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 UnicodeUtil ( intsToUtf8 )
73 import SrcLoc ( Located(..), unLoc )
74 import Util ( isSingleton, notNull, zipEqual, sortWith )
75 import ListSetOps ( assocDefault )
81 %************************************************************************
85 %************************************************************************
88 dsSyntaxTable :: SyntaxTable Id
89 -> DsM ([CoreBind], -- Auxiliary bindings
90 [(Name,Id)]) -- Maps the standard name to its value
92 dsSyntaxTable rebound_ids
93 = mapAndUnzipDs mk_bind rebound_ids `thenDs` \ (binds_s, prs) ->
94 return (concat binds_s, prs)
96 -- The cheapo special case can happen when we
97 -- make an intermediate HsDo when desugaring a RecStmt
98 mk_bind (std_name, HsVar id) = return ([], (std_name, id))
99 mk_bind (std_name, expr)
100 = dsExpr expr `thenDs` \ rhs ->
101 newSysLocalDs (exprType rhs) `thenDs` \ id ->
102 return ([NonRec id rhs], (std_name, id))
104 lookupEvidence :: [(Name, Id)] -> Name -> Id
105 lookupEvidence prs std_name
106 = assocDefault (mk_panic std_name) prs std_name
108 mk_panic std_name = pprPanic "dsSyntaxTable" (ptext SLIT("Not found:") <+> ppr std_name)
112 %************************************************************************
114 \subsection{Building lets}
116 %************************************************************************
118 Use case, not let for unlifted types. The simplifier will turn some
122 mkDsLet :: CoreBind -> CoreExpr -> CoreExpr
123 mkDsLet (NonRec bndr rhs) body
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.
190 firstPat :: EquationInfo -> Pat Id
191 firstPat eqn = head (eqn_pats eqn)
193 shiftEqns :: [EquationInfo] -> [EquationInfo]
194 -- Drop the first pattern in each equation
195 shiftEqns eqns = [ eqn { eqn_pats = tail (eqn_pats eqn) } | eqn <- eqns ]
198 Functions on MatchResults
201 matchCanFail :: MatchResult -> Bool
202 matchCanFail (MatchResult CanFail _) = True
203 matchCanFail (MatchResult CantFail _) = False
205 alwaysFailMatchResult :: MatchResult
206 alwaysFailMatchResult = MatchResult CanFail (\fail -> returnDs fail)
208 cantFailMatchResult :: CoreExpr -> MatchResult
209 cantFailMatchResult expr = MatchResult CantFail (\ ignore -> returnDs expr)
211 extractMatchResult :: MatchResult -> CoreExpr -> DsM CoreExpr
212 extractMatchResult (MatchResult CantFail match_fn) fail_expr
213 = match_fn (error "It can't fail!")
215 extractMatchResult (MatchResult CanFail match_fn) fail_expr
216 = mkFailurePair fail_expr `thenDs` \ (fail_bind, if_it_fails) ->
217 match_fn if_it_fails `thenDs` \ body ->
218 returnDs (mkDsLet fail_bind body)
221 combineMatchResults :: MatchResult -> MatchResult -> MatchResult
222 combineMatchResults (MatchResult CanFail body_fn1)
223 (MatchResult can_it_fail2 body_fn2)
224 = MatchResult can_it_fail2 body_fn
226 body_fn fail = body_fn2 fail `thenDs` \ body2 ->
227 mkFailurePair body2 `thenDs` \ (fail_bind, duplicatable_expr) ->
228 body_fn1 duplicatable_expr `thenDs` \ body1 ->
229 returnDs (Let fail_bind body1)
231 combineMatchResults match_result1@(MatchResult CantFail body_fn1) match_result2
234 adjustMatchResult :: (CoreExpr -> CoreExpr) -> MatchResult -> MatchResult
235 adjustMatchResult encl_fn (MatchResult can_it_fail body_fn)
236 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
237 returnDs (encl_fn body))
239 adjustMatchResultDs :: (CoreExpr -> DsM CoreExpr) -> MatchResult -> MatchResult
240 adjustMatchResultDs encl_fn (MatchResult can_it_fail body_fn)
241 = MatchResult can_it_fail (\fail -> body_fn fail `thenDs` \ body ->
244 wrapBinds :: [(Var,Var)] -> CoreExpr -> CoreExpr
246 wrapBinds ((new,old):prs) e = wrapBind new old (wrapBinds prs e)
248 wrapBind :: Var -> Var -> CoreExpr -> CoreExpr
249 wrapBind new old body
251 | isTyVar new = App (Lam new body) (Type (mkTyVarTy old))
252 | otherwise = Let (NonRec new (Var old)) body
254 mkCoLetMatchResult :: CoreBind -> MatchResult -> MatchResult
255 mkCoLetMatchResult bind match_result
256 = adjustMatchResult (mkDsLet bind) match_result
258 mkGuardedMatchResult :: CoreExpr -> MatchResult -> MatchResult
259 mkGuardedMatchResult pred_expr (MatchResult can_it_fail body_fn)
260 = MatchResult CanFail (\fail -> body_fn fail `thenDs` \ body ->
261 returnDs (mkIfThenElse pred_expr body fail))
263 mkCoPrimCaseMatchResult :: Id -- Scrutinee
264 -> Type -- Type of the case
265 -> [(Literal, MatchResult)] -- Alternatives
267 mkCoPrimCaseMatchResult var ty match_alts
268 = MatchResult CanFail mk_case
271 = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
272 returnDs (Case (Var var) var ty ((DEFAULT, [], fail) : alts))
274 sorted_alts = sortWith fst match_alts -- Right order for a Case
275 mk_alt fail (lit, MatchResult _ body_fn) = body_fn fail `thenDs` \ body ->
276 returnDs (LitAlt lit, [], body)
279 mkCoAlgCaseMatchResult :: Id -- Scrutinee
280 -> Type -- Type of exp
281 -> [(DataCon, [CoreBndr], MatchResult)] -- Alternatives
283 mkCoAlgCaseMatchResult var ty match_alts
284 | isNewTyCon tycon -- Newtype case; use a let
285 = ASSERT( null (tail match_alts) && null (tail arg_ids1) )
286 mkCoLetMatchResult (NonRec arg_id1 newtype_rhs) match_result1
288 | isPArrFakeAlts match_alts -- Sugared parallel array; use a literal case
289 = MatchResult CanFail mk_parrCase
291 | otherwise -- Datatype case; use a case
292 = MatchResult fail_flag mk_case
294 tycon = dataConTyCon con1
295 -- [Interesting: becuase of GADTs, we can't rely on the type of
296 -- the scrutinised Id to be sufficiently refined to have a TyCon in it]
299 (con1, arg_ids1, match_result1) = head match_alts
300 arg_id1 = head arg_ids1
301 newtype_rhs = mkNewTypeBody tycon (idType arg_id1) (Var var)
303 -- Stuff for data types
304 data_cons = tyConDataCons tycon
305 match_results = [match_result | (_,_,match_result) <- match_alts]
307 fail_flag | exhaustive_case
308 = foldr1 orFail [can_it_fail | MatchResult can_it_fail _ <- match_results]
312 wild_var = mkWildId (idType var)
313 sorted_alts = sortWith get_tag match_alts
314 get_tag (con, _, _) = dataConTag con
315 mk_case fail = mappM (mk_alt fail) sorted_alts `thenDs` \ alts ->
316 returnDs (Case (Var var) wild_var ty (mk_default fail ++ alts))
318 mk_alt fail (con, args, MatchResult _ body_fn)
319 = body_fn fail `thenDs` \ body ->
320 newUniqueSupply `thenDs` \ us ->
321 returnDs (mkReboxingAlt (uniqsFromSupply us) con args body)
323 mk_default fail | exhaustive_case = []
324 | otherwise = [(DEFAULT, [], fail)]
326 un_mentioned_constructors
327 = mkUniqSet data_cons `minusUniqSet` mkUniqSet [ con | (con, _, _) <- match_alts]
328 exhaustive_case = isEmptyUniqSet un_mentioned_constructors
330 -- Stuff for parallel arrays
332 -- * the following is to desugar cases over fake constructors for
333 -- parallel arrays, which are introduced by `tidy1' in the `PArrPat'
336 -- Concerning `isPArrFakeAlts':
338 -- * it is *not* sufficient to just check the type of the type
339 -- constructor, as we have to be careful not to confuse the real
340 -- representation of parallel arrays with the fake constructors;
341 -- moreover, a list of alternatives must not mix fake and real
342 -- constructors (this is checked earlier on)
344 -- FIXME: We actually go through the whole list and make sure that
345 -- either all or none of the constructors are fake parallel
346 -- array constructors. This is to spot equations that mix fake
347 -- constructors with the real representation defined in
348 -- `PrelPArr'. It would be nicer to spot this situation
349 -- earlier and raise a proper error message, but it can really
350 -- only happen in `PrelPArr' anyway.
352 isPArrFakeAlts [(dcon, _, _)] = isPArrFakeCon dcon
353 isPArrFakeAlts ((dcon, _, _):alts) =
354 case (isPArrFakeCon dcon, isPArrFakeAlts alts) of
355 (True , True ) -> True
356 (False, False) -> False
358 panic "DsUtils: You may not mix `[:...:]' with `PArr' patterns"
361 dsLookupGlobalId lengthPName `thenDs` \lengthP ->
362 unboxAlt `thenDs` \alt ->
363 returnDs (Case (len lengthP) (mkWildId intTy) ty [alt])
365 elemTy = case splitTyConApp (idType var) of
366 (_, [elemTy]) -> elemTy
368 panicMsg = "DsUtils.mkCoAlgCaseMatchResult: not a parallel array?"
369 len lengthP = mkApps (Var lengthP) [Type elemTy, Var var]
372 newSysLocalDs intPrimTy `thenDs` \l ->
373 dsLookupGlobalId indexPName `thenDs` \indexP ->
374 mappM (mkAlt indexP) sorted_alts `thenDs` \alts ->
375 returnDs (DataAlt intDataCon, [l], (Case (Var l) wild ty (dft : alts)))
377 wild = mkWildId intPrimTy
378 dft = (DEFAULT, [], fail)
380 -- each alternative matches one array length (corresponding to one
381 -- fake array constructor), so the match is on a literal; each
382 -- alternative's body is extended by a local binding for each
383 -- constructor argument, which are bound to array elements starting
386 mkAlt indexP (con, args, MatchResult _ bodyFun) =
387 bodyFun fail `thenDs` \body ->
388 returnDs (LitAlt lit, [], mkDsLets binds body)
390 lit = MachInt $ toInteger (dataConSourceArity con)
391 binds = [NonRec arg (indexExpr i) | (i, arg) <- zip [1..] args]
393 indexExpr i = mkApps (Var indexP) [Type elemTy, Var var, mkIntExpr i]
397 %************************************************************************
399 \subsection{Desugarer's versions of some Core functions}
401 %************************************************************************
404 mkErrorAppDs :: Id -- The error function
405 -> Type -- Type to which it should be applied
406 -> String -- The error message string to pass
409 mkErrorAppDs err_id ty msg
410 = getSrcSpanDs `thenDs` \ src_loc ->
412 full_msg = showSDoc (hcat [ppr src_loc, text "|", text msg])
413 core_msg = Lit (mkStringLit full_msg)
414 -- mkStringLit returns a result of type String#
416 returnDs (mkApps (Var err_id) [Type ty, core_msg])
420 *************************************************************
422 \subsection{Making literals}
424 %************************************************************************
427 mkCharExpr :: Char -> CoreExpr -- Returns C# c :: Int
428 mkIntExpr :: Integer -> CoreExpr -- Returns I# i :: Int
429 mkIntegerExpr :: Integer -> DsM CoreExpr -- Result :: Integer
430 mkStringExpr :: String -> DsM CoreExpr -- Result :: String
431 mkStringExprFS :: FastString -> DsM CoreExpr -- Result :: String
433 mkIntExpr i = mkConApp intDataCon [mkIntLit i]
434 mkCharExpr c = mkConApp charDataCon [mkLit (MachChar c)]
437 | inIntRange i -- Small enough, so start from an Int
438 = dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
439 returnDs (mkSmallIntegerLit integer_dc i)
441 -- Special case for integral literals with a large magnitude:
442 -- They are transformed into an expression involving only smaller
443 -- integral literals. This improves constant folding.
445 | otherwise -- Big, so start from a string
446 = dsLookupGlobalId plusIntegerName `thenDs` \ plus_id ->
447 dsLookupGlobalId timesIntegerName `thenDs` \ times_id ->
448 dsLookupDataCon smallIntegerDataConName `thenDs` \ integer_dc ->
450 lit i = mkSmallIntegerLit integer_dc i
451 plus a b = Var plus_id `App` a `App` b
452 times a b = Var times_id `App` a `App` b
454 -- Transform i into (x1 + (x2 + (x3 + (...) * b) * b) * b) with abs xi <= b
455 horner :: Integer -> Integer -> CoreExpr
456 horner b i | abs q <= 1 = if r == 0 || r == i
458 else lit r `plus` lit (i-r)
459 | r == 0 = horner b q `times` lit b
460 | otherwise = lit r `plus` (horner b q `times` lit b)
462 (q,r) = i `quotRem` b
465 returnDs (horner tARGET_MAX_INT i)
467 mkSmallIntegerLit small_integer_data_con i = mkConApp small_integer_data_con [mkIntLit i]
469 mkStringExpr str = mkStringExprFS (mkFastString str)
473 = returnDs (mkNilExpr charTy)
477 the_char = mkCharExpr (headFS str)
479 returnDs (mkConsExpr charTy the_char (mkNilExpr charTy))
481 | all safeChar int_chars
482 = dsLookupGlobalId unpackCStringName `thenDs` \ unpack_id ->
483 returnDs (App (Var unpack_id) (Lit (MachStr str)))
486 = dsLookupGlobalId unpackCStringUtf8Name `thenDs` \ unpack_id ->
487 returnDs (App (Var unpack_id) (Lit (MachStr (mkFastString (intsToUtf8 int_chars)))))
490 int_chars = unpackIntFS str
491 safeChar c = c >= 1 && c <= 0xFF
495 %************************************************************************
497 \subsection[mkSelectorBind]{Make a selector bind}
499 %************************************************************************
501 This is used in various places to do with lazy patterns.
502 For each binder $b$ in the pattern, we create a binding:
504 b = case v of pat' -> b'
506 where @pat'@ is @pat@ with each binder @b@ cloned into @b'@.
508 ToDo: making these bindings should really depend on whether there's
509 much work to be done per binding. If the pattern is complex, it
510 should be de-mangled once, into a tuple (and then selected from).
511 Otherwise the demangling can be in-line in the bindings (as here).
513 Boring! Boring! One error message per binder. The above ToDo is
514 even more helpful. Something very similar happens for pattern-bound
518 mkSelectorBinds :: LPat Id -- The pattern
519 -> CoreExpr -- Expression to which the pattern is bound
520 -> DsM [(Id,CoreExpr)]
522 mkSelectorBinds (L _ (VarPat v)) val_expr
523 = returnDs [(v, val_expr)]
525 mkSelectorBinds pat val_expr
526 | isSingleton binders || is_simple_lpat pat
527 = -- Given p = e, where p binds x,y
528 -- we are going to make
529 -- v = p (where v is fresh)
530 -- x = case v of p -> x
531 -- y = case v of p -> x
534 -- NB: give it the type of *pattern* p, not the type of the *rhs* e.
535 -- This does not matter after desugaring, but there's a subtle
536 -- issue with implicit parameters. Consider
538 -- Then, ?i is given type {?i :: Int}, a PredType, which is opaque
539 -- to the desugarer. (Why opaque? Because newtypes have to be. Why
540 -- does it get that type? So that when we abstract over it we get the
541 -- right top-level type (?i::Int) => ...)
543 -- So to get the type of 'v', use the pattern not the rhs. Often more
545 newSysLocalDs (hsPatType pat) `thenDs` \ val_var ->
547 -- For the error message we make one error-app, to avoid duplication.
548 -- But we need it at different types... so we use coerce for that
549 mkErrorAppDs iRREFUT_PAT_ERROR_ID
550 unitTy (showSDoc (ppr pat)) `thenDs` \ err_expr ->
551 newSysLocalDs unitTy `thenDs` \ err_var ->
552 mappM (mk_bind val_var err_var) binders `thenDs` \ binds ->
553 returnDs ( (val_var, val_expr) :
554 (err_var, err_expr) :
559 = mkErrorAppDs iRREFUT_PAT_ERROR_ID
560 tuple_ty (showSDoc (ppr pat)) `thenDs` \ error_expr ->
561 matchSimply val_expr PatBindRhs pat local_tuple error_expr `thenDs` \ tuple_expr ->
562 newSysLocalDs tuple_ty `thenDs` \ tuple_var ->
565 = (binder, mkTupleSelector binders binder tuple_var (Var tuple_var))
567 returnDs ( (tuple_var, tuple_expr) : map mk_tup_bind binders )
569 binders = collectPatBinders pat
570 local_tuple = mkTupleExpr binders
571 tuple_ty = exprType local_tuple
573 mk_bind scrut_var err_var bndr_var
574 -- (mk_bind sv err_var) generates
575 -- bv = case sv of { pat -> bv; other -> coerce (type-of-bv) err_var }
576 -- Remember, pat binds bv
577 = matchSimply (Var scrut_var) PatBindRhs pat
578 (Var bndr_var) error_expr `thenDs` \ rhs_expr ->
579 returnDs (bndr_var, rhs_expr)
581 error_expr = mkCoerce (idType bndr_var) (Var err_var)
583 is_simple_lpat p = is_simple_pat (unLoc p)
585 is_simple_pat (TuplePat ps Boxed) = all is_triv_lpat ps
586 is_simple_pat (ConPatOut _ _ _ _ ps _) = all is_triv_lpat (hsConArgs ps)
587 is_simple_pat (VarPat _) = True
588 is_simple_pat (ParPat p) = is_simple_lpat p
589 is_simple_pat other = False
591 is_triv_lpat p = is_triv_pat (unLoc p)
593 is_triv_pat (VarPat v) = True
594 is_triv_pat (WildPat _) = True
595 is_triv_pat (ParPat p) = is_triv_lpat p
596 is_triv_pat other = False
600 %************************************************************************
604 %************************************************************************
606 @mkTupleExpr@ builds a tuple; the inverse to @mkTupleSelector@.
608 * If it has only one element, it is the identity function.
610 * If there are more elements than a big tuple can have, it nests
613 Nesting policy. Better a 2-tuple of 10-tuples (3 objects) than
614 a 10-tuple of 2-tuples (11 objects). So we want the leaves to be big.
617 mkTupleExpr :: [Id] -> CoreExpr
618 mkTupleExpr ids = mkBigCoreTup (map Var ids)
620 -- corresponding type
621 mkTupleType :: [Id] -> Type
622 mkTupleType ids = mkBigTuple mkCoreTupTy (map idType ids)
624 mkBigCoreTup :: [CoreExpr] -> CoreExpr
625 mkBigCoreTup = mkBigTuple mkCoreTup
627 mkBigTuple :: ([a] -> a) -> [a] -> a
628 mkBigTuple small_tuple as = mk_big_tuple (chunkify as)
630 -- Each sub-list is short enough to fit in a tuple
631 mk_big_tuple [as] = small_tuple as
632 mk_big_tuple as_s = mk_big_tuple (chunkify (map small_tuple as_s))
634 chunkify :: [a] -> [[a]]
635 -- The sub-lists of the result all have length <= mAX_TUPLE_SIZE
636 -- But there may be more than mAX_TUPLE_SIZE sub-lists
638 | n_xs <= mAX_TUPLE_SIZE = {- pprTrace "Small" (ppr n_xs) -} [xs]
639 | otherwise = {- pprTrace "Big" (ppr n_xs) -} (split xs)
643 split xs = take mAX_TUPLE_SIZE xs : split (drop mAX_TUPLE_SIZE xs)
647 @mkTupleSelector@ builds a selector which scrutises the given
648 expression and extracts the one name from the list given.
649 If you want the no-shadowing rule to apply, the caller
650 is responsible for making sure that none of these names
653 If there is just one id in the ``tuple'', then the selector is
656 If it's big, it does nesting
657 mkTupleSelector [a,b,c,d] b v e
659 (p,q) -> case p of p {
661 We use 'tpl' vars for the p,q, since shadowing does not matter.
663 In fact, it's more convenient to generate it innermost first, getting
670 mkTupleSelector :: [Id] -- The tuple args
671 -> Id -- The selected one
672 -> Id -- A variable of the same type as the scrutinee
673 -> CoreExpr -- Scrutinee
676 mkTupleSelector vars the_var scrut_var scrut
677 = mk_tup_sel (chunkify vars) the_var
679 mk_tup_sel [vars] the_var = mkCoreSel vars the_var scrut_var scrut
680 mk_tup_sel vars_s the_var = mkCoreSel group the_var tpl_v $
681 mk_tup_sel (chunkify tpl_vs) tpl_v
683 tpl_tys = [mkCoreTupTy (map idType gp) | gp <- vars_s]
684 tpl_vs = mkTemplateLocals tpl_tys
685 [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
689 A generalization of @mkTupleSelector@, allowing the body
690 of the case to be an arbitrary expression.
692 If the tuple is big, it is nested:
694 mkTupleCase uniqs [a,b,c,d] body v e
695 = case e of v { (p,q) ->
696 case p of p { (a,b) ->
697 case q of q { (c,d) ->
700 To avoid shadowing, we use uniqs to invent new variables p,q.
702 ToDo: eliminate cases where none of the variables are needed.
706 :: UniqSupply -- for inventing names of intermediate variables
707 -> [Id] -- the tuple args
708 -> CoreExpr -- body of the case
709 -> Id -- a variable of the same type as the scrutinee
710 -> CoreExpr -- scrutinee
713 mkTupleCase uniqs vars body scrut_var scrut
714 = mk_tuple_case uniqs (chunkify vars) body
716 mk_tuple_case us [vars] body
717 = mkSmallTupleCase vars body scrut_var scrut
718 mk_tuple_case us vars_s body
720 (us', vars', body') = foldr one_tuple_case (us, [], body) vars_s
722 mk_tuple_case us' (chunkify vars') body'
723 one_tuple_case chunk_vars (us, vs, body)
725 (us1, us2) = splitUniqSupply us
726 scrut_var = mkSysLocal FSLIT("ds") (uniqFromSupply us1)
727 (mkCoreTupTy (map idType chunk_vars))
728 body' = mkSmallTupleCase chunk_vars body scrut_var (Var scrut_var)
729 in (us2, scrut_var:vs, body')
732 The same, but with a tuple small enough not to need nesting.
736 :: [Id] -- the tuple args
737 -> CoreExpr -- body of the case
738 -> Id -- a variable of the same type as the scrutinee
739 -> CoreExpr -- scrutinee
742 mkSmallTupleCase [var] body _scrut_var scrut
743 = bindNonRec var scrut body
744 mkSmallTupleCase vars body scrut_var scrut
745 -- One branch no refinement?
746 = Case scrut scrut_var (exprType body) [(DataAlt (tupleCon Boxed (length vars)), vars, body)]
749 %************************************************************************
751 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
753 %************************************************************************
755 Call the constructor Ids when building explicit lists, so that they
756 interact well with rules.
759 mkNilExpr :: Type -> CoreExpr
760 mkNilExpr ty = mkConApp nilDataCon [Type ty]
762 mkConsExpr :: Type -> CoreExpr -> CoreExpr -> CoreExpr
763 mkConsExpr ty hd tl = mkConApp consDataCon [Type ty, hd, tl]
765 mkListExpr :: Type -> [CoreExpr] -> CoreExpr
766 mkListExpr ty xs = foldr (mkConsExpr ty) (mkNilExpr ty) xs
769 -- The next three functions make tuple types, constructors and selectors,
770 -- with the rule that a 1-tuple is represented by the thing itselg
771 mkCoreTupTy :: [Type] -> Type
772 mkCoreTupTy [ty] = ty
773 mkCoreTupTy tys = mkTupleTy Boxed (length tys) tys
775 mkCoreTup :: [CoreExpr] -> CoreExpr
776 -- Builds exactly the specified tuple.
777 -- No fancy business for big tuples
778 mkCoreTup [] = Var unitDataConId
780 mkCoreTup cs = mkConApp (tupleCon Boxed (length cs))
781 (map (Type . exprType) cs ++ cs)
783 mkCoreSel :: [Id] -- The tuple args
784 -> Id -- The selected one
785 -> Id -- A variable of the same type as the scrutinee
786 -> CoreExpr -- Scrutinee
788 -- mkCoreSel [x,y,z] x v e
789 -- ===> case e of v { (x,y,z) -> x
790 mkCoreSel [var] should_be_the_same_var scrut_var scrut
791 = ASSERT(var == should_be_the_same_var)
794 mkCoreSel vars the_var scrut_var scrut
795 = ASSERT( notNull vars )
796 Case scrut scrut_var (idType the_var)
797 [(DataAlt (tupleCon Boxed (length vars)), vars, Var the_var)]
801 %************************************************************************
803 \subsection[mkFailurePair]{Code for pattern-matching and other failures}
805 %************************************************************************
807 Generally, we handle pattern matching failure like this: let-bind a
808 fail-variable, and use that variable if the thing fails:
810 let fail.33 = error "Help"
821 If the case can't fail, then there'll be no mention of @fail.33@, and the
822 simplifier will later discard it.
825 If it can fail in only one way, then the simplifier will inline it.
828 Only if it is used more than once will the let-binding remain.
831 There's a problem when the result of the case expression is of
832 unboxed type. Then the type of @fail.33@ is unboxed too, and
833 there is every chance that someone will change the let into a case:
839 which is of course utterly wrong. Rather than drop the condition that
840 only boxed types can be let-bound, we just turn the fail into a function
841 for the primitive case:
843 let fail.33 :: Void -> Int#
844 fail.33 = \_ -> error "Help"
853 Now @fail.33@ is a function, so it can be let-bound.
856 mkFailurePair :: CoreExpr -- Result type of the whole case expression
857 -> DsM (CoreBind, -- Binds the newly-created fail variable
858 -- to either the expression or \ _ -> expression
859 CoreExpr) -- Either the fail variable, or fail variable
860 -- applied to unit tuple
863 = newFailLocalDs (unitTy `mkFunTy` ty) `thenDs` \ fail_fun_var ->
864 newSysLocalDs unitTy `thenDs` \ fail_fun_arg ->
865 returnDs (NonRec fail_fun_var (Lam fail_fun_arg expr),
866 App (Var fail_fun_var) (Var unitDataConId))
869 = newFailLocalDs ty `thenDs` \ fail_var ->
870 returnDs (NonRec fail_var expr, Var fail_var)