2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utilities for desugaring
8 This module exports some utility functions of no great interest.
16 mkDsLet, mkDsLets, mkDsApp, mkDsApps,
18 MatchResult(..), CanItFail(..),
19 cantFailMatchResult, alwaysFailMatchResult,
20 extractMatchResult, combineMatchResults,
21 adjustMatchResult, adjustMatchResultDs,
22 mkCoLetMatchResult, mkViewMatchResult, mkGuardedMatchResult,
23 matchCanFail, mkEvalMatchResult,
24 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
27 mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr,
28 mkIntExpr, mkCharExpr,
29 mkStringExpr, mkStringExprFS, mkIntegerExpr,
30 mkBuildExpr, mkFoldrExpr,
35 mkCoreVarTup, mkCoreTup, mkCoreVarTupTy, mkCoreTupTy,
36 mkBigCoreVarTup, mkBigCoreTup, mkBigCoreVarTupTy, mkBigCoreTupTy,
39 mkLHsVarTup, mkLHsTup, mkLHsVarPatTup, mkLHsPatTup,
40 mkBigLHsVarTup, mkBigLHsTup, mkBigLHsVarPatTup, mkBigLHsPatTup,
43 mkSelectorBinds, mkTupleSelector,
44 mkSmallTupleCase, mkTupleCase,
46 dsSyntaxTable, lookupEvidence,
48 selectSimpleMatchVarL, selectMatchVars, selectMatchVar,
49 mkTickBox, mkOptTickBox, mkBinaryTickBox
52 #include "HsVersions.h"
54 import {-# SOURCE #-} Match ( matchSimply )
55 import {-# SOURCE #-} DsExpr( dsExpr )
88 infixl 4 `mkDsApp`, `mkDsApps`
93 %************************************************************************
97 %************************************************************************
100 dsSyntaxTable :: SyntaxTable Id
101 -> DsM ([CoreBind], -- Auxiliary bindings
102 [(Name,Id)]) -- Maps the standard name to its value
104 dsSyntaxTable rebound_ids = do
105 (binds_s, prs) <- mapAndUnzipM mk_bind rebound_ids
106 return (concat binds_s, prs)
108 -- The cheapo special case can happen when we
109 -- make an intermediate HsDo when desugaring a RecStmt
110 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
111 mk_bind (std_name, expr) = do
113 id <- newSysLocalDs (exprType rhs)
114 return ([NonRec id rhs], (std_name, id))
116 lookupEvidence :: [(Name, Id)] -> Name -> Id
117 lookupEvidence prs std_name
118 = assocDefault (mk_panic std_name) prs std_name
120 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext (sLit "Not found:") <+> ppr std_name)
124 %************************************************************************
126 \subsection{Building lets}
128 %************************************************************************
130 Use case, not let for unlifted types. The simplifier will turn some
134 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
135 mkDsLet (NonRec bndr rhs) body -- See Note [CoreSyn let/app invariant]
136 | isUnLiftedType (idType bndr) && not (exprOkForSpeculation rhs)
137 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
141 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
142 mkDsLets binds body = foldr mkDsLet body binds
145 mkDsApp :: CoreExpr -> CoreExpr -> CoreExpr
146 -- Check the invariant that the arg of an App is ok-for-speculation if unlifted
147 -- See CoreSyn Note [CoreSyn let/app invariant]
148 mkDsApp fun (Type ty) = App fun (Type ty)
149 mkDsApp fun arg = mk_val_app fun arg arg_ty res_ty
151 (arg_ty, res_ty) = splitFunTy (exprType fun)
154 mkDsApps :: CoreExpr -> [CoreExpr] -> CoreExpr
155 -- Slightly more efficient version of (foldl mkDsApp)
157 = go fun (exprType fun) args
160 go fun fun_ty (Type ty : args) = go (App fun (Type ty)) (applyTy fun_ty ty) args
161 go fun fun_ty (arg : args) = go (mk_val_app fun arg arg_ty res_ty) res_ty args
163 (arg_ty, res_ty) = splitFunTy fun_ty
165 mk_val_app :: CoreExpr -> CoreExpr -> Type -> Type -> CoreExpr
166 mk_val_app (Var f `App` Type ty1 `App` Type _ `App` arg1) arg2 _ res_ty
167 | f == seqId -- Note [Desugaring seq (1), (2)]
168 = Case arg1 case_bndr res_ty [(DEFAULT,[],arg2)]
170 case_bndr = case arg1 of
171 Var v1 | isLocalId v1 -> v1 -- Note [Desugaring seq (2) and (3)]
174 mk_val_app fun arg arg_ty _ -- See Note [CoreSyn let/app invariant]
175 | not (isUnLiftedType arg_ty) || exprOkForSpeculation arg
176 = App fun arg -- The vastly common case
178 mk_val_app fun arg arg_ty res_ty
179 = Case arg (mkWildId arg_ty) res_ty [(DEFAULT,[],App fun (Var arg_id))]
181 arg_id = mkWildId arg_ty -- Lots of shadowing, but it doesn't matter,
182 -- because 'fun ' should not have a free wild-id
185 Note [Desugaring seq (1)] cf Trac #1031
186 ~~~~~~~~~~~~~~~~~~~~~~~~~
187 f x y = x `seq` (y `seq` (# x,y #))
189 The [CoreSyn let/app invariant] means that, other things being equal, because
190 the argument to the outer 'seq' has an unlifted type, we'll use call-by-value thus:
192 f x y = case (y `seq` (# x,y #)) of v -> x `seq` v
194 But that is bad for two reasons:
195 (a) we now evaluate y before x, and
196 (b) we can't bind v to an unboxed pair
198 Seq is very, very special! So we recognise it right here, and desugar to
199 case x of _ -> case y of _ -> (# x,y #)
201 Note [Desugaring seq (2)] cf Trac #2231
202 ~~~~~~~~~~~~~~~~~~~~~~~~~
204 let chp = case b of { True -> fst x; False -> 0 }
205 in chp `seq` ...chp...
206 Here the seq is designed to plug the space leak of retaining (snd x)
209 If we rely on the ordinary inlining of seq, we'll get
210 let chp = case b of { True -> fst x; False -> 0 }
211 case chp of _ { I# -> ...chp... }
213 But since chp is cheap, and the case is an alluring contet, we'll
214 inline chp into the case scrutinee. Now there is only one use of chp,
215 so we'll inline a second copy. Alas, we've now ruined the purpose of
216 the seq, by re-introducing the space leak:
217 case (case b of {True -> fst x; False -> 0}) of
218 I# _ -> ...case b of {True -> fst x; False -> 0}...
220 We can try to avoid doing this by ensuring that the binder-swap in the
221 case happens, so we get his at an early stage:
222 case chp of chp2 { I# -> ...chp2... }
223 But this is fragile. The real culprit is the source program. Perhaps we
224 should have said explicitly
225 let !chp2 = chp in ...chp2...
227 But that's painful. So the code here does a little hack to make seq
228 more robust: a saturated application of 'seq' is turned *directly* into
229 the case expression. So we desugar to:
230 let chp = case b of { True -> fst x; False -> 0 }
231 case chp of chp { I# -> ...chp... }
232 Notice the shadowing of the case binder! And now all is well.
234 The reason it's a hack is because if you define mySeq=seq, the hack
237 Note [Desugaring seq (3)] cf Trac #2409
238 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
239 The isLocalId ensures that we don't turn
242 case True of True { ... }
243 which stupidly tries to bind the datacon 'True'.
246 %************************************************************************
248 \subsection{ Selecting match variables}
250 %************************************************************************
252 We're about to match against some patterns. We want to make some
253 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
254 hand, which should indeed be bound to the pattern as a whole, then use it;
255 otherwise, make one up.
258 selectSimpleMatchVarL :: LPat Id -> DsM Id
259 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
261 -- (selectMatchVars ps tys) chooses variables of type tys
262 -- to use for matching ps against. If the pattern is a variable,
263 -- we try to use that, to save inventing lots of fresh variables.
265 -- OLD, but interesting note:
266 -- But even if it is a variable, its type might not match. Consider
268 -- T1 :: Int -> T Int
271 -- f :: T a -> a -> Int
272 -- f (T1 i) (x::Int) = x
273 -- f (T2 i) (y::a) = 0
274 -- Then we must not choose (x::Int) as the matching variable!
275 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
277 selectMatchVars :: [Pat Id] -> DsM [Id]
278 selectMatchVars ps = mapM selectMatchVar ps
280 selectMatchVar :: Pat Id -> DsM Id
281 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
282 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
283 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
284 selectMatchVar (VarPat var) = return var
285 selectMatchVar (AsPat var _) = return (unLoc var)
286 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
287 -- OK, better make up one...
291 %************************************************************************
293 %* type synonym EquationInfo and access functions for its pieces *
295 %************************************************************************
296 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
298 The ``equation info'' used by @match@ is relatively complicated and
299 worthy of a type synonym and a few handy functions.
302 firstPat :: EquationInfo -> Pat Id
303 firstPat eqn = ASSERT( notNull (eqn_pats eqn) ) head (eqn_pats eqn)
305 shiftEqns :: [EquationInfo] -> [EquationInfo]
306 -- Drop the first pattern in each equation
307 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
310 Functions on MatchResults
313 matchCanFail :: MatchResult -> Bool
314 matchCanFail (MatchResult CanFail _) = True
315 matchCanFail (MatchResult CantFail _) = False
317 alwaysFailMatchResult :: MatchResult
318 alwaysFailMatchResult = MatchResult CanFail (\fail -> return fail)
320 cantFailMatchResult :: CoreExpr -> MatchResult
321 cantFailMatchResult expr = MatchResult CantFail (\_ -> return expr)
323 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
324 extractMatchResult (MatchResult CantFail match_fn) _
325 = match_fn (error "It can't fail!")
327 extractMatchResult (MatchResult CanFail match_fn) fail_expr = do
328 (fail_bind, if_it_fails) <- mkFailurePair fail_expr
329 body <- match_fn if_it_fails
330 return (mkDsLet fail_bind body)
333 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
334 combineMatchResults (MatchResult CanFail body_fn1)
335 (MatchResult can_it_fail2 body_fn2)
336 = MatchResult can_it_fail2 body_fn
338 body_fn fail = do body2 <- body_fn2 fail
339 (fail_bind, duplicatable_expr) <- mkFailurePair body2
340 body1 <- body_fn1 duplicatable_expr
341 return (Let fail_bind body1)
343 combineMatchResults match_result1@(MatchResult CantFail _) _
346 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
347 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
348 = MatchResult can_it_fail (\fail -> encl_fn <$> body_fn fail)
350 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
351 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
352 = MatchResult can_it_fail (\fail -> encl_fn =<< body_fn fail)
354 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
356 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
358 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
359 wrapBind new old body -- Can deal with term variables *or* type variables
361 | isTyVar new = Let (mkTyBind new (mkTyVarTy old)) body
362 | otherwise = Let (NonRec new (Var old)) body
364 seqVar :: Var -> CoreExpr -> CoreExpr
365 seqVar var body = Case (Var var) var (exprType body)
366 [(DEFAULT, [], body)]
368 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
369 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
371 -- (mkViewMatchResult var' viewExpr var mr) makes the expression
372 -- let var' = viewExpr var in mr
373 mkViewMatchResult :: Id -> CoreExpr -> Id -> MatchResult -> MatchResult
374 mkViewMatchResult var' viewExpr var =
375 adjustMatchResult (mkDsLet (NonRec var' (mkDsApp viewExpr (Var var))))
377 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
378 mkEvalMatchResult var ty
379 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
381 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
382 mkGuardedMatchResult pred_expr (MatchResult _ body_fn)
383 = MatchResult CanFail (\fail -> do body <- body_fn fail
384 return (mkIfThenElse pred_expr body fail))
386 mkCoPrimCaseMatchResult :: Id -- Scrutinee
387 -> Type -- Type of the case
388 -> [(Literal, MatchResult)] -- Alternatives
390 mkCoPrimCaseMatchResult var ty match_alts
391 = MatchResult CanFail mk_case
394 alts <- mapM (mk_alt fail) sorted_alts
395 return (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
397 sorted_alts = sortWith fst match_alts -- Right order for a Case
398 mk_alt fail (lit, MatchResult _ body_fn) = do body <- body_fn fail
399 return (LitAlt lit, [], body)
402 mkCoAlgCaseMatchResult :: Id -- Scrutinee
403 -> Type -- Type of exp
404 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
406 mkCoAlgCaseMatchResult var ty match_alts
407 | isNewTyCon tycon -- Newtype case; use a let
408 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
409 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
411 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
412 = MatchResult CanFail mk_parrCase
414 | otherwise -- Datatype case; use a case
415 = MatchResult fail_flag mk_case
417 tycon = dataConTyCon con1
418 -- [Interesting: becuase of GADTs, we can't rely on the type of
419 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
422 (con1, arg_ids1, match_result1) = ASSERT( notNull match_alts ) head match_alts
423 arg_id1 = ASSERT( notNull arg_ids1 ) head arg_ids1
425 (tc, ty_args) = splitNewTyConApp var_ty
426 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
428 -- Stuff for data types
429 data_cons = tyConDataCons tycon
430 match_results = [match_result | (_,_,match_result) <- match_alts]
432 fail_flag | exhaustive_case
433 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
437 wild_var = mkWildId (idType var)
438 sorted_alts = sortWith get_tag match_alts
439 get_tag (con, _, _) = dataConTag con
440 mk_case fail = do alts <- mapM (mk_alt fail) sorted_alts
441 return (Case (Var var) wild_var ty (mk_default fail ++ alts))
443 mk_alt fail (con, args, MatchResult _ body_fn) = do
445 us <- newUniqueSupply
446 return (mkReboxingAlt (uniqsFromSupply us) con args body)
448 mk_default fail | exhaustive_case = []
449 | otherwise = [(DEFAULT, [], fail)]
451 un_mentioned_constructors
452 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
453 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
455 -- Stuff for parallel arrays
457 -- * the following is to desugar cases over fake constructors for
458 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
461 -- Concerning `isPArrFakeAlts':
463 -- * it is *not* sufficient to just check the type of the type
464 -- constructor, as we have to be careful not to confuse the real
465 -- representation of parallel arrays with the fake constructors;
466 -- moreover, a list of alternatives must not mix fake and real
467 -- constructors (this is checked earlier on)
469 -- FIXME: We actually go through the whole list and make sure that
470 -- either all or none of the constructors are fake parallel
471 -- array constructors. This is to spot equations that mix fake
472 -- constructors with the real representation defined in
473 -- `PrelPArr'. It would be nicer to spot this situation
474 -- earlier and raise a proper error message, but it can really
475 -- only happen in `PrelPArr' anyway.
477 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
478 isPArrFakeAlts ((dcon, _, _):alts) =
479 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
480 (True , True ) -> True
481 (False, False) -> False
482 _ -> panic "DsUtils: you may not mix `[:...:]' with `PArr' patterns"
483 isPArrFakeAlts [] = panic "DsUtils: unexpectedly found an empty list of PArr fake alternatives"
485 mk_parrCase fail = do
486 lengthP <- dsLookupGlobalId lengthPName
488 return (Case (len lengthP) (mkWildId intTy) ty [alt])
490 elemTy = case splitTyConApp (idType var) of
491 (_, [elemTy]) -> elemTy
493 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
494 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
497 l <- newSysLocalDs intPrimTy
498 indexP <- dsLookupGlobalId indexPName
499 alts <- mapM (mkAlt indexP) sorted_alts
500 return (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
502 wild = mkWildId intPrimTy
503 dft = (DEFAULT, [], fail)
505 -- each alternative matches one array length (corresponding to one
506 -- fake array constructor), so the match is on a literal; each
507 -- alternative's body is extended by a local binding for each
508 -- constructor argument, which are bound to array elements starting
511 mkAlt indexP (con, args, MatchResult _ bodyFun) = do
513 return (LitAlt lit, [], mkDsLets binds body)
515 lit = MachInt $ toInteger (dataConSourceArity con)
516 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
518 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
522 %************************************************************************
524 \subsection{Desugarer's versions of some Core functions}
526 %************************************************************************
529 mkErrorAppDs :: Id -- The error function
530 -> Type -- Type to which it should be applied
531 -> String -- The error message string to pass
534 mkErrorAppDs err_id ty msg = do
535 src_loc <- getSrcSpanDs
537 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
538 core_msg = Lit (mkStringLit full_msg)
539 -- mkStringLit returns a result of type String#
540 return (mkApps (Var err_id) [Type ty, core_msg])
544 *************************************************************
546 \subsection{Making literals}
548 %************************************************************************
551 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
552 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
553 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
554 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
555 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
557 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
558 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
561 | inIntRange i -- Small enough, so start from an Int
562 = do integer_id <- dsLookupGlobalId smallIntegerName
563 return (mkSmallIntegerLit integer_id i)
565 -- Special case for integral literals with a large magnitude:
566 -- They are transformed into an expression involving only smaller
567 -- integral literals. This improves constant folding.
569 | otherwise = do -- Big, so start from a string
570 plus_id <- dsLookupGlobalId plusIntegerName
571 times_id <- dsLookupGlobalId timesIntegerName
572 integer_id <- dsLookupGlobalId smallIntegerName
574 lit i = mkSmallIntegerLit integer_id i
575 plus a b = Var plus_id `App` a `App` b
576 times a b = Var times_id `App` a `App` b
578 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
579 horner :: Integer -> Integer -> CoreExpr
580 horner b i | abs q <= 1 = if r == 0 || r == i
582 else lit r `plus` lit (i-r)
583 | r == 0 = horner b q `times` lit b
584 | otherwise = lit r `plus` (horner b q `times` lit b)
586 (q,r) = i `quotRem` b
588 return (horner tARGET_MAX_INT i)
590 mkSmallIntegerLit :: Id -> Integer -> CoreExpr
591 mkSmallIntegerLit small_integer i = mkApps (Var small_integer) [mkIntLit i]
593 mkStringExpr str = mkStringExprFS (mkFastString str)
597 = return (mkNilExpr charTy)
600 = do let the_char = mkCharExpr (headFS str)
601 return (mkConsExpr charTy the_char (mkNilExpr charTy))
604 = do unpack_id <- dsLookupGlobalId unpackCStringName
605 return (App (Var unpack_id) (Lit (MachStr str)))
608 = do unpack_id <- dsLookupGlobalId unpackCStringUtf8Name
609 return (App (Var unpack_id) (Lit (MachStr str)))
613 safeChar c = ord c >= 1 && ord c <= 0x7F
617 %************************************************************************
619 \subsection[mkSelectorBind]{Make a selector bind}
621 %************************************************************************
623 This is used in various places to do with lazy patterns.
624 For each binder $b$ in the pattern, we create a binding:
626 b = case v of pat' -> b'
628 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
630 ToDo: making these bindings should really depend on whether there's
631 much work to be done per binding. If the pattern is complex, it
632 should be de-mangled once, into a tuple (and then selected from).
633 Otherwise the demangling can be in-line in the bindings (as here).
635 Boring! Boring! One error message per binder. The above ToDo is
636 even more helpful. Something very similar happens for pattern-bound
640 mkSelectorBinds :: LPat Id -- The pattern
641 -> CoreExpr -- Expression to which the pattern is bound
642 -> DsM [(Id,CoreExpr)]
644 mkSelectorBinds (L _ (VarPat v)) val_expr
645 = return [(v, val_expr)]
647 mkSelectorBinds pat val_expr
648 | isSingleton binders || is_simple_lpat pat = do
649 -- Given p = e, where p binds x,y
650 -- we are going to make
651 -- v = p (where v is fresh)
652 -- x = case v of p -> x
653 -- y = case v of p -> x
656 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
657 -- This does not matter after desugaring, but there's a subtle
658 -- issue with implicit parameters. Consider
660 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
661 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
662 -- does it get that type? So that when we abstract over it we get the
663 -- right top-level type (?i::Int) => ...)
665 -- So to get the type of 'v', use the pattern not the rhs. Often more
667 val_var <- newSysLocalDs (hsLPatType pat)
669 -- For the error message we make one error-app, to avoid duplication.
670 -- But we need it at different types... so we use coerce for that
671 err_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID unitTy (showSDoc (ppr pat))
672 err_var <- newSysLocalDs unitTy
673 binds <- mapM (mk_bind val_var err_var) binders
674 return ( (val_var, val_expr) :
675 (err_var, err_expr) :
680 error_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID tuple_ty (showSDoc (ppr pat))
681 tuple_expr <- matchSimply val_expr PatBindRhs pat local_tuple error_expr
682 tuple_var <- newSysLocalDs tuple_ty
685 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
686 return ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
688 binders = collectPatBinders pat
689 local_tuple = mkBigCoreVarTup binders
690 tuple_ty = exprType local_tuple
692 mk_bind scrut_var err_var bndr_var = do
693 -- (mk_bind sv err_var) generates
694 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
695 -- Remember, pat binds bv
696 rhs_expr <- matchSimply (Var scrut_var) PatBindRhs pat
697 (Var bndr_var) error_expr
698 return (bndr_var, rhs_expr)
700 error_expr = mkCoerce co (Var err_var)
701 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
703 is_simple_lpat p = is_simple_pat (unLoc p)
705 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
706 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConPatArgs ps)
707 is_simple_pat (VarPat _) = True
708 is_simple_pat (ParPat p) = is_simple_lpat p
709 is_simple_pat _ = False
711 is_triv_lpat p = is_triv_pat (unLoc p)
713 is_triv_pat (VarPat _) = True
714 is_triv_pat (WildPat _) = True
715 is_triv_pat (ParPat p) = is_triv_lpat p
716 is_triv_pat _ = False
720 %************************************************************************
724 %************************************************************************
726 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
727 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
731 mkBigTuple :: ([a] -> a) -> [a] -> a
732 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
734 -- Each sub-list is short enough to fit in a tuple
735 mk_big_tuple [as] = small_tuple as
736 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
738 chunkify :: [a] -> [[a]]
739 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
740 -- But there may be more than mAX_TUPLE_SIZE sub-lists
742 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
743 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
747 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
751 Creating tuples and their types for Core expressions
753 @mkBigCoreVarTup@ builds a tuple; the inverse to @mkTupleSelector@.
755 * If it has only one element, it is the identity function.
757 * If there are more elements than a big tuple can have, it nests
762 -- Small tuples: build exactly the specified tuple
763 mkCoreVarTup :: [Id] -> CoreExpr
764 mkCoreVarTup ids = mkCoreTup (map Var ids)
766 mkCoreVarTupTy :: [Id] -> Type
767 mkCoreVarTupTy ids = mkCoreTupTy (map idType ids)
770 mkCoreTup :: [CoreExpr] -> CoreExpr
771 mkCoreTup [] = Var unitDataConId
773 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
774 (map (Type . exprType) cs ++ cs)
776 mkCoreTupTy :: [Type] -> Type
777 mkCoreTupTy [ty] = ty
778 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
783 mkBigCoreVarTup :: [Id] -> CoreExpr
784 mkBigCoreVarTup ids = mkBigCoreTup (map Var ids)
786 mkBigCoreVarTupTy :: [Id] -> Type
787 mkBigCoreVarTupTy ids = mkBigCoreTupTy (map idType ids)
790 mkBigCoreTup :: [CoreExpr] -> CoreExpr
791 mkBigCoreTup = mkBigTuple mkCoreTup
793 mkBigCoreTupTy :: [Type] -> Type
794 mkBigCoreTupTy = mkBigTuple mkCoreTupTy
798 Creating tuples and their types for full Haskell expressions
802 -- Smart constructors for source tuple expressions
803 mkLHsVarTup :: [Id] -> LHsExpr Id
804 mkLHsVarTup ids = mkLHsTup (map nlHsVar ids)
806 mkLHsTup :: [LHsExpr Id] -> LHsExpr Id
807 mkLHsTup [] = nlHsVar unitDataConId
808 mkLHsTup [lexp] = lexp
809 mkLHsTup lexps = L (getLoc (head lexps)) $
810 ExplicitTuple lexps Boxed
812 -- Smart constructors for source tuple patterns
813 mkLHsVarPatTup :: [Id] -> LPat Id
814 mkLHsVarPatTup bs = mkLHsPatTup (map nlVarPat bs)
816 mkLHsPatTup :: [LPat Id] -> LPat Id
817 mkLHsPatTup [] = noLoc $ mkVanillaTuplePat [] Boxed
818 mkLHsPatTup [lpat] = lpat
819 mkLHsPatTup lpats = L (getLoc (head lpats)) $
820 mkVanillaTuplePat lpats Boxed
822 -- The Big equivalents for the source tuple expressions
823 mkBigLHsVarTup :: [Id] -> LHsExpr Id
824 mkBigLHsVarTup ids = mkBigLHsTup (map nlHsVar ids)
826 mkBigLHsTup :: [LHsExpr Id] -> LHsExpr Id
827 mkBigLHsTup = mkBigTuple mkLHsTup
830 -- The Big equivalents for the source tuple patterns
831 mkBigLHsVarPatTup :: [Id] -> LPat Id
832 mkBigLHsVarPatTup bs = mkBigLHsPatTup (map nlVarPat bs)
834 mkBigLHsPatTup :: [LPat Id] -> LPat Id
835 mkBigLHsPatTup = mkBigTuple mkLHsPatTup
839 @mkTupleSelector@ builds a selector which scrutises the given
840 expression and extracts the one name from the list given.
841 If you want the no-shadowing rule to apply, the caller
842 is responsible for making sure that none of these names
845 If there is just one id in the ``tuple'', then the selector is
848 If it's big, it does nesting
849 mkTupleSelector [a,b,c,d] b v e
851 (p,q) -> case p of p {
853 We use 'tpl' vars for the p,q, since shadowing does not matter.
855 In fact, it's more convenient to generate it innermost first, getting
862 mkTupleSelector :: [Id] -- The tuple args
863 -> Id -- The selected one
864 -> Id -- A variable of the same type as the scrutinee
865 -> CoreExpr -- Scrutinee
868 mkTupleSelector vars the_var scrut_var scrut
869 = mk_tup_sel (chunkify vars) the_var
871 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
872 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
873 mk_tup_sel (chunkify tpl_vs) tpl_v
875 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
876 tpl_vs = mkTemplateLocals tpl_tys
877 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
881 A generalization of @mkTupleSelector@, allowing the body
882 of the case to be an arbitrary expression.
884 If the tuple is big, it is nested:
886 mkTupleCase uniqs [a,b,c,d] body v e
887 = case e of v { (p,q) ->
888 case p of p { (a,b) ->
889 case q of q { (c,d) ->
892 To avoid shadowing, we use uniqs to invent new variables p,q.
894 ToDo: eliminate cases where none of the variables are needed.
898 :: UniqSupply -- for inventing names of intermediate variables
899 -> [Id] -- the tuple args
900 -> CoreExpr -- body of the case
901 -> Id -- a variable of the same type as the scrutinee
902 -> CoreExpr -- scrutinee
905 mkTupleCase uniqs vars body scrut_var scrut
906 = mk_tuple_case uniqs (chunkify vars) body
908 -- This is the case where don't need any nesting
909 mk_tuple_case _ [vars] body
910 = mkSmallTupleCase vars body scrut_var scrut
912 -- This is the case where we must make nest tuples at least once
913 mk_tuple_case us vars_s body
914 = let (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
915 in mk_tuple_case us' (chunkify vars') body'
917 one_tuple_case chunk_vars (us, vs, body)
918 = let (us1, us2) = splitUniqSupply us
919 scrut_var = mkSysLocal (fsLit "ds") (uniqFromSupply us1)
920 (mkCoreTupTy (map idType chunk_vars))
921 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
922 in (us2, scrut_var:vs, body')
925 The same, but with a tuple small enough not to need nesting.
929 :: [Id] -- the tuple args
930 -> CoreExpr -- body of the case
931 -> Id -- a variable of the same type as the scrutinee
932 -> CoreExpr -- scrutinee
935 mkSmallTupleCase [var] body _scrut_var scrut
936 = bindNonRec var scrut body
937 mkSmallTupleCase vars body scrut_var scrut
938 -- One branch no refinement?
939 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
942 %************************************************************************
944 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
946 %************************************************************************
948 Call the constructor Ids when building explicit lists, so that they
949 interact well with rules.
952 mkNilExpr :: Type -> CoreExpr
953 mkNilExpr ty = mkConApp nilDataCon [Type ty]
955 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
956 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
958 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
959 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
961 mkFoldrExpr :: PostTcType -> PostTcType -> CoreExpr -> CoreExpr -> CoreExpr -> DsM CoreExpr
962 mkFoldrExpr elt_ty result_ty c n list = do
963 foldr_id <- dsLookupGlobalId foldrName
964 return (Var foldr_id `App` Type elt_ty
970 mkBuildExpr :: Type -> ((Id, Type) -> (Id, Type) -> DsM CoreExpr) -> DsM CoreExpr
971 mkBuildExpr elt_ty mk_build_inside = do
972 [n_tyvar] <- newTyVarsDs [alphaTyVar]
973 let n_ty = mkTyVarTy n_tyvar
974 c_ty = mkFunTys [elt_ty, n_ty] n_ty
975 [c, n] <- newSysLocalsDs [c_ty, n_ty]
977 build_inside <- mk_build_inside (c, c_ty) (n, n_ty)
979 build_id <- dsLookupGlobalId buildName
980 return $ Var build_id `App` Type elt_ty `App` mkLams [n_tyvar, c, n] build_inside
982 mkCoreSel :: [Id] -- The tuple args
983 -> Id -- The selected one
984 -> Id -- A variable of the same type as the scrutinee
985 -> CoreExpr -- Scrutinee
988 -- mkCoreSel [x] x v e
990 mkCoreSel [var] should_be_the_same_var _ scrut
991 = ASSERT(var == should_be_the_same_var)
994 -- mkCoreSel [x,y,z] x v e
995 -- ===> case e of v { (x,y,z) -> x
996 mkCoreSel vars the_var scrut_var scrut
997 = ASSERT( notNull vars )
998 Case scrut scrut_var (idType the_var)
999 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
1002 %************************************************************************
1004 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
1006 %************************************************************************
1008 Generally, we handle pattern matching failure like this: let-bind a
1009 fail-variable, and use that variable if the thing fails:
1011 let fail.33 = error "Help"
1022 If the case can't fail, then there'll be no mention of @fail.33@, and the
1023 simplifier will later discard it.
1026 If it can fail in only one way, then the simplifier will inline it.
1029 Only if it is used more than once will the let-binding remain.
1032 There's a problem when the result of the case expression is of
1033 unboxed type. Then the type of @fail.33@ is unboxed too, and
1034 there is every chance that someone will change the let into a case:
1036 case error "Help" of
1037 fail.33 -> case ....
1040 which is of course utterly wrong. Rather than drop the condition that
1041 only boxed types can be let-bound, we just turn the fail into a function
1042 for the primitive case:
1044 let fail.33 :: Void -> Int#
1045 fail.33 = \_ -> error "Help"
1054 Now @fail.33@ is a function, so it can be let-bound.
1057 mkFailurePair :: CoreExpr -- Result type of the whole case expression
1058 -> DsM (CoreBind, -- Binds the newly-created fail variable
1059 -- to either the expression or \ _ -> expression
1060 CoreExpr) -- Either the fail variable, or fail variable
1061 -- applied to unit tuple
1063 | isUnLiftedType ty = do
1064 fail_fun_var <- newFailLocalDs (unitTy `mkFunTy` ty)
1065 fail_fun_arg <- newSysLocalDs unitTy
1066 return (NonRec fail_fun_var (Lam fail_fun_arg expr),
1067 App (Var fail_fun_var) (Var unitDataConId))
1070 fail_var <- newFailLocalDs ty
1071 return (NonRec fail_var expr, Var fail_var)
1077 mkOptTickBox :: Maybe (Int,[Id]) -> CoreExpr -> DsM CoreExpr
1078 mkOptTickBox Nothing e = return e
1079 mkOptTickBox (Just (ix,ids)) e = mkTickBox ix ids e
1081 mkTickBox :: Int -> [Id] -> CoreExpr -> DsM CoreExpr
1082 mkTickBox ix vars e = do
1085 let tick | opt_Hpc = mkTickBoxOpId uq mod ix
1086 | otherwise = mkBreakPointOpId uq mod ix
1088 let occName = mkVarOcc "tick"
1089 let name = mkInternalName uq2 occName noSrcSpan -- use mkSysLocal?
1090 let var = Id.mkLocalId name realWorldStatePrimTy
1093 then return (Var tick)
1095 let tickVar = Var tick
1096 let tickType = mkFunTys (map idType vars) realWorldStatePrimTy
1097 let scrutApTy = App tickVar (Type tickType)
1098 return (mkApps scrutApTy (map Var vars) :: Expr Id)
1099 return $ Case scrut var ty [(DEFAULT,[],e)]
1103 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
1104 mkBinaryTickBox ixT ixF e = do
1106 let bndr1 = mkSysLocal (fsLit "t1") uq boolTy
1107 falseBox <- mkTickBox ixF [] $ Var falseDataConId
1108 trueBox <- mkTickBox ixT [] $ Var trueDataConId
1109 return $ Case e bndr1 boolTy
1110 [ (DataAlt falseDataCon, [], falseBox)
1111 , (DataAlt trueDataCon, [], trueBox)