2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsExpr]{Matching expressions (Exprs)}
7 module DsExpr ( dsExpr, dsLExpr, dsLet, dsLit ) where
9 #include "HsVersions.h"
12 import Match ( matchWrapper, matchSimply )
13 import MatchLit ( dsLit )
14 import DsBinds ( dsHsBinds, AutoScc(..) )
15 import DsGRHSs ( dsGuarded )
16 import DsListComp ( dsListComp, dsPArrComp )
17 import DsUtils ( mkErrorAppDs, mkStringLit, mkConsExpr, mkNilExpr,
18 mkCoreTupTy, selectMatchVarL,
19 dsReboundNames, lookupReboundName )
20 import DsArrows ( dsProcExpr )
24 -- Template Haskell stuff iff bootstrapped
25 import DsMeta ( dsBracket )
29 import TcHsSyn ( hsPatType )
31 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
32 -- needs to see source types (newtypes etc), and sometimes not
33 -- So WATCH OUT; check each use of split*Ty functions.
34 -- Sigh. This is a pain.
36 import TcType ( tcSplitAppTy, tcSplitFunTys, tcTyConAppArgs,
37 tcSplitTyConApp, isUnLiftedType, Type,
39 import Type ( splitFunTys )
41 import CoreUtils ( exprType, mkIfThenElse, bindNonRec )
43 import FieldLabel ( FieldLabel, fieldLabelTyCon )
44 import CostCentre ( mkUserCC )
45 import Id ( Id, idType, idName, recordSelectorFieldLabel )
46 import PrelInfo ( rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID )
47 import DataCon ( DataCon, dataConWrapId, dataConFieldLabels, dataConInstOrigArgTys )
48 import DataCon ( isExistentialDataCon )
50 import TyCon ( tyConDataCons )
51 import TysWiredIn ( tupleCon )
52 import BasicTypes ( RecFlag(..), Boxity(..), ipNameName )
53 import PrelNames ( toPName,
54 returnMName, bindMName, thenMName, failMName,
56 import SrcLoc ( Located(..), unLoc, getLoc, noLoc )
57 import Util ( zipEqual, zipWithEqual )
58 import Bag ( bagToList )
64 %************************************************************************
68 %************************************************************************
70 @dsLet@ is a match-result transformer, taking the @MatchResult@ for the body
71 and transforming it into one for the let-bindings enclosing the body.
73 This may seem a bit odd, but (source) let bindings can contain unboxed
78 This must be transformed to a case expression and, if the type has
79 more than one constructor, may fail.
82 dsLet :: [HsBindGroup Id] -> CoreExpr -> DsM CoreExpr
83 dsLet groups body = foldlDs dsBindGroup body (reverse groups)
85 dsBindGroup :: CoreExpr -> HsBindGroup Id -> DsM CoreExpr
86 dsBindGroup body (HsIPBinds binds)
87 = foldlDs dsIPBind body binds
89 dsIPBind body (L _ (IPBind n e))
90 = dsLExpr e `thenDs` \ e' ->
91 returnDs (Let (NonRec (ipNameName n) e') body)
93 -- Special case for bindings which bind unlifted variables
94 -- We need to do a case right away, rather than building
95 -- a tuple and doing selections.
96 -- Silently ignore INLINE pragmas...
97 dsBindGroup body bind@(HsBindGroup hsbinds sigs is_rec)
98 | [L _ (AbsBinds [] [] exports inlines binds)] <- bagToList hsbinds,
99 or [isUnLiftedType (idType g) | (_, g, l) <- exports]
100 = ASSERT (case is_rec of {NonRecursive -> True; other -> False})
101 -- Unlifted bindings are always non-recursive
102 -- and are always a Fun or Pat monobind
104 -- ToDo: in some bizarre case it's conceivable that there
105 -- could be dict binds in the 'binds'. (See the notes
106 -- below. Then pattern-match would fail. Urk.)
108 body_w_exports = foldr bind_export body exports
109 bind_export (tvs, g, l) body = ASSERT( null tvs )
110 bindNonRec g (Var l) body
112 mk_error_app pat = mkErrorAppDs iRREFUT_PAT_ERROR_ID
116 case bagToList binds of
117 [L loc (FunBind (L _ fun) _ matches)]
118 -> putSrcSpanDs loc $
119 matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, rhs) ->
120 ASSERT( null args ) -- Functions aren't lifted
121 returnDs (bindNonRec fun rhs body_w_exports)
123 [L loc (PatBind pat grhss)]
124 -> putSrcSpanDs loc $
125 dsGuarded grhss `thenDs` \ rhs ->
126 mk_error_app pat `thenDs` \ error_expr ->
127 matchSimply rhs PatBindRhs pat body_w_exports error_expr
129 other -> pprPanic "dsLet: unlifted" (ppr bind $$ ppr body)
131 -- Ordinary case for bindings
132 dsBindGroup body (HsBindGroup binds sigs is_rec)
133 = dsHsBinds NoSccs binds [] `thenDs` \ prs ->
134 returnDs (Let (Rec prs) body)
135 -- Use a Rec regardless of is_rec.
136 -- Why? Because it allows the binds to be all
137 -- mixed up, which is what happens in one rare case
138 -- Namely, for an AbsBind with no tyvars and no dicts,
139 -- but which does have dictionary bindings.
140 -- See notes with TcSimplify.inferLoop [NO TYVARS]
141 -- It turned out that wrapping a Rec here was the easiest solution
143 -- NB The previous case dealt with unlifted bindings, so we
144 -- only have to deal with lifted ones now; so Rec is ok
147 %************************************************************************
149 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
151 %************************************************************************
154 dsLExpr :: LHsExpr Id -> DsM CoreExpr
155 dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e
157 dsExpr :: HsExpr Id -> DsM CoreExpr
159 dsExpr (HsPar e) = dsLExpr e
160 dsExpr (ExprWithTySigOut e _) = dsLExpr e
161 dsExpr (HsVar var) = returnDs (Var var)
162 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
163 dsExpr (HsLit lit) = dsLit lit
164 -- HsOverLit has been gotten rid of by the type checker
166 dsExpr expr@(HsLam a_Match)
167 = matchWrapper LambdaExpr [a_Match] `thenDs` \ (binders, matching_code) ->
168 returnDs (mkLams binders matching_code)
170 dsExpr expr@(HsApp fun arg)
171 = dsLExpr fun `thenDs` \ core_fun ->
172 dsLExpr arg `thenDs` \ core_arg ->
173 returnDs (core_fun `App` core_arg)
176 Operator sections. At first it looks as if we can convert
185 But no! expr might be a redex, and we can lose laziness badly this
190 for example. So we convert instead to
192 let y = expr in \x -> op y x
194 If \tr{expr} is actually just a variable, say, then the simplifier
198 dsExpr (OpApp e1 op _ e2)
199 = dsLExpr op `thenDs` \ core_op ->
200 -- for the type of y, we need the type of op's 2nd argument
201 dsLExpr e1 `thenDs` \ x_core ->
202 dsLExpr e2 `thenDs` \ y_core ->
203 returnDs (mkApps core_op [x_core, y_core])
205 dsExpr (SectionL expr op)
206 = dsLExpr op `thenDs` \ core_op ->
207 -- for the type of y, we need the type of op's 2nd argument
209 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
210 -- Must look through an implicit-parameter type;
211 -- newtype impossible; hence Type.splitFunTys
213 dsLExpr expr `thenDs` \ x_core ->
214 newSysLocalDs x_ty `thenDs` \ x_id ->
215 newSysLocalDs y_ty `thenDs` \ y_id ->
217 returnDs (bindNonRec x_id x_core $
218 Lam y_id (mkApps core_op [Var x_id, Var y_id]))
220 -- dsLExpr (SectionR op expr) -- \ x -> op x expr
221 dsExpr (SectionR op expr)
222 = dsLExpr op `thenDs` \ core_op ->
223 -- for the type of x, we need the type of op's 2nd argument
225 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
226 -- See comment with SectionL
228 dsLExpr expr `thenDs` \ y_core ->
229 newSysLocalDs x_ty `thenDs` \ x_id ->
230 newSysLocalDs y_ty `thenDs` \ y_id ->
232 returnDs (bindNonRec y_id y_core $
233 Lam x_id (mkApps core_op [Var x_id, Var y_id]))
235 dsExpr (HsSCC cc expr)
236 = dsLExpr expr `thenDs` \ core_expr ->
237 getModuleDs `thenDs` \ mod_name ->
238 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
241 -- hdaume: core annotation
243 dsExpr (HsCoreAnn fs expr)
244 = dsLExpr expr `thenDs` \ core_expr ->
245 returnDs (Note (CoreNote $ unpackFS fs) core_expr)
247 -- special case to handle unboxed tuple patterns.
249 dsExpr (HsCase discrim matches)
250 | all ubx_tuple_match matches
251 = dsLExpr discrim `thenDs` \ core_discrim ->
252 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
253 case matching_code of
254 Case (Var x) bndr alts | x == discrim_var ->
255 returnDs (Case core_discrim bndr alts)
256 _ -> panic ("dsLExpr: tuple pattern:\n" ++ showSDoc (ppr matching_code))
258 ubx_tuple_match (L _ (Match [L _ (TuplePat _ Unboxed)] _ _)) = True
259 ubx_tuple_match _ = False
261 dsExpr (HsCase discrim matches)
262 = dsLExpr discrim `thenDs` \ core_discrim ->
263 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
264 returnDs (bindNonRec discrim_var core_discrim matching_code)
266 dsExpr (HsLet binds body)
267 = dsLExpr body `thenDs` \ body' ->
270 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
271 -- because the interpretation of `stmts' depends on what sort of thing it is.
273 dsExpr (HsDo ListComp stmts _ result_ty)
274 = -- Special case for list comprehensions
275 dsListComp stmts elt_ty
277 (_, [elt_ty]) = tcSplitTyConApp result_ty
279 dsExpr (HsDo do_or_lc stmts ids result_ty)
281 = dsDo do_or_lc stmts ids result_ty
283 dsExpr (HsDo PArrComp stmts _ result_ty)
284 = -- Special case for array comprehensions
285 dsPArrComp (map unLoc stmts) elt_ty
287 (_, [elt_ty]) = tcSplitTyConApp result_ty
289 dsExpr (HsIf guard_expr then_expr else_expr)
290 = dsLExpr guard_expr `thenDs` \ core_guard ->
291 dsLExpr then_expr `thenDs` \ core_then ->
292 dsLExpr else_expr `thenDs` \ core_else ->
293 returnDs (mkIfThenElse core_guard core_then core_else)
298 \underline{\bf Type lambda and application}
299 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~
301 dsExpr (TyLam tyvars expr)
302 = dsLExpr expr `thenDs` \ core_expr ->
303 returnDs (mkLams tyvars core_expr)
305 dsExpr (TyApp expr tys)
306 = dsLExpr expr `thenDs` \ core_expr ->
307 returnDs (mkTyApps core_expr tys)
312 \underline{\bf Various data construction things}
313 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
315 dsExpr (ExplicitList ty xs)
318 go [] = returnDs (mkNilExpr ty)
319 go (x:xs) = dsLExpr x `thenDs` \ core_x ->
320 go xs `thenDs` \ core_xs ->
321 returnDs (mkConsExpr ty core_x core_xs)
323 -- we create a list from the array elements and convert them into a list using
326 -- * the main disadvantage to this scheme is that `toP' traverses the list
327 -- twice: once to determine the length and a second time to put to elements
328 -- into the array; this inefficiency could be avoided by exposing some of
329 -- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
330 -- that we can exploit the fact that we already know the length of the array
331 -- here at compile time
333 dsExpr (ExplicitPArr ty xs)
334 = dsLookupGlobalId toPName `thenDs` \toP ->
335 dsExpr (ExplicitList ty xs) `thenDs` \coreList ->
336 returnDs (mkApps (Var toP) [Type ty, coreList])
338 dsExpr (ExplicitTuple expr_list boxity)
339 = mappM dsLExpr expr_list `thenDs` \ core_exprs ->
340 returnDs (mkConApp (tupleCon boxity (length expr_list))
341 (map (Type . exprType) core_exprs ++ core_exprs))
343 dsExpr (ArithSeqOut expr (From from))
344 = dsLExpr expr `thenDs` \ expr2 ->
345 dsLExpr from `thenDs` \ from2 ->
346 returnDs (App expr2 from2)
348 dsExpr (ArithSeqOut expr (FromTo from two))
349 = dsLExpr expr `thenDs` \ expr2 ->
350 dsLExpr from `thenDs` \ from2 ->
351 dsLExpr two `thenDs` \ two2 ->
352 returnDs (mkApps expr2 [from2, two2])
354 dsExpr (ArithSeqOut expr (FromThen from thn))
355 = dsLExpr expr `thenDs` \ expr2 ->
356 dsLExpr from `thenDs` \ from2 ->
357 dsLExpr thn `thenDs` \ thn2 ->
358 returnDs (mkApps expr2 [from2, thn2])
360 dsExpr (ArithSeqOut expr (FromThenTo from thn two))
361 = dsLExpr expr `thenDs` \ expr2 ->
362 dsLExpr from `thenDs` \ from2 ->
363 dsLExpr thn `thenDs` \ thn2 ->
364 dsLExpr two `thenDs` \ two2 ->
365 returnDs (mkApps expr2 [from2, thn2, two2])
367 dsExpr (PArrSeqOut expr (FromTo from two))
368 = dsLExpr expr `thenDs` \ expr2 ->
369 dsLExpr from `thenDs` \ from2 ->
370 dsLExpr two `thenDs` \ two2 ->
371 returnDs (mkApps expr2 [from2, two2])
373 dsExpr (PArrSeqOut expr (FromThenTo from thn two))
374 = dsLExpr expr `thenDs` \ expr2 ->
375 dsLExpr from `thenDs` \ from2 ->
376 dsLExpr thn `thenDs` \ thn2 ->
377 dsLExpr two `thenDs` \ two2 ->
378 returnDs (mkApps expr2 [from2, thn2, two2])
380 dsExpr (PArrSeqOut expr _)
381 = panic "DsExpr.dsExpr: Infinite parallel array!"
382 -- the parser shouldn't have generated it and the renamer and typechecker
383 -- shouldn't have let it through
387 \underline{\bf Record construction and update}
388 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
389 For record construction we do this (assuming T has three arguments)
393 let err = /\a -> recConErr a
394 T (recConErr t1 "M.lhs/230/op1")
396 (recConErr t1 "M.lhs/230/op3")
398 @recConErr@ then converts its arugment string into a proper message
399 before printing it as
401 M.lhs, line 230: missing field op1 was evaluated
404 We also handle @C{}@ as valid construction syntax for an unlabelled
405 constructor @C@, setting all of @C@'s fields to bottom.
408 dsExpr (RecordConOut data_con con_expr rbinds)
409 = dsLExpr con_expr `thenDs` \ con_expr' ->
411 (arg_tys, _) = tcSplitFunTys (exprType con_expr')
412 -- A newtype in the corner should be opaque;
413 -- hence TcType.tcSplitFunTys
416 = case [rhs | (L _ sel_id, rhs) <- rbinds,
417 lbl == recordSelectorFieldLabel sel_id] of
418 (rhs:rhss) -> ASSERT( null rhss )
420 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
421 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
423 labels = dataConFieldLabels data_con
427 then mappM unlabelled_bottom arg_tys
428 else mappM mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels))
429 `thenDs` \ con_args ->
431 returnDs (mkApps con_expr' con_args)
434 Record update is a little harder. Suppose we have the decl:
436 data T = T1 {op1, op2, op3 :: Int}
437 | T2 {op4, op2 :: Int}
440 Then we translate as follows:
446 T1 op1 _ op3 -> T1 op1 op2 op3
447 T2 op4 _ -> T2 op4 op2
448 other -> recUpdError "M.lhs/230"
450 It's important that we use the constructor Ids for @T1@, @T2@ etc on the
451 RHSs, and do not generate a Core constructor application directly, because the constructor
452 might do some argument-evaluation first; and may have to throw away some
456 dsExpr (RecordUpdOut record_expr record_in_ty record_out_ty [])
457 = dsLExpr record_expr
459 dsExpr expr@(RecordUpdOut record_expr record_in_ty record_out_ty rbinds)
460 = dsLExpr record_expr `thenDs` \ record_expr' ->
462 -- Desugar the rbinds, and generate let-bindings if
463 -- necessary so that we don't lose sharing
466 in_inst_tys = tcTyConAppArgs record_in_ty -- Newtype opaque
467 out_inst_tys = tcTyConAppArgs record_out_ty -- Newtype opaque
469 mk_val_arg field old_arg_id
470 = case [rhs | (L _ sel_id, rhs) <- rbinds,
471 field == recordSelectorFieldLabel sel_id] of
472 (rhs:rest) -> ASSERT(null rest) rhs
473 [] -> nlHsVar old_arg_id
476 = newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids ->
477 -- This call to dataConArgTys won't work for existentials
479 val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
480 (dataConFieldLabels con) arg_ids
481 rhs = foldl (\a b -> nlHsApp a b)
482 (noLoc $ TyApp (nlHsVar (dataConWrapId con))
486 returnDs (mkSimpleMatch [noLoc $ ConPatOut con (PrefixCon (map nlVarPat arg_ids)) record_in_ty [] []]
490 -- Record stuff doesn't work for existentials
491 -- The type checker checks for this, but we need
492 -- worry only about the constructors that are to be updated
493 ASSERT2( all (not . isExistentialDataCon) cons_to_upd, ppr expr )
495 -- It's important to generate the match with matchWrapper,
496 -- and the right hand sides with applications of the wrapper Id
497 -- so that everything works when we are doing fancy unboxing on the
498 -- constructor aguments.
499 mappM mk_alt cons_to_upd `thenDs` \ alts ->
500 matchWrapper RecUpd alts `thenDs` \ ([discrim_var], matching_code) ->
502 returnDs (bindNonRec discrim_var record_expr' matching_code)
505 updated_fields :: [FieldLabel]
506 updated_fields = [ recordSelectorFieldLabel sel_id
507 | (L _ sel_id,_) <- rbinds]
509 -- Get the type constructor from the first field label,
510 -- so that we are sure it'll have all its DataCons
511 -- (In GHCI, it's possible that some TyCons may not have all
512 -- their constructors, in a module-loop situation.)
513 tycon = fieldLabelTyCon (head updated_fields)
514 data_cons = tyConDataCons tycon
515 cons_to_upd = filter has_all_fields data_cons
517 has_all_fields :: DataCon -> Bool
518 has_all_fields con_id
519 = all (`elem` con_fields) updated_fields
521 con_fields = dataConFieldLabels con_id
526 \underline{\bf Dictionary lambda and application}
527 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
528 @DictLam@ and @DictApp@ turn into the regular old things.
529 (OLD:) @DictFunApp@ also becomes a curried application, albeit slightly more
530 complicated; reminiscent of fully-applied constructors.
532 dsExpr (DictLam dictvars expr)
533 = dsLExpr expr `thenDs` \ core_expr ->
534 returnDs (mkLams dictvars core_expr)
538 dsExpr (DictApp expr dicts) -- becomes a curried application
539 = dsLExpr expr `thenDs` \ core_expr ->
540 returnDs (foldl (\f d -> f `App` (Var d)) core_expr dicts)
543 Here is where we desugar the Template Haskell brackets and escapes
546 -- Template Haskell stuff
548 #ifdef GHCI /* Only if bootstrapping */
549 dsExpr (HsBracketOut x ps) = dsBracket x ps
550 dsExpr (HsSpliceE s) = pprPanic "dsExpr:splice" (ppr s)
553 -- Arrow notation extension
554 dsExpr (HsProc pat cmd) = dsProcExpr pat cmd
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 Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
572 handled in DsListComp). Basically does the translation given in the
576 dsDo :: HsStmtContext Name
578 -> ReboundNames Id -- id for: [return,fail,>>=,>>] and possibly mfixName
579 -> Type -- Element type; the whole expression has type (m t)
582 dsDo do_or_lc stmts ids result_ty
583 = dsReboundNames ids `thenDs` \ (meth_binds, ds_meths) ->
585 return_id = lookupReboundName ds_meths returnMName
586 fail_id = lookupReboundName ds_meths failMName
587 bind_id = lookupReboundName ds_meths bindMName
588 then_id = lookupReboundName ds_meths thenMName
590 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
592 -- For ExprStmt, see the comments near HsExpr.Stmt about
593 -- exactly what ExprStmts mean!
595 -- In dsDo we can only see DoStmt and ListComp (no guards)
597 go [ResultStmt expr] = dsLExpr expr
600 go (ExprStmt expr a_ty : stmts)
601 = dsLExpr expr `thenDs` \ expr2 ->
602 go stmts `thenDs` \ rest ->
603 returnDs (mkApps then_id [Type a_ty, Type b_ty, expr2, rest])
605 go (LetStmt binds : stmts)
606 = go stmts `thenDs` \ rest ->
609 go (BindStmt pat expr : stmts)
610 = go stmts `thenDs` \ body ->
611 dsLExpr expr `thenDs` \ rhs ->
612 mkStringLit (mk_msg (getLoc pat)) `thenDs` \ core_msg ->
614 -- In a do expression, pattern-match failure just calls
615 -- the monadic 'fail' rather than throwing an exception
616 fail_expr = mkApps fail_id [Type b_ty, core_msg]
619 selectMatchVarL pat `thenDs` \ var ->
620 matchSimply (Var var) (StmtCtxt do_or_lc) pat
621 body fail_expr `thenDs` \ match_code ->
622 returnDs (mkApps bind_id [Type a_ty, Type b_ty, rhs, Lam var match_code])
624 go (RecStmt rec_stmts later_vars rec_vars rec_rets : stmts)
625 = go (bind_stmt : stmts)
627 bind_stmt = dsRecStmt m_ty ds_meths rec_stmts later_vars rec_vars rec_rets
630 go (map unLoc stmts) `thenDs` \ stmts_code ->
631 returnDs (foldr Let stmts_code meth_binds)
634 mk_msg locn = "Pattern match failure in do expression at " ++ showSDoc (ppr locn)
637 Translation for RecStmt's:
638 -----------------------------
639 We turn (RecStmt [v1,..vn] stmts) into:
641 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
645 dsRecStmt :: Type -- Monad type constructor :: * -> *
646 -> [(Name,Id)] -- Rebound Ids
648 -> [Id] -> [Id] -> [LHsExpr Id]
650 dsRecStmt m_ty ds_meths stmts later_vars rec_vars rec_rets
651 = ASSERT( length vars == length rets )
652 BindStmt tup_pat mfix_app
654 vars@(var1:rest) = later_vars ++ rec_vars -- Always at least one
655 rets@(ret1:_) = map nlHsVar later_vars ++ rec_rets
658 mfix_app = nlHsApp (noLoc $ TyApp (nlHsVar mfix_id) [tup_ty]) mfix_arg
659 mfix_arg = noLoc $ HsLam (mkSimpleMatch [tup_pat] body tup_ty)
661 tup_expr | one_var = ret1
662 | otherwise = noLoc $ ExplicitTuple rets Boxed
663 tup_ty = mkCoreTupTy (map idType vars)
664 -- Deals with singleton case
665 tup_pat | one_var = nlVarPat var1
666 | otherwise = noLoc $ LazyPat (noLoc $ TuplePat (map nlVarPat vars) Boxed)
668 body = noLoc $ HsDo DoExpr (stmts ++ [return_stmt])
669 [(n, HsVar id) | (n,id) <- ds_meths] -- A bit of a hack
670 (mkAppTy m_ty tup_ty)
672 Var return_id = lookupReboundName ds_meths returnMName
673 Var mfix_id = lookupReboundName ds_meths mfixName
675 return_stmt = noLoc $ ResultStmt return_app
676 return_app = nlHsApp (noLoc $ TyApp (nlHsVar return_id) [tup_ty]) tup_expr