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 fun arg arg_ty _ -- See Note [CoreSyn let/app invariant]
167 | not (isUnLiftedType arg_ty) || exprOkForSpeculation arg
168 = App fun arg -- The vastly common case
170 mk_val_app (Var f `App` Type ty1 `App` Type _ `App` arg1) arg2 _ res_ty
171 | f == seqId -- Note [Desugaring seq]
172 = Case arg1 (mkWildId ty1) res_ty [(DEFAULT,[],arg2)]
174 mk_val_app fun arg arg_ty res_ty
175 = Case arg (mkWildId arg_ty) res_ty [(DEFAULT,[],App fun (Var arg_id))]
177 arg_id = mkWildId arg_ty -- Lots of shadowing, but it doesn't matter,
178 -- because 'fun ' should not have a free wild-id
181 Note [Desugaring seq] cf Trac #1031
182 ~~~~~~~~~~~~~~~~~~~~~
183 f x y = x `seq` (y `seq` (# x,y #))
185 The [CoreSyn let/app invariant] means that, other things being equal, because
186 the argument to the outer 'seq' has an unlifted type, we'll use call-by-value thus:
188 f x y = case (y `seq` (# x,y #)) of v -> x `seq` v
190 But that is bad for two reasons:
191 (a) we now evaluate y before x, and
192 (b) we can't bind v to an unboxed pair
194 Seq is very, very special! So we recognise it right here, and desugar to
195 case x of _ -> case y of _ -> (# x,y #)
197 The special case would be valid for all calls to 'seq', but it's only *necessary*
198 for ones whose second argument has an unlifted type. So we only catch the latter
199 case here, to avoid unnecessary tests.
202 %************************************************************************
204 \subsection{ Selecting match variables}
206 %************************************************************************
208 We're about to match against some patterns. We want to make some
209 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
210 hand, which should indeed be bound to the pattern as a whole, then use it;
211 otherwise, make one up.
214 selectSimpleMatchVarL :: LPat Id -> DsM Id
215 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat)
217 -- (selectMatchVars ps tys) chooses variables of type tys
218 -- to use for matching ps against. If the pattern is a variable,
219 -- we try to use that, to save inventing lots of fresh variables.
221 -- OLD, but interesting note:
222 -- But even if it is a variable, its type might not match. Consider
224 -- T1 :: Int -> T Int
227 -- f :: T a -> a -> Int
228 -- f (T1 i) (x::Int) = x
229 -- f (T2 i) (y::a) = 0
230 -- Then we must not choose (x::Int) as the matching variable!
231 -- And nowadays we won't, because the (x::Int) will be wrapped in a CoPat
233 selectMatchVars :: [Pat Id] -> DsM [Id]
234 selectMatchVars ps = mapM selectMatchVar ps
236 selectMatchVar :: Pat Id -> DsM Id
237 selectMatchVar (BangPat pat) = selectMatchVar (unLoc pat)
238 selectMatchVar (LazyPat pat) = selectMatchVar (unLoc pat)
239 selectMatchVar (ParPat pat) = selectMatchVar (unLoc pat)
240 selectMatchVar (VarPat var) = return var
241 selectMatchVar (AsPat var _) = return (unLoc var)
242 selectMatchVar other_pat = newSysLocalDs (hsPatType other_pat)
243 -- OK, better make up one...
247 %************************************************************************
249 %* type synonym EquationInfo and access functions for its pieces *
251 %************************************************************************
252 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
254 The ``equation info'' used by @match@ is relatively complicated and
255 worthy of a type synonym and a few handy functions.
258 firstPat :: EquationInfo -> Pat Id
259 firstPat eqn = ASSERT( notNull (eqn_pats eqn) ) head (eqn_pats eqn)
261 shiftEqns :: [EquationInfo] -> [EquationInfo]
262 -- Drop the first pattern in each equation
263 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
266 Functions on MatchResults
269 matchCanFail :: MatchResult -> Bool
270 matchCanFail (MatchResult CanFail _) = True
271 matchCanFail (MatchResult CantFail _) = False
273 alwaysFailMatchResult :: MatchResult
274 alwaysFailMatchResult = MatchResult CanFail (\fail -> return fail)
276 cantFailMatchResult :: CoreExpr -> MatchResult
277 cantFailMatchResult expr = MatchResult CantFail (\_ -> return expr)
279 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
280 extractMatchResult (MatchResult CantFail match_fn) _
281 = match_fn (error "It can't fail!")
283 extractMatchResult (MatchResult CanFail match_fn) fail_expr = do
284 (fail_bind, if_it_fails) <- mkFailurePair fail_expr
285 body <- match_fn if_it_fails
286 return (mkDsLet fail_bind body)
289 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
290 combineMatchResults (MatchResult CanFail body_fn1)
291 (MatchResult can_it_fail2 body_fn2)
292 = MatchResult can_it_fail2 body_fn
294 body_fn fail = do body2 <- body_fn2 fail
295 (fail_bind, duplicatable_expr) <- mkFailurePair body2
296 body1 <- body_fn1 duplicatable_expr
297 return (Let fail_bind body1)
299 combineMatchResults match_result1@(MatchResult CantFail _) _
302 adjustMatchResult :: DsWrapper -> MatchResult -> MatchResult
303 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
304 = MatchResult can_it_fail (\fail -> encl_fn <$> body_fn fail)
306 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
307 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
308 = MatchResult can_it_fail (\fail -> encl_fn =<< body_fn fail)
310 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
312 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
314 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
315 wrapBind new old body
317 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
318 | otherwise = Let (NonRec new (Var old)) body
320 seqVar :: Var -> CoreExpr -> CoreExpr
321 seqVar var body = Case (Var var) var (exprType body)
322 [(DEFAULT, [], body)]
324 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
325 mkCoLetMatchResult bind = adjustMatchResult (mkDsLet bind)
327 -- (mkViewMatchResult var' viewExpr var mr) makes the expression
328 -- let var' = viewExpr var in mr
329 mkViewMatchResult :: Id -> CoreExpr -> Id -> MatchResult -> MatchResult
330 mkViewMatchResult var' viewExpr var =
331 adjustMatchResult (mkDsLet (NonRec var' (mkDsApp viewExpr (Var var))))
333 mkEvalMatchResult :: Id -> Type -> MatchResult -> MatchResult
334 mkEvalMatchResult var ty
335 = adjustMatchResult (\e -> Case (Var var) var ty [(DEFAULT, [], e)])
337 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
338 mkGuardedMatchResult pred_expr (MatchResult _ body_fn)
339 = MatchResult CanFail (\fail -> do body <- body_fn fail
340 return (mkIfThenElse pred_expr body fail))
342 mkCoPrimCaseMatchResult :: Id -- Scrutinee
343 -> Type -- Type of the case
344 -> [(Literal, MatchResult)] -- Alternatives
346 mkCoPrimCaseMatchResult var ty match_alts
347 = MatchResult CanFail mk_case
350 alts <- mapM (mk_alt fail) sorted_alts
351 return (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
353 sorted_alts = sortWith fst match_alts -- Right order for a Case
354 mk_alt fail (lit, MatchResult _ body_fn) = do body <- body_fn fail
355 return (LitAlt lit, [], body)
358 mkCoAlgCaseMatchResult :: Id -- Scrutinee
359 -> Type -- Type of exp
360 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
362 mkCoAlgCaseMatchResult var ty match_alts
363 | isNewTyCon tycon -- Newtype case; use a let
364 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
365 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
367 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
368 = MatchResult CanFail mk_parrCase
370 | otherwise -- Datatype case; use a case
371 = MatchResult fail_flag mk_case
373 tycon = dataConTyCon con1
374 -- [Interesting: becuase of GADTs, we can't rely on the type of
375 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
378 (con1, arg_ids1, match_result1) = ASSERT( notNull match_alts ) head match_alts
379 arg_id1 = ASSERT( notNull arg_ids1 ) head arg_ids1
381 (tc, ty_args) = splitNewTyConApp var_ty
382 newtype_rhs = unwrapNewTypeBody tc ty_args (Var var)
384 -- Stuff for data types
385 data_cons = tyConDataCons tycon
386 match_results = [match_result | (_,_,match_result) <- match_alts]
388 fail_flag | exhaustive_case
389 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
393 wild_var = mkWildId (idType var)
394 sorted_alts = sortWith get_tag match_alts
395 get_tag (con, _, _) = dataConTag con
396 mk_case fail = do alts <- mapM (mk_alt fail) sorted_alts
397 return (Case (Var var) wild_var ty (mk_default fail ++ alts))
399 mk_alt fail (con, args, MatchResult _ body_fn) = do
401 us <- newUniqueSupply
402 return (mkReboxingAlt (uniqsFromSupply us) con args body)
404 mk_default fail | exhaustive_case = []
405 | otherwise = [(DEFAULT, [], fail)]
407 un_mentioned_constructors
408 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
409 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
411 -- Stuff for parallel arrays
413 -- * the following is to desugar cases over fake constructors for
414 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
417 -- Concerning `isPArrFakeAlts':
419 -- * it is *not* sufficient to just check the type of the type
420 -- constructor, as we have to be careful not to confuse the real
421 -- representation of parallel arrays with the fake constructors;
422 -- moreover, a list of alternatives must not mix fake and real
423 -- constructors (this is checked earlier on)
425 -- FIXME: We actually go through the whole list and make sure that
426 -- either all or none of the constructors are fake parallel
427 -- array constructors. This is to spot equations that mix fake
428 -- constructors with the real representation defined in
429 -- `PrelPArr'. It would be nicer to spot this situation
430 -- earlier and raise a proper error message, but it can really
431 -- only happen in `PrelPArr' anyway.
433 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
434 isPArrFakeAlts ((dcon, _, _):alts) =
435 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
436 (True , True ) -> True
437 (False, False) -> False
438 _ -> panic "DsUtils: you may not mix `[:...:]' with `PArr' patterns"
439 isPArrFakeAlts [] = panic "DsUtils: unexpectedly found an empty list of PArr fake alternatives"
441 mk_parrCase fail = do
442 lengthP <- dsLookupGlobalId lengthPName
444 return (Case (len lengthP) (mkWildId intTy) ty [alt])
446 elemTy = case splitTyConApp (idType var) of
447 (_, [elemTy]) -> elemTy
449 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
450 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
453 l <- newSysLocalDs intPrimTy
454 indexP <- dsLookupGlobalId indexPName
455 alts <- mapM (mkAlt indexP) sorted_alts
456 return (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
458 wild = mkWildId intPrimTy
459 dft = (DEFAULT, [], fail)
461 -- each alternative matches one array length (corresponding to one
462 -- fake array constructor), so the match is on a literal; each
463 -- alternative's body is extended by a local binding for each
464 -- constructor argument, which are bound to array elements starting
467 mkAlt indexP (con, args, MatchResult _ bodyFun) = do
469 return (LitAlt lit, [], mkDsLets binds body)
471 lit = MachInt $ toInteger (dataConSourceArity con)
472 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
474 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
478 %************************************************************************
480 \subsection{Desugarer's versions of some Core functions}
482 %************************************************************************
485 mkErrorAppDs :: Id -- The error function
486 -> Type -- Type to which it should be applied
487 -> String -- The error message string to pass
490 mkErrorAppDs err_id ty msg = do
491 src_loc <- getSrcSpanDs
493 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
494 core_msg = Lit (mkStringLit full_msg)
495 -- mkStringLit returns a result of type String#
496 return (mkApps (Var err_id) [Type ty, core_msg])
500 *************************************************************
502 \subsection{Making literals}
504 %************************************************************************
507 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
508 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
509 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
510 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
511 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
513 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
514 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
517 | inIntRange i -- Small enough, so start from an Int
518 = do integer_id <- dsLookupGlobalId smallIntegerName
519 return (mkSmallIntegerLit integer_id i)
521 -- Special case for integral literals with a large magnitude:
522 -- They are transformed into an expression involving only smaller
523 -- integral literals. This improves constant folding.
525 | otherwise = do -- Big, so start from a string
526 plus_id <- dsLookupGlobalId plusIntegerName
527 times_id <- dsLookupGlobalId timesIntegerName
528 integer_id <- dsLookupGlobalId smallIntegerName
530 lit i = mkSmallIntegerLit integer_id i
531 plus a b = Var plus_id `App` a `App` b
532 times a b = Var times_id `App` a `App` b
534 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
535 horner :: Integer -> Integer -> CoreExpr
536 horner b i | abs q <= 1 = if r == 0 || r == i
538 else lit r `plus` lit (i-r)
539 | r == 0 = horner b q `times` lit b
540 | otherwise = lit r `plus` (horner b q `times` lit b)
542 (q,r) = i `quotRem` b
544 return (horner tARGET_MAX_INT i)
546 mkSmallIntegerLit :: Id -> Integer -> CoreExpr
547 mkSmallIntegerLit small_integer i = mkApps (Var small_integer) [mkIntLit i]
549 mkStringExpr str = mkStringExprFS (mkFastString str)
553 = return (mkNilExpr charTy)
556 = do let the_char = mkCharExpr (headFS str)
557 return (mkConsExpr charTy the_char (mkNilExpr charTy))
560 = do unpack_id <- dsLookupGlobalId unpackCStringName
561 return (App (Var unpack_id) (Lit (MachStr str)))
564 = do unpack_id <- dsLookupGlobalId unpackCStringUtf8Name
565 return (App (Var unpack_id) (Lit (MachStr str)))
569 safeChar c = ord c >= 1 && ord c <= 0x7F
573 %************************************************************************
575 \subsection[mkSelectorBind]{Make a selector bind}
577 %************************************************************************
579 This is used in various places to do with lazy patterns.
580 For each binder $b$ in the pattern, we create a binding:
582 b = case v of pat' -> b'
584 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
586 ToDo: making these bindings should really depend on whether there's
587 much work to be done per binding. If the pattern is complex, it
588 should be de-mangled once, into a tuple (and then selected from).
589 Otherwise the demangling can be in-line in the bindings (as here).
591 Boring! Boring! One error message per binder. The above ToDo is
592 even more helpful. Something very similar happens for pattern-bound
596 mkSelectorBinds :: LPat Id -- The pattern
597 -> CoreExpr -- Expression to which the pattern is bound
598 -> DsM [(Id,CoreExpr)]
600 mkSelectorBinds (L _ (VarPat v)) val_expr
601 = return [(v, val_expr)]
603 mkSelectorBinds pat val_expr
604 | isSingleton binders || is_simple_lpat pat = do
605 -- Given p = e, where p binds x,y
606 -- we are going to make
607 -- v = p (where v is fresh)
608 -- x = case v of p -> x
609 -- y = case v of p -> x
612 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
613 -- This does not matter after desugaring, but there's a subtle
614 -- issue with implicit parameters. Consider
616 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
617 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
618 -- does it get that type? So that when we abstract over it we get the
619 -- right top-level type (?i::Int) => ...)
621 -- So to get the type of 'v', use the pattern not the rhs. Often more
623 val_var <- newSysLocalDs (hsLPatType pat)
625 -- For the error message we make one error-app, to avoid duplication.
626 -- But we need it at different types... so we use coerce for that
627 err_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID unitTy (showSDoc (ppr pat))
628 err_var <- newSysLocalDs unitTy
629 binds <- mapM (mk_bind val_var err_var) binders
630 return ( (val_var, val_expr) :
631 (err_var, err_expr) :
636 error_expr <- mkErrorAppDs iRREFUT_PAT_ERROR_ID tuple_ty (showSDoc (ppr pat))
637 tuple_expr <- matchSimply val_expr PatBindRhs pat local_tuple error_expr
638 tuple_var <- newSysLocalDs tuple_ty
641 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
642 return ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
644 binders = collectPatBinders pat
645 local_tuple = mkBigCoreVarTup binders
646 tuple_ty = exprType local_tuple
648 mk_bind scrut_var err_var bndr_var = do
649 -- (mk_bind sv err_var) generates
650 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
651 -- Remember, pat binds bv
652 rhs_expr <- matchSimply (Var scrut_var) PatBindRhs pat
653 (Var bndr_var) error_expr
654 return (bndr_var, rhs_expr)
656 error_expr = mkCoerce co (Var err_var)
657 co = mkUnsafeCoercion (exprType (Var err_var)) (idType bndr_var)
659 is_simple_lpat p = is_simple_pat (unLoc p)
661 is_simple_pat (TuplePat ps Boxed _) = all is_triv_lpat ps
662 is_simple_pat (ConPatOut{ pat_args = ps }) = all is_triv_lpat (hsConPatArgs ps)
663 is_simple_pat (VarPat _) = True
664 is_simple_pat (ParPat p) = is_simple_lpat p
665 is_simple_pat _ = False
667 is_triv_lpat p = is_triv_pat (unLoc p)
669 is_triv_pat (VarPat _) = True
670 is_triv_pat (WildPat _) = True
671 is_triv_pat (ParPat p) = is_triv_lpat p
672 is_triv_pat _ = False
676 %************************************************************************
680 %************************************************************************
682 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
683 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
687 mkBigTuple :: ([a] -> a) -> [a] -> a
688 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
690 -- Each sub-list is short enough to fit in a tuple
691 mk_big_tuple [as] = small_tuple as
692 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
694 chunkify :: [a] -> [[a]]
695 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
696 -- But there may be more than mAX_TUPLE_SIZE sub-lists
698 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
699 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
703 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
707 Creating tuples and their types for Core expressions
709 @mkBigCoreVarTup@ builds a tuple; the inverse to @mkTupleSelector@.
711 * If it has only one element, it is the identity function.
713 * If there are more elements than a big tuple can have, it nests
718 -- Small tuples: build exactly the specified tuple
719 mkCoreVarTup :: [Id] -> CoreExpr
720 mkCoreVarTup ids = mkCoreTup (map Var ids)
722 mkCoreVarTupTy :: [Id] -> Type
723 mkCoreVarTupTy ids = mkCoreTupTy (map idType ids)
726 mkCoreTup :: [CoreExpr] -> CoreExpr
727 mkCoreTup [] = Var unitDataConId
729 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
730 (map (Type . exprType) cs ++ cs)
732 mkCoreTupTy :: [Type] -> Type
733 mkCoreTupTy [ty] = ty
734 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
739 mkBigCoreVarTup :: [Id] -> CoreExpr
740 mkBigCoreVarTup ids = mkBigCoreTup (map Var ids)
742 mkBigCoreVarTupTy :: [Id] -> Type
743 mkBigCoreVarTupTy ids = mkBigCoreTupTy (map idType ids)
746 mkBigCoreTup :: [CoreExpr] -> CoreExpr
747 mkBigCoreTup = mkBigTuple mkCoreTup
749 mkBigCoreTupTy :: [Type] -> Type
750 mkBigCoreTupTy = mkBigTuple mkCoreTupTy
754 Creating tuples and their types for full Haskell expressions
758 -- Smart constructors for source tuple expressions
759 mkLHsVarTup :: [Id] -> LHsExpr Id
760 mkLHsVarTup ids = mkLHsTup (map nlHsVar ids)
762 mkLHsTup :: [LHsExpr Id] -> LHsExpr Id
763 mkLHsTup [] = nlHsVar unitDataConId
764 mkLHsTup [lexp] = lexp
765 mkLHsTup lexps = noLoc $ ExplicitTuple lexps Boxed
768 -- Smart constructors for source tuple patterns
769 mkLHsVarPatTup :: [Id] -> LPat Id
770 mkLHsVarPatTup bs = mkLHsPatTup (map nlVarPat bs)
772 mkLHsPatTup :: [LPat Id] -> LPat Id
773 mkLHsPatTup [lpat] = lpat
774 mkLHsPatTup lpats = noLoc $ mkVanillaTuplePat lpats Boxed -- Handles the case where lpats = [] gracefully
777 -- The Big equivalents for the source tuple expressions
778 mkBigLHsVarTup :: [Id] -> LHsExpr Id
779 mkBigLHsVarTup ids = mkBigLHsTup (map nlHsVar ids)
781 mkBigLHsTup :: [LHsExpr Id] -> LHsExpr Id
782 mkBigLHsTup = mkBigTuple mkLHsTup
785 -- The Big equivalents for the source tuple patterns
786 mkBigLHsVarPatTup :: [Id] -> LPat Id
787 mkBigLHsVarPatTup bs = mkBigLHsPatTup (map nlVarPat bs)
789 mkBigLHsPatTup :: [LPat Id] -> LPat Id
790 mkBigLHsPatTup = mkBigTuple mkLHsPatTup
795 @mkTupleSelector@ builds a selector which scrutises the given
796 expression and extracts the one name from the list given.
797 If you want the no-shadowing rule to apply, the caller
798 is responsible for making sure that none of these names
801 If there is just one id in the ``tuple'', then the selector is
804 If it's big, it does nesting
805 mkTupleSelector [a,b,c,d] b v e
807 (p,q) -> case p of p {
809 We use 'tpl' vars for the p,q, since shadowing does not matter.
811 In fact, it's more convenient to generate it innermost first, getting
818 mkTupleSelector :: [Id] -- The tuple args
819 -> Id -- The selected one
820 -> Id -- A variable of the same type as the scrutinee
821 -> CoreExpr -- Scrutinee
824 mkTupleSelector vars the_var scrut_var scrut
825 = mk_tup_sel (chunkify vars) the_var
827 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
828 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
829 mk_tup_sel (chunkify tpl_vs) tpl_v
831 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
832 tpl_vs = mkTemplateLocals tpl_tys
833 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
837 A generalization of @mkTupleSelector@, allowing the body
838 of the case to be an arbitrary expression.
840 If the tuple is big, it is nested:
842 mkTupleCase uniqs [a,b,c,d] body v e
843 = case e of v { (p,q) ->
844 case p of p { (a,b) ->
845 case q of q { (c,d) ->
848 To avoid shadowing, we use uniqs to invent new variables p,q.
850 ToDo: eliminate cases where none of the variables are needed.
854 :: UniqSupply -- for inventing names of intermediate variables
855 -> [Id] -- the tuple args
856 -> CoreExpr -- body of the case
857 -> Id -- a variable of the same type as the scrutinee
858 -> CoreExpr -- scrutinee
861 mkTupleCase uniqs vars body scrut_var scrut
862 = mk_tuple_case uniqs (chunkify vars) body
864 -- This is the case where don't need any nesting
865 mk_tuple_case _ [vars] body
866 = mkSmallTupleCase vars body scrut_var scrut
868 -- This is the case where we must make nest tuples at least once
869 mk_tuple_case us vars_s body
870 = let (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
871 in mk_tuple_case us' (chunkify vars') body'
873 one_tuple_case chunk_vars (us, vs, body)
874 = let (us1, us2) = splitUniqSupply us
875 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
876 (mkCoreTupTy (map idType chunk_vars))
877 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
878 in (us2, scrut_var:vs, body')
881 The same, but with a tuple small enough not to need nesting.
885 :: [Id] -- the tuple args
886 -> CoreExpr -- body of the case
887 -> Id -- a variable of the same type as the scrutinee
888 -> CoreExpr -- scrutinee
891 mkSmallTupleCase [var] body _scrut_var scrut
892 = bindNonRec var scrut body
893 mkSmallTupleCase vars body scrut_var scrut
894 -- One branch no refinement?
895 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
898 %************************************************************************
900 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
902 %************************************************************************
904 Call the constructor Ids when building explicit lists, so that they
905 interact well with rules.
908 mkNilExpr :: Type -> CoreExpr
909 mkNilExpr ty = mkConApp nilDataCon [Type ty]
911 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
912 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
914 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
915 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
917 mkFoldrExpr :: PostTcType -> PostTcType -> CoreExpr -> CoreExpr -> CoreExpr -> DsM CoreExpr
918 mkFoldrExpr elt_ty result_ty c n list = do
919 foldr_id <- dsLookupGlobalId foldrName
920 return (Var foldr_id `App` Type elt_ty
926 mkBuildExpr :: Type -> ((Id, Type) -> (Id, Type) -> DsM CoreExpr) -> DsM CoreExpr
927 mkBuildExpr elt_ty mk_build_inside = do
928 [n_tyvar] <- newTyVarsDs [alphaTyVar]
929 let n_ty = mkTyVarTy n_tyvar
930 c_ty = mkFunTys [elt_ty, n_ty] n_ty
931 [c, n] <- newSysLocalsDs [c_ty, n_ty]
933 build_inside <- mk_build_inside (c, c_ty) (n, n_ty)
935 build_id <- dsLookupGlobalId buildName
936 return $ Var build_id `App` Type elt_ty `App` mkLams [n_tyvar, c, n] build_inside
938 mkCoreSel :: [Id] -- The tuple args
939 -> Id -- The selected one
940 -> Id -- A variable of the same type as the scrutinee
941 -> CoreExpr -- Scrutinee
944 -- mkCoreSel [x] x v e
946 mkCoreSel [var] should_be_the_same_var _ scrut
947 = ASSERT(var == should_be_the_same_var)
950 -- mkCoreSel [x,y,z] x v e
951 -- ===> case e of v { (x,y,z) -> x
952 mkCoreSel vars the_var scrut_var scrut
953 = ASSERT( notNull vars )
954 Case scrut scrut_var (idType the_var)
955 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
958 %************************************************************************
960 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
962 %************************************************************************
964 Generally, we handle pattern matching failure like this: let-bind a
965 fail-variable, and use that variable if the thing fails:
967 let fail.33 = error "Help"
978 If the case can't fail, then there'll be no mention of @fail.33@, and the
979 simplifier will later discard it.
982 If it can fail in only one way, then the simplifier will inline it.
985 Only if it is used more than once will the let-binding remain.
988 There's a problem when the result of the case expression is of
989 unboxed type. Then the type of @fail.33@ is unboxed too, and
990 there is every chance that someone will change the let into a case:
996 which is of course utterly wrong. Rather than drop the condition that
997 only boxed types can be let-bound, we just turn the fail into a function
998 for the primitive case:
1000 let fail.33 :: Void -> Int#
1001 fail.33 = \_ -> error "Help"
1010 Now @fail.33@ is a function, so it can be let-bound.
1013 mkFailurePair :: CoreExpr -- Result type of the whole case expression
1014 -> DsM (CoreBind, -- Binds the newly-created fail variable
1015 -- to either the expression or \ _ -> expression
1016 CoreExpr) -- Either the fail variable, or fail variable
1017 -- applied to unit tuple
1019 | isUnLiftedType ty = do
1020 fail_fun_var <- newFailLocalDs (unitTy `mkFunTy` ty)
1021 fail_fun_arg <- newSysLocalDs unitTy
1022 return (NonRec fail_fun_var (Lam fail_fun_arg expr),
1023 App (Var fail_fun_var) (Var unitDataConId))
1026 fail_var <- newFailLocalDs ty
1027 return (NonRec fail_var expr, Var fail_var)
1033 mkOptTickBox :: Maybe (Int,[Id]) -> CoreExpr -> DsM CoreExpr
1034 mkOptTickBox Nothing e = return e
1035 mkOptTickBox (Just (ix,ids)) e = mkTickBox ix ids e
1037 mkTickBox :: Int -> [Id] -> CoreExpr -> DsM CoreExpr
1038 mkTickBox ix vars e = do
1041 let tick | opt_Hpc = mkTickBoxOpId uq mod ix
1042 | otherwise = mkBreakPointOpId uq mod ix
1044 let occName = mkVarOcc "tick"
1045 let name = mkInternalName uq2 occName noSrcSpan -- use mkSysLocal?
1046 let var = Id.mkLocalId name realWorldStatePrimTy
1049 then return (Var tick)
1051 let tickVar = Var tick
1052 let tickType = mkFunTys (map idType vars) realWorldStatePrimTy
1053 let scrutApTy = App tickVar (Type tickType)
1054 return (mkApps scrutApTy (map Var vars) :: Expr Id)
1055 return $ Case scrut var ty [(DEFAULT,[],e)]
1059 mkBinaryTickBox :: Int -> Int -> CoreExpr -> DsM CoreExpr
1060 mkBinaryTickBox ixT ixF e = do
1062 let bndr1 = mkSysLocal FSLIT("t1") uq boolTy
1063 falseBox <- mkTickBox ixF [] $ Var falseDataConId
1064 trueBox <- mkTickBox ixT [] $ Var trueDataConId
1065 return $ Case e bndr1 boolTy
1066 [ (DataAlt falseDataCon, [], falseBox)
1067 , (DataAlt trueDataCon, [], trueBox)