2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsUtils]{Utilities for desugaring}
6 This module exports some utility functions of no great interest.
15 MatchResult(..), CanItFail(..),
16 cantFailMatchResult, alwaysFailMatchResult,
17 extractMatchResult, combineMatchResults,
18 adjustMatchResult, adjustMatchResultDs,
19 mkCoLetsMatchResult, mkCoLetMatchResult,
21 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
22 bindInMatchResult, bindOneInMatchResult,
24 mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr,
25 mkIntExpr, mkCharExpr,
26 mkStringExpr, mkStringExprFS, mkIntegerExpr,
28 mkSelectorBinds, mkTupleExpr, mkTupleSelector,
29 mkTupleType, mkTupleCase, mkBigCoreTup,
30 mkCoreTup, mkCoreTupTy,
32 dsReboundNames, lookupReboundName,
34 selectSimpleMatchVarL, selectMatchVars
37 #include "HsVersions.h"
39 import {-# SOURCE #-} Match ( matchSimply )
40 import {-# SOURCE #-} DsExpr( dsExpr )
43 import TcHsSyn ( hsPatType )
45 import Constants ( mAX_TUPLE_SIZE )
48 import CoreUtils ( exprType, mkIfThenElse, mkCoerce, bindNonRec )
49 import MkId ( iRREFUT_PAT_ERROR_ID, mkReboxingAlt, mkNewTypeBody )
50 import Id ( idType, Id, mkWildId, mkTemplateLocals, mkSysLocal )
53 import Literal ( Literal(..), mkStringLit, inIntRange, tARGET_MAX_INT )
54 import TyCon ( isNewTyCon, tyConDataCons )
55 import DataCon ( DataCon, dataConSourceArity, dataConTyCon )
56 import Type ( mkFunTy, isUnLiftedType, Type, splitTyConApp, mkTyVarTy )
57 import TcType ( tcTyConAppTyCon, tcEqType )
58 import TysPrim ( intPrimTy )
59 import TysWiredIn ( nilDataCon, consDataCon,
61 unitDataConId, unitTy,
65 import BasicTypes ( Boxity(..) )
66 import UniqSet ( mkUniqSet, minusUniqSet, isEmptyUniqSet )
67 import UniqSupply ( splitUniqSupply, uniqFromSupply, uniqsFromSupply )
68 import PrelNames ( unpackCStringName, unpackCStringUtf8Name,
69 plusIntegerName, timesIntegerName, smallIntegerDataConName,
70 lengthPName, indexPName )
72 import UnicodeUtil ( intsToUtf8 )
73 import SrcLoc ( Located(..), unLoc, noLoc )
74 import Util ( isSingleton, notNull, zipEqual )
75 import ListSetOps ( assocDefault )
81 %************************************************************************
85 %************************************************************************
88 dsReboundNames :: ReboundNames Id
89 -> DsM ([CoreBind], -- Auxiliary bindings
90 [(Name,Id)]) -- Maps the standard name to its value
92 dsReboundNames 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 lookupReboundName :: [(Name,Id)] -> Name -> CoreExpr
105 lookupReboundName prs std_name
106 = Var (assocDefault (mk_panic std_name) prs std_name)
108 mk_panic std_name = pprPanic "dsReboundNames" (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
124 | isUnLiftedType (idType bndr)
125 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
129 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
130 mkDsLets binds body = foldr mkDsLet body binds
134 %************************************************************************
136 \subsection{ Selecting match variables}
138 %************************************************************************
140 We're about to match against some patterns. We want to make some
141 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
142 hand, which should indeed be bound to the pattern as a whole, then use it;
143 otherwise, make one up.
146 selectSimpleMatchVarL :: LPat Id -> DsM Id
147 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat) (hsPatType pat)
149 -- (selectMatchVars ps tys) chooses variables of type tys
150 -- to use for matching ps against. If the pattern is a variable,
151 -- we try to use that, to save inventing lots of fresh variables.
152 -- But even if it is a variable, its type might not match. Consider
154 -- T1 :: Int -> T Int
157 -- f :: T a -> a -> Int
158 -- f (T1 i) (x::Int) = x
159 -- f (T2 i) (y::a) = 0
160 -- Then we must not choose (x::Int) as the matching variable!
162 selectMatchVars :: [Pat Id] -> [Type] -> DsM [Id]
163 selectMatchVars [] [] = return []
164 selectMatchVars (p:ps) (ty:tys) = do { v <- selectMatchVar p ty
165 ; vs <- selectMatchVars ps tys
168 selectMatchVar (LazyPat pat) pat_ty = selectMatchVar (unLoc pat) pat_ty
169 selectMatchVar (VarPat var) pat_ty = try_for var pat_ty
170 selectMatchVar (AsPat var pat) pat_ty = try_for (unLoc var) pat_ty
171 selectMatchVar other_pat pat_ty = newSysLocalDs pat_ty -- OK, better make up one...
174 | idType var `tcEqType` pat_ty = returnDs var
175 | otherwise = newSysLocalDs pat_ty
179 %************************************************************************
181 %* type synonym EquationInfo and access functions for its pieces *
183 %************************************************************************
184 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
186 The ``equation info'' used by @match@ is relatively complicated and
187 worthy of a type synonym and a few handy functions.
191 = EqnInfo { eqn_pats :: [Pat Id], -- The patterns for an eqn
192 eqn_rhs :: MatchResult } -- What to do after match
194 -- The semantics of (match vs (EqnInfo wrap pats rhs)) is the MatchResult
195 -- \fail. wrap (case vs of { pats -> rhs fail })
196 -- where vs are not in the domain of wrap
198 firstPat :: EquationInfo -> Pat Id
199 firstPat eqn = head (eqn_pats eqn)
201 shiftEqns :: [EquationInfo] -> [EquationInfo]
202 -- Drop the outermost layer of the first pattern in each equation
203 shiftEqns eqns = [ eqn { eqn_pats = shiftPats (eqn_pats eqn) }
206 shiftPats :: [Pat Id] -> [Pat Id]
207 shiftPats (ConPatOut _ _ _ _ (PrefixCon arg_pats) _ : pats) = map unLoc arg_pats ++ pats
208 shiftPats (pat_with_no_sub_pats : pats) = pats
213 -- A MatchResult is an expression with a hole in it
216 CanItFail -- Tells whether the failure expression is used
217 (CoreExpr -> DsM CoreExpr)
218 -- Takes a expression to plug in at the
219 -- failure point(s). The expression should
222 data CanItFail = CanFail | CantFail
224 orFail CantFail CantFail = CantFail
228 Functions on MatchResults
231 alwaysFailMatchResult :: MatchResult
232 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
234 cantFailMatchResult :: CoreExpr -> MatchResult
235 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
237 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
238 extractMatchResult (MatchResult CantFail match_fn) fail_expr
239 = match_fn (error "It can't fail!")
241 extractMatchResult (MatchResult CanFail match_fn) fail_expr
242 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
243 match_fn if_it_fails `thenDs` \ body ->
244 returnDs (mkDsLet fail_bind body)
247 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
248 combineMatchResults (MatchResult CanFail body_fn1)
249 (MatchResult can_it_fail2 body_fn2)
250 = MatchResult can_it_fail2 body_fn
252 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
253 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
254 body_fn1 duplicatable_expr `thenDs` \ body1 ->
255 returnDs (Let fail_bind body1)
257 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
260 adjustMatchResult :: (CoreExpr -> CoreExpr) -> MatchResult -> MatchResult
261 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
262 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
263 returnDs (encl_fn body))
265 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
266 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
267 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
270 bindInMatchResult :: [(Var,Var)] -> MatchResult -> MatchResult
271 bindInMatchResult binds = adjustMatchResult (\e -> foldr bind e binds)
273 bind (new,old) body = bindMR new old body
275 bindOneInMatchResult :: Var -> Var -> MatchResult -> MatchResult
276 bindOneInMatchResult new old = adjustMatchResult (bindMR new old)
278 bindMR :: Var -> Var -> CoreExpr -> CoreExpr
281 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
282 | otherwise = Let (NonRec new (Var old)) body
284 mkCoLetsMatchResult :: [CoreBind] -> MatchResult -> MatchResult
285 mkCoLetsMatchResult binds match_result
286 = adjustMatchResult (mkDsLets binds) match_result
288 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
289 mkCoLetMatchResult bind match_result
290 = adjustMatchResult (mkDsLet bind) match_result
292 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
293 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
294 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
295 returnDs (mkIfThenElse pred_expr body fail))
297 mkCoPrimCaseMatchResult :: Id -- Scrutinee
298 -> Type -- Type of the case
299 -> [(Literal, MatchResult)] -- Alternatives
301 mkCoPrimCaseMatchResult var ty match_alts
302 = MatchResult CanFail mk_case
305 = mappM (mk_alt fail) match_alts `thenDs` \ alts ->
306 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
308 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
309 returnDs (LitAlt lit, [], body)
312 mkCoAlgCaseMatchResult :: Id -- Scrutinee
313 -> Type -- Type of exp
314 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
316 mkCoAlgCaseMatchResult var ty match_alts
317 | isNewTyCon tycon -- Newtype case; use a let
318 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
319 mkCoLetsMatchResult [NonRec arg_id1 newtype_rhs] match_result1
321 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
322 = MatchResult CanFail mk_parrCase
324 | otherwise -- Datatype case; use a case
325 = MatchResult fail_flag mk_case
327 tycon = dataConTyCon con1
328 -- [Interesting: becuase of GADTs, we can't rely on the type of
329 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
332 (con1, arg_ids1, match_result1) = head match_alts
333 arg_id1 = head arg_ids1
334 newtype_rhs = mkNewTypeBody tycon (idType arg_id1) (Var var)
336 -- Stuff for data types
337 data_cons = tyConDataCons tycon
338 match_results = [match_result | (_,_,match_result) <- match_alts]
340 fail_flag | exhaustive_case
341 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
345 wild_var = mkWildId (idType var)
346 mk_case fail = mappM (mk_alt fail) match_alts `thenDs` \ alts ->
347 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
349 mk_alt fail (con, args, MatchResult _ body_fn)
350 = body_fn fail `thenDs` \ body ->
351 newUniqueSupply `thenDs` \ us ->
352 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
354 mk_default fail | exhaustive_case = []
355 | otherwise = [(DEFAULT, [], fail)]
357 un_mentioned_constructors
358 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
359 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
361 -- Stuff for parallel arrays
363 -- * the following is to desugar cases over fake constructors for
364 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
367 -- Concerning `isPArrFakeAlts':
369 -- * it is *not* sufficient to just check the type of the type
370 -- constructor, as we have to be careful not to confuse the real
371 -- representation of parallel arrays with the fake constructors;
372 -- moreover, a list of alternatives must not mix fake and real
373 -- constructors (this is checked earlier on)
375 -- FIXME: We actually go through the whole list and make sure that
376 -- either all or none of the constructors are fake parallel
377 -- array constructors. This is to spot equations that mix fake
378 -- constructors with the real representation defined in
379 -- `PrelPArr'. It would be nicer to spot this situation
380 -- earlier and raise a proper error message, but it can really
381 -- only happen in `PrelPArr' anyway.
383 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
384 isPArrFakeAlts ((dcon, _, _):alts) =
385 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
386 (True , True ) -> True
387 (False, False) -> False
389 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
392 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
393 unboxAlt `thenDs` \alt ->
394 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
396 elemTy = case splitTyConApp (idType var) of
397 (_, [elemTy]) -> elemTy
399 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
400 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
403 newSysLocalDs intPrimTy `thenDs` \l ->
404 dsLookupGlobalId indexPName `thenDs` \indexP ->
405 mappM (mkAlt indexP) match_alts `thenDs` \alts ->
406 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
408 wild = mkWildId intPrimTy
409 dft = (DEFAULT, [], fail)
411 -- each alternative matches one array length (corresponding to one
412 -- fake array constructor), so the match is on a literal; each
413 -- alternative's body is extended by a local binding for each
414 -- constructor argument, which are bound to array elements starting
417 mkAlt indexP (con, args, MatchResult _ bodyFun) =
418 bodyFun fail `thenDs` \body ->
419 returnDs (LitAlt lit, [], mkDsLets binds body)
421 lit = MachInt $ toInteger (dataConSourceArity con)
422 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
424 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
428 %************************************************************************
430 \subsection{Desugarer's versions of some Core functions}
432 %************************************************************************
435 mkErrorAppDs :: Id -- The error function
436 -> Type -- Type to which it should be applied
437 -> String -- The error message string to pass
440 mkErrorAppDs err_id ty msg
441 = getSrcSpanDs `thenDs` \ src_loc ->
443 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
444 core_msg = Lit (mkStringLit full_msg)
446 returnDs (mkApps (Var err_id) [Type ty, core_msg])
450 *************************************************************
452 \subsection{Making literals}
454 %************************************************************************
457 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
458 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
459 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
460 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
461 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
463 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
464 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
467 | inIntRange i -- Small enough, so start from an Int
468 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
469 returnDs (mkSmallIntegerLit integer_dc i)
471 -- Special case for integral literals with a large magnitude:
472 -- They are transformed into an expression involving only smaller
473 -- integral literals. This improves constant folding.
475 | otherwise -- Big, so start from a string
476 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
477 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
478 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
480 lit i = mkSmallIntegerLit integer_dc i
481 plus a b = Var plus_id `App` a `App` b
482 times a b = Var times_id `App` a `App` b
484 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
485 horner :: Integer -> Integer -> CoreExpr
486 horner b i | abs q <= 1 = if r == 0 || r == i
488 else lit r `plus` lit (i-r)
489 | r == 0 = horner b q `times` lit b
490 | otherwise = lit r `plus` (horner b q `times` lit b)
492 (q,r) = i `quotRem` b
495 returnDs (horner tARGET_MAX_INT i)
497 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
499 mkStringExpr str = mkStringExprFS (mkFastString str)
503 = returnDs (mkNilExpr charTy)
507 the_char = mkCharExpr (headFS str)
509 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
511 | all safeChar int_chars
512 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
513 returnDs (App (Var unpack_id) (Lit (MachStr str)))
516 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
517 returnDs (App (Var unpack_id) (Lit (MachStr (mkFastString (intsToUtf8 int_chars)))))
520 int_chars = unpackIntFS str
521 safeChar c = c >= 1 && c <= 0xFF
525 %************************************************************************
527 \subsection[mkSelectorBind]{Make a selector bind}
529 %************************************************************************
531 This is used in various places to do with lazy patterns.
532 For each binder $b$ in the pattern, we create a binding:
534 b = case v of pat' -> b'
536 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
538 ToDo: making these bindings should really depend on whether there's
539 much work to be done per binding. If the pattern is complex, it
540 should be de-mangled once, into a tuple (and then selected from).
541 Otherwise the demangling can be in-line in the bindings (as here).
543 Boring! Boring! One error message per binder. The above ToDo is
544 even more helpful. Something very similar happens for pattern-bound
548 mkSelectorBinds :: LPat Id -- The pattern
549 -> CoreExpr -- Expression to which the pattern is bound
550 -> DsM [(Id,CoreExpr)]
552 mkSelectorBinds (L _ (VarPat v)) val_expr
553 = returnDs [(v, val_expr)]
555 mkSelectorBinds pat val_expr
556 | isSingleton binders || is_simple_lpat pat
557 = -- Given p = e, where p binds x,y
558 -- we are going to make
559 -- v = p (where v is fresh)
560 -- x = case v of p -> x
561 -- y = case v of p -> x
564 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
565 -- This does not matter after desugaring, but there's a subtle
566 -- issue with implicit parameters. Consider
568 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
569 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
570 -- does it get that type? So that when we abstract over it we get the
571 -- right top-level type (?i::Int) => ...)
573 -- So to get the type of 'v', use the pattern not the rhs. Often more
575 newSysLocalDs (hsPatType pat) `thenDs` \ val_var ->
577 -- For the error message we make one error-app, to avoid duplication.
578 -- But we need it at different types... so we use coerce for that
579 mkErrorAppDs iRREFUT_PAT_ERROR_ID
580 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
581 newSysLocalDs unitTy `thenDs` \ err_var ->
582 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
583 returnDs ( (val_var, val_expr) :
584 (err_var, err_expr) :
589 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
590 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
591 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
592 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
595 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
597 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
599 binders = collectPatBinders pat
600 local_tuple = mkTupleExpr binders
601 tuple_ty = exprType local_tuple
603 mk_bind scrut_var err_var bndr_var
604 -- (mk_bind sv err_var) generates
605 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
606 -- Remember, pat binds bv
607 = matchSimply (Var scrut_var) PatBindRhs pat
608 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
609 returnDs (bndr_var, rhs_expr)
611 error_expr = mkCoerce (idType bndr_var) (Var err_var)
613 is_simple_lpat p = is_simple_pat (unLoc p)
615 is_simple_pat (TuplePat ps Boxed) = all is_triv_lpat ps
616 is_simple_pat (ConPatOut _ _ _ _ ps _) = all is_triv_lpat (hsConArgs ps)
617 is_simple_pat (VarPat _) = True
618 is_simple_pat (ParPat p) = is_simple_lpat p
619 is_simple_pat other = False
621 is_triv_lpat p = is_triv_pat (unLoc p)
623 is_triv_pat (VarPat v) = True
624 is_triv_pat (WildPat _) = True
625 is_triv_pat (ParPat p) = is_triv_lpat p
626 is_triv_pat other = False
630 %************************************************************************
634 %************************************************************************
636 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
638 * If it has only one element, it is the identity function.
640 * If there are more elements than a big tuple can have, it nests
643 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
644 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
647 mkTupleExpr :: [Id] -> CoreExpr
648 mkTupleExpr ids = mkBigCoreTup (map Var ids)
650 -- corresponding type
651 mkTupleType :: [Id] -> Type
652 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
654 mkBigCoreTup :: [CoreExpr] -> CoreExpr
655 mkBigCoreTup = mkBigTuple mkCoreTup
657 mkBigTuple :: ([a] -> a) -> [a] -> a
658 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
660 -- Each sub-list is short enough to fit in a tuple
661 mk_big_tuple [as] = small_tuple as
662 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
664 chunkify :: [a] -> [[a]]
665 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
666 -- But there may be more than mAX_TUPLE_SIZE sub-lists
668 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
669 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
673 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
677 @mkTupleSelector@ builds a selector which scrutises the given
678 expression and extracts the one name from the list given.
679 If you want the no-shadowing rule to apply, the caller
680 is responsible for making sure that none of these names
683 If there is just one id in the ``tuple'', then the selector is
686 If it's big, it does nesting
687 mkTupleSelector [a,b,c,d] b v e
689 (p,q) -> case p of p {
691 We use 'tpl' vars for the p,q, since shadowing does not matter.
693 In fact, it's more convenient to generate it innermost first, getting
700 mkTupleSelector :: [Id] -- The tuple args
701 -> Id -- The selected one
702 -> Id -- A variable of the same type as the scrutinee
703 -> CoreExpr -- Scrutinee
706 mkTupleSelector vars the_var scrut_var scrut
707 = mk_tup_sel (chunkify vars) the_var
709 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
710 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
711 mk_tup_sel (chunkify tpl_vs) tpl_v
713 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
714 tpl_vs = mkTemplateLocals tpl_tys
715 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
719 A generalization of @mkTupleSelector@, allowing the body
720 of the case to be an arbitrary expression.
722 If the tuple is big, it is nested:
724 mkTupleCase uniqs [a,b,c,d] body v e
725 = case e of v { (p,q) ->
726 case p of p { (a,b) ->
727 case q of q { (c,d) ->
730 To avoid shadowing, we use uniqs to invent new variables p,q.
732 ToDo: eliminate cases where none of the variables are needed.
736 :: UniqSupply -- for inventing names of intermediate variables
737 -> [Id] -- the tuple args
738 -> CoreExpr -- body of the case
739 -> Id -- a variable of the same type as the scrutinee
740 -> CoreExpr -- scrutinee
743 mkTupleCase uniqs vars body scrut_var scrut
744 = mk_tuple_case uniqs (chunkify vars) body
746 mk_tuple_case us [vars] body
747 = mkSmallTupleCase vars body scrut_var scrut
748 mk_tuple_case us vars_s body
750 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
752 mk_tuple_case us' (chunkify vars') body'
753 one_tuple_case chunk_vars (us, vs, body)
755 (us1, us2) = splitUniqSupply us
756 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
757 (mkCoreTupTy (map idType chunk_vars))
758 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
759 in (us2, scrut_var:vs, body')
762 The same, but with a tuple small enough not to need nesting.
766 :: [Id] -- the tuple args
767 -> CoreExpr -- body of the case
768 -> Id -- a variable of the same type as the scrutinee
769 -> CoreExpr -- scrutinee
772 mkSmallTupleCase [var] body _scrut_var scrut
773 = bindNonRec var scrut body
774 mkSmallTupleCase vars body scrut_var scrut
776 -- One branch no refinement?
777 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
780 %************************************************************************
782 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
784 %************************************************************************
786 Call the constructor Ids when building explicit lists, so that they
787 interact well with rules.
790 mkNilExpr :: Type -> CoreExpr
791 mkNilExpr ty = mkConApp nilDataCon [Type ty]
793 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
794 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
796 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
797 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
800 -- The next three functions make tuple types, constructors and selectors,
801 -- with the rule that a 1-tuple is represented by the thing itselg
802 mkCoreTupTy :: [Type] -> Type
803 mkCoreTupTy [ty] = ty
804 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
806 mkCoreTup :: [CoreExpr] -> CoreExpr
807 -- Builds exactly the specified tuple.
808 -- No fancy business for big tuples
809 mkCoreTup [] = Var unitDataConId
811 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
812 (map (Type . exprType) cs ++ cs)
814 mkCoreSel :: [Id] -- The tuple args
815 -> Id -- The selected one
816 -> Id -- A variable of the same type as the scrutinee
817 -> CoreExpr -- Scrutinee
819 -- mkCoreSel [x,y,z] x v e
820 -- ===> case e of v { (x,y,z) -> x
821 mkCoreSel [var] should_be_the_same_var scrut_var scrut
822 = ASSERT(var == should_be_the_same_var)
825 mkCoreSel vars the_var scrut_var scrut
826 = ASSERT( notNull vars )
828 Case scrut scrut_var (idType the_var)
829 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
833 %************************************************************************
835 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
837 %************************************************************************
839 Generally, we handle pattern matching failure like this: let-bind a
840 fail-variable, and use that variable if the thing fails:
842 let fail.33 = error "Help"
853 If the case can't fail, then there'll be no mention of @fail.33@, and the
854 simplifier will later discard it.
857 If it can fail in only one way, then the simplifier will inline it.
860 Only if it is used more than once will the let-binding remain.
863 There's a problem when the result of the case expression is of
864 unboxed type. Then the type of @fail.33@ is unboxed too, and
865 there is every chance that someone will change the let into a case:
871 which is of course utterly wrong. Rather than drop the condition that
872 only boxed types can be let-bound, we just turn the fail into a function
873 for the primitive case:
875 let fail.33 :: Void -> Int#
876 fail.33 = \_ -> error "Help"
885 Now @fail.33@ is a function, so it can be let-bound.
888 mkFailurePair :: CoreExpr -- Result type of the whole case expression
889 -> DsM (CoreBind, -- Binds the newly-created fail variable
890 -- to either the expression or \ _ -> expression
891 CoreExpr) -- Either the fail variable, or fail variable
892 -- applied to unit tuple
895 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
896 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
897 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
898 App (Var fail_fun_var) (Var unitDataConId))
901 = newFailLocalDs ty `thenDs` \ fail_var ->
902 returnDs (NonRec fail_var expr, Var fail_var)