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,
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 dsSyntaxTable, lookupEvidence,
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 SrcLoc ( Located(..), unLoc )
73 import Util ( isSingleton, notNull, zipEqual, sortWith )
74 import ListSetOps ( assocDefault )
77 import Data.Char ( ord )
82 %************************************************************************
86 %************************************************************************
89 dsSyntaxTable :: SyntaxTable Id
90 -> DsM ([CoreBind], -- Auxiliary bindings
91 [(Name,Id)]) -- Maps the standard name to its value
93 dsSyntaxTable rebound_ids
94 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
95 return (concat binds_s, prs)
97 -- The cheapo special case can happen when we
98 -- make an intermediate HsDo when desugaring a RecStmt
99 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
100 mk_bind (std_name, expr)
101 = dsExpr expr `thenDs` \ rhs ->
102 newSysLocalDs (exprType rhs) `thenDs` \ id ->
103 return ([NonRec id rhs], (std_name, id))
105 lookupEvidence :: [(Name, Id)] -> Name -> Id
106 lookupEvidence prs std_name
107 = assocDefault (mk_panic std_name) prs std_name
109 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
113 %************************************************************************
115 \subsection{Building lets}
117 %************************************************************************
119 Use case, not let for unlifted types. The simplifier will turn some
123 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
124 mkDsLet (NonRec bndr rhs) body
125 | isUnLiftedType (idType bndr)
126 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
130 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
131 mkDsLets binds body = foldr mkDsLet body binds
135 %************************************************************************
137 \subsection{ Selecting match variables}
139 %************************************************************************
141 We're about to match against some patterns. We want to make some
142 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
143 hand, which should indeed be bound to the pattern as a whole, then use it;
144 otherwise, make one up.
147 selectSimpleMatchVarL :: LPat Id -> DsM Id
148 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat) (hsPatType pat)
150 -- (selectMatchVars ps tys) chooses variables of type tys
151 -- to use for matching ps against. If the pattern is a variable,
152 -- we try to use that, to save inventing lots of fresh variables.
153 -- But even if it is a variable, its type might not match. Consider
155 -- T1 :: Int -> T Int
158 -- f :: T a -> a -> Int
159 -- f (T1 i) (x::Int) = x
160 -- f (T2 i) (y::a) = 0
161 -- Then we must not choose (x::Int) as the matching variable!
163 selectMatchVars :: [Pat Id] -> [Type] -> DsM [Id]
164 selectMatchVars [] [] = return []
165 selectMatchVars (p:ps) (ty:tys) = do { v <- selectMatchVar p ty
166 ; vs <- selectMatchVars ps tys
169 selectMatchVar (LazyPat pat) pat_ty = selectMatchVar (unLoc pat) pat_ty
170 selectMatchVar (VarPat var) pat_ty = try_for var pat_ty
171 selectMatchVar (AsPat var pat) pat_ty = try_for (unLoc var) pat_ty
172 selectMatchVar other_pat pat_ty = newSysLocalDs pat_ty -- OK, better make up one...
175 | idType var `tcEqType` pat_ty = returnDs var
176 | otherwise = newSysLocalDs pat_ty
180 %************************************************************************
182 %* type synonym EquationInfo and access functions for its pieces *
184 %************************************************************************
185 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
187 The ``equation info'' used by @match@ is relatively complicated and
188 worthy of a type synonym and a few handy functions.
191 firstPat :: EquationInfo -> Pat Id
192 firstPat eqn = head (eqn_pats eqn)
194 shiftEqns :: [EquationInfo] -> [EquationInfo]
195 -- Drop the first pattern in each equation
196 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
199 Functions on MatchResults
202 matchCanFail :: MatchResult -> Bool
203 matchCanFail (MatchResult CanFail _) = True
204 matchCanFail (MatchResult CantFail _) = False
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 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
247 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
249 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
250 wrapBind new old body
252 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
253 | otherwise = Let (NonRec new (Var old)) body
255 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
256 mkCoLetMatchResult bind match_result
257 = adjustMatchResult (mkDsLet bind) match_result
259 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
260 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
261 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
262 returnDs (mkIfThenElse pred_expr body fail))
264 mkCoPrimCaseMatchResult :: Id -- Scrutinee
265 -> Type -- Type of the case
266 -> [(Literal, MatchResult)] -- Alternatives
268 mkCoPrimCaseMatchResult var ty match_alts
269 = MatchResult CanFail mk_case
272 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
273 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
275 sorted_alts = sortWith fst match_alts -- Right order for a Case
276 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
277 returnDs (LitAlt lit, [], body)
280 mkCoAlgCaseMatchResult :: Id -- Scrutinee
281 -> Type -- Type of exp
282 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
284 mkCoAlgCaseMatchResult var ty match_alts
285 | isNewTyCon tycon -- Newtype case; use a let
286 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
287 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
289 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
290 = MatchResult CanFail mk_parrCase
292 | otherwise -- Datatype case; use a case
293 = MatchResult fail_flag mk_case
295 tycon = dataConTyCon con1
296 -- [Interesting: becuase of GADTs, we can't rely on the type of
297 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
300 (con1, arg_ids1, match_result1) = head match_alts
301 arg_id1 = head arg_ids1
302 newtype_rhs = mkNewTypeBody tycon (idType arg_id1) (Var var)
304 -- Stuff for data types
305 data_cons = tyConDataCons tycon
306 match_results = [match_result | (_,_,match_result) <- match_alts]
308 fail_flag | exhaustive_case
309 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
313 wild_var = mkWildId (idType var)
314 sorted_alts = sortWith get_tag match_alts
315 get_tag (con, _, _) = dataConTag con
316 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
317 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
319 mk_alt fail (con, args, MatchResult _ body_fn)
320 = body_fn fail `thenDs` \ body ->
321 newUniqueSupply `thenDs` \ us ->
322 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
324 mk_default fail | exhaustive_case = []
325 | otherwise = [(DEFAULT, [], fail)]
327 un_mentioned_constructors
328 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
329 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
331 -- Stuff for parallel arrays
333 -- * the following is to desugar cases over fake constructors for
334 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
337 -- Concerning `isPArrFakeAlts':
339 -- * it is *not* sufficient to just check the type of the type
340 -- constructor, as we have to be careful not to confuse the real
341 -- representation of parallel arrays with the fake constructors;
342 -- moreover, a list of alternatives must not mix fake and real
343 -- constructors (this is checked earlier on)
345 -- FIXME: We actually go through the whole list and make sure that
346 -- either all or none of the constructors are fake parallel
347 -- array constructors. This is to spot equations that mix fake
348 -- constructors with the real representation defined in
349 -- `PrelPArr'. It would be nicer to spot this situation
350 -- earlier and raise a proper error message, but it can really
351 -- only happen in `PrelPArr' anyway.
353 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
354 isPArrFakeAlts ((dcon, _, _):alts) =
355 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
356 (True , True ) -> True
357 (False, False) -> False
359 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
362 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
363 unboxAlt `thenDs` \alt ->
364 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
366 elemTy = case splitTyConApp (idType var) of
367 (_, [elemTy]) -> elemTy
369 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
370 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
373 newSysLocalDs intPrimTy `thenDs` \l ->
374 dsLookupGlobalId indexPName `thenDs` \indexP ->
375 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
376 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
378 wild = mkWildId intPrimTy
379 dft = (DEFAULT, [], fail)
381 -- each alternative matches one array length (corresponding to one
382 -- fake array constructor), so the match is on a literal; each
383 -- alternative's body is extended by a local binding for each
384 -- constructor argument, which are bound to array elements starting
387 mkAlt indexP (con, args, MatchResult _ bodyFun) =
388 bodyFun fail `thenDs` \body ->
389 returnDs (LitAlt lit, [], mkDsLets binds body)
391 lit = MachInt $ toInteger (dataConSourceArity con)
392 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
394 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
398 %************************************************************************
400 \subsection{Desugarer's versions of some Core functions}
402 %************************************************************************
405 mkErrorAppDs :: Id -- The error function
406 -> Type -- Type to which it should be applied
407 -> String -- The error message string to pass
410 mkErrorAppDs err_id ty msg
411 = getSrcSpanDs `thenDs` \ src_loc ->
413 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
414 core_msg = Lit (mkStringLit full_msg)
415 -- mkStringLit returns a result of type String#
417 returnDs (mkApps (Var err_id) [Type ty, core_msg])
421 *************************************************************
423 \subsection{Making literals}
425 %************************************************************************
428 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
429 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
430 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
431 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
432 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
434 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
435 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
438 | inIntRange i -- Small enough, so start from an Int
439 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
440 returnDs (mkSmallIntegerLit integer_dc i)
442 -- Special case for integral literals with a large magnitude:
443 -- They are transformed into an expression involving only smaller
444 -- integral literals. This improves constant folding.
446 | otherwise -- Big, so start from a string
447 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
448 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
449 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
451 lit i = mkSmallIntegerLit integer_dc i
452 plus a b = Var plus_id `App` a `App` b
453 times a b = Var times_id `App` a `App` b
455 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
456 horner :: Integer -> Integer -> CoreExpr
457 horner b i | abs q <= 1 = if r == 0 || r == i
459 else lit r `plus` lit (i-r)
460 | r == 0 = horner b q `times` lit b
461 | otherwise = lit r `plus` (horner b q `times` lit b)
463 (q,r) = i `quotRem` b
466 returnDs (horner tARGET_MAX_INT i)
468 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
470 mkStringExpr str = mkStringExprFS (mkFastString str)
474 = returnDs (mkNilExpr charTy)
478 the_char = mkCharExpr (headFS str)
480 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
483 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
484 returnDs (App (Var unpack_id) (Lit (MachStr str)))
487 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
488 returnDs (App (Var unpack_id) (Lit (MachStr str)))
492 safeChar c = ord c >= 1 && ord c <= 0x7F
496 %************************************************************************
498 \subsection[mkSelectorBind]{Make a selector bind}
500 %************************************************************************
502 This is used in various places to do with lazy patterns.
503 For each binder $b$ in the pattern, we create a binding:
505 b = case v of pat' -> b'
507 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
509 ToDo: making these bindings should really depend on whether there's
510 much work to be done per binding. If the pattern is complex, it
511 should be de-mangled once, into a tuple (and then selected from).
512 Otherwise the demangling can be in-line in the bindings (as here).
514 Boring! Boring! One error message per binder. The above ToDo is
515 even more helpful. Something very similar happens for pattern-bound
519 mkSelectorBinds :: LPat Id -- The pattern
520 -> CoreExpr -- Expression to which the pattern is bound
521 -> DsM [(Id,CoreExpr)]
523 mkSelectorBinds (L _ (VarPat v)) val_expr
524 = returnDs [(v, val_expr)]
526 mkSelectorBinds pat val_expr
527 | isSingleton binders || is_simple_lpat pat
528 = -- Given p = e, where p binds x,y
529 -- we are going to make
530 -- v = p (where v is fresh)
531 -- x = case v of p -> x
532 -- y = case v of p -> x
535 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
536 -- This does not matter after desugaring, but there's a subtle
537 -- issue with implicit parameters. Consider
539 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
540 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
541 -- does it get that type? So that when we abstract over it we get the
542 -- right top-level type (?i::Int) => ...)
544 -- So to get the type of 'v', use the pattern not the rhs. Often more
546 newSysLocalDs (hsPatType pat) `thenDs` \ val_var ->
548 -- For the error message we make one error-app, to avoid duplication.
549 -- But we need it at different types... so we use coerce for that
550 mkErrorAppDs iRREFUT_PAT_ERROR_ID
551 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
552 newSysLocalDs unitTy `thenDs` \ err_var ->
553 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
554 returnDs ( (val_var, val_expr) :
555 (err_var, err_expr) :
560 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
561 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
562 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
563 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
566 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
568 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
570 binders = collectPatBinders pat
571 local_tuple = mkTupleExpr binders
572 tuple_ty = exprType local_tuple
574 mk_bind scrut_var err_var bndr_var
575 -- (mk_bind sv err_var) generates
576 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
577 -- Remember, pat binds bv
578 = matchSimply (Var scrut_var) PatBindRhs pat
579 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
580 returnDs (bndr_var, rhs_expr)
582 error_expr = mkCoerce (idType bndr_var) (Var err_var)
584 is_simple_lpat p = is_simple_pat (unLoc p)
586 is_simple_pat (TuplePat ps Boxed) = all is_triv_lpat ps
587 is_simple_pat (ConPatOut _ _ _ _ ps _) = all is_triv_lpat (hsConArgs ps)
588 is_simple_pat (VarPat _) = True
589 is_simple_pat (ParPat p) = is_simple_lpat p
590 is_simple_pat other = False
592 is_triv_lpat p = is_triv_pat (unLoc p)
594 is_triv_pat (VarPat v) = True
595 is_triv_pat (WildPat _) = True
596 is_triv_pat (ParPat p) = is_triv_lpat p
597 is_triv_pat other = False
601 %************************************************************************
605 %************************************************************************
607 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
609 * If it has only one element, it is the identity function.
611 * If there are more elements than a big tuple can have, it nests
614 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
615 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
618 mkTupleExpr :: [Id] -> CoreExpr
619 mkTupleExpr ids = mkBigCoreTup (map Var ids)
621 -- corresponding type
622 mkTupleType :: [Id] -> Type
623 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
625 mkBigCoreTup :: [CoreExpr] -> CoreExpr
626 mkBigCoreTup = mkBigTuple mkCoreTup
628 mkBigTuple :: ([a] -> a) -> [a] -> a
629 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
631 -- Each sub-list is short enough to fit in a tuple
632 mk_big_tuple [as] = small_tuple as
633 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
635 chunkify :: [a] -> [[a]]
636 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
637 -- But there may be more than mAX_TUPLE_SIZE sub-lists
639 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
640 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
644 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
648 @mkTupleSelector@ builds a selector which scrutises the given
649 expression and extracts the one name from the list given.
650 If you want the no-shadowing rule to apply, the caller
651 is responsible for making sure that none of these names
654 If there is just one id in the ``tuple'', then the selector is
657 If it's big, it does nesting
658 mkTupleSelector [a,b,c,d] b v e
660 (p,q) -> case p of p {
662 We use 'tpl' vars for the p,q, since shadowing does not matter.
664 In fact, it's more convenient to generate it innermost first, getting
671 mkTupleSelector :: [Id] -- The tuple args
672 -> Id -- The selected one
673 -> Id -- A variable of the same type as the scrutinee
674 -> CoreExpr -- Scrutinee
677 mkTupleSelector vars the_var scrut_var scrut
678 = mk_tup_sel (chunkify vars) the_var
680 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
681 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
682 mk_tup_sel (chunkify tpl_vs) tpl_v
684 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
685 tpl_vs = mkTemplateLocals tpl_tys
686 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
690 A generalization of @mkTupleSelector@, allowing the body
691 of the case to be an arbitrary expression.
693 If the tuple is big, it is nested:
695 mkTupleCase uniqs [a,b,c,d] body v e
696 = case e of v { (p,q) ->
697 case p of p { (a,b) ->
698 case q of q { (c,d) ->
701 To avoid shadowing, we use uniqs to invent new variables p,q.
703 ToDo: eliminate cases where none of the variables are needed.
707 :: UniqSupply -- for inventing names of intermediate variables
708 -> [Id] -- the tuple args
709 -> CoreExpr -- body of the case
710 -> Id -- a variable of the same type as the scrutinee
711 -> CoreExpr -- scrutinee
714 mkTupleCase uniqs vars body scrut_var scrut
715 = mk_tuple_case uniqs (chunkify vars) body
717 mk_tuple_case us [vars] body
718 = mkSmallTupleCase vars body scrut_var scrut
719 mk_tuple_case us vars_s body
721 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
723 mk_tuple_case us' (chunkify vars') body'
724 one_tuple_case chunk_vars (us, vs, body)
726 (us1, us2) = splitUniqSupply us
727 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
728 (mkCoreTupTy (map idType chunk_vars))
729 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
730 in (us2, scrut_var:vs, body')
733 The same, but with a tuple small enough not to need nesting.
737 :: [Id] -- the tuple args
738 -> CoreExpr -- body of the case
739 -> Id -- a variable of the same type as the scrutinee
740 -> CoreExpr -- scrutinee
743 mkSmallTupleCase [var] body _scrut_var scrut
744 = bindNonRec var scrut body
745 mkSmallTupleCase vars body scrut_var scrut
746 -- One branch no refinement?
747 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
750 %************************************************************************
752 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
754 %************************************************************************
756 Call the constructor Ids when building explicit lists, so that they
757 interact well with rules.
760 mkNilExpr :: Type -> CoreExpr
761 mkNilExpr ty = mkConApp nilDataCon [Type ty]
763 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
764 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
766 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
767 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
770 -- The next three functions make tuple types, constructors and selectors,
771 -- with the rule that a 1-tuple is represented by the thing itselg
772 mkCoreTupTy :: [Type] -> Type
773 mkCoreTupTy [ty] = ty
774 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
776 mkCoreTup :: [CoreExpr] -> CoreExpr
777 -- Builds exactly the specified tuple.
778 -- No fancy business for big tuples
779 mkCoreTup [] = Var unitDataConId
781 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
782 (map (Type . exprType) cs ++ cs)
784 mkCoreSel :: [Id] -- The tuple args
785 -> Id -- The selected one
786 -> Id -- A variable of the same type as the scrutinee
787 -> CoreExpr -- Scrutinee
789 -- mkCoreSel [x,y,z] x v e
790 -- ===> case e of v { (x,y,z) -> x
791 mkCoreSel [var] should_be_the_same_var scrut_var scrut
792 = ASSERT(var == should_be_the_same_var)
795 mkCoreSel vars the_var scrut_var scrut
796 = ASSERT( notNull vars )
797 Case scrut scrut_var (idType the_var)
798 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
802 %************************************************************************
804 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
806 %************************************************************************
808 Generally, we handle pattern matching failure like this: let-bind a
809 fail-variable, and use that variable if the thing fails:
811 let fail.33 = error "Help"
822 If the case can't fail, then there'll be no mention of @fail.33@, and the
823 simplifier will later discard it.
826 If it can fail in only one way, then the simplifier will inline it.
829 Only if it is used more than once will the let-binding remain.
832 There's a problem when the result of the case expression is of
833 unboxed type. Then the type of @fail.33@ is unboxed too, and
834 there is every chance that someone will change the let into a case:
840 which is of course utterly wrong. Rather than drop the condition that
841 only boxed types can be let-bound, we just turn the fail into a function
842 for the primitive case:
844 let fail.33 :: Void -> Int#
845 fail.33 = \_ -> error "Help"
854 Now @fail.33@ is a function, so it can be let-bound.
857 mkFailurePair :: CoreExpr -- Result type of the whole case expression
858 -> DsM (CoreBind, -- Binds the newly-created fail variable
859 -- to either the expression or \ _ -> expression
860 CoreExpr) -- Either the fail variable, or fail variable
861 -- applied to unit tuple
864 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
865 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
866 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
867 App (Var fail_fun_var) (Var unitDataConId))
870 = newFailLocalDs ty `thenDs` \ fail_var ->
871 returnDs (NonRec fail_var expr, Var fail_var)