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.
10 CanItFail(..), EquationInfo(..), MatchResult(..),
17 cantFailMatchResult, extractMatchResult,
19 adjustMatchResult, adjustMatchResultDs,
20 mkCoLetsMatchResult, mkGuardedMatchResult,
21 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
23 mkErrorAppDs, mkNilExpr, mkConsExpr,
24 mkStringLit, mkStringLitFS, mkIntegerLit,
26 mkSelectorBinds, mkTupleExpr, mkTupleSelector,
31 #include "HsVersions.h"
33 import {-# SOURCE #-} Match ( matchSimply )
36 import TcHsSyn ( TypecheckedPat, outPatType, collectTypedPatBinders )
41 import CoreUtils ( exprType, mkIfThenElse, mkCoerce )
42 import PrelInfo ( iRREFUT_PAT_ERROR_ID )
43 import MkId ( mkReboxingAlt, mkNewTypeBody )
44 import Id ( idType, Id, mkWildId )
45 import Literal ( Literal(..), inIntRange, tARGET_MAX_INT )
46 import TyCon ( isNewTyCon, tyConDataCons, isRecursiveTyCon )
47 import DataCon ( DataCon, dataConSourceArity )
48 import Type ( mkFunTy, isUnLiftedType, Type, splitTyConApp )
49 import TcType ( tcTyConAppTyCon, isIntTy, isFloatTy, isDoubleTy )
50 import TysPrim ( intPrimTy, charPrimTy, floatPrimTy, doublePrimTy )
51 import TysWiredIn ( nilDataCon, consDataCon,
53 unitDataConId, unitTy,
55 intTy, intDataCon, smallIntegerDataCon,
58 stringTy, isPArrFakeCon )
59 import BasicTypes ( Boxity(..) )
60 import UniqSet ( mkUniqSet, minusUniqSet, isEmptyUniqSet, UniqSet )
61 import PrelNames ( unpackCStringName, unpackCStringUtf8Name,
62 plusIntegerName, timesIntegerName,
63 lengthPName, indexPName )
65 import UnicodeUtil ( intsToUtf8, stringToUtf8 )
66 import Util ( isSingleton, notNull )
72 %************************************************************************
74 \subsection{Tidying lit pats}
76 %************************************************************************
79 tidyLitPat :: HsLit -> TypecheckedPat -> TypecheckedPat
80 tidyLitPat (HsChar c) pat = ConPat charDataCon charTy [] [] [LitPat (HsCharPrim c) charPrimTy]
81 tidyLitPat lit pat = pat
83 tidyNPat :: HsLit -> Type -> TypecheckedPat -> TypecheckedPat
84 tidyNPat (HsString s) _ pat
85 | lengthFS s <= 1 -- Short string literals only
86 = foldr (\c pat -> ConPat consDataCon stringTy [] [] [mk_char_lit c,pat])
87 (ConPat nilDataCon stringTy [] [] []) (unpackIntFS s)
88 -- The stringTy is the type of the whole pattern, not
89 -- the type to instantiate (:) or [] with!
91 mk_char_lit c = ConPat charDataCon charTy [] [] [LitPat (HsCharPrim c) charPrimTy]
93 tidyNPat lit lit_ty default_pat
94 | isIntTy lit_ty = ConPat intDataCon lit_ty [] [] [LitPat (mk_int lit) intPrimTy]
95 | isFloatTy lit_ty = ConPat floatDataCon lit_ty [] [] [LitPat (mk_float lit) floatPrimTy]
96 | isDoubleTy lit_ty = ConPat doubleDataCon lit_ty [] [] [LitPat (mk_double lit) doublePrimTy]
97 | otherwise = default_pat
100 mk_int (HsInteger i) = HsIntPrim i
102 mk_float (HsInteger i) = HsFloatPrim (fromInteger i)
103 mk_float (HsRat f _) = HsFloatPrim f
105 mk_double (HsInteger i) = HsDoublePrim (fromInteger i)
106 mk_double (HsRat f _) = HsDoublePrim f
110 %************************************************************************
112 \subsection{Building lets}
114 %************************************************************************
116 Use case, not let for unlifted types. The simplifier will turn some
120 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
121 mkDsLet (NonRec bndr rhs) body
122 | isUnLiftedType (idType bndr) = Case rhs bndr [(DEFAULT,[],body)]
126 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
127 mkDsLets binds body = foldr mkDsLet body binds
131 %************************************************************************
133 \subsection{ Selecting match variables}
135 %************************************************************************
137 We're about to match against some patterns. We want to make some
138 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
139 hand, which should indeed be bound to the pattern as a whole, then use it;
140 otherwise, make one up.
143 selectMatchVar :: TypecheckedPat -> DsM Id
144 selectMatchVar (VarPat var) = returnDs var
145 selectMatchVar (AsPat var pat) = returnDs var
146 selectMatchVar (LazyPat pat) = selectMatchVar pat
147 selectMatchVar other_pat = newSysLocalDs (outPatType other_pat) -- OK, better make up one...
151 %************************************************************************
153 %* type synonym EquationInfo and access functions for its pieces *
155 %************************************************************************
156 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
158 The ``equation info'' used by @match@ is relatively complicated and
159 worthy of a type synonym and a few handy functions.
164 type EqnSet = UniqSet EqnNo
168 EqnNo -- The number of the equation
170 DsMatchContext -- The context info is used when producing warnings
171 -- about shadowed patterns. It's the context
172 -- of the *first* thing matched in this group.
173 -- Should perhaps be a list of them all!
175 [TypecheckedPat] -- The patterns for an eqn
177 MatchResult -- Encapsulates the guards and bindings
183 CanItFail -- Tells whether the failure expression is used
184 (CoreExpr -> DsM CoreExpr)
185 -- Takes a expression to plug in at the
186 -- failure point(s). The expression should
189 data CanItFail = CanFail | CantFail
191 orFail CantFail CantFail = CantFail
195 Functions on MatchResults
198 cantFailMatchResult :: CoreExpr -> MatchResult
199 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
201 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
202 extractMatchResult (MatchResult CantFail match_fn) fail_expr
203 = match_fn (error "It can't fail!")
205 extractMatchResult (MatchResult CanFail match_fn) fail_expr
206 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
207 match_fn if_it_fails `thenDs` \ body ->
208 returnDs (mkDsLet fail_bind body)
211 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
212 combineMatchResults (MatchResult CanFail body_fn1)
213 (MatchResult can_it_fail2 body_fn2)
214 = MatchResult can_it_fail2 body_fn
216 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
217 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
218 body_fn1 duplicatable_expr `thenDs` \ body1 ->
219 returnDs (Let fail_bind body1)
221 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
225 adjustMatchResult :: (CoreExpr -> CoreExpr) -> MatchResult -> MatchResult
226 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
227 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
228 returnDs (encl_fn body))
230 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
231 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
232 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
236 mkCoLetsMatchResult :: [CoreBind] -> MatchResult -> MatchResult
237 mkCoLetsMatchResult binds match_result
238 = adjustMatchResult (mkDsLets binds) match_result
241 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
242 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
243 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
244 returnDs (mkIfThenElse pred_expr body fail))
246 mkCoPrimCaseMatchResult :: Id -- Scrutinee
247 -> [(Literal, MatchResult)] -- Alternatives
249 mkCoPrimCaseMatchResult var match_alts
250 = MatchResult CanFail mk_case
253 = mapDs (mk_alt fail) match_alts `thenDs` \ alts ->
254 returnDs (Case (Var var) var ((DEFAULT, [], fail) : alts))
256 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
257 returnDs (LitAlt lit, [], body)
260 mkCoAlgCaseMatchResult :: Id -- Scrutinee
261 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
264 mkCoAlgCaseMatchResult var match_alts
265 | isNewTyCon tycon -- Newtype case; use a let
266 = ASSERT( null (tail match_alts) && null (tail arg_ids) )
267 mkCoLetsMatchResult [NonRec arg_id newtype_rhs] match_result
269 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
270 = MatchResult CanFail mk_parrCase
272 | otherwise -- Datatype case; use a case
273 = MatchResult fail_flag mk_case
276 scrut_ty = idType var
277 tycon = tcTyConAppTyCon scrut_ty -- Newtypes must be opaque here
280 (_, arg_ids, match_result) = head match_alts
281 arg_id = head arg_ids
282 newtype_rhs = mkNewTypeBody tycon (idType arg_id) (Var var)
284 -- Stuff for data types
285 data_cons = tyConDataCons tycon
286 match_results = [match_result | (_,_,match_result) <- match_alts]
288 fail_flag | exhaustive_case
289 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
293 wild_var = mkWildId (idType var)
294 mk_case fail = mapDs (mk_alt fail) match_alts `thenDs` \ alts ->
295 returnDs (Case (Var var) wild_var (mk_default fail ++ alts))
297 mk_alt fail (con, args, MatchResult _ body_fn)
298 = body_fn fail `thenDs` \ body ->
299 getUniquesDs `thenDs` \ us ->
300 returnDs (mkReboxingAlt us con args body)
302 mk_default fail | exhaustive_case = []
303 | otherwise = [(DEFAULT, [], fail)]
305 un_mentioned_constructors
306 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
307 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
309 -- Stuff for parallel arrays
311 -- * the following is to desugar cases over fake constructors for
312 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
315 -- Concerning `isPArrFakeAlts':
317 -- * it is *not* sufficient to just check the type of the type
318 -- constructor, as we have to be careful not to confuse the real
319 -- representation of parallel arrays with the fake constructors;
320 -- moreover, a list of alternatives must not mix fake and real
321 -- constructors (this is checked earlier on)
323 -- FIXME: We actually go through the whole list and make sure that
324 -- either all or none of the constructors are fake parallel
325 -- array constructors. This is to spot equations that mix fake
326 -- constructors with the real representation defined in
327 -- `PrelPArr'. It would be nicer to spot this situation
328 -- earlier and raise a proper error message, but it can really
329 -- only happen in `PrelPArr' anyway.
331 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
332 isPArrFakeAlts ((dcon, _, _):alts) =
333 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
334 (True , True ) -> True
335 (False, False) -> False
337 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
340 dsLookupGlobalValue lengthPName `thenDs` \lengthP ->
341 unboxAlt `thenDs` \alt ->
342 returnDs (Case (len lengthP) (mkWildId intTy) [alt])
344 elemTy = case splitTyConApp (idType var) of
345 (_, [elemTy]) -> elemTy
347 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
348 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
351 newSysLocalDs intPrimTy `thenDs` \l ->
352 dsLookupGlobalValue indexPName `thenDs` \indexP ->
353 mapDs (mkAlt indexP) match_alts `thenDs` \alts ->
354 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild (dft : alts)))
356 wild = mkWildId intPrimTy
357 dft = (DEFAULT, [], fail)
359 -- each alternative matches one array length (corresponding to one
360 -- fake array constructor), so the match is on a literal; each
361 -- alternative's body is extended by a local binding for each
362 -- constructor argument, which are bound to array elements starting
365 mkAlt indexP (con, args, MatchResult _ bodyFun) =
366 bodyFun fail `thenDs` \body ->
367 returnDs (LitAlt lit, [], mkDsLets binds body)
369 lit = MachInt $ toInteger (dataConSourceArity con)
370 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
372 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, toInt i]
373 toInt i = mkConApp intDataCon [Lit $ MachInt i]
377 %************************************************************************
379 \subsection{Desugarer's versions of some Core functions}
381 %************************************************************************
384 mkErrorAppDs :: Id -- The error function
385 -> Type -- Type to which it should be applied
386 -> String -- The error message string to pass
389 mkErrorAppDs err_id ty msg
390 = getSrcLocDs `thenDs` \ src_loc ->
392 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
393 core_msg = Lit (MachStr (mkFastString (stringToUtf8 full_msg)))
395 returnDs (mkApps (Var err_id) [Type ty, core_msg])
399 *************************************************************
401 \subsection{Making literals}
403 %************************************************************************
406 mkIntegerLit :: Integer -> DsM CoreExpr
408 | inIntRange i -- Small enough, so start from an Int
409 = returnDs (mkSmallIntegerLit i)
411 -- Special case for integral literals with a large magnitude:
412 -- They are transformed into an expression involving only smaller
413 -- integral literals. This improves constant folding.
415 | otherwise -- Big, so start from a string
416 = dsLookupGlobalValue plusIntegerName `thenDs` \ plus_id ->
417 dsLookupGlobalValue timesIntegerName `thenDs` \ times_id ->
419 plus a b = Var plus_id `App` a `App` b
420 times a b = Var times_id `App` a `App` b
422 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
423 horner :: Integer -> Integer -> CoreExpr
424 horner b i | abs q <= 1 = if r == 0 || r == i
425 then mkSmallIntegerLit i
426 else mkSmallIntegerLit r `plus` mkSmallIntegerLit (i-r)
427 | r == 0 = horner b q `times` mkSmallIntegerLit b
428 | otherwise = mkSmallIntegerLit r `plus` (horner b q `times` mkSmallIntegerLit b)
430 (q,r) = i `quotRem` b
433 returnDs (horner tARGET_MAX_INT i)
435 mkSmallIntegerLit i = mkConApp smallIntegerDataCon [mkIntLit i]
437 mkStringLit :: String -> DsM CoreExpr
438 mkStringLit str = mkStringLitFS (mkFastString str)
440 mkStringLitFS :: FastString -> DsM CoreExpr
443 = returnDs (mkNilExpr charTy)
447 the_char = mkConApp charDataCon [mkLit (MachChar (headIntFS str))]
449 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
451 | all safeChar int_chars
452 = dsLookupGlobalValue unpackCStringName `thenDs` \ unpack_id ->
453 returnDs (App (Var unpack_id) (Lit (MachStr str)))
456 = dsLookupGlobalValue unpackCStringUtf8Name `thenDs` \ unpack_id ->
457 returnDs (App (Var unpack_id) (Lit (MachStr (mkFastString (intsToUtf8 int_chars)))))
460 int_chars = unpackIntFS str
461 safeChar c = c >= 1 && c <= 0xFF
465 %************************************************************************
467 \subsection[mkSelectorBind]{Make a selector bind}
469 %************************************************************************
471 This is used in various places to do with lazy patterns.
472 For each binder $b$ in the pattern, we create a binding:
474 b = case v of pat' -> b'
476 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
478 ToDo: making these bindings should really depend on whether there's
479 much work to be done per binding. If the pattern is complex, it
480 should be de-mangled once, into a tuple (and then selected from).
481 Otherwise the demangling can be in-line in the bindings (as here).
483 Boring! Boring! One error message per binder. The above ToDo is
484 even more helpful. Something very similar happens for pattern-bound
488 mkSelectorBinds :: TypecheckedPat -- The pattern
489 -> CoreExpr -- Expression to which the pattern is bound
490 -> DsM [(Id,CoreExpr)]
492 mkSelectorBinds (VarPat v) val_expr
493 = returnDs [(v, val_expr)]
495 mkSelectorBinds pat val_expr
496 | isSingleton binders || is_simple_pat pat
497 = newSysLocalDs (exprType val_expr) `thenDs` \ val_var ->
499 -- For the error message we make one error-app, to avoid duplication.
500 -- But we need it at different types... so we use coerce for that
501 mkErrorAppDs iRREFUT_PAT_ERROR_ID
502 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
503 newSysLocalDs unitTy `thenDs` \ err_var ->
504 mapDs (mk_bind val_var err_var) binders `thenDs` \ binds ->
505 returnDs ( (val_var, val_expr) :
506 (err_var, err_expr) :
511 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
512 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
513 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
514 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
517 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
519 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
521 binders = collectTypedPatBinders pat
522 local_tuple = mkTupleExpr binders
523 tuple_ty = exprType local_tuple
525 mk_bind scrut_var err_var bndr_var
526 -- (mk_bind sv err_var) generates
527 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
528 -- Remember, pat binds bv
529 = matchSimply (Var scrut_var) PatBindRhs pat
530 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
531 returnDs (bndr_var, rhs_expr)
533 error_expr = mkCoerce (idType bndr_var) (Var err_var)
535 is_simple_pat (TuplePat ps Boxed) = all is_triv_pat ps
536 is_simple_pat (ConPat _ _ _ _ ps) = all is_triv_pat ps
537 is_simple_pat (VarPat _) = True
538 is_simple_pat (RecPat _ _ _ _ ps) = and [is_triv_pat p | (_,p,_) <- ps]
539 is_simple_pat other = False
541 is_triv_pat (VarPat v) = True
542 is_triv_pat (WildPat _) = True
543 is_triv_pat other = False
547 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@. If it
548 has only one element, it is the identity function.
551 mkTupleExpr :: [Id] -> CoreExpr
553 mkTupleExpr [] = Var unitDataConId
554 mkTupleExpr [id] = Var id
555 mkTupleExpr ids = mkConApp (tupleCon Boxed (length ids))
556 (map (Type . idType) ids ++ [ Var i | i <- ids ])
560 @mkTupleSelector@ builds a selector which scrutises the given
561 expression and extracts the one name from the list given.
562 If you want the no-shadowing rule to apply, the caller
563 is responsible for making sure that none of these names
566 If there is just one id in the ``tuple'', then the selector is
570 mkTupleSelector :: [Id] -- The tuple args
571 -> Id -- The selected one
572 -> Id -- A variable of the same type as the scrutinee
573 -> CoreExpr -- Scrutinee
576 mkTupleSelector [var] should_be_the_same_var scrut_var scrut
577 = ASSERT(var == should_be_the_same_var)
580 mkTupleSelector vars the_var scrut_var scrut
581 = ASSERT( notNull vars )
582 Case scrut scrut_var [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
586 %************************************************************************
588 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
590 %************************************************************************
592 Call the constructor Ids when building explicit lists, so that they
593 interact well with rules.
596 mkNilExpr :: Type -> CoreExpr
597 mkNilExpr ty = mkConApp nilDataCon [Type ty]
599 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
600 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
604 %************************************************************************
606 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
608 %************************************************************************
610 Generally, we handle pattern matching failure like this: let-bind a
611 fail-variable, and use that variable if the thing fails:
613 let fail.33 = error "Help"
624 If the case can't fail, then there'll be no mention of @fail.33@, and the
625 simplifier will later discard it.
628 If it can fail in only one way, then the simplifier will inline it.
631 Only if it is used more than once will the let-binding remain.
634 There's a problem when the result of the case expression is of
635 unboxed type. Then the type of @fail.33@ is unboxed too, and
636 there is every chance that someone will change the let into a case:
642 which is of course utterly wrong. Rather than drop the condition that
643 only boxed types can be let-bound, we just turn the fail into a function
644 for the primitive case:
646 let fail.33 :: Void -> Int#
647 fail.33 = \_ -> error "Help"
656 Now @fail.33@ is a function, so it can be let-bound.
659 mkFailurePair :: CoreExpr -- Result type of the whole case expression
660 -> DsM (CoreBind, -- Binds the newly-created fail variable
661 -- to either the expression or \ _ -> expression
662 CoreExpr) -- Either the fail variable, or fail variable
663 -- applied to unit tuple
666 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
667 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
668 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
669 App (Var fail_fun_var) (Var unitDataConId))
672 = newFailLocalDs ty `thenDs` \ fail_var ->
673 returnDs (NonRec fail_var expr, Var fail_var)