders
584 tuple_ty = exprType local_tuple
586 mk_bind scrut_var err_var bndr_var
587 -- (mk_bind sv err_var) generates
588 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
589 -- Remember, pat binds bv
590 = matchSimply (Var scrut_var) PatBindRhs pat
591 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
592 returnDs (bndr_var, rhs_expr)
594 error_expr = mkCoerce co (Var err_var)
595 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
597 is_simple_lpat p = is_simple_pat (unLoc p)
599 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
600 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConArgs ps)
601 is_simple_pat (VarPat _) = True
602 is_simple_pat (ParPat p) = is_simple_lpat p
603 is_simple_pat other = False
605 is_triv_lpat p = is_triv_pat (unLoc p)
607 is_triv_pat (VarPat v) = True
608 is_triv_pat (WildPat _) = True
609 is_triv_pat (ParPat p) = is_triv_lpat p
610 is_triv_pat other = False
614 %************************************************************************
618 %************************************************************************
620 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
622 * If it has only one element, it is the identity function.
624 * If there are more elements than a big tuple can have, it nests
627 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
628 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
631 mkTupleExpr :: [Id] -> CoreExpr
632 mkTupleExpr ids = mkBigCoreTup (map Var ids)
634 -- corresponding type
635 mkTupleType :: [Id] -> Type
636 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
638 mkBigCoreTup :: [CoreExpr] -> CoreExpr
639 mkBigCoreTup = mkBigTuple mkCoreTup
641 mkBigTuple :: ([a] -> a) -> [a] -> a
642 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
644 -- Each sub-list is short enough to fit in a tuple
645 mk_big_tuple [as] = small_tuple as
646 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
648 chunkify :: [a] -> [[a]]
649 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
650 -- But there may be more than mAX_TUPLE_SIZE sub-lists
652 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
653 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
657 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
661 @mkTupleSelector@ builds a selector which scrutises the given
662 expression and extracts the one name from the list given.
663 If you want the no-shadowing rule to apply, the caller
664 is responsible for making sure that none of these names
667 If there is just one id in the ``tuple'', then the selector is
670 If it's big, it does nesting
671 mkTupleSelector [a,b,c,d] b v e
673 (p,q) -> case p of p {
675 We use 'tpl' vars for the p,q, since shadowing does not matter.
677 In fact, it's more convenient to generate it innermost first, getting
684 mkTupleSelector :: [Id] -- The tuple args
685 -> Id -- The selected one
686 -> Id -- A variable of the same type as the scrutinee
687 -> CoreExpr -- Scrutinee
690 mkTupleSelector vars the_var scrut_var scrut
691 = mk_tup_sel (chunkify vars) the_var
693 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
694 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
695 mk_tup_sel (chunkify tpl_vs) tpl_v
697 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
698 tpl_vs = mkTemplateLocals tpl_tys
699 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
703 A generalization of @mkTupleSelector@, allowing the body
704 of the case to be an arbitrary expression.
706 If the tuple is big, it is nested:
708 mkTupleCase uniqs [a,b,c,d] body v e
709 = case e of v { (p,q) ->
710 case p of p { (a,b) ->
711 case q of q { (c,d) ->
714 To avoid shadowing, we use uniqs to invent new variables p,q.
716 ToDo: eliminate cases where none of the variables are needed.
720 :: UniqSupply -- for inventing names of intermediate variables
721 -> [Id] -- the tuple args
722 -> CoreExpr -- body of the case
723 -> Id -- a variable of the same type as the scrutinee
724 -> CoreExpr -- scrutinee
727 mkTupleCase uniqs vars body scrut_var scrut
728 = mk_tuple_case uniqs (chunkify vars) body
730 mk_tuple_case us [vars] body
731 = mkSmallTupleCase vars body scrut_var scrut
732 mk_tuple_case us vars_s body
734 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
736 mk_tuple_case us' (chunkify vars') body'
737 one_tuple_case chunk_vars (us, vs, body)
739 (us1, us2) = splitUniqSupply us
740 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
741 (mkCoreTupTy (map idType chunk_vars))
742 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
743 in (us2, scrut_var:vs, body')
746 The same, but with a tuple small enough not to need nesting.
750 :: [Id] -- the tuple args
751 -> CoreExpr -- body of the case
752 -> Id -- a variable of the same type as the scrutinee
753 -> CoreExpr -- scrutinee
756 mkSmallTupleCase [var] body _scrut_var scrut
757 = bindNonRec var scrut body
758 mkSmallTupleCase vars body scrut_var scrut
759 -- One branch no refinement?
760 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
763 %************************************************************************
765 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
767 %************************************************************************
769 Call the constructor Ids when building explicit lists, so that they
770 interact well with rules.
773 mkNilExpr :: Type -> CoreExpr
774 mkNilExpr ty = mkConApp nilDataCon [Type ty]
776 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
777 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
779 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
780 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
783 -- The next three functions make tuple types, constructors and selectors,
784 -- with the rule that a 1-tuple is represented by the thing itselg
785 mkCoreTupTy :: [Type] -> Type
786 mkCoreTupTy [ty] = ty
787 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
789 mkCoreTup :: [CoreExpr] -> CoreExpr
790 -- Builds exactly the specified tuple.
791 -- No fancy business for big tuples
792 mkCoreTup [] = Var unitDataConId
794 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
795 (map (Type . exprType) cs ++ cs)
797 mkCoreSel :: [Id] -- The tuple args
798 -> Id -- The selected one
799 -> Id -- A variable of the same type as the scrutinee
800 -> CoreExpr -- Scrutinee
802 -- mkCoreSel [x,y,z] x v e
803 -- ===> case e of v { (x,y,z) -> x
804 mkCoreSel [var] should_be_the_same_var scrut_var scrut
805 = ASSERT(var == should_be_the_same_var)
808 mkCoreSel vars the_var scrut_var scrut
809 = ASSERT( notNull vars )
810 Case scrut scrut_var (idType the_var)
811 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
815 %************************************************************************
817 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
819 %************************************************************************
821 Generally, we handle pattern matching failure like this: let-bind a
822 fail-variable, and use that variable if the thing fails:
824 let fail.33 = error "Help"
835 If the case can't fail, then there'll be no mention of @fail.33@, and the
836 simplifier will later discard it.
839 If it can fail in only one way, then the simplifier will inline it.
842 Only if it is used more than once will the let-binding remain.
845 There's a problem when the result of the case expression is of
846 unboxed type. Then the type of @fail.33@ is unboxed too, and
847 there is every chance that someone will change the let into a case:
853 which is of course utterly wrong. Rather than drop the condition that
854 only boxed types can be let-bound, we just turn the fail into a function
855 for the primitive case:
857 let fail.33 :: Void -> Int#
858 fail.33 = \_ -> error "Help"
867 Now @fail.33@ is a function, so it can be let-bound.
870 mkFailurePair :: CoreExpr -- Result type of the whole case expression
871 -> DsM (CoreBind, -- Binds the newly-created fail variable
872 -- to either the expression or \ _ -> expression
873 CoreExpr) -- Either the fail variable, or fail variable
874 -- applied to unit tuple
877 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
878 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
879 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
880 App (Var fail_fun_var) (Var unitDataConId))
883 = newFailLocalDs ty `thenDs` \ fail_var ->
884 returnDs (NonRec fail_var expr, Var fail_var)