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 mkCoLetMatchResult, mkGuardedMatchResult,
21 mkCoPrimCaseMatchResult, mkCoAlgCaseMatchResult,
24 mkErrorAppDs, mkNilExpr, mkConsExpr, mkListExpr,
25 mkIntExpr, mkCharExpr,
26 mkStringExpr, mkStringExprFS, mkIntegerExpr,
28 mkSelectorBinds, mkTupleExpr, mkTupleSelector,
29 mkTupleType, mkTupleCase, mkBigCoreTup,
30 mkCoreTup, mkCoreTupTy,
32 dsSyntaxTable, lookupEvidence,
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, dataConTag )
56 import Type ( mkFunTy, isUnLiftedType, Type, splitTyConApp, mkTyVarTy )
57 import TcType ( 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 SrcLoc ( Located(..), unLoc )
73 import Util ( isSingleton, zipEqual, sortWith )
74 import ListSetOps ( assocDefault )
76 import Data.Char ( ord )
79 import Util ( notNull ) -- Used in an assertion
85 %************************************************************************
89 %************************************************************************
92 dsSyntaxTable :: SyntaxTable Id
93 -> DsM ([CoreBind], -- Auxiliary bindings
94 [(Name,Id)]) -- Maps the standard name to its value
96 dsSyntaxTable rebound_ids
97 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
98 return (concat binds_s, prs)
100 -- The cheapo special case can happen when we
101 -- make an intermediate HsDo when desugaring a RecStmt
102 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
103 mk_bind (std_name, expr)
104 = dsExpr expr `thenDs` \ rhs ->
105 newSysLocalDs (exprType rhs) `thenDs` \ id ->
106 return ([NonRec id rhs], (std_name, id))
108 lookupEvidence :: [(Name, Id)] -> Name -> Id
109 lookupEvidence prs std_name
110 = assocDefault (mk_panic std_name) prs std_name
112 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
116 %************************************************************************
118 \subsection{Building lets}
120 %************************************************************************
122 Use case, not let for unlifted types. The simplifier will turn some
126 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
127 mkDsLet (NonRec bndr rhs) body
128 | isUnLiftedType (idType bndr)
129 = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
133 mkDsLets :: [CoreBind] -> CoreExpr -> CoreExpr
134 mkDsLets binds body = foldr mkDsLet body binds
138 %************************************************************************
140 \subsection{ Selecting match variables}
142 %************************************************************************
144 We're about to match against some patterns. We want to make some
145 @Ids@ to use as match variables. If a pattern has an @Id@ readily at
146 hand, which should indeed be bound to the pattern as a whole, then use it;
147 otherwise, make one up.
150 selectSimpleMatchVarL :: LPat Id -> DsM Id
151 selectSimpleMatchVarL pat = selectMatchVar (unLoc pat) (hsPatType pat)
153 -- (selectMatchVars ps tys) chooses variables of type tys
154 -- to use for matching ps against. If the pattern is a variable,
155 -- we try to use that, to save inventing lots of fresh variables.
156 -- But even if it is a variable, its type might not match. Consider
158 -- T1 :: Int -> T Int
161 -- f :: T a -> a -> Int
162 -- f (T1 i) (x::Int) = x
163 -- f (T2 i) (y::a) = 0
164 -- Then we must not choose (x::Int) as the matching variable!
166 selectMatchVars :: [Pat Id] -> [Type] -> DsM [Id]
167 selectMatchVars [] [] = return []
168 selectMatchVars (p:ps) (ty:tys) = do { v <- selectMatchVar p ty
169 ; vs <- selectMatchVars ps tys
172 selectMatchVar (LazyPat pat) pat_ty = selectMatchVar (unLoc pat) pat_ty
173 selectMatchVar (VarPat var) pat_ty = try_for var pat_ty
174 selectMatchVar (AsPat var pat) pat_ty = try_for (unLoc var) pat_ty
175 selectMatchVar other_pat pat_ty = newSysLocalDs pat_ty -- OK, better make up one...
178 | idType var `tcEqType` pat_ty = returnDs var
179 | otherwise = newSysLocalDs pat_ty
183 %************************************************************************
185 %* type synonym EquationInfo and access functions for its pieces *
187 %************************************************************************
188 \subsection[EquationInfo-synonym]{@EquationInfo@: a useful synonym}
190 The ``equation info'' used by @match@ is relatively complicated and
191 worthy of a type synonym and a few handy functions.
194 firstPat :: EquationInfo -> Pat Id
195 firstPat eqn = head (eqn_pats eqn)
197 shiftEqns :: [EquationInfo] -> [EquationInfo]
198 -- Drop the first pattern in each equation
199 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
202 Functions on MatchResults
205 matchCanFail :: MatchResult -> Bool
206 matchCanFail (MatchResult CanFail _) = True
207 matchCanFail (MatchResult CantFail _) = False
209 alwaysFailMatchResult :: MatchResult
210 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
212 cantFailMatchResult :: CoreExpr -> MatchResult
213 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
215 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
216 extractMatchResult (MatchResult CantFail match_fn) fail_expr
217 = match_fn (error "It can't fail!")
219 extractMatchResult (MatchResult CanFail match_fn) fail_expr
220 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
221 match_fn if_it_fails `thenDs` \ body ->
222 returnDs (mkDsLet fail_bind body)
225 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
226 combineMatchResults (MatchResult CanFail body_fn1)
227 (MatchResult can_it_fail2 body_fn2)
228 = MatchResult can_it_fail2 body_fn
230 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
231 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
232 body_fn1 duplicatable_expr `thenDs` \ body1 ->
233 returnDs (Let fail_bind body1)
235 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
238 adjustMatchResult :: (CoreExpr -> CoreExpr) -> MatchResult -> MatchResult
239 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
240 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
241 returnDs (encl_fn body))
243 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
244 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
245 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
248 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
250 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
252 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
253 wrapBind new old body
255 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
256 | otherwise = Let (NonRec new (Var old)) body
258 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
259 mkCoLetMatchResult bind match_result
260 = adjustMatchResult (mkDsLet bind) match_result
262 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
263 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
264 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
265 returnDs (mkIfThenElse pred_expr body fail))
267 mkCoPrimCaseMatchResult :: Id -- Scrutinee
268 -> Type -- Type of the case
269 -> [(Literal, MatchResult)] -- Alternatives
271 mkCoPrimCaseMatchResult var ty match_alts
272 = MatchResult CanFail mk_case
275 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
276 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
278 sorted_alts = sortWith fst match_alts -- Right order for a Case
279 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
280 returnDs (LitAlt lit, [], body)
283 mkCoAlgCaseMatchResult :: Id -- Scrutinee
284 -> Type -- Type of exp
285 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
287 mkCoAlgCaseMatchResult var ty match_alts
288 | isNewTyCon tycon -- Newtype case; use a let
289 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
290 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
292 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
293 = MatchResult CanFail mk_parrCase
295 | otherwise -- Datatype case; use a case
296 = MatchResult fail_flag mk_case
298 tycon = dataConTyCon con1
299 -- [Interesting: becuase of GADTs, we can't rely on the type of
300 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
303 (con1, arg_ids1, match_result1) = head match_alts
304 arg_id1 = head arg_ids1
305 newtype_rhs = mkNewTypeBody tycon (idType arg_id1) (Var var)
307 -- Stuff for data types
308 data_cons = tyConDataCons tycon
309 match_results = [match_result | (_,_,match_result) <- match_alts]
311 fail_flag | exhaustive_case
312 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
316 wild_var = mkWildId (idType var)
317 sorted_alts = sortWith get_tag match_alts
318 get_tag (con, _, _) = dataConTag con
319 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
320 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
322 mk_alt fail (con, args, MatchResult _ body_fn)
323 = body_fn fail `thenDs` \ body ->
324 newUniqueSupply `thenDs` \ us ->
325 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
327 mk_default fail | exhaustive_case = []
328 | otherwise = [(DEFAULT, [], fail)]
330 un_mentioned_constructors
331 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
332 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
334 -- Stuff for parallel arrays
336 -- * the following is to desugar cases over fake constructors for
337 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
340 -- Concerning `isPArrFakeAlts':
342 -- * it is *not* sufficient to just check the type of the type
343 -- constructor, as we have to be careful not to confuse the real
344 -- representation of parallel arrays with the fake constructors;
345 -- moreover, a list of alternatives must not mix fake and real
346 -- constructors (this is checked earlier on)
348 -- FIXME: We actually go through the whole list and make sure that
349 -- either all or none of the constructors are fake parallel
350 -- array constructors. This is to spot equations that mix fake
351 -- constructors with the real representation defined in
352 -- `PrelPArr'. It would be nicer to spot this situation
353 -- earlier and raise a proper error message, but it can really
354 -- only happen in `PrelPArr' anyway.
356 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
357 isPArrFakeAlts ((dcon, _, _):alts) =
358 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
359 (True , True ) -> True
360 (False, False) -> False
362 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
365 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
366 unboxAlt `thenDs` \alt ->
367 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
369 elemTy = case splitTyConApp (idType var) of
370 (_, [elemTy]) -> elemTy
372 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
373 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
376 newSysLocalDs intPrimTy `thenDs` \l ->
377 dsLookupGlobalId indexPName `thenDs` \indexP ->
378 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
379 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
381 wild = mkWildId intPrimTy
382 dft = (DEFAULT, [], fail)
384 -- each alternative matches one array length (corresponding to one
385 -- fake array constructor), so the match is on a literal; each
386 -- alternative's body is extended by a local binding for each
387 -- constructor argument, which are bound to array elements starting
390 mkAlt indexP (con, args, MatchResult _ bodyFun) =
391 bodyFun fail `thenDs` \body ->
392 returnDs (LitAlt lit, [], mkDsLets binds body)
394 lit = MachInt $ toInteger (dataConSourceArity con)
395 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
397 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
401 %************************************************************************
403 \subsection{Desugarer's versions of some Core functions}
405 %************************************************************************
408 mkErrorAppDs :: Id -- The error function
409 -> Type -- Type to which it should be applied
410 -> String -- The error message string to pass
413 mkErrorAppDs err_id ty msg
414 = getSrcSpanDs `thenDs` \ src_loc ->
416 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
417 core_msg = Lit (mkStringLit full_msg)
418 -- mkStringLit returns a result of type String#
420 returnDs (mkApps (Var err_id) [Type ty, core_msg])
424 *************************************************************
426 \subsection{Making literals}
428 %************************************************************************
431 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
432 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
433 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
434 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
435 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
437 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
438 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
441 | inIntRange i -- Small enough, so start from an Int
442 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
443 returnDs (mkSmallIntegerLit integer_dc i)
445 -- Special case for integral literals with a large magnitude:
446 -- They are transformed into an expression involving only smaller
447 -- integral literals. This improves constant folding.
449 | otherwise -- Big, so start from a string
450 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
451 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
452 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
454 lit i = mkSmallIntegerLit integer_dc i
455 plus a b = Var plus_id `App` a `App` b
456 times a b = Var times_id `App` a `App` b
458 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
459 horner :: Integer -> Integer -> CoreExpr
460 horner b i | abs q <= 1 = if r == 0 || r == i
462 else lit r `plus` lit (i-r)
463 | r == 0 = horner b q `times` lit b
464 | otherwise = lit r `plus` (horner b q `times` lit b)
466 (q,r) = i `quotRem` b
469 returnDs (horner tARGET_MAX_INT i)
471 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
473 mkStringExpr str = mkStringExprFS (mkFastString str)
477 = returnDs (mkNilExpr charTy)
481 the_char = mkCharExpr (headFS str)
483 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
486 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
487 returnDs (App (Var unpack_id) (Lit (MachStr str)))
490 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
491 returnDs (App (Var unpack_id) (Lit (MachStr str)))
495 safeChar c = ord c >= 1 && ord c <= 0x7F
499 %************************************************************************
501 \subsection[mkSelectorBind]{Make a selector bind}
503 %************************************************************************
505 This is used in various places to do with lazy patterns.
506 For each binder $b$ in the pattern, we create a binding:
508 b = case v of pat' -> b'
510 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
512 ToDo: making these bindings should really depend on whether there's
513 much work to be done per binding. If the pattern is complex, it
514 should be de-mangled once, into a tuple (and then selected from).
515 Otherwise the demangling can be in-line in the bindings (as here).
517 Boring! Boring! One error message per binder. The above ToDo is
518 even more helpful. Something very similar happens for pattern-bound
522 mkSelectorBinds :: LPat Id -- The pattern
523 -> CoreExpr -- Expression to which the pattern is bound
524 -> DsM [(Id,CoreExpr)]
526 mkSelectorBinds (L _ (VarPat v)) val_expr
527 = returnDs [(v, val_expr)]
529 mkSelectorBinds pat val_expr
530 | isSingleton binders || is_simple_lpat pat
531 = -- Given p = e, where p binds x,y
532 -- we are going to make
533 -- v = p (where v is fresh)
534 -- x = case v of p -> x
535 -- y = case v of p -> x
538 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
539 -- This does not matter after desugaring, but there's a subtle
540 -- issue with implicit parameters. Consider
542 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
543 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
544 -- does it get that type? So that when we abstract over it we get the
545 -- right top-level type (?i::Int) => ...)
547 -- So to get the type of 'v', use the pattern not the rhs. Often more
549 newSysLocalDs (hsPatType pat) `thenDs` \ val_var ->
551 -- For the error message we make one error-app, to avoid duplication.
552 -- But we need it at different types... so we use coerce for that
553 mkErrorAppDs iRREFUT_PAT_ERROR_ID
554 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
555 newSysLocalDs unitTy `thenDs` \ err_var ->
556 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
557 returnDs ( (val_var, val_expr) :
558 (err_var, err_expr) :
563 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
564 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
565 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
566 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
569 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
571 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
573 binders = collectPatBinders pat
574 local_tuple = mkTupleExpr binders
575 tuple_ty = exprType local_tuple
577 mk_bind scrut_var err_var bndr_var
578 -- (mk_bind sv err_var) generates
579 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
580 -- Remember, pat binds bv
581 = matchSimply (Var scrut_var) PatBindRhs pat
582 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
583 returnDs (bndr_var, rhs_expr)
585 error_expr = mkCoerce (idType bndr_var) (Var err_var)
587 is_simple_lpat p = is_simple_pat (unLoc p)
589 is_simple_pat (TuplePat ps Boxed) = all is_triv_lpat ps
590 is_simple_pat (ConPatOut _ _ _ _ ps _) = all is_triv_lpat (hsConArgs ps)
591 is_simple_pat (VarPat _) = True
592 is_simple_pat (ParPat p) = is_simple_lpat p
593 is_simple_pat other = False
595 is_triv_lpat p = is_triv_pat (unLoc p)
597 is_triv_pat (VarPat v) = True
598 is_triv_pat (WildPat _) = True
599 is_triv_pat (ParPat p) = is_triv_lpat p
600 is_triv_pat other = False
604 %************************************************************************
608 %************************************************************************
610 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
612 * If it has only one element, it is the identity function.
614 * If there are more elements than a big tuple can have, it nests
617 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
618 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
621 mkTupleExpr :: [Id] -> CoreExpr
622 mkTupleExpr ids = mkBigCoreTup (map Var ids)
624 -- corresponding type
625 mkTupleType :: [Id] -> Type
626 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
628 mkBigCoreTup :: [CoreExpr] -> CoreExpr
629 mkBigCoreTup = mkBigTuple mkCoreTup
631 mkBigTuple :: ([a] -> a) -> [a] -> a
632 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
634 -- Each sub-list is short enough to fit in a tuple
635 mk_big_tuple [as] = small_tuple as
636 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
638 chunkify :: [a] -> [[a]]
639 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
640 -- But there may be more than mAX_TUPLE_SIZE sub-lists
642 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
643 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
647 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
651 @mkTupleSelector@ builds a selector which scrutises the given
652 expression and extracts the one name from the list given.
653 If you want the no-shadowing rule to apply, the caller
654 is responsible for making sure that none of these names
657 If there is just one id in the ``tuple'', then the selector is
660 If it's big, it does nesting
661 mkTupleSelector [a,b,c,d] b v e
663 (p,q) -> case p of p {
665 We use 'tpl' vars for the p,q, since shadowing does not matter.
667 In fact, it's more convenient to generate it innermost first, getting
674 mkTupleSelector :: [Id] -- The tuple args
675 -> Id -- The selected one
676 -> Id -- A variable of the same type as the scrutinee
677 -> CoreExpr -- Scrutinee
680 mkTupleSelector vars the_var scrut_var scrut
681 = mk_tup_sel (chunkify vars) the_var
683 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
684 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
685 mk_tup_sel (chunkify tpl_vs) tpl_v
687 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
688 tpl_vs = mkTemplateLocals tpl_tys
689 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
693 A generalization of @mkTupleSelector@, allowing the body
694 of the case to be an arbitrary expression.
696 If the tuple is big, it is nested:
698 mkTupleCase uniqs [a,b,c,d] body v e
699 = case e of v { (p,q) ->
700 case p of p { (a,b) ->
701 case q of q { (c,d) ->
704 To avoid shadowing, we use uniqs to invent new variables p,q.
706 ToDo: eliminate cases where none of the variables are needed.
710 :: UniqSupply -- for inventing names of intermediate variables
711 -> [Id] -- the tuple args
712 -> CoreExpr -- body of the case
713 -> Id -- a variable of the same type as the scrutinee
714 -> CoreExpr -- scrutinee
717 mkTupleCase uniqs vars body scrut_var scrut
718 = mk_tuple_case uniqs (chunkify vars) body
720 mk_tuple_case us [vars] body
721 = mkSmallTupleCase vars body scrut_var scrut
722 mk_tuple_case us vars_s body
724 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
726 mk_tuple_case us' (chunkify vars') body'
727 one_tuple_case chunk_vars (us, vs, body)
729 (us1, us2) = splitUniqSupply us
730 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
731 (mkCoreTupTy (map idType chunk_vars))
732 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
733 in (us2, scrut_var:vs, body')
736 The same, but with a tuple small enough not to need nesting.
740 :: [Id] -- the tuple args
741 -> CoreExpr -- body of the case
742 -> Id -- a variable of the same type as the scrutinee
743 -> CoreExpr -- scrutinee
746 mkSmallTupleCase [var] body _scrut_var scrut
747 = bindNonRec var scrut body
748 mkSmallTupleCase vars body scrut_var scrut
749 -- One branch no refinement?
750 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
753 %************************************************************************
755 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
757 %************************************************************************
759 Call the constructor Ids when building explicit lists, so that they
760 interact well with rules.
763 mkNilExpr :: Type -> CoreExpr
764 mkNilExpr ty = mkConApp nilDataCon [Type ty]
766 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
767 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
769 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
770 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
773 -- The next three functions make tuple types, constructors and selectors,
774 -- with the rule that a 1-tuple is represented by the thing itselg
775 mkCoreTupTy :: [Type] -> Type
776 mkCoreTupTy [ty] = ty
777 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
779 mkCoreTup :: [CoreExpr] -> CoreExpr
780 -- Builds exactly the specified tuple.
781 -- No fancy business for big tuples
782 mkCoreTup [] = Var unitDataConId
784 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
785 (map (Type . exprType) cs ++ cs)
787 mkCoreSel :: [Id] -- The tuple args
788 -> Id -- The selected one
789 -> Id -- A variable of the same type as the scrutinee
790 -> CoreExpr -- Scrutinee
792 -- mkCoreSel [x,y,z] x v e
793 -- ===> case e of v { (x,y,z) -> x
794 mkCoreSel [var] should_be_the_same_var scrut_var scrut
795 = ASSERT(var == should_be_the_same_var)
798 mkCoreSel vars the_var scrut_var scrut
799 = ASSERT( notNull vars )
800 Case scrut scrut_var (idType the_var)
801 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
805 %************************************************************************
807 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
809 %************************************************************************
811 Generally, we handle pattern matching failure like this: let-bind a
812 fail-variable, and use that variable if the thing fails:
814 let fail.33 = error "Help"
825 If the case can't fail, then there'll be no mention of @fail.33@, and the
826 simplifier will later discard it.
829 If it can fail in only one way, then the simplifier will inline it.
832 Only if it is used more than once will the let-binding remain.
835 There's a problem when the result of the case expression is of
836 unboxed type. Then the type of @fail.33@ is unboxed too, and
837 there is every chance that someone will change the let into a case:
843 which is of course utterly wrong. Rather than drop the condition that
844 only boxed types can be let-bound, we just turn the fail into a function
845 for the primitive case:
847 let fail.33 :: Void -> Int#
848 fail.33 = \_ -> error "Help"
857 Now @fail.33@ is a function, so it can be let-bound.
860 mkFailurePair :: CoreExpr -- Result type of the whole case expression
861 -> DsM (CoreBind, -- Binds the newly-created fail variable
862 -- to either the expression or \ _ -> expression
863 CoreExpr) -- Either the fail variable, or fail variable
864 -- applied to unit tuple
867 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
868 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
869 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
870 App (Var fail_fun_var) (Var unitDataConId))
873 = newFailLocalDs ty `thenDs` \ fail_var ->
874 returnDs (NonRec fail_var expr, Var fail_var)