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,
34 mkCoreVarTup, mkCoreTup, mkCoreVarTupTy, mkCoreTupTy,
35 mkBigCoreVarTup, mkBigCoreTup, mkBigCoreVarTupTy, mkBigCoreTupTy,
38 mkLHsVarTup, mkLHsTup, mkLHsVarPatTup, mkLHsPatTup,
39 mkBigLHsVarTup, mkBigLHsTup, mkBigLHsVarPatTup, mkBigLHsPatTup,
42 mkSelectorBinds, mkTupleSelector,
43 mkSmallTupleCase, mkTupleCase,
45 dsSyntaxTable, lookupEvidence,
47 selectSimpleMatchVarL, selectMatchVars, selectMatchVar,
48 mkTickBox, mkOptTickBox, mkBinaryTickBox
51 #include "HsVersions.h"
53 import {-# SOURCE #-} Match ( matchSimply )
54 import {-# SOURCE #-} DsExpr( dsExpr )
87 infixl 4 `mkDsApp`, `mkDsApps`
92 %************************************************************************
96 %************************************************************************
99 dsSyntaxTable :: SyntaxTable Id
100 -> DsM ([CoreBind], -- Auxiliary bindings
101 [(Name,Id)]) -- Maps the standard name to its value
103 dsSyntaxTable rebound_ids
104 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
105 return (concat binds_s, prs)
107 -- The cheapo special case can happen when we
108 -- make an intermediate HsDo when desugaring a RecStmt
109 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
110 mk_bind (std_name, expr)
111 = dsExpr expr `thenDs` \ rhs ->
112 newSysLocalDs (exprType rhs) `thenDs` \ id ->
113 return ([NonRec id rhs], (std_name, id))
115 lookupEvidence :: [(Name, Id)] -> Name -> Id
116 lookupEvidence prs std_name
117 = assocDefault (mk_panic std_name) prs std_name
119 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
123 %************************************************************************
125 \subsection{Building lets}
127 %************************************************************************
129 Use case, not let for unlifted types. The simplifier will turn some
133 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
134 mkDsLet (NonRec bndr rhs) body -- See Note [CoreSyn let/app invariant]
135 | isUnLiftedType (idType bndr) && not (exprOkForSpeculation rhs)
136 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
140 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
141 mkDsLets binds body = foldr mkDsLet body binds
144 mkDsApp :: CoreExpr -> CoreExpr -> CoreExpr
145 -- Check the invariant that the arg of an App is ok-for-speculation if unlifted
146 -- See CoreSyn Note [CoreSyn let/app invariant]
147 mkDsApp fun (Type ty) = App fun (Type ty)
148 mkDsApp fun arg = mk_val_app fun arg arg_ty res_ty
150 (arg_ty, res_ty) = splitFunTy (exprType fun)
153 mkDsApps :: CoreExpr -> [CoreExpr] -> CoreExpr
154 -- Slightly more efficient version of (foldl mkDsApp)
156 = go fun (exprType fun) args
159 go fun fun_ty (Type ty : args) = go (App fun (Type ty)) (applyTy fun_ty ty) args
160 go fun fun_ty (arg : args) = go (mk_val_app fun arg arg_ty res_ty) res_ty args
162 (arg_ty, res_ty) = splitFunTy fun_ty
164 mk_val_app :: CoreExpr -> CoreExpr -> Type -> Type -> CoreExpr
165 mk_val_app fun arg arg_ty _ -- See Note [CoreSyn let/app invariant]
166 | not (isUnLiftedType arg_ty) || exprOkForSpeculation arg
167 = App fun arg -- The vastly common case
169 mk_val_app (Var f `App` Type ty1 `App` Type _ `App` arg1) arg2 _ res_ty
170 | f == seqId -- Note [Desugaring seq]
171 = Case arg1 (mkWildId ty1) res_ty [(DEFAULT,[],arg2)]
173 mk_val_app fun arg arg_ty res_ty
174 = Case arg (mkWildId arg_ty) res_ty [(DEFAULT,[],App fun (Var arg_id))]
176 arg_id = mkWildId arg_ty -- Lots of shadowing, but it doesn't matter,
177 -- because 'fun ' should not have a free wild-id
180 Note [Desugaring seq] cf Trac #1031
181 ~~~~~~~~~~~~~~~~~~~~~
182 f x y = x `seq` (y `seq` (# x,y #))
184 The [CoreSyn let/app invariant] means that, other things being equal, because
185 the argument to the outer 'seq' has an unlifted type, we'll use call-by-value thus:
187 f x y = case (y `seq` (# x,y #)) of v -> x `seq` v
189 But that is bad for two reasons:
190 (a) we now evaluate y before x, and
191 (b) we can't bind v to an unboxed pair
193 Seq is very, very special! So we recognise it right here, and desugar to
194 case x of _ -> case y of _ -> (# x,y #)
196 The special case would be valid for all calls to 'seq', but it's only *necessary*
197 for ones whose second argument has an unlifted type. So we only catch the latter
198 case here, to avoid unnecessary tests.
201 %************************************************************************
203 \subsection{ Selecting match variables}
205 %************************************************************************
207 We're about to match against some patterns. We want to make some
208 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
209 hand, which should indeed be bound to the pattern as a whole, then use it;
210 otherwise, make one up.
213 selectSimpleMatchVarL :: LPat Id -> DsM Id
214 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
216 -- (selectMatchVars ps tys) chooses variables of type tys
217 -- to use for matching ps against. If the pattern is a variable,
218 -- we try to use that, to save inventing lots of fresh variables.
220 -- OLD, but interesting note:
221 -- But even if it is a variable, its type might not match. Consider
223 -- T1 :: Int -> T Int
226 -- f :: T a -> a -> Int
227 -- f (T1 i) (x::Int) = x
228 -- f (T2 i) (y::a) = 0
229 -- Then we must not choose (x::Int) as the matching variable!
230 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
232 selectMatchVars :: [Pat Id] -> DsM [Id]
233 selectMatchVars ps = mapM selectMatchVar ps
235 selectMatchVar :: Pat Id -> DsM Id
236 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
237 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
238 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
239 selectMatchVar (VarPat var) = return var
240 selectMatchVar (AsPat var _) = return (unLoc var)
241 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
242 -- OK, better make up one...
246 %************************************************************************
248 %* type synonym EquationInfo and access functions for its pieces *
250 %************************************************************************
251 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
253 The ``equation info'' used by @match@ is relatively complicated and
254 worthy of a type synonym and a few handy functions.
257 firstPat :: EquationInfo -> Pat Id
258 firstPat eqn = ASSERT( notNull (eqn_pats eqn) ) head (eqn_pats eqn)
260 shiftEqns :: [EquationInfo] -> [EquationInfo]
261 -- Drop the first pattern in each equation
262 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
265 Functions on MatchResults
268 matchCanFail :: MatchResult -> Bool
269 matchCanFail (MatchResult CanFail _) = True
270 matchCanFail (MatchResult CantFail _) = False
272 alwaysFailMatchResult :: MatchResult
273 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
275 cantFailMatchResult :: CoreExpr -> MatchResult
276 cantFailMatchResult expr = MatchResult CantFail (\_ -> returnDs expr)
278 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
279 extractMatchResult (MatchResult CantFail match_fn) _
280 = match_fn (error "It can't fail!")
282 extractMatchResult (MatchResult CanFail match_fn) fail_expr
283 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
284 match_fn if_it_fails `thenDs` \ body ->
285 returnDs (mkDsLet fail_bind body)
288 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
289 combineMatchResults (MatchResult CanFail body_fn1)
290 (MatchResult can_it_fail2 body_fn2)
291 = MatchResult can_it_fail2 body_fn
293 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
294 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
295 body_fn1 duplicatable_expr `thenDs` \ body1 ->
296 returnDs (Let fail_bind body1)
298 combineMatchResults match_result1@(MatchResult CantFail _) _
301 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
302 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
303 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
304 returnDs (encl_fn body))
306 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
307 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
308 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
311 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
313 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
315 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
316 wrapBind new old body
318 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
319 | otherwise = Let (NonRec new (Var old)) body
321 seqVar :: Var -> CoreExpr -> CoreExpr
322 seqVar var body = Case (Var var) var (exprType body)
323 [(DEFAULT, [], body)]
325 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
326 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
328 -- (mkViewMatchResult var' viewExpr var mr) makes the expression
329 -- let var' = viewExpr var in mr
330 mkViewMatchResult :: Id -> CoreExpr -> Id -> MatchResult -> MatchResult
331 mkViewMatchResult var' viewExpr var =
332 adjustMatchResult (mkDsLet (NonRec var' (mkDsApp viewExpr (Var var))))
334 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
335 mkEvalMatchResult var ty
336 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
338 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
339 mkGuardedMatchResult pred_expr (MatchResult _ body_fn)
340 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
341 returnDs (mkIfThenElse pred_expr body fail))
343 mkCoPrimCaseMatchResult :: Id -- Scrutinee
344 -> Type -- Type of the case
345 -> [(Literal, MatchResult)] -- Alternatives
347 mkCoPrimCaseMatchResult var ty match_alts
348 = MatchResult CanFail mk_case
351 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
352 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
354 sorted_alts = sortWith fst match_alts -- Right order for a Case
355 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
356 returnDs (LitAlt lit, [], body)
359 mkCoAlgCaseMatchResult :: Id -- Scrutinee
360 -> Type -- Type of exp
361 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
363 mkCoAlgCaseMatchResult var ty match_alts
364 | isNewTyCon tycon -- Newtype case; use a let
365 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
366 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
368 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
369 = MatchResult CanFail mk_parrCase
371 | otherwise -- Datatype case; use a case
372 = MatchResult fail_flag mk_case
374 tycon = dataConTyCon con1
375 -- [Interesting: becuase of GADTs, we can't rely on the type of
376 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
379 (con1, arg_ids1, match_result1) = ASSERT( notNull match_alts ) head match_alts
380 arg_id1 = ASSERT( notNull arg_ids1 ) head arg_ids1
382 (tc, ty_args) = splitNewTyConApp var_ty
383 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
385 -- Stuff for data types
386 data_cons = tyConDataCons tycon
387 match_results = [match_result | (_,_,match_result) <- match_alts]
389 fail_flag | exhaustive_case
390 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
394 wild_var = mkWildId (idType var)
395 sorted_alts = sortWith get_tag match_alts
396 get_tag (con, _, _) = dataConTag con
397 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
398 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
400 mk_alt fail (con, args, MatchResult _ body_fn)
401 = body_fn fail `thenDs` \ body ->
402 newUniqueSupply `thenDs` \ us ->
403 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
405 mk_default fail | exhaustive_case = []
406 | otherwise = [(DEFAULT, [], fail)]
408 un_mentioned_constructors
409 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
410 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
412 -- Stuff for parallel arrays
414 -- * the following is to desugar cases over fake constructors for
415 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
418 -- Concerning `isPArrFakeAlts':
420 -- * it is *not* sufficient to just check the type of the type
421 -- constructor, as we have to be careful not to confuse the real
422 -- representation of parallel arrays with the fake constructors;
423 -- moreover, a list of alternatives must not mix fake and real
424 -- constructors (this is checked earlier on)
426 -- FIXME: We actually go through the whole list and make sure that
427 -- either all or none of the constructors are fake parallel
428 -- array constructors. This is to spot equations that mix fake
429 -- constructors with the real representation defined in
430 -- `PrelPArr'. It would be nicer to spot this situation
431 -- earlier and raise a proper error message, but it can really
432 -- only happen in `PrelPArr' anyway.
434 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
435 isPArrFakeAlts ((dcon, _, _):alts) =
436 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
437 (True , True ) -> True
438 (False, False) -> False
439 _ -> panic "DsUtils: you may not mix `[:...:]' with `PArr' patterns"
440 isPArrFakeAlts [] = panic "DsUtils: unexpectedly found an empty list of PArr fake alternatives"
443 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
444 unboxAlt `thenDs` \alt ->
445 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
447 elemTy = case splitTyConApp (idType var) of
448 (_, [elemTy]) -> elemTy
450 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
451 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
454 newSysLocalDs intPrimTy `thenDs` \l ->
455 dsLookupGlobalId indexPName `thenDs` \indexP ->
456 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
457 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
459 wild = mkWildId intPrimTy
460 dft = (DEFAULT, [], fail)
462 -- each alternative matches one array length (corresponding to one
463 -- fake array constructor), so the match is on a literal; each
464 -- alternative's body is extended by a local binding for each
465 -- constructor argument, which are bound to array elements starting
468 mkAlt indexP (con, args, MatchResult _ bodyFun) =
469 bodyFun fail `thenDs` \body ->
470 returnDs (LitAlt lit, [], mkDsLets binds body)
472 lit = MachInt $ toInteger (dataConSourceArity con)
473 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
475 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
479 %************************************************************************
481 \subsection{Desugarer's versions of some Core functions}
483 %************************************************************************
486 mkErrorAppDs :: Id -- The error function
487 -> Type -- Type to which it should be applied
488 -> String -- The error message string to pass
491 mkErrorAppDs err_id ty msg
492 = getSrcSpanDs `thenDs` \ src_loc ->
494 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
495 core_msg = Lit (mkStringLit full_msg)
496 -- mkStringLit returns a result of type String#
498 returnDs (mkApps (Var err_id) [Type ty, core_msg])
502 *************************************************************
504 \subsection{Making literals}
506 %************************************************************************
509 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
510 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
511 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
512 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
513 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
515 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
516 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
519 | inIntRange i -- Small enough, so start from an Int
520 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
521 returnDs (mkSmallIntegerLit integer_dc i)
523 -- Special case for integral literals with a large magnitude:
524 -- They are transformed into an expression involving only smaller
525 -- integral literals. This improves constant folding.
527 | otherwise -- Big, so start from a string
528 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
529 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
530 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
532 lit i = mkSmallIntegerLit integer_dc i
533 plus a b = Var plus_id `App` a `App` b
534 times a b = Var times_id `App` a `App` b
536 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
537 horner :: Integer -> Integer -> CoreExpr
538 horner b i | abs q <= 1 = if r == 0 || r == i
540 else lit r `plus` lit (i-r)
541 | r == 0 = horner b q `times` lit b
542 | otherwise = lit r `plus` (horner b q `times` lit b)
544 (q,r) = i `quotRem` b
547 returnDs (horner tARGET_MAX_INT i)
549 mkSmallIntegerLit :: DataCon -> Integer -> CoreExpr
550 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
552 mkStringExpr str = mkStringExprFS (mkFastString str)
556 = returnDs (mkNilExpr charTy)
560 the_char = mkCharExpr (headFS str)
562 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
565 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
566 returnDs (App (Var unpack_id) (Lit (MachStr str)))
569 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
570 returnDs (App (Var unpack_id) (Lit (MachStr str)))
574 safeChar c = ord c >= 1 && ord c <= 0x7F
578 %************************************************************************
580 \subsection[mkSelectorBind]{Make a selector bind}
582 %************************************************************************
584 This is used in various places to do with lazy patterns.
585 For each binder $b$ in the pattern, we create a binding:
587 b = case v of pat' -> b'
589 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
591 ToDo: making these bindings should really depend on whether there's
592 much work to be done per binding. If the pattern is complex, it
593 should be de-mangled once, into a tuple (and then selected from).
594 Otherwise the demangling can be in-line in the bindings (as here).
596 Boring! Boring! One error message per binder. The above ToDo is
597 even more helpful. Something very similar happens for pattern-bound
601 mkSelectorBinds :: LPat Id -- The pattern
602 -> CoreExpr -- Expression to which the pattern is bound
603 -> DsM [(Id,CoreExpr)]
605 mkSelectorBinds (L _ (VarPat v)) val_expr
606 = returnDs [(v, val_expr)]
608 mkSelectorBinds pat val_expr
609 | isSingleton binders || is_simple_lpat pat
610 = -- Given p = e, where p binds x,y
611 -- we are going to make
612 -- v = p (where v is fresh)
613 -- x = case v of p -> x
614 -- y = case v of p -> x
617 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
618 -- This does not matter after desugaring, but there's a subtle
619 -- issue with implicit parameters. Consider
621 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
622 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
623 -- does it get that type? So that when we abstract over it we get the
624 -- right top-level type (?i::Int) => ...)
626 -- So to get the type of 'v', use the pattern not the rhs. Often more
628 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
630 -- For the error message we make one error-app, to avoid duplication.
631 -- But we need it at different types... so we use coerce for that
632 mkErrorAppDs iRREFUT_PAT_ERROR_ID
633 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
634 newSysLocalDs unitTy `thenDs` \ err_var ->
635 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
636 returnDs ( (val_var, val_expr) :
637 (err_var, err_expr) :
642 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
643 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
644 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
645 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
648 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
650 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
652 binders = collectPatBinders pat
653 local_tuple = mkBigCoreVarTup binders
654 tuple_ty = exprType local_tuple
656 mk_bind scrut_var err_var bndr_var
657 -- (mk_bind sv err_var) generates
658 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
659 -- Remember, pat binds bv
660 = matchSimply (Var scrut_var) PatBindRhs pat
661 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
662 returnDs (bndr_var, rhs_expr)
664 error_expr = mkCoerce co (Var err_var)
665 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
667 is_simple_lpat p = is_simple_pat (unLoc p)
669 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
670 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConPatArgs ps)
671 is_simple_pat (VarPat _) = True
672 is_simple_pat (ParPat p) = is_simple_lpat p
673 is_simple_pat _ = False
675 is_triv_lpat p = is_triv_pat (unLoc p)
677 is_triv_pat (VarPat _) = True
678 is_triv_pat (WildPat _) = True
679 is_triv_pat (ParPat p) = is_triv_lpat p
680 is_triv_pat _ = False
684 %************************************************************************
688 %************************************************************************
690 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
691 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
695 mkBigTuple :: ([a] -> a) -> [a] -> a
696 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
698 -- Each sub-list is short enough to fit in a tuple
699 mk_big_tuple [as] = small_tuple as
700 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
702 chunkify :: [a] -> [[a]]
703 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
704 -- But there may be more than mAX_TUPLE_SIZE sub-lists
706 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
707 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
711 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
715 Creating tuples and their types for Core expressions
717 @mkBigCoreVarTup@ builds a tuple; the inverse to @mkTupleSelector@.
719 * If it has only one element, it is the identity function.
721 * If there are more elements than a big tuple can have, it nests
726 -- Small tuples: build exactly the specified tuple
727 mkCoreVarTup :: [Id] -> CoreExpr
728 mkCoreVarTup ids = mkCoreTup (map Var ids)
730 mkCoreVarTupTy :: [Id] -> Type
731 mkCoreVarTupTy ids = mkCoreTupTy (map idType ids)
734 mkCoreTup :: [CoreExpr] -> CoreExpr
735 mkCoreTup [] = Var unitDataConId
737 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
738 (map (Type . exprType) cs ++ cs)
740 mkCoreTupTy :: [Type] -> Type
741 mkCoreTupTy [ty] = ty
742 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
747 mkBigCoreVarTup :: [Id] -> CoreExpr
748 mkBigCoreVarTup ids = mkBigCoreTup (map Var ids)
750 mkBigCoreVarTupTy :: [Id] -> Type
751 mkBigCoreVarTupTy ids = mkBigCoreTupTy (map idType ids)
754 mkBigCoreTup :: [CoreExpr] -> CoreExpr
755 mkBigCoreTup = mkBigTuple mkCoreTup
757 mkBigCoreTupTy :: [Type] -> Type
758 mkBigCoreTupTy = mkBigTuple mkCoreTupTy
762 Creating tuples and their types for full Haskell expressions
766 -- Smart constructors for source tuple expressions
767 mkLHsVarTup :: [Id] -> LHsExpr Id
768 mkLHsVarTup ids = mkLHsTup (map nlHsVar ids)
770 mkLHsTup :: [LHsExpr Id] -> LHsExpr Id
771 mkLHsTup [] = nlHsVar unitDataConId
772 mkLHsTup [lexp] = lexp
773 mkLHsTup lexps = noLoc $ ExplicitTuple lexps Boxed
776 -- Smart constructors for source tuple patterns
777 mkLHsVarPatTup :: [Id] -> LPat Id
778 mkLHsVarPatTup bs = mkLHsPatTup (map nlVarPat bs)
780 mkLHsPatTup :: [LPat Id] -> LPat Id
781 mkLHsPatTup [lpat] = lpat
782 mkLHsPatTup lpats = noLoc $ mkVanillaTuplePat lpats Boxed -- Handles the case where lpats = [] gracefully
785 -- The Big equivalents for the source tuple expressions
786 mkBigLHsVarTup :: [Id] -> LHsExpr Id
787 mkBigLHsVarTup ids = mkBigLHsTup (map nlHsVar ids)
789 mkBigLHsTup :: [LHsExpr Id] -> LHsExpr Id
790 mkBigLHsTup = mkBigTuple mkLHsTup
793 -- The Big equivalents for the source tuple patterns
794 mkBigLHsVarPatTup :: [Id] -> LPat Id
795 mkBigLHsVarPatTup bs = mkBigLHsPatTup (map nlVarPat bs)
797 mkBigLHsPatTup :: [LPat Id] -> LPat Id
798 mkBigLHsPatTup = mkBigTuple mkLHsPatTup
803 @mkTupleSelector@ builds a selector which scrutises the given
804 expression and extracts the one name from the list given.
805 If you want the no-shadowing rule to apply, the caller
806 is responsible for making sure that none of these names
809 If there is just one id in the ``tuple'', then the selector is
812 If it's big, it does nesting
813 mkTupleSelector [a,b,c,d] b v e
815 (p,q) -> case p of p {
817 We use 'tpl' vars for the p,q, since shadowing does not matter.
819 In fact, it's more convenient to generate it innermost first, getting
826 mkTupleSelector :: [Id] -- The tuple args
827 -> Id -- The selected one
828 -> Id -- A variable of the same type as the scrutinee
829 -> CoreExpr -- Scrutinee
832 mkTupleSelector vars the_var scrut_var scrut
833 = mk_tup_sel (chunkify vars) the_var
835 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
836 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
837 mk_tup_sel (chunkify tpl_vs) tpl_v
839 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
840 tpl_vs = mkTemplateLocals tpl_tys
841 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
845 A generalization of @mkTupleSelector@, allowing the body
846 of the case to be an arbitrary expression.
848 If the tuple is big, it is nested:
850 mkTupleCase uniqs [a,b,c,d] body v e
851 = case e of v { (p,q) ->
852 case p of p { (a,b) ->
853 case q of q { (c,d) ->
856 To avoid shadowing, we use uniqs to invent new variables p,q.
858 ToDo: eliminate cases where none of the variables are needed.
862 :: UniqSupply -- for inventing names of intermediate variables
863 -> [Id] -- the tuple args
864 -> CoreExpr -- body of the case
865 -> Id -- a variable of the same type as the scrutinee
866 -> CoreExpr -- scrutinee
869 mkTupleCase uniqs vars body scrut_var scrut
870 = mk_tuple_case uniqs (chunkify vars) body
872 -- This is the case where don't need any nesting
873 mk_tuple_case _ [vars] body
874 = mkSmallTupleCase vars body scrut_var scrut
876 -- This is the case where we must make nest tuples at least once
877 mk_tuple_case us vars_s body
878 = let (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
879 in mk_tuple_case us' (chunkify vars') body'
881 one_tuple_case chunk_vars (us, vs, body)
882 = let (us1, us2) = splitUniqSupply us
883 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
884 (mkCoreTupTy (map idType chunk_vars))
885 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
886 in (us2, scrut_var:vs, body')
889 The same, but with a tuple small enough not to need nesting.
893 :: [Id] -- the tuple args
894 -> CoreExpr -- body of the case
895 -> Id -- a variable of the same type as the scrutinee
896 -> CoreExpr -- scrutinee
899 mkSmallTupleCase [var] body _scrut_var scrut
900 = bindNonRec var scrut body
901 mkSmallTupleCase vars body scrut_var scrut
902 -- One branch no refinement?
903 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
906 %************************************************************************
908 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
910 %************************************************************************
912 Call the constructor Ids when building explicit lists, so that they
913 interact well with rules.
916 mkNilExpr :: Type -> CoreExpr
917 mkNilExpr ty = mkConApp nilDataCon [Type ty]
919 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
920 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
922 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
923 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
925 mkCoreSel :: [Id] -- The tuple args
926 -> Id -- The selected one
927 -> Id -- A variable of the same type as the scrutinee
928 -> CoreExpr -- Scrutinee
931 -- mkCoreSel [x] x v e
933 mkCoreSel [var] should_be_the_same_var _ scrut
934 = ASSERT(var == should_be_the_same_var)
937 -- mkCoreSel [x,y,z] x v e
938 -- ===> case e of v { (x,y,z) -> x
939 mkCoreSel vars the_var scrut_var scrut
940 = ASSERT( notNull vars )
941 Case scrut scrut_var (idType the_var)
942 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
945 %************************************************************************
947 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
949 %************************************************************************
951 Generally, we handle pattern matching failure like this: let-bind a
952 fail-variable, and use that variable if the thing fails:
954 let fail.33 = error "Help"
965 If the case can't fail, then there'll be no mention of @fail.33@, and the
966 simplifier will later discard it.
969 If it can fail in only one way, then the simplifier will inline it.
972 Only if it is used more than once will the let-binding remain.
975 There's a problem when the result of the case expression is of
976 unboxed type. Then the type of @fail.33@ is unboxed too, and
977 there is every chance that someone will change the let into a case:
983 which is of course utterly wrong. Rather than drop the condition that
984 only boxed types can be let-bound, we just turn the fail into a function
985 for the primitive case:
987 let fail.33 :: Void -> Int#
988 fail.33 = \_ -> error "Help"
997 Now @fail.33@ is a function, so it can be let-bound.
1000 mkFailurePair :: CoreExpr -- Result type of the whole case expression
1001 -> DsM (CoreBind, -- Binds the newly-created fail variable
1002 -- to either the expression or \ _ -> expression
1003 CoreExpr) -- Either the fail variable, or fail variable
1004 -- applied to unit tuple
1007 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
1008 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
1009 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
1010 App (Var fail_fun_var) (Var unitDataConId))
1013 = newFailLocalDs ty `thenDs` \ fail_var ->
1014 returnDs (NonRec fail_var expr, Var fail_var)
1020 mkOptTickBox :: Maybe (Int,[Id]) -> CoreExpr -> DsM CoreExpr
1021 mkOptTickBox Nothing e = return e
1022 mkOptTickBox (Just (ix,ids)) e = mkTickBox ix ids e
1024 mkTickBox :: Int -> [Id] -> CoreExpr -> DsM CoreExpr
1025 mkTickBox ix vars e = do
1028 let tick | opt_Hpc = mkTickBoxOpId uq mod ix
1029 | otherwise = mkBreakPointOpId uq mod ix
1031 let occName = mkVarOcc "tick"
1032 let name = mkInternalName uq2 occName noSrcSpan -- use mkSysLocal?
1033 let var = Id.mkLocalId name realWorldStatePrimTy
1036 then return (Var tick)
1038 let tickVar = Var tick
1039 let tickType = mkFunTys (map idType vars) realWorldStatePrimTy
1040 let scrutApTy = App tickVar (Type tickType)
1041 return (mkApps scrutApTy (map Var vars) :: Expr Id)
1042 return $ Case scrut var ty [(DEFAULT,[],e)]
1046 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
1047 mkBinaryTickBox ixT ixF e = do
1049 let bndr1 = mkSysLocal FSLIT("t1") uq boolTy
1050 falseBox <- mkTickBox ixF [] $ Var falseDataConId
1051 trueBox <- mkTickBox ixT [] $ Var trueDataConId
1052 return $ Case e bndr1 boolTy
1053 [ (DataAlt falseDataCon, [], falseBox)
1054 , (DataAlt trueDataCon, [], trueBox)