2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsExpr]{Matching expressions (Exprs)}
7 module DsExpr ( dsExpr, dsLet, dsLit ) where
9 #include "HsVersions.h"
12 import Match ( matchWrapper, matchSimply )
13 import MatchLit ( dsLit )
14 import DsBinds ( dsMonoBinds, AutoScc(..) )
15 import DsGRHSs ( dsGuarded )
16 import DsCCall ( dsCCall )
17 import DsListComp ( dsListComp, dsPArrComp )
18 import DsUtils ( mkErrorAppDs, mkStringLit, mkConsExpr, mkNilExpr)
22 -- Template Haskell stuff iff bootstrapped
23 import DsMeta ( dsBracket )
26 import HsSyn ( failureFreePat,
27 HsExpr(..), Pat(..), HsLit(..), ArithSeqInfo(..),
28 Stmt(..), HsMatchContext(..), HsStmtContext(..),
29 Match(..), HsBinds(..), MonoBinds(..), HsConDetails(..),
30 mkSimpleMatch, isDoExpr
32 import TcHsSyn ( TypecheckedHsExpr, TypecheckedHsBinds, TypecheckedStmt, hsPatType )
34 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
35 -- needs to see source types (newtypes etc), and sometimes not
36 -- So WATCH OUT; check each use of split*Ty functions.
37 -- Sigh. This is a pain.
39 import TcType ( tcSplitAppTy, tcSplitFunTys, tcTyConAppArgs,
40 tcSplitTyConApp, isUnLiftedType, Type,
42 import Type ( splitFunTys )
44 import CoreUtils ( exprType, mkIfThenElse, bindNonRec )
46 import FieldLabel ( FieldLabel, fieldLabelTyCon )
47 import CostCentre ( mkUserCC )
48 import Id ( Id, idType, recordSelectorFieldLabel )
49 import PrelInfo ( rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID )
50 import DataCon ( DataCon, dataConWrapId, dataConFieldLabels, dataConInstOrigArgTys )
51 import DataCon ( isExistentialDataCon )
52 import TyCon ( tyConDataCons )
53 import TysWiredIn ( tupleCon, mkTupleTy )
54 import BasicTypes ( RecFlag(..), Boxity(..), ipNameName )
55 import PrelNames ( toPName )
56 import SrcLoc ( noSrcLoc )
57 import Util ( zipEqual, zipWithEqual )
63 %************************************************************************
67 %************************************************************************
69 @dsLet@ is a match-result transformer, taking the @MatchResult@ for the body
70 and transforming it into one for the let-bindings enclosing the body.
72 This may seem a bit odd, but (source) let bindings can contain unboxed
77 This must be transformed to a case expression and, if the type has
78 more than one constructor, may fail.
81 dsLet :: TypecheckedHsBinds -> CoreExpr -> DsM CoreExpr
86 dsLet (ThenBinds b1 b2) body
87 = dsLet b2 body `thenDs` \ body' ->
90 -- Special case for bindings which bind unlifted variables
91 -- We need to do a case right away, rather than building
92 -- a tuple and doing selections.
93 -- Silently ignore INLINE pragmas...
94 dsLet bind@(MonoBind (AbsBinds [] [] exports inlines binds) sigs is_rec) body
95 | or [isUnLiftedType (idType g) | (_, g, l) <- exports]
96 = ASSERT (case is_rec of {NonRecursive -> True; other -> False})
97 -- Unlifted bindings are always non-recursive
98 -- and are always a Fun or Pat monobind
100 -- ToDo: in some bizarre case it's conceivable that there
101 -- could be dict binds in the 'binds'. (See the notes
102 -- below. Then pattern-match would fail. Urk.)
104 FunMonoBind fun _ matches loc
106 matchWrapper (FunRhs fun) matches `thenDs` \ (args, rhs) ->
107 ASSERT( null args ) -- Functions aren't lifted
108 returnDs (bindNonRec fun rhs body_w_exports)
110 PatMonoBind pat grhss loc
112 dsGuarded grhss `thenDs` \ rhs ->
113 mk_error_app pat `thenDs` \ error_expr ->
114 matchSimply rhs PatBindRhs pat body_w_exports error_expr
116 other -> pprPanic "dsLet: unlifted" (ppr bind $$ ppr body)
118 body_w_exports = foldr bind_export body exports
119 bind_export (tvs, g, l) body = ASSERT( null tvs )
120 bindNonRec g (Var l) body
122 mk_error_app pat = mkErrorAppDs iRREFUT_PAT_ERROR_ID
126 -- Ordinary case for bindings
127 dsLet (MonoBind binds sigs is_rec) body
128 = dsMonoBinds NoSccs binds [] `thenDs` \ prs ->
129 returnDs (Let (Rec prs) body)
130 -- Use a Rec regardless of is_rec.
131 -- Why? Because it allows the MonoBinds to be all
132 -- mixed up, which is what happens in one rare case
133 -- Namely, for an AbsBind with no tyvars and no dicts,
134 -- but which does have dictionary bindings.
135 -- See notes with TcSimplify.inferLoop [NO TYVARS]
136 -- It turned out that wrapping a Rec here was the easiest solution
138 -- NB The previous case dealt with unlifted bindings, so we
139 -- only have to deal with lifted ones now; so Rec is ok
142 %************************************************************************
144 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
146 %************************************************************************
149 dsExpr :: TypecheckedHsExpr -> DsM CoreExpr
151 dsExpr (HsPar x) = dsExpr x
152 dsExpr (HsVar var) = returnDs (Var var)
153 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
154 dsExpr (HsLit lit) = dsLit lit
155 -- HsOverLit has been gotten rid of by the type checker
157 dsExpr expr@(HsLam a_Match)
158 = matchWrapper LambdaExpr [a_Match] `thenDs` \ (binders, matching_code) ->
159 returnDs (mkLams binders matching_code)
161 dsExpr expr@(HsApp fun arg)
162 = dsExpr fun `thenDs` \ core_fun ->
163 dsExpr arg `thenDs` \ core_arg ->
164 returnDs (core_fun `App` core_arg)
167 Operator sections. At first it looks as if we can convert
176 But no! expr might be a redex, and we can lose laziness badly this
181 for example. So we convert instead to
183 let y = expr in \x -> op y x
185 If \tr{expr} is actually just a variable, say, then the simplifier
189 dsExpr (OpApp e1 op _ e2)
190 = dsExpr op `thenDs` \ core_op ->
191 -- for the type of y, we need the type of op's 2nd argument
192 dsExpr e1 `thenDs` \ x_core ->
193 dsExpr e2 `thenDs` \ y_core ->
194 returnDs (mkApps core_op [x_core, y_core])
196 dsExpr (SectionL expr op)
197 = dsExpr op `thenDs` \ core_op ->
198 -- for the type of y, we need the type of op's 2nd argument
200 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
201 -- Must look through an implicit-parameter type;
202 -- newtype impossible; hence Type.splitFunTys
204 dsExpr expr `thenDs` \ x_core ->
205 newSysLocalDs x_ty `thenDs` \ x_id ->
206 newSysLocalDs y_ty `thenDs` \ y_id ->
208 returnDs (bindNonRec x_id x_core $
209 Lam y_id (mkApps core_op [Var x_id, Var y_id]))
211 -- dsExpr (SectionR op expr) -- \ x -> op x expr
212 dsExpr (SectionR op expr)
213 = dsExpr op `thenDs` \ core_op ->
214 -- for the type of x, we need the type of op's 2nd argument
216 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
217 -- See comment with SectionL
219 dsExpr expr `thenDs` \ y_core ->
220 newSysLocalDs x_ty `thenDs` \ x_id ->
221 newSysLocalDs y_ty `thenDs` \ y_id ->
223 returnDs (bindNonRec y_id y_core $
224 Lam x_id (mkApps core_op [Var x_id, Var y_id]))
226 dsExpr (HsCCall lbl args may_gc is_asm result_ty)
227 = mapDs dsExpr args `thenDs` \ core_args ->
228 dsCCall lbl core_args may_gc is_asm result_ty
229 -- dsCCall does all the unboxification, etc.
231 dsExpr (HsSCC cc expr)
232 = dsExpr expr `thenDs` \ core_expr ->
233 getModuleDs `thenDs` \ mod_name ->
234 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
236 -- special case to handle unboxed tuple patterns.
238 dsExpr (HsCase discrim matches src_loc)
239 | all ubx_tuple_match matches
240 = putSrcLocDs src_loc $
241 dsExpr discrim `thenDs` \ core_discrim ->
242 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
243 case matching_code of
244 Case (Var x) bndr alts | x == discrim_var ->
245 returnDs (Case core_discrim bndr alts)
246 _ -> panic ("dsExpr: tuple pattern:\n" ++ showSDoc (ppr matching_code))
248 ubx_tuple_match (Match [TuplePat ps Unboxed] _ _) = True
249 ubx_tuple_match _ = False
251 dsExpr (HsCase discrim matches src_loc)
252 = putSrcLocDs src_loc $
253 dsExpr discrim `thenDs` \ core_discrim ->
254 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
255 returnDs (bindNonRec discrim_var core_discrim matching_code)
257 dsExpr (HsLet binds body)
258 = dsExpr body `thenDs` \ body' ->
261 dsExpr (HsWith expr binds is_with)
262 = dsExpr expr `thenDs` \ expr' ->
263 foldlDs dsIPBind expr' binds
266 = dsExpr e `thenDs` \ e' ->
267 returnDs (Let (NonRec (ipNameName n) e') body)
269 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
270 -- because the interpretation of `stmts' depends on what sort of thing it is.
272 dsExpr (HsDo ListComp stmts _ result_ty src_loc)
273 = -- Special case for list comprehensions
274 putSrcLocDs src_loc $
275 dsListComp stmts elt_ty
277 (_, [elt_ty]) = tcSplitTyConApp result_ty
279 dsExpr (HsDo do_or_lc stmts ids result_ty src_loc)
281 = putSrcLocDs src_loc $
282 dsDo do_or_lc stmts ids result_ty
284 dsExpr (HsDo PArrComp stmts _ result_ty src_loc)
285 = -- Special case for array comprehensions
286 putSrcLocDs src_loc $
287 dsPArrComp stmts elt_ty
289 (_, [elt_ty]) = tcSplitTyConApp result_ty
291 dsExpr (HsIf guard_expr then_expr else_expr src_loc)
292 = putSrcLocDs src_loc $
293 dsExpr guard_expr `thenDs` \ core_guard ->
294 dsExpr then_expr `thenDs` \ core_then ->
295 dsExpr else_expr `thenDs` \ core_else ->
296 returnDs (mkIfThenElse core_guard core_then core_else)
301 \underline{\bf Type lambda and application}
302 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~
304 dsExpr (TyLam tyvars expr)
305 = dsExpr expr `thenDs` \ core_expr ->
306 returnDs (mkLams tyvars core_expr)
308 dsExpr (TyApp expr tys)
309 = dsExpr expr `thenDs` \ core_expr ->
310 returnDs (mkTyApps core_expr tys)
315 \underline{\bf Various data construction things}
316 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
318 dsExpr (ExplicitList ty xs)
321 go [] = returnDs (mkNilExpr ty)
322 go (x:xs) = dsExpr x `thenDs` \ core_x ->
323 go xs `thenDs` \ core_xs ->
324 returnDs (mkConsExpr ty core_x core_xs)
326 -- we create a list from the array elements and convert them into a list using
329 -- * the main disadvantage to this scheme is that `toP' traverses the list
330 -- twice: once to determine the length and a second time to put to elements
331 -- into the array; this inefficiency could be avoided by exposing some of
332 -- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
333 -- that we can exploit the fact that we already know the length of the array
334 -- here at compile time
336 dsExpr (ExplicitPArr ty xs)
337 = dsLookupGlobalId toPName `thenDs` \toP ->
338 dsExpr (ExplicitList ty xs) `thenDs` \coreList ->
339 returnDs (mkApps (Var toP) [Type ty, coreList])
341 dsExpr (ExplicitTuple expr_list boxity)
342 = mapDs dsExpr expr_list `thenDs` \ core_exprs ->
343 returnDs (mkConApp (tupleCon boxity (length expr_list))
344 (map (Type . exprType) core_exprs ++ core_exprs))
346 dsExpr (ArithSeqOut expr (From from))
347 = dsExpr expr `thenDs` \ expr2 ->
348 dsExpr from `thenDs` \ from2 ->
349 returnDs (App expr2 from2)
351 dsExpr (ArithSeqOut expr (FromTo from two))
352 = dsExpr expr `thenDs` \ expr2 ->
353 dsExpr from `thenDs` \ from2 ->
354 dsExpr two `thenDs` \ two2 ->
355 returnDs (mkApps expr2 [from2, two2])
357 dsExpr (ArithSeqOut expr (FromThen from thn))
358 = dsExpr expr `thenDs` \ expr2 ->
359 dsExpr from `thenDs` \ from2 ->
360 dsExpr thn `thenDs` \ thn2 ->
361 returnDs (mkApps expr2 [from2, thn2])
363 dsExpr (ArithSeqOut expr (FromThenTo from thn two))
364 = dsExpr expr `thenDs` \ expr2 ->
365 dsExpr from `thenDs` \ from2 ->
366 dsExpr thn `thenDs` \ thn2 ->
367 dsExpr two `thenDs` \ two2 ->
368 returnDs (mkApps expr2 [from2, thn2, two2])
370 dsExpr (PArrSeqOut expr (FromTo from two))
371 = dsExpr expr `thenDs` \ expr2 ->
372 dsExpr from `thenDs` \ from2 ->
373 dsExpr two `thenDs` \ two2 ->
374 returnDs (mkApps expr2 [from2, two2])
376 dsExpr (PArrSeqOut expr (FromThenTo from thn two))
377 = dsExpr expr `thenDs` \ expr2 ->
378 dsExpr from `thenDs` \ from2 ->
379 dsExpr thn `thenDs` \ thn2 ->
380 dsExpr two `thenDs` \ two2 ->
381 returnDs (mkApps expr2 [from2, thn2, two2])
383 dsExpr (PArrSeqOut expr _)
384 = panic "DsExpr.dsExpr: Infinite parallel array!"
385 -- the parser shouldn't have generated it and the renamer and typechecker
386 -- shouldn't have let it through
390 \underline{\bf Record construction and update}
391 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
392 For record construction we do this (assuming T has three arguments)
396 let err = /\a -> recConErr a
397 T (recConErr t1 "M.lhs/230/op1")
399 (recConErr t1 "M.lhs/230/op3")
401 @recConErr@ then converts its arugment string into a proper message
402 before printing it as
404 M.lhs, line 230: missing field op1 was evaluated
407 We also handle @C{}@ as valid construction syntax for an unlabelled
408 constructor @C@, setting all of @C@'s fields to bottom.
411 dsExpr (RecordConOut data_con con_expr rbinds)
412 = dsExpr con_expr `thenDs` \ con_expr' ->
414 (arg_tys, _) = tcSplitFunTys (exprType con_expr')
415 -- A newtype in the corner should be opaque;
416 -- hence TcType.tcSplitFunTys
419 = case [rhs | (sel_id,rhs) <- rbinds,
420 lbl == recordSelectorFieldLabel sel_id] of
421 (rhs:rhss) -> ASSERT( null rhss )
423 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
424 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
426 labels = dataConFieldLabels data_con
430 then mapDs unlabelled_bottom arg_tys
431 else mapDs mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels))
432 `thenDs` \ con_args ->
434 returnDs (mkApps con_expr' con_args)
437 Record update is a little harder. Suppose we have the decl:
439 data T = T1 {op1, op2, op3 :: Int}
440 | T2 {op4, op2 :: Int}
443 Then we translate as follows:
449 T1 op1 _ op3 -> T1 op1 op2 op3
450 T2 op4 _ -> T2 op4 op2
451 other -> recUpdError "M.lhs/230"
453 It's important that we use the constructor Ids for @T1@, @T2@ etc on the
454 RHSs, and do not generate a Core constructor application directly, because the constructor
455 might do some argument-evaluation first; and may have to throw away some
459 dsExpr (RecordUpdOut record_expr record_in_ty record_out_ty [])
462 dsExpr expr@(RecordUpdOut record_expr record_in_ty record_out_ty rbinds)
463 = getSrcLocDs `thenDs` \ src_loc ->
464 dsExpr record_expr `thenDs` \ record_expr' ->
466 -- Desugar the rbinds, and generate let-bindings if
467 -- necessary so that we don't lose sharing
470 in_inst_tys = tcTyConAppArgs record_in_ty -- Newtype opaque
471 out_inst_tys = tcTyConAppArgs record_out_ty -- Newtype opaque
473 mk_val_arg field old_arg_id
474 = case [rhs | (sel_id, rhs) <- rbinds,
475 field == recordSelectorFieldLabel sel_id] of
476 (rhs:rest) -> ASSERT(null rest) rhs
477 [] -> HsVar old_arg_id
480 = newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids ->
481 -- This call to dataConArgTys won't work for existentials
483 val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
484 (dataConFieldLabels con) arg_ids
485 rhs = foldl HsApp (TyApp (HsVar (dataConWrapId con)) out_inst_tys)
488 returnDs (mkSimpleMatch [ConPatOut con (PrefixCon (map VarPat arg_ids)) record_in_ty [] []]
493 -- Record stuff doesn't work for existentials
494 -- The type checker checks for this, but we need
495 -- worry only about the constructors that are to be updated
496 ASSERT2( all (not . isExistentialDataCon) cons_to_upd, ppr expr )
498 -- It's important to generate the match with matchWrapper,
499 -- and the right hand sides with applications of the wrapper Id
500 -- so that everything works when we are doing fancy unboxing on the
501 -- constructor aguments.
502 mapDs mk_alt cons_to_upd `thenDs` \ alts ->
503 matchWrapper RecUpd alts `thenDs` \ ([discrim_var], matching_code) ->
505 returnDs (bindNonRec discrim_var record_expr' matching_code)
508 updated_fields :: [FieldLabel]
509 updated_fields = [recordSelectorFieldLabel sel_id | (sel_id,_) <- rbinds]
511 -- Get the type constructor from the first field label,
512 -- so that we are sure it'll have all its DataCons
513 -- (In GHCI, it's possible that some TyCons may not have all
514 -- their constructors, in a module-loop situation.)
515 tycon = fieldLabelTyCon (head updated_fields)
516 data_cons = tyConDataCons tycon
517 cons_to_upd = filter has_all_fields data_cons
519 has_all_fields :: DataCon -> Bool
520 has_all_fields con_id
521 = all (`elem` con_fields) updated_fields
523 con_fields = dataConFieldLabels con_id
528 \underline{\bf Dictionary lambda and application}
529 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
530 @DictLam@ and @DictApp@ turn into the regular old things.
531 (OLD:) @DictFunApp@ also becomes a curried application, albeit slightly more
532 complicated; reminiscent of fully-applied constructors.
534 dsExpr (DictLam dictvars expr)
535 = dsExpr expr `thenDs` \ core_expr ->
536 returnDs (mkLams dictvars core_expr)
540 dsExpr (DictApp expr dicts) -- becomes a curried application
541 = dsExpr expr `thenDs` \ core_expr ->
542 returnDs (foldl (\f d -> f `App` (Var d)) core_expr dicts)
545 Here is where we desugar the Template Haskell brackets and escapes
548 -- Template Haskell stuff
550 #ifdef GHCI /* Only if bootstrapping */
551 dsExpr (HsBracketOut x ps) = dsBracket x ps
552 dsExpr (HsSplice n e) = pprPanic "dsExpr:splice" (ppr e)
561 -- HsSyn constructs that just shouldn't be here:
562 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
563 dsExpr (ArithSeqIn _) = panic "dsExpr:ArithSeqIn"
564 dsExpr (PArrSeqIn _) = panic "dsExpr:PArrSeqIn"
569 %--------------------------------------------------------------------
571 Basically does the translation given in the Haskell~1.3 report:
574 dsDo :: HsStmtContext
576 -> [Id] -- id for: [return,fail,>>=,>>] and possibly mfixName
577 -> Type -- Element type; the whole expression has type (m t)
580 dsDo do_or_lc stmts ids result_ty
582 (return_id : fail_id : bind_id : then_id : _) = ids
583 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
584 is_do = isDoExpr do_or_lc -- True for both MDo and Do
586 -- For ExprStmt, see the comments near HsExpr.Stmt about
587 -- exactly what ExprStmts mean!
589 -- In dsDo we can only see DoStmt and ListComp (no guards)
591 go [ResultStmt expr locn]
592 | is_do = do_expr expr locn
593 | otherwise = do_expr expr locn `thenDs` \ expr2 ->
594 returnDs (mkApps (Var return_id) [Type b_ty, expr2])
596 go (ExprStmt expr a_ty locn : stmts)
597 | is_do -- Do expression
598 = do_expr expr locn `thenDs` \ expr2 ->
599 go stmts `thenDs` \ rest ->
600 returnDs (mkApps (Var then_id) [Type a_ty, Type b_ty, expr2, rest])
602 | otherwise -- List comprehension
603 = do_expr expr locn `thenDs` \ expr2 ->
604 go stmts `thenDs` \ rest ->
606 msg = "Pattern match failure in do expression, " ++ showSDoc (ppr locn)
608 mkStringLit msg `thenDs` \ core_msg ->
609 returnDs (mkIfThenElse expr2 rest
610 (App (App (Var fail_id) (Type b_ty)) core_msg))
612 go (LetStmt binds : stmts )
613 = go stmts `thenDs` \ rest ->
616 go (BindStmt pat expr locn : stmts)
618 dsExpr expr `thenDs` \ expr2 ->
621 fail_expr = HsApp (TyApp (HsVar fail_id) [b_ty])
622 (HsLit (HsString (mkFastString msg)))
623 msg = "Pattern match failure in do expression, " ++ showSDoc (ppr locn)
624 main_match = mkSimpleMatch [pat]
625 (HsDo do_or_lc stmts ids result_ty locn)
628 | failureFreePat pat = [main_match]
631 , mkSimpleMatch [WildPat a_ty] fail_expr result_ty locn
634 matchWrapper (StmtCtxt do_or_lc) the_matches `thenDs` \ (binders, matching_code) ->
635 returnDs (mkApps (Var bind_id) [Type a_ty, Type b_ty, expr2,
636 mkLams binders matching_code])
638 go (RecStmt rec_vars rec_stmts : stmts)
639 = go (bind_stmt : stmts)
641 bind_stmt = dsRecStmt m_ty ids rec_vars rec_stmts
647 do_expr expr locn = putSrcLocDs locn (dsExpr expr)
650 Translation for RecStmt's:
651 -----------------------------
652 We turn (RecStmt [v1,..vn] stmts) into:
654 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
658 dsRecStmt :: Type -- Monad type constructor :: * -> *
659 -> [Id] -- Ids for: [return,fail,>>=,>>,mfix]
660 -> [Id] -> [TypecheckedStmt] -- Guts of the RecStmt
662 dsRecStmt m_ty ids@[return_id, _, _, _, mfix_id] vars stmts
663 = BindStmt tup_pat mfix_app noSrcLoc
665 (var1:rest) = vars -- Always at least one
668 mfix_app = HsApp (TyApp (HsVar mfix_id) [tup_ty]) mfix_arg
669 mfix_arg = HsLam (mkSimpleMatch [tup_pat] body tup_ty noSrcLoc)
671 tup_expr | one_var = HsVar var1
672 | otherwise = ExplicitTuple (map HsVar vars) Boxed
673 tup_ty | one_var = idType var1
674 | otherwise = mkTupleTy Boxed (length vars) (map idType vars)
675 tup_pat | one_var = VarPat var1
676 | otherwise = LazyPat (TuplePat (map VarPat vars) Boxed)
678 body = HsDo DoExpr (stmts ++ [return_stmt])
679 ids -- Don't need the mfix, but it does no harm
680 (mkAppTy m_ty tup_ty)
683 return_stmt = ResultStmt return_app noSrcLoc
684 return_app = HsApp (TyApp (HsVar return_id) [tup_ty]) tup_expr