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.
190 firstPat :: EquationInfo -> Pat Id
191 firstPat eqn = head (eqn_pats eqn)
193 shiftEqns :: [EquationInfo] -> [EquationInfo]
194 -- Drop the outermost layer of the first pattern in each equation
195 shiftEqns eqns = [ eqn { eqn_pats = shiftPats (eqn_pats eqn) }
198 shiftPats :: [Pat Id] -> [Pat Id]
199 shiftPats (ConPatOut _ _ _ _ (PrefixCon arg_pats) _ : pats) = map unLoc arg_pats ++ pats
200 shiftPats (pat_with_no_sub_pats : pats) = pats
203 Functions on MatchResults
206 alwaysFailMatchResult :: MatchResult
207 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
209 cantFailMatchResult :: CoreExpr -> MatchResult
210 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
212 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
213 extractMatchResult (MatchResult CantFail match_fn) fail_expr
214 = match_fn (error "It can't fail!")
216 extractMatchResult (MatchResult CanFail match_fn) fail_expr
217 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
218 match_fn if_it_fails `thenDs` \ body ->
219 returnDs (mkDsLet fail_bind body)
222 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
223 combineMatchResults (MatchResult CanFail body_fn1)
224 (MatchResult can_it_fail2 body_fn2)
225 = MatchResult can_it_fail2 body_fn
227 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
228 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
229 body_fn1 duplicatable_expr `thenDs` \ body1 ->
230 returnDs (Let fail_bind body1)
232 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
235 adjustMatchResult :: (CoreExpr -> CoreExpr) -> MatchResult -> MatchResult
236 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
237 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
238 returnDs (encl_fn body))
240 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
241 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
242 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
245 bindInMatchResult :: [(Var,Var)] -> MatchResult -> MatchResult
246 bindInMatchResult binds = adjustMatchResult (\e -> foldr bind e binds)
248 bind (new,old) body = bindMR new old body
250 bindOneInMatchResult :: Var -> Var -> MatchResult -> MatchResult
251 bindOneInMatchResult new old = adjustMatchResult (bindMR new old)
253 bindMR :: Var -> Var -> CoreExpr -> CoreExpr
256 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
257 | otherwise = Let (NonRec new (Var old)) body
259 mkCoLetsMatchResult :: [CoreBind] -> MatchResult -> MatchResult
260 mkCoLetsMatchResult binds match_result
261 = adjustMatchResult (mkDsLets binds) match_result
263 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
264 mkCoLetMatchResult bind match_result
265 = adjustMatchResult (mkDsLet bind) match_result
267 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
268 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
269 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
270 returnDs (mkIfThenElse pred_expr body fail))
272 mkCoPrimCaseMatchResult :: Id -- Scrutinee
273 -> Type -- Type of the case
274 -> [(Literal, MatchResult)] -- Alternatives
276 mkCoPrimCaseMatchResult var ty match_alts
277 = MatchResult CanFail mk_case
280 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
281 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
283 sorted_alts = sortWith fst match_alts -- Right order for a Case
284 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
285 returnDs (LitAlt lit, [], body)
288 mkCoAlgCaseMatchResult :: Id -- Scrutinee
289 -> Type -- Type of exp
290 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
292 mkCoAlgCaseMatchResult var ty match_alts
293 | isNewTyCon tycon -- Newtype case; use a let
294 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
295 mkCoLetsMatchResult [NonRec arg_id1 newtype_rhs] match_result1
297 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
298 = MatchResult CanFail mk_parrCase
300 | otherwise -- Datatype case; use a case
301 = MatchResult fail_flag mk_case
303 tycon = dataConTyCon con1
304 -- [Interesting: becuase of GADTs, we can't rely on the type of
305 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
308 (con1, arg_ids1, match_result1) = head match_alts
309 arg_id1 = head arg_ids1
310 newtype_rhs = mkNewTypeBody tycon (idType arg_id1) (Var var)
312 -- Stuff for data types
313 data_cons = tyConDataCons tycon
314 match_results = [match_result | (_,_,match_result) <- match_alts]
316 fail_flag | exhaustive_case
317 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
321 wild_var = mkWildId (idType var)
322 sorted_alts = sortWith get_tag match_alts
323 get_tag (con, _, _) = dataConTag con
324 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
325 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
327 mk_alt fail (con, args, MatchResult _ body_fn)
328 = body_fn fail `thenDs` \ body ->
329 newUniqueSupply `thenDs` \ us ->
330 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
332 mk_default fail | exhaustive_case = []
333 | otherwise = [(DEFAULT, [], fail)]
335 un_mentioned_constructors
336 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
337 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
339 -- Stuff for parallel arrays
341 -- * the following is to desugar cases over fake constructors for
342 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
345 -- Concerning `isPArrFakeAlts':
347 -- * it is *not* sufficient to just check the type of the type
348 -- constructor, as we have to be careful not to confuse the real
349 -- representation of parallel arrays with the fake constructors;
350 -- moreover, a list of alternatives must not mix fake and real
351 -- constructors (this is checked earlier on)
353 -- FIXME: We actually go through the whole list and make sure that
354 -- either all or none of the constructors are fake parallel
355 -- array constructors. This is to spot equations that mix fake
356 -- constructors with the real representation defined in
357 -- `PrelPArr'. It would be nicer to spot this situation
358 -- earlier and raise a proper error message, but it can really
359 -- only happen in `PrelPArr' anyway.
361 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
362 isPArrFakeAlts ((dcon, _, _):alts) =
363 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
364 (True , True ) -> True
365 (False, False) -> False
367 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
370 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
371 unboxAlt `thenDs` \alt ->
372 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
374 elemTy = case splitTyConApp (idType var) of
375 (_, [elemTy]) -> elemTy
377 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
378 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
381 newSysLocalDs intPrimTy `thenDs` \l ->
382 dsLookupGlobalId indexPName `thenDs` \indexP ->
383 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
384 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
386 wild = mkWildId intPrimTy
387 dft = (DEFAULT, [], fail)
389 -- each alternative matches one array length (corresponding to one
390 -- fake array constructor), so the match is on a literal; each
391 -- alternative's body is extended by a local binding for each
392 -- constructor argument, which are bound to array elements starting
395 mkAlt indexP (con, args, MatchResult _ bodyFun) =
396 bodyFun fail `thenDs` \body ->
397 returnDs (LitAlt lit, [], mkDsLets binds body)
399 lit = MachInt $ toInteger (dataConSourceArity con)
400 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
402 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
406 %************************************************************************
408 \subsection{Desugarer's versions of some Core functions}
410 %************************************************************************
413 mkErrorAppDs :: Id -- The error function
414 -> Type -- Type to which it should be applied
415 -> String -- The error message string to pass
418 mkErrorAppDs err_id ty msg
419 = getSrcSpanDs `thenDs` \ src_loc ->
421 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
422 core_msg = Lit (mkStringLit full_msg)
424 returnDs (mkApps (Var err_id) [Type ty, core_msg])
428 *************************************************************
430 \subsection{Making literals}
432 %************************************************************************
435 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
436 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
437 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
438 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
439 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
441 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
442 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
445 | inIntRange i -- Small enough, so start from an Int
446 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
447 returnDs (mkSmallIntegerLit integer_dc i)
449 -- Special case for integral literals with a large magnitude:
450 -- They are transformed into an expression involving only smaller
451 -- integral literals. This improves constant folding.
453 | otherwise -- Big, so start from a string
454 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
455 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
456 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
458 lit i = mkSmallIntegerLit integer_dc i
459 plus a b = Var plus_id `App` a `App` b
460 times a b = Var times_id `App` a `App` b
462 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
463 horner :: Integer -> Integer -> CoreExpr
464 horner b i | abs q <= 1 = if r == 0 || r == i
466 else lit r `plus` lit (i-r)
467 | r == 0 = horner b q `times` lit b
468 | otherwise = lit r `plus` (horner b q `times` lit b)
470 (q,r) = i `quotRem` b
473 returnDs (horner tARGET_MAX_INT i)
475 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
477 mkStringExpr str = mkStringExprFS (mkFastString str)
481 = returnDs (mkNilExpr charTy)
485 the_char = mkCharExpr (headFS str)
487 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
489 | all safeChar int_chars
490 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
491 returnDs (App (Var unpack_id) (Lit (MachStr str)))
494 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
495 returnDs (App (Var unpack_id) (Lit (MachStr (mkFastString (intsToUtf8 int_chars)))))
498 int_chars = unpackIntFS str
499 safeChar c = c >= 1 && c <= 0xFF
503 %************************************************************************
505 \subsection[mkSelectorBind]{Make a selector bind}
507 %************************************************************************
509 This is used in various places to do with lazy patterns.
510 For each binder $b$ in the pattern, we create a binding:
512 b = case v of pat' -> b'
514 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
516 ToDo: making these bindings should really depend on whether there's
517 much work to be done per binding. If the pattern is complex, it
518 should be de-mangled once, into a tuple (and then selected from).
519 Otherwise the demangling can be in-line in the bindings (as here).
521 Boring! Boring! One error message per binder. The above ToDo is
522 even more helpful. Something very similar happens for pattern-bound
526 mkSelectorBinds :: LPat Id -- The pattern
527 -> CoreExpr -- Expression to which the pattern is bound
528 -> DsM [(Id,CoreExpr)]
530 mkSelectorBinds (L _ (VarPat v)) val_expr
531 = returnDs [(v, val_expr)]
533 mkSelectorBinds pat val_expr
534 | isSingleton binders || is_simple_lpat pat
535 = -- Given p = e, where p binds x,y
536 -- we are going to make
537 -- v = p (where v is fresh)
538 -- x = case v of p -> x
539 -- y = case v of p -> x
542 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
543 -- This does not matter after desugaring, but there's a subtle
544 -- issue with implicit parameters. Consider
546 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
547 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
548 -- does it get that type? So that when we abstract over it we get the
549 -- right top-level type (?i::Int) => ...)
551 -- So to get the type of 'v', use the pattern not the rhs. Often more
553 newSysLocalDs (hsPatType pat) `thenDs` \ val_var ->
555 -- For the error message we make one error-app, to avoid duplication.
556 -- But we need it at different types... so we use coerce for that
557 mkErrorAppDs iRREFUT_PAT_ERROR_ID
558 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
559 newSysLocalDs unitTy `thenDs` \ err_var ->
560 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
561 returnDs ( (val_var, val_expr) :
562 (err_var, err_expr) :
567 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
568 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
569 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
570 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
573 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
575 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
577 binders = collectPatBinders pat
578 local_tuple = mkTupleExpr binders
579 tuple_ty = exprType local_tuple
581 mk_bind scrut_var err_var bndr_var
582 -- (mk_bind sv err_var) generates
583 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
584 -- Remember, pat binds bv
585 = matchSimply (Var scrut_var) PatBindRhs pat
586 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
587 returnDs (bndr_var, rhs_expr)
589 error_expr = mkCoerce (idType bndr_var) (Var err_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 _ _ _ _ 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)