2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Desugaring exporessions.
9 module DsExpr ( dsExpr, dsLExpr, dsLocalBinds, dsValBinds, dsLit ) where
11 #include "HsVersions.h"
25 -- Template Haskell stuff iff bootstrapped
32 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
33 -- needs to see source types
54 %************************************************************************
56 dsLocalBinds, dsValBinds
58 %************************************************************************
61 dsLocalBinds :: HsLocalBinds Id -> CoreExpr -> DsM CoreExpr
62 dsLocalBinds EmptyLocalBinds body = return body
63 dsLocalBinds (HsValBinds binds) body = dsValBinds binds body
64 dsLocalBinds (HsIPBinds binds) body = dsIPBinds binds body
66 -------------------------
67 dsValBinds :: HsValBinds Id -> CoreExpr -> DsM CoreExpr
68 dsValBinds (ValBindsOut binds _) body = foldrDs ds_val_bind body binds
70 -------------------------
71 dsIPBinds (IPBinds ip_binds dict_binds) body
72 = do { prs <- dsLHsBinds dict_binds
73 ; let inner = Let (Rec prs) body
74 -- The dict bindings may not be in
75 -- dependency order; hence Rec
76 ; foldrDs ds_ip_bind inner ip_binds }
78 ds_ip_bind (L _ (IPBind n e)) body
79 = dsLExpr e `thenDs` \ e' ->
80 returnDs (Let (NonRec (ipNameName n) e') body)
82 -------------------------
83 ds_val_bind :: (RecFlag, LHsBinds Id) -> CoreExpr -> DsM CoreExpr
84 -- Special case for bindings which bind unlifted variables
85 -- We need to do a case right away, rather than building
86 -- a tuple and doing selections.
87 -- Silently ignore INLINE and SPECIALISE pragmas...
88 ds_val_bind (NonRecursive, hsbinds) body
89 | [L _ (AbsBinds [] [] exports binds)] <- bagToList hsbinds,
90 (L loc bind : null_binds) <- bagToList binds,
92 || isUnboxedTupleBind bind
93 || or [isUnLiftedType (idType g) | (_, g, _, _) <- exports]
95 body_w_exports = foldr bind_export body exports
96 bind_export (tvs, g, l, _) body = ASSERT( null tvs )
97 bindNonRec g (Var l) body
99 ASSERT (null null_binds)
100 -- Non-recursive, non-overloaded bindings only come in ones
101 -- ToDo: in some bizarre case it's conceivable that there
102 -- could be dict binds in the 'binds'. (See the notes
103 -- below. Then pattern-match would fail. Urk.)
106 FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn, fun_tick = tick }
107 -> matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, rhs) ->
108 ASSERT( null args ) -- Functions aren't lifted
109 ASSERT( isIdHsWrapper co_fn )
110 mkOptTickBox tick rhs `thenDs` \ rhs' ->
111 returnDs (bindNonRec fun rhs' body_w_exports)
113 PatBind {pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }
114 -> -- let C x# y# = rhs in body
115 -- ==> case rhs of C x# y# -> body
117 do { rhs <- dsGuarded grhss ty
118 ; let upat = unLoc pat
119 eqn = EqnInfo { eqn_pats = [upat],
120 eqn_rhs = cantFailMatchResult body_w_exports }
121 ; var <- selectMatchVar upat
122 ; result <- matchEquations PatBindRhs [var] [eqn] (exprType body)
123 ; return (scrungleMatch var rhs result) }
125 other -> pprPanic "dsLet: unlifted" (pprLHsBinds hsbinds $$ ppr body)
128 -- Ordinary case for bindings; none should be unlifted
129 ds_val_bind (is_rec, binds) body
130 = do { prs <- dsLHsBinds binds
131 ; ASSERT( not (any (isUnLiftedType . idType . fst) prs) )
134 other -> return (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
146 isUnboxedTupleBind :: HsBind Id -> Bool
147 isUnboxedTupleBind (PatBind { pat_rhs_ty = ty }) = isUnboxedTupleType ty
148 isUnboxedTupleBind other = False
150 scrungleMatch :: Id -> CoreExpr -> CoreExpr -> CoreExpr
151 -- Returns something like (let var = scrut in body)
152 -- but if var is an unboxed-tuple type, it inlines it in a fragile way
153 -- Special case to handle unboxed tuple patterns; they can't appear nested
155 -- case e of (# p1, p2 #) -> rhs
157 -- case e of (# x1, x2 #) -> ... match p1, p2 ...
159 -- let x = e in case x of ....
161 -- But there may be a big
162 -- let fail = ... in case e of ...
163 -- wrapping the whole case, which complicates matters slightly
164 -- It all seems a bit fragile. Test is dsrun013.
166 scrungleMatch var scrut body
167 | isUnboxedTupleType (idType var) = scrungle body
168 | otherwise = bindNonRec var scrut body
170 scrungle (Case (Var x) bndr ty alts)
171 | x == var = Case scrut bndr ty alts
172 scrungle (Let binds body) = Let binds (scrungle body)
173 scrungle other = panic ("scrungleMatch: tuple pattern:\n" ++ showSDoc (ppr other))
177 %************************************************************************
179 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
181 %************************************************************************
184 dsLExpr :: LHsExpr Id -> DsM CoreExpr
186 dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e
188 dsExpr :: HsExpr Id -> DsM CoreExpr
189 dsExpr (HsPar e) = dsLExpr e
190 dsExpr (ExprWithTySigOut e _) = dsLExpr e
191 dsExpr (HsVar var) = returnDs (Var var)
192 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
193 dsExpr (HsLit lit) = dsLit lit
194 dsExpr (HsOverLit lit) = dsOverLit lit
195 dsExpr (HsWrap co_fn e) = dsCoercion co_fn (dsExpr e)
197 dsExpr (NegApp expr neg_expr)
198 = do { core_expr <- dsLExpr expr
199 ; core_neg <- dsExpr neg_expr
200 ; return (core_neg `App` core_expr) }
202 dsExpr expr@(HsLam a_Match)
203 = matchWrapper LambdaExpr a_Match `thenDs` \ (binders, matching_code) ->
204 returnDs (mkLams binders matching_code)
206 dsExpr expr@(HsApp fun arg)
207 = dsLExpr fun `thenDs` \ core_fun ->
208 dsLExpr arg `thenDs` \ core_arg ->
209 returnDs (core_fun `mkDsApp` core_arg)
212 Operator sections. At first it looks as if we can convert
221 But no! expr might be a redex, and we can lose laziness badly this
226 for example. So we convert instead to
228 let y = expr in \x -> op y x
230 If \tr{expr} is actually just a variable, say, then the simplifier
234 dsExpr (OpApp e1 op _ e2)
235 = dsLExpr op `thenDs` \ core_op ->
236 -- for the type of y, we need the type of op's 2nd argument
237 dsLExpr e1 `thenDs` \ x_core ->
238 dsLExpr e2 `thenDs` \ y_core ->
239 returnDs (mkDsApps core_op [x_core, y_core])
241 dsExpr (SectionL expr op) -- Desugar (e !) to ((!) e)
242 = dsLExpr op `thenDs` \ core_op ->
243 dsLExpr expr `thenDs` \ x_core ->
244 returnDs (mkDsApp core_op x_core)
246 -- dsLExpr (SectionR op expr) -- \ x -> op x expr
247 dsExpr (SectionR op expr)
248 = dsLExpr op `thenDs` \ core_op ->
249 -- for the type of x, we need the type of op's 2nd argument
251 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
252 -- See comment with SectionL
254 dsLExpr expr `thenDs` \ y_core ->
255 newSysLocalDs x_ty `thenDs` \ x_id ->
256 newSysLocalDs y_ty `thenDs` \ y_id ->
258 returnDs (bindNonRec y_id y_core $
259 Lam x_id (mkDsApps core_op [Var x_id, Var y_id]))
261 dsExpr (HsSCC cc expr)
262 = dsLExpr expr `thenDs` \ core_expr ->
263 getModuleDs `thenDs` \ mod_name ->
264 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
267 -- hdaume: core annotation
269 dsExpr (HsCoreAnn fs expr)
270 = dsLExpr expr `thenDs` \ core_expr ->
271 returnDs (Note (CoreNote $ unpackFS fs) core_expr)
273 dsExpr (HsCase discrim matches)
274 = dsLExpr discrim `thenDs` \ core_discrim ->
275 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
276 returnDs (scrungleMatch discrim_var core_discrim matching_code)
278 -- Pepe: The binds are in scope in the body but NOT in the binding group
279 -- This is to avoid silliness in breakpoints
280 dsExpr (HsLet binds body)
281 = dsLExpr body `thenDs` \ body' ->
282 dsLocalBinds binds body'
284 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
285 -- because the interpretation of `stmts' depends on what sort of thing it is.
287 dsExpr (HsDo ListComp stmts body result_ty)
288 = -- Special case for list comprehensions
289 dsListComp stmts body elt_ty
291 [elt_ty] = tcTyConAppArgs result_ty
293 dsExpr (HsDo DoExpr stmts body result_ty)
294 = dsDo stmts body result_ty
296 dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
297 = dsMDo tbl stmts body result_ty
299 dsExpr (HsDo PArrComp stmts body result_ty)
300 = -- Special case for array comprehensions
301 dsPArrComp (map unLoc stmts) body elt_ty
303 [elt_ty] = tcTyConAppArgs result_ty
305 dsExpr (HsIf guard_expr then_expr else_expr)
306 = dsLExpr guard_expr `thenDs` \ core_guard ->
307 dsLExpr then_expr `thenDs` \ core_then ->
308 dsLExpr else_expr `thenDs` \ core_else ->
309 returnDs (mkIfThenElse core_guard core_then core_else)
314 \underline{\bf Various data construction things}
315 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
317 dsExpr (ExplicitList ty xs)
320 go [] = returnDs (mkNilExpr ty)
321 go (x:xs) = dsLExpr x `thenDs` \ core_x ->
322 go xs `thenDs` \ core_xs ->
323 returnDs (mkConsExpr ty core_x core_xs)
325 -- we create a list from the array elements and convert them into a list using
328 -- * the main disadvantage to this scheme is that `toP' traverses the list
329 -- twice: once to determine the length and a second time to put to elements
330 -- into the array; this inefficiency could be avoided by exposing some of
331 -- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
332 -- that we can exploit the fact that we already know the length of the array
333 -- here at compile time
335 dsExpr (ExplicitPArr ty xs)
336 = dsLookupGlobalId toPName `thenDs` \toP ->
337 dsExpr (ExplicitList ty xs) `thenDs` \coreList ->
338 returnDs (mkApps (Var toP) [Type ty, coreList])
340 dsExpr (ExplicitTuple expr_list boxity)
341 = mappM dsLExpr expr_list `thenDs` \ core_exprs ->
342 returnDs (mkConApp (tupleCon boxity (length expr_list))
343 (map (Type . exprType) core_exprs ++ core_exprs))
345 dsExpr (ArithSeq expr (From from))
346 = dsExpr expr `thenDs` \ expr2 ->
347 dsLExpr from `thenDs` \ from2 ->
348 returnDs (App expr2 from2)
350 dsExpr (ArithSeq expr (FromTo from two))
351 = dsExpr expr `thenDs` \ expr2 ->
352 dsLExpr from `thenDs` \ from2 ->
353 dsLExpr two `thenDs` \ two2 ->
354 returnDs (mkApps expr2 [from2, two2])
356 dsExpr (ArithSeq expr (FromThen from thn))
357 = dsExpr expr `thenDs` \ expr2 ->
358 dsLExpr from `thenDs` \ from2 ->
359 dsLExpr thn `thenDs` \ thn2 ->
360 returnDs (mkApps expr2 [from2, thn2])
362 dsExpr (ArithSeq expr (FromThenTo from thn two))
363 = dsExpr expr `thenDs` \ expr2 ->
364 dsLExpr from `thenDs` \ from2 ->
365 dsLExpr thn `thenDs` \ thn2 ->
366 dsLExpr two `thenDs` \ two2 ->
367 returnDs (mkApps expr2 [from2, thn2, two2])
369 dsExpr (PArrSeq expr (FromTo from two))
370 = dsExpr expr `thenDs` \ expr2 ->
371 dsLExpr from `thenDs` \ from2 ->
372 dsLExpr two `thenDs` \ two2 ->
373 returnDs (mkApps expr2 [from2, two2])
375 dsExpr (PArrSeq expr (FromThenTo from thn two))
376 = dsExpr expr `thenDs` \ expr2 ->
377 dsLExpr from `thenDs` \ from2 ->
378 dsLExpr thn `thenDs` \ thn2 ->
379 dsLExpr two `thenDs` \ two2 ->
380 returnDs (mkApps expr2 [from2, thn2, two2])
382 dsExpr (PArrSeq expr _)
383 = panic "DsExpr.dsExpr: Infinite parallel array!"
384 -- the parser shouldn't have generated it and the renamer and typechecker
385 -- shouldn't have let it through
389 \underline{\bf Record construction and update}
390 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
391 For record construction we do this (assuming T has three arguments)
395 let err = /\a -> recConErr a
396 T (recConErr t1 "M.lhs/230/op1")
398 (recConErr t1 "M.lhs/230/op3")
400 @recConErr@ then converts its arugment string into a proper message
401 before printing it as
403 M.lhs, line 230: missing field op1 was evaluated
406 We also handle @C{}@ as valid construction syntax for an unlabelled
407 constructor @C@, setting all of @C@'s fields to bottom.
410 dsExpr (RecordCon (L _ data_con_id) con_expr (HsRecordBinds rbinds))
411 = dsExpr con_expr `thenDs` \ con_expr' ->
413 (arg_tys, _) = tcSplitFunTys (exprType con_expr')
414 -- A newtype in the corner should be opaque;
415 -- hence TcType.tcSplitFunTys
417 mk_arg (arg_ty, lbl) -- Selector id has the field label as its name
418 = case [rhs | (L _ sel_id, rhs) <- rbinds, lbl == idName sel_id] of
419 (rhs:rhss) -> ASSERT( null rhss )
421 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
422 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
424 labels = dataConFieldLabels (idDataCon data_con_id)
425 -- The data_con_id is guaranteed to be the wrapper id of the constructor
429 then mappM unlabelled_bottom arg_tys
430 else mappM mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels))
431 `thenDs` \ con_args ->
433 returnDs (mkApps con_expr' con_args)
436 Record update is a little harder. Suppose we have the decl:
438 data T = T1 {op1, op2, op3 :: Int}
439 | T2 {op4, op2 :: Int}
442 Then we translate as follows:
448 T1 op1 _ op3 -> T1 op1 op2 op3
449 T2 op4 _ -> T2 op4 op2
450 other -> recUpdError "M.lhs/230"
452 It's important that we use the constructor Ids for @T1@, @T2@ etc on the
453 RHSs, and do not generate a Core constructor application directly, because the constructor
454 might do some argument-evaluation first; and may have to throw away some
458 dsExpr (RecordUpd record_expr (HsRecordBinds []) _ _ _)
459 = dsLExpr record_expr
461 dsExpr expr@(RecordUpd record_expr (HsRecordBinds rbinds) cons_to_upd in_inst_tys out_inst_tys)
462 = -- Record stuff doesn't work for existentials
463 -- The type checker checks for this, but we need
464 -- worry only about the constructors that are to be updated
465 ASSERT2( notNull cons_to_upd && all isVanillaDataCon cons_to_upd, ppr expr )
467 do { record_expr' <- dsLExpr record_expr
468 ; let -- Awkwardly, for families, the match goes
469 -- from instance type to family type
470 tycon = dataConTyCon (head cons_to_upd)
471 in_ty = mkTyConApp tycon in_inst_tys
472 in_out_ty = mkFunTy in_ty
473 (mkFamilyTyConApp tycon out_inst_tys)
475 mk_val_arg field old_arg_id
476 = case [rhs | (L _ sel_id, rhs) <- rbinds, field == idName sel_id] of
477 (rhs:rest) -> ASSERT(null rest) rhs
478 [] -> nlHsVar old_arg_id
481 = ASSERT( isVanillaDataCon con )
482 do { arg_ids <- newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys)
483 -- This call to dataConInstOrigArgTys won't work for existentials
484 -- but existentials don't have record types anyway
485 ; let val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
486 (dataConFieldLabels con) arg_ids
487 rhs = foldl (\a b -> nlHsApp a b)
488 (nlHsTyApp (dataConWrapId con) out_inst_tys)
490 pat = mkPrefixConPat con (map nlVarPat arg_ids) in_ty
492 ; return (mkSimpleMatch [pat] rhs) }
494 -- It's important to generate the match with matchWrapper,
495 -- and the right hand sides with applications of the wrapper Id
496 -- so that everything works when we are doing fancy unboxing on the
497 -- constructor aguments.
498 ; alts <- mapM mk_alt cons_to_upd
499 ; ([discrim_var], matching_code) <- matchWrapper RecUpd (MatchGroup alts in_out_ty)
501 ; return (bindNonRec discrim_var record_expr' matching_code) }
504 Here is where we desugar the Template Haskell brackets and escapes
507 -- Template Haskell stuff
509 #ifdef GHCI /* Only if bootstrapping */
510 dsExpr (HsBracketOut x ps) = dsBracket x ps
511 dsExpr (HsSpliceE s) = pprPanic "dsExpr:splice" (ppr s)
514 -- Arrow notation extension
515 dsExpr (HsProc pat cmd) = dsProcExpr pat cmd
521 dsExpr (HsTick ix vars e) = do
525 -- There is a problem here. The then and else branches
526 -- have no free variables, so they are open to lifting.
527 -- We need someway of stopping this.
528 -- This will make no difference to binary coverage
529 -- (did you go here: YES or NO), but will effect accurate
532 dsExpr (HsBinTick ixT ixF e) = do
534 do { ASSERT(exprType e2 `coreEqType` boolTy)
535 mkBinaryTickBox ixT ixF e2
542 -- HsSyn constructs that just shouldn't be here:
543 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
548 %--------------------------------------------------------------------
550 Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
551 handled in DsListComp). Basically does the translation given in the
557 -> Type -- Type of the whole expression
560 dsDo stmts body result_ty
561 = go (map unLoc stmts)
565 go (ExprStmt rhs then_expr _ : stmts)
566 = do { rhs2 <- dsLExpr rhs
567 ; then_expr2 <- dsExpr then_expr
569 ; returnDs (mkApps then_expr2 [rhs2, rest]) }
571 go (LetStmt binds : stmts)
572 = do { rest <- go stmts
573 ; dsLocalBinds binds rest }
575 go (BindStmt pat rhs bind_op fail_op : stmts)
577 do { body <- go stmts
578 ; var <- selectSimpleMatchVarL pat
579 ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
580 result_ty (cantFailMatchResult body)
581 ; match_code <- handle_failure pat match fail_op
582 ; rhs' <- dsLExpr rhs
583 ; bind_op' <- dsExpr bind_op
584 ; returnDs (mkApps bind_op' [rhs', Lam var match_code]) }
586 -- In a do expression, pattern-match failure just calls
587 -- the monadic 'fail' rather than throwing an exception
588 handle_failure pat match fail_op
590 = do { fail_op' <- dsExpr fail_op
591 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
592 ; extractMatchResult match (App fail_op' fail_msg) }
594 = extractMatchResult match (error "It can't fail")
596 mk_fail_msg pat = "Pattern match failure in do expression at " ++
597 showSDoc (ppr (getLoc pat))
600 Translation for RecStmt's:
601 -----------------------------
602 We turn (RecStmt [v1,..vn] stmts) into:
604 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
611 -> Type -- Type of the whole expression
614 dsMDo tbl stmts body result_ty
615 = go (map unLoc stmts)
617 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
618 mfix_id = lookupEvidence tbl mfixName
619 return_id = lookupEvidence tbl returnMName
620 bind_id = lookupEvidence tbl bindMName
621 then_id = lookupEvidence tbl thenMName
622 fail_id = lookupEvidence tbl failMName
627 go (LetStmt binds : stmts)
628 = do { rest <- go stmts
629 ; dsLocalBinds binds rest }
631 go (ExprStmt rhs _ rhs_ty : stmts)
632 = do { rhs2 <- dsLExpr rhs
634 ; returnDs (mkApps (Var then_id) [Type rhs_ty, Type b_ty, rhs2, rest]) }
636 go (BindStmt pat rhs _ _ : stmts)
637 = do { body <- go stmts
638 ; var <- selectSimpleMatchVarL pat
639 ; match <- matchSinglePat (Var var) (StmtCtxt ctxt) pat
640 result_ty (cantFailMatchResult body)
641 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
642 ; let fail_expr = mkApps (Var fail_id) [Type b_ty, fail_msg]
643 ; match_code <- extractMatchResult match fail_expr
645 ; rhs' <- dsLExpr rhs
646 ; returnDs (mkApps (Var bind_id) [Type (hsLPatType pat), Type b_ty,
647 rhs', Lam var match_code]) }
649 go (RecStmt rec_stmts later_ids rec_ids rec_rets binds : stmts)
650 = ASSERT( length rec_ids > 0 )
651 ASSERT( length rec_ids == length rec_rets )
652 go (new_bind_stmt : let_stmt : stmts)
654 new_bind_stmt = mkBindStmt (mk_tup_pat later_pats) mfix_app
655 let_stmt = LetStmt (HsValBinds (ValBindsOut [(Recursive, binds)] []))
658 -- Remove the later_ids that appear (without fancy coercions)
659 -- in rec_rets, because there's no need to knot-tie them separately
660 -- See Note [RecStmt] in HsExpr
661 later_ids' = filter (`notElem` mono_rec_ids) later_ids
662 mono_rec_ids = [ id | HsVar id <- rec_rets ]
664 mfix_app = nlHsApp (nlHsTyApp mfix_id [tup_ty]) mfix_arg
665 mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [mfix_pat] body]
666 (mkFunTy tup_ty body_ty))
668 -- The rec_tup_pat must bind the rec_ids only; remember that the
669 -- trimmed_laters may share the same Names
670 -- Meanwhile, the later_pats must bind the later_vars
671 rec_tup_pats = map mk_wild_pat later_ids' ++ map nlVarPat rec_ids
672 later_pats = map nlVarPat later_ids' ++ map mk_later_pat rec_ids
673 rets = map nlHsVar later_ids' ++ map noLoc rec_rets
675 mfix_pat = noLoc $ LazyPat $ mk_tup_pat rec_tup_pats
676 body = noLoc $ HsDo ctxt rec_stmts return_app body_ty
677 body_ty = mkAppTy m_ty tup_ty
678 tup_ty = mkCoreTupTy (map idType (later_ids' ++ rec_ids))
679 -- mkCoreTupTy deals with singleton case
681 return_app = nlHsApp (nlHsTyApp return_id [tup_ty])
684 mk_wild_pat :: Id -> LPat Id
685 mk_wild_pat v = noLoc $ WildPat $ idType v
687 mk_later_pat :: Id -> LPat Id
688 mk_later_pat v | v `elem` later_ids' = mk_wild_pat v
689 | otherwise = nlVarPat v
691 mk_tup_pat :: [LPat Id] -> LPat Id
693 mk_tup_pat ps = noLoc $ mkVanillaTuplePat ps Boxed
695 mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id
697 mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed