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.
15 mkDsLet, mkDsLets, mkDsApp, mkDsApps,
17 MatchResult(..), CanItFail(..),
18 cantFailMatchResult, alwaysFailMatchResult,
19 extractMatchResult, combineMatchResults,
20 adjustMatchResult, adjustMatchResultDs,
21 mkCoLetMatchResult, mkGuardedMatchResult,
22 matchCanFail, mkEvalMatchResult,
23 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
26 mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr,
27 mkIntExpr, mkCharExpr,
28 mkStringExpr, mkStringExprFS, mkIntegerExpr,
30 mkSelectorBinds, mkTupleExpr, mkTupleSelector,
31 mkTupleType, mkTupleCase, mkBigCoreTup,
32 mkCoreTup, mkCoreTupTy, seqVar,
34 dsSyntaxTable, lookupEvidence,
36 selectSimpleMatchVarL, selectMatchVars, selectMatchVar,
37 mkTickBox, mkOptTickBox, mkBinaryTickBox
40 #include "HsVersions.h"
42 import {-# SOURCE #-} Match ( matchSimply )
43 import {-# SOURCE #-} DsExpr( dsExpr )
76 infixl 4 `mkDsApp`, `mkDsApps`
81 %************************************************************************
85 %************************************************************************
88 dsSyntaxTable :: SyntaxTable Id
89 -> DsM ([CoreBind], -- Auxiliary bindings
90 [(Name,Id)]) -- Maps the standard name to its value
92 dsSyntaxTable rebound_ids
93 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
94 return (concat binds_s, prs)
96 -- The cheapo special case can happen when we
97 -- make an intermediate HsDo when desugaring a RecStmt
98 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
99 mk_bind (std_name, expr)
100 = dsExpr expr `thenDs` \ rhs ->
101 newSysLocalDs (exprType rhs) `thenDs` \ id ->
102 return ([NonRec id rhs], (std_name, id))
104 lookupEvidence :: [(Name, Id)] -> Name -> Id
105 lookupEvidence prs std_name
106 = assocDefault (mk_panic std_name) prs std_name
108 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
112 %************************************************************************
114 \subsection{Building lets}
116 %************************************************************************
118 Use case, not let for unlifted types. The simplifier will turn some
122 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
123 mkDsLet (NonRec bndr rhs) body -- See Note [CoreSyn let/app invariant]
124 | isUnLiftedType (idType bndr) && not (exprOkForSpeculation rhs)
125 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
129 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
130 mkDsLets binds body = foldr mkDsLet body binds
133 mkDsApp :: CoreExpr -> CoreExpr -> CoreExpr
134 -- Check the invariant that the arg of an App is ok-for-speculation if unlifted
135 -- See CoreSyn Note [CoreSyn let/app invariant]
136 mkDsApp fun (Type ty) = App fun (Type ty)
137 mkDsApp fun arg = mk_val_app fun arg arg_ty res_ty
139 (arg_ty, res_ty) = splitFunTy (exprType fun)
142 mkDsApps :: CoreExpr -> [CoreExpr] -> CoreExpr
143 -- Slightly more efficient version of (foldl mkDsApp)
145 = go fun (exprType fun) args
147 go fun fun_ty [] = fun
148 go fun fun_ty (Type ty : args) = go (App fun (Type ty)) (applyTy fun_ty ty) args
149 go fun fun_ty (arg : args) = go (mk_val_app fun arg arg_ty res_ty) res_ty args
151 (arg_ty, res_ty) = splitFunTy fun_ty
153 mk_val_app fun arg arg_ty res_ty -- See Note [CoreSyn let/app invariant]
154 | not (isUnLiftedType arg_ty) || exprOkForSpeculation arg
155 = App fun arg -- The vastly common case
157 mk_val_app (Var f `App` Type ty1 `App` Type ty2 `App` arg1) arg2 _ res_ty
158 | f == seqId -- Note [Desugaring seq]
159 = Case arg1 (mkWildId ty1) res_ty [(DEFAULT,[],arg2)]
161 mk_val_app fun arg arg_ty res_ty
162 = Case arg (mkWildId arg_ty) res_ty [(DEFAULT,[],App fun (Var arg_id))]
164 arg_id = mkWildId arg_ty -- Lots of shadowing, but it doesn't matter,
165 -- because 'fun ' should not have a free wild-id
168 Note [Desugaring seq] cf Trac #1031
169 ~~~~~~~~~~~~~~~~~~~~~
170 f x y = x `seq` (y `seq` (# x,y #))
172 The [CoreSyn let/app invariant] means that, other things being equal, because
173 the argument to the outer 'seq' has an unlifted type, we'll use call-by-value thus:
175 f x y = case (y `seq` (# x,y #)) of v -> x `seq` v
177 But that is bad for two reasons:
178 (a) we now evaluate y before x, and
179 (b) we can't bind v to an unboxed pair
181 Seq is very, very special! So we recognise it right here, and desugar to
182 case x of _ -> case y of _ -> (# x,y #)
184 The special case would be valid for all calls to 'seq', but it's only *necessary*
185 for ones whose second argument has an unlifted type. So we only catch the latter
186 case here, to avoid unnecessary tests.
189 %************************************************************************
191 \subsection{ Selecting match variables}
193 %************************************************************************
195 We're about to match against some patterns. We want to make some
196 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
197 hand, which should indeed be bound to the pattern as a whole, then use it;
198 otherwise, make one up.
201 selectSimpleMatchVarL :: LPat Id -> DsM Id
202 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
204 -- (selectMatchVars ps tys) chooses variables of type tys
205 -- to use for matching ps against. If the pattern is a variable,
206 -- we try to use that, to save inventing lots of fresh variables.
208 -- OLD, but interesting note:
209 -- But even if it is a variable, its type might not match. Consider
211 -- T1 :: Int -> T Int
214 -- f :: T a -> a -> Int
215 -- f (T1 i) (x::Int) = x
216 -- f (T2 i) (y::a) = 0
217 -- Then we must not choose (x::Int) as the matching variable!
218 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
220 selectMatchVars :: [Pat Id] -> DsM [Id]
221 selectMatchVars ps = mapM selectMatchVar ps
223 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
224 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
225 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
226 selectMatchVar (VarPat var) = return var
227 selectMatchVar (AsPat var pat) = return (unLoc var)
228 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
229 -- OK, better make up one...
233 %************************************************************************
235 %* type synonym EquationInfo and access functions for its pieces *
237 %************************************************************************
238 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
240 The ``equation info'' used by @match@ is relatively complicated and
241 worthy of a type synonym and a few handy functions.
244 firstPat :: EquationInfo -> Pat Id
245 firstPat eqn = ASSERT( notNull (eqn_pats eqn) ) head (eqn_pats eqn)
247 shiftEqns :: [EquationInfo] -> [EquationInfo]
248 -- Drop the first pattern in each equation
249 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
252 Functions on MatchResults
255 matchCanFail :: MatchResult -> Bool
256 matchCanFail (MatchResult CanFail _) = True
257 matchCanFail (MatchResult CantFail _) = False
259 alwaysFailMatchResult :: MatchResult
260 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
262 cantFailMatchResult :: CoreExpr -> MatchResult
263 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
265 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
266 extractMatchResult (MatchResult CantFail match_fn) fail_expr
267 = match_fn (error "It can't fail!")
269 extractMatchResult (MatchResult CanFail match_fn) fail_expr
270 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
271 match_fn if_it_fails `thenDs` \ body ->
272 returnDs (mkDsLet fail_bind body)
275 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
276 combineMatchResults (MatchResult CanFail body_fn1)
277 (MatchResult can_it_fail2 body_fn2)
278 = MatchResult can_it_fail2 body_fn
280 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
281 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
282 body_fn1 duplicatable_expr `thenDs` \ body1 ->
283 returnDs (Let fail_bind body1)
285 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
288 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
289 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
290 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
291 returnDs (encl_fn body))
293 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
294 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
295 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
298 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
300 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
302 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
303 wrapBind new old body
305 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
306 | otherwise = Let (NonRec new (Var old)) body
308 seqVar :: Var -> CoreExpr -> CoreExpr
309 seqVar var body = Case (Var var) var (exprType body)
310 [(DEFAULT, [], body)]
312 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
313 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
315 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
316 mkEvalMatchResult var ty
317 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
319 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
320 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
321 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
322 returnDs (mkIfThenElse pred_expr body fail))
324 mkCoPrimCaseMatchResult :: Id -- Scrutinee
325 -> Type -- Type of the case
326 -> [(Literal, MatchResult)] -- Alternatives
328 mkCoPrimCaseMatchResult var ty match_alts
329 = MatchResult CanFail mk_case
332 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
333 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
335 sorted_alts = sortWith fst match_alts -- Right order for a Case
336 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
337 returnDs (LitAlt lit, [], body)
340 mkCoAlgCaseMatchResult :: Id -- Scrutinee
341 -> Type -- Type of exp
342 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
344 mkCoAlgCaseMatchResult var ty match_alts
345 | isNewTyCon tycon -- Newtype case; use a let
346 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
347 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
349 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
350 = MatchResult CanFail mk_parrCase
352 | otherwise -- Datatype case; use a case
353 = MatchResult fail_flag mk_case
355 tycon = dataConTyCon con1
356 -- [Interesting: becuase of GADTs, we can't rely on the type of
357 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
360 (con1, arg_ids1, match_result1) = ASSERT( notNull match_alts ) head match_alts
361 arg_id1 = ASSERT( notNull arg_ids1 ) head arg_ids1
363 (tc, ty_args) = splitNewTyConApp var_ty
364 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
366 -- Stuff for data types
367 data_cons = tyConDataCons tycon
368 match_results = [match_result | (_,_,match_result) <- match_alts]
370 fail_flag | exhaustive_case
371 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
375 wild_var = mkWildId (idType var)
376 sorted_alts = sortWith get_tag match_alts
377 get_tag (con, _, _) = dataConTag con
378 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
379 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
381 mk_alt fail (con, args, MatchResult _ body_fn)
382 = body_fn fail `thenDs` \ body ->
383 newUniqueSupply `thenDs` \ us ->
384 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
386 mk_default fail | exhaustive_case = []
387 | otherwise = [(DEFAULT, [], fail)]
389 un_mentioned_constructors
390 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
391 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
393 -- Stuff for parallel arrays
395 -- * the following is to desugar cases over fake constructors for
396 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
399 -- Concerning `isPArrFakeAlts':
401 -- * it is *not* sufficient to just check the type of the type
402 -- constructor, as we have to be careful not to confuse the real
403 -- representation of parallel arrays with the fake constructors;
404 -- moreover, a list of alternatives must not mix fake and real
405 -- constructors (this is checked earlier on)
407 -- FIXME: We actually go through the whole list and make sure that
408 -- either all or none of the constructors are fake parallel
409 -- array constructors. This is to spot equations that mix fake
410 -- constructors with the real representation defined in
411 -- `PrelPArr'. It would be nicer to spot this situation
412 -- earlier and raise a proper error message, but it can really
413 -- only happen in `PrelPArr' anyway.
415 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
416 isPArrFakeAlts ((dcon, _, _):alts) =
417 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
418 (True , True ) -> True
419 (False, False) -> False
421 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
424 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
425 unboxAlt `thenDs` \alt ->
426 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
428 elemTy = case splitTyConApp (idType var) of
429 (_, [elemTy]) -> elemTy
431 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
432 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
435 newSysLocalDs intPrimTy `thenDs` \l ->
436 dsLookupGlobalId indexPName `thenDs` \indexP ->
437 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
438 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
440 wild = mkWildId intPrimTy
441 dft = (DEFAULT, [], fail)
443 -- each alternative matches one array length (corresponding to one
444 -- fake array constructor), so the match is on a literal; each
445 -- alternative's body is extended by a local binding for each
446 -- constructor argument, which are bound to array elements starting
449 mkAlt indexP (con, args, MatchResult _ bodyFun) =
450 bodyFun fail `thenDs` \body ->
451 returnDs (LitAlt lit, [], mkDsLets binds body)
453 lit = MachInt $ toInteger (dataConSourceArity con)
454 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
456 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
460 %************************************************************************
462 \subsection{Desugarer's versions of some Core functions}
464 %************************************************************************
467 mkErrorAppDs :: Id -- The error function
468 -> Type -- Type to which it should be applied
469 -> String -- The error message string to pass
472 mkErrorAppDs err_id ty msg
473 = getSrcSpanDs `thenDs` \ src_loc ->
475 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
476 core_msg = Lit (mkStringLit full_msg)
477 -- mkStringLit returns a result of type String#
479 returnDs (mkApps (Var err_id) [Type ty, core_msg])
483 *************************************************************
485 \subsection{Making literals}
487 %************************************************************************
490 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
491 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
492 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
493 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
494 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
496 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
497 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
500 | inIntRange i -- Small enough, so start from an Int
501 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
502 returnDs (mkSmallIntegerLit integer_dc i)
504 -- Special case for integral literals with a large magnitude:
505 -- They are transformed into an expression involving only smaller
506 -- integral literals. This improves constant folding.
508 | otherwise -- Big, so start from a string
509 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
510 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
511 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
513 lit i = mkSmallIntegerLit integer_dc i
514 plus a b = Var plus_id `App` a `App` b
515 times a b = Var times_id `App` a `App` b
517 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
518 horner :: Integer -> Integer -> CoreExpr
519 horner b i | abs q <= 1 = if r == 0 || r == i
521 else lit r `plus` lit (i-r)
522 | r == 0 = horner b q `times` lit b
523 | otherwise = lit r `plus` (horner b q `times` lit b)
525 (q,r) = i `quotRem` b
528 returnDs (horner tARGET_MAX_INT i)
530 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
532 mkStringExpr str = mkStringExprFS (mkFastString str)
536 = returnDs (mkNilExpr charTy)
540 the_char = mkCharExpr (headFS str)
542 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
545 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
546 returnDs (App (Var unpack_id) (Lit (MachStr str)))
549 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
550 returnDs (App (Var unpack_id) (Lit (MachStr str)))
554 safeChar c = ord c >= 1 && ord c <= 0x7F
558 %************************************************************************
560 \subsection[mkSelectorBind]{Make a selector bind}
562 %************************************************************************
564 This is used in various places to do with lazy patterns.
565 For each binder $b$ in the pattern, we create a binding:
567 b = case v of pat' -> b'
569 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
571 ToDo: making these bindings should really depend on whether there's
572 much work to be done per binding. If the pattern is complex, it
573 should be de-mangled once, into a tuple (and then selected from).
574 Otherwise the demangling can be in-line in the bindings (as here).
576 Boring! Boring! One error message per binder. The above ToDo is
577 even more helpful. Something very similar happens for pattern-bound
581 mkSelectorBinds :: LPat Id -- The pattern
582 -> CoreExpr -- Expression to which the pattern is bound
583 -> DsM [(Id,CoreExpr)]
585 mkSelectorBinds (L _ (VarPat v)) val_expr
586 = returnDs [(v, val_expr)]
588 mkSelectorBinds pat val_expr
589 | isSingleton binders || is_simple_lpat pat
590 = -- Given p = e, where p binds x,y
591 -- we are going to make
592 -- v = p (where v is fresh)
593 -- x = case v of p -> x
594 -- y = case v of p -> x
597 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
598 -- This does not matter after desugaring, but there's a subtle
599 -- issue with implicit parameters. Consider
601 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
602 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
603 -- does it get that type? So that when we abstract over it we get the
604 -- right top-level type (?i::Int) => ...)
606 -- So to get the type of 'v', use the pattern not the rhs. Often more
608 newSysLocalDs (hsLPatType pat) `thenDs` \ val_var ->
610 -- For the error message we make one error-app, to avoid duplication.
611 -- But we need it at different types... so we use coerce for that
612 mkErrorAppDs iRREFUT_PAT_ERROR_ID
613 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
614 newSysLocalDs unitTy `thenDs` \ err_var ->
615 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
616 returnDs ( (val_var, val_expr) :
617 (err_var, err_expr) :
622 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
623 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
624 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
625 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
628 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
630 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
632 binders = collectPatBinders pat
633 local_tuple = mkTupleExpr binders
634 tuple_ty = exprType local_tuple
636 mk_bind scrut_var err_var bndr_var
637 -- (mk_bind sv err_var) generates
638 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
639 -- Remember, pat binds bv
640 = matchSimply (Var scrut_var) PatBindRhs pat
641 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
642 returnDs (bndr_var, rhs_expr)
644 error_expr = mkCoerce co (Var err_var)
645 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
647 is_simple_lpat p = is_simple_pat (unLoc p)
649 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
650 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConPatArgs ps)
651 is_simple_pat (VarPat _) = True
652 is_simple_pat (ParPat p) = is_simple_lpat p
653 is_simple_pat other = False
655 is_triv_lpat p = is_triv_pat (unLoc p)
657 is_triv_pat (VarPat v) = True
658 is_triv_pat (WildPat _) = True
659 is_triv_pat (ParPat p) = is_triv_lpat p
660 is_triv_pat other = False
664 %************************************************************************
668 %************************************************************************
670 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
672 * If it has only one element, it is the identity function.
674 * If there are more elements than a big tuple can have, it nests
677 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
678 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
681 mkTupleExpr :: [Id] -> CoreExpr
682 mkTupleExpr ids = mkBigCoreTup (map Var ids)
684 -- corresponding type
685 mkTupleType :: [Id] -> Type
686 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
688 mkBigCoreTup :: [CoreExpr] -> CoreExpr
689 mkBigCoreTup = mkBigTuple mkCoreTup
691 mkBigTuple :: ([a] -> a) -> [a] -> a
692 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
694 -- Each sub-list is short enough to fit in a tuple
695 mk_big_tuple [as] = small_tuple as
696 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
698 chunkify :: [a] -> [[a]]
699 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
700 -- But there may be more than mAX_TUPLE_SIZE sub-lists
702 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
703 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
707 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
711 @mkTupleSelector@ builds a selector which scrutises the given
712 expression and extracts the one name from the list given.
713 If you want the no-shadowing rule to apply, the caller
714 is responsible for making sure that none of these names
717 If there is just one id in the ``tuple'', then the selector is
720 If it's big, it does nesting
721 mkTupleSelector [a,b,c,d] b v e
723 (p,q) -> case p of p {
725 We use 'tpl' vars for the p,q, since shadowing does not matter.
727 In fact, it's more convenient to generate it innermost first, getting
734 mkTupleSelector :: [Id] -- The tuple args
735 -> Id -- The selected one
736 -> Id -- A variable of the same type as the scrutinee
737 -> CoreExpr -- Scrutinee
740 mkTupleSelector vars the_var scrut_var scrut
741 = mk_tup_sel (chunkify vars) the_var
743 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
744 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
745 mk_tup_sel (chunkify tpl_vs) tpl_v
747 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
748 tpl_vs = mkTemplateLocals tpl_tys
749 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
753 A generalization of @mkTupleSelector@, allowing the body
754 of the case to be an arbitrary expression.
756 If the tuple is big, it is nested:
758 mkTupleCase uniqs [a,b,c,d] body v e
759 = case e of v { (p,q) ->
760 case p of p { (a,b) ->
761 case q of q { (c,d) ->
764 To avoid shadowing, we use uniqs to invent new variables p,q.
766 ToDo: eliminate cases where none of the variables are needed.
770 :: UniqSupply -- for inventing names of intermediate variables
771 -> [Id] -- the tuple args
772 -> CoreExpr -- body of the case
773 -> Id -- a variable of the same type as the scrutinee
774 -> CoreExpr -- scrutinee
777 mkTupleCase uniqs vars body scrut_var scrut
778 = mk_tuple_case uniqs (chunkify vars) body
780 mk_tuple_case us [vars] body
781 = mkSmallTupleCase vars body scrut_var scrut
782 mk_tuple_case us vars_s body
784 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
786 mk_tuple_case us' (chunkify vars') body'
787 one_tuple_case chunk_vars (us, vs, body)
789 (us1, us2) = splitUniqSupply us
790 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
791 (mkCoreTupTy (map idType chunk_vars))
792 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
793 in (us2, scrut_var:vs, body')
796 The same, but with a tuple small enough not to need nesting.
800 :: [Id] -- the tuple args
801 -> CoreExpr -- body of the case
802 -> Id -- a variable of the same type as the scrutinee
803 -> CoreExpr -- scrutinee
806 mkSmallTupleCase [var] body _scrut_var scrut
807 = bindNonRec var scrut body
808 mkSmallTupleCase vars body scrut_var scrut
809 -- One branch no refinement?
810 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
813 %************************************************************************
815 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
817 %************************************************************************
819 Call the constructor Ids when building explicit lists, so that they
820 interact well with rules.
823 mkNilExpr :: Type -> CoreExpr
824 mkNilExpr ty = mkConApp nilDataCon [Type ty]
826 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
827 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
829 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
830 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
833 -- The next three functions make tuple types, constructors and selectors,
834 -- with the rule that a 1-tuple is represented by the thing itselg
835 mkCoreTupTy :: [Type] -> Type
836 mkCoreTupTy [ty] = ty
837 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
839 mkCoreTup :: [CoreExpr] -> CoreExpr
840 -- Builds exactly the specified tuple.
841 -- No fancy business for big tuples
842 mkCoreTup [] = Var unitDataConId
844 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
845 (map (Type . exprType) cs ++ cs)
847 mkCoreSel :: [Id] -- The tuple args
848 -> Id -- The selected one
849 -> Id -- A variable of the same type as the scrutinee
850 -> CoreExpr -- Scrutinee
852 -- mkCoreSel [x,y,z] x v e
853 -- ===> case e of v { (x,y,z) -> x
854 mkCoreSel [var] should_be_the_same_var scrut_var scrut
855 = ASSERT(var == should_be_the_same_var)
858 mkCoreSel vars the_var scrut_var scrut
859 = ASSERT( notNull vars )
860 Case scrut scrut_var (idType the_var)
861 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
864 %************************************************************************
866 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
868 %************************************************************************
870 Generally, we handle pattern matching failure like this: let-bind a
871 fail-variable, and use that variable if the thing fails:
873 let fail.33 = error "Help"
884 If the case can't fail, then there'll be no mention of @fail.33@, and the
885 simplifier will later discard it.
888 If it can fail in only one way, then the simplifier will inline it.
891 Only if it is used more than once will the let-binding remain.
894 There's a problem when the result of the case expression is of
895 unboxed type. Then the type of @fail.33@ is unboxed too, and
896 there is every chance that someone will change the let into a case:
902 which is of course utterly wrong. Rather than drop the condition that
903 only boxed types can be let-bound, we just turn the fail into a function
904 for the primitive case:
906 let fail.33 :: Void -> Int#
907 fail.33 = \_ -> error "Help"
916 Now @fail.33@ is a function, so it can be let-bound.
919 mkFailurePair :: CoreExpr -- Result type of the whole case expression
920 -> DsM (CoreBind, -- Binds the newly-created fail variable
921 -- to either the expression or \ _ -> expression
922 CoreExpr) -- Either the fail variable, or fail variable
923 -- applied to unit tuple
926 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
927 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
928 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
929 App (Var fail_fun_var) (Var unitDataConId))
932 = newFailLocalDs ty `thenDs` \ fail_var ->
933 returnDs (NonRec fail_var expr, Var fail_var)
939 mkOptTickBox :: Maybe (Int,[Id]) -> CoreExpr -> DsM CoreExpr
940 mkOptTickBox Nothing e = return e
941 mkOptTickBox (Just (ix,ids)) e = mkTickBox ix ids e
943 mkTickBox :: Int -> [Id] -> CoreExpr -> DsM CoreExpr
944 mkTickBox ix vars e = do
947 let tick | opt_Hpc = mkTickBoxOpId uq mod ix
948 | otherwise = mkBreakPointOpId uq mod ix
950 let occName = mkVarOcc "tick"
951 let name = mkInternalName uq2 occName noSrcSpan -- use mkSysLocal?
952 let var = Id.mkLocalId name realWorldStatePrimTy
955 then return (Var tick)
957 let tickVar = Var tick
958 let tickType = mkFunTys (map idType vars) realWorldStatePrimTy
959 let scrutApTy = App tickVar (Type tickType)
960 return (mkApps scrutApTy (map Var vars) :: Expr Id)
961 return $ Case scrut var ty [(DEFAULT,[],e)]
965 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
966 mkBinaryTickBox ixT ixF e = do
970 let bndr1 = mkSysLocal FSLIT("t1") uq boolTy
971 falseBox <- mkTickBox ixF [] $ Var falseDataConId
972 trueBox <- mkTickBox ixT [] $ Var trueDataConId
973 return $ Case e bndr1 boolTy
974 [ (DataAlt falseDataCon, [], falseBox)
975 , (DataAlt trueDataCon, [], trueBox)