2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Desugaring exporessions.
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 module DsExpr ( dsExpr, dsLExpr, dsLocalBinds, dsValBinds, dsLit ) where
18 #include "HsVersions.h"
33 -- Template Haskell stuff iff bootstrapped
40 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
41 -- needs to see source types
62 %************************************************************************
64 dsLocalBinds, dsValBinds
66 %************************************************************************
69 dsLocalBinds :: HsLocalBinds Id -> CoreExpr -> DsM CoreExpr
70 dsLocalBinds EmptyLocalBinds body = return body
71 dsLocalBinds (HsValBinds binds) body = dsValBinds binds body
72 dsLocalBinds (HsIPBinds binds) body = dsIPBinds binds body
74 -------------------------
75 dsValBinds :: HsValBinds Id -> CoreExpr -> DsM CoreExpr
76 dsValBinds (ValBindsOut binds _) body = foldrDs ds_val_bind body binds
78 -------------------------
79 dsIPBinds (IPBinds ip_binds dict_binds) body
80 = do { prs <- dsLHsBinds dict_binds
81 ; let inner = Let (Rec prs) body
82 -- The dict bindings may not be in
83 -- dependency order; hence Rec
84 ; foldrDs ds_ip_bind inner ip_binds }
86 ds_ip_bind (L _ (IPBind n e)) body
87 = dsLExpr e `thenDs` \ e' ->
88 returnDs (Let (NonRec (ipNameName n) e') body)
90 -------------------------
91 ds_val_bind :: (RecFlag, LHsBinds Id) -> CoreExpr -> DsM CoreExpr
92 -- Special case for bindings which bind unlifted variables
93 -- We need to do a case right away, rather than building
94 -- a tuple and doing selections.
95 -- Silently ignore INLINE and SPECIALISE pragmas...
96 ds_val_bind (NonRecursive, hsbinds) body
97 | [L _ (AbsBinds [] [] exports binds)] <- bagToList hsbinds,
98 (L loc bind : null_binds) <- bagToList binds,
100 || isUnboxedTupleBind bind
101 || or [isUnLiftedType (idType g) | (_, g, _, _) <- exports]
103 body_w_exports = foldr bind_export body exports
104 bind_export (tvs, g, l, _) body = ASSERT( null tvs )
105 bindNonRec g (Var l) body
107 ASSERT (null null_binds)
108 -- Non-recursive, non-overloaded bindings only come in ones
109 -- ToDo: in some bizarre case it's conceivable that there
110 -- could be dict binds in the 'binds'. (See the notes
111 -- below. Then pattern-match would fail. Urk.)
114 FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn,
115 fun_tick = tick, fun_infix = inf }
116 -> matchWrapper (FunRhs (idName fun ) inf) matches `thenDs` \ (args, rhs) ->
117 ASSERT( null args ) -- Functions aren't lifted
118 ASSERT( isIdHsWrapper co_fn )
119 mkOptTickBox tick rhs `thenDs` \ rhs' ->
120 returnDs (bindNonRec fun rhs' body_w_exports)
122 PatBind {pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }
123 -> -- let C x# y# = rhs in body
124 -- ==> case rhs of C x# y# -> body
126 do { rhs <- dsGuarded grhss ty
127 ; let upat = unLoc pat
128 eqn = EqnInfo { eqn_pats = [upat],
129 eqn_rhs = cantFailMatchResult body_w_exports }
130 ; var <- selectMatchVar upat
131 ; result <- matchEquations PatBindRhs [var] [eqn] (exprType body)
132 ; return (scrungleMatch var rhs result) }
134 other -> pprPanic "dsLet: unlifted" (pprLHsBinds hsbinds $$ ppr body)
137 -- Ordinary case for bindings; none should be unlifted
138 ds_val_bind (is_rec, binds) body
139 = do { prs <- dsLHsBinds binds
140 ; ASSERT( not (any (isUnLiftedType . idType . fst) prs) )
143 other -> return (Let (Rec prs) body) }
144 -- Use a Rec regardless of is_rec.
145 -- Why? Because it allows the binds to be all
146 -- mixed up, which is what happens in one rare case
147 -- Namely, for an AbsBind with no tyvars and no dicts,
148 -- but which does have dictionary bindings.
149 -- See notes with TcSimplify.inferLoop [NO TYVARS]
150 -- It turned out that wrapping a Rec here was the easiest solution
152 -- NB The previous case dealt with unlifted bindings, so we
153 -- only have to deal with lifted ones now; so Rec is ok
155 isUnboxedTupleBind :: HsBind Id -> Bool
156 isUnboxedTupleBind (PatBind { pat_rhs_ty = ty }) = isUnboxedTupleType ty
157 isUnboxedTupleBind other = False
159 scrungleMatch :: Id -> CoreExpr -> CoreExpr -> CoreExpr
160 -- Returns something like (let var = scrut in body)
161 -- but if var is an unboxed-tuple type, it inlines it in a fragile way
162 -- Special case to handle unboxed tuple patterns; they can't appear nested
164 -- case e of (# p1, p2 #) -> rhs
166 -- case e of (# x1, x2 #) -> ... match p1, p2 ...
168 -- let x = e in case x of ....
170 -- But there may be a big
171 -- let fail = ... in case e of ...
172 -- wrapping the whole case, which complicates matters slightly
173 -- It all seems a bit fragile. Test is dsrun013.
175 scrungleMatch var scrut body
176 | isUnboxedTupleType (idType var) = scrungle body
177 | otherwise = bindNonRec var scrut body
179 scrungle (Case (Var x) bndr ty alts)
180 | x == var = Case scrut bndr ty alts
181 scrungle (Let binds body) = Let binds (scrungle body)
182 scrungle other = panic ("scrungleMatch: tuple pattern:\n" ++ showSDoc (ppr other))
186 %************************************************************************
188 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
190 %************************************************************************
193 dsLExpr :: LHsExpr Id -> DsM CoreExpr
195 dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e
197 dsExpr :: HsExpr Id -> DsM CoreExpr
198 dsExpr (HsPar e) = dsLExpr e
199 dsExpr (ExprWithTySigOut e _) = dsLExpr e
200 dsExpr (HsVar var) = returnDs (Var var)
201 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
202 dsExpr (HsLit lit) = dsLit lit
203 dsExpr (HsOverLit lit) = dsOverLit lit
204 dsExpr (HsWrap co_fn e) = dsCoercion co_fn (dsExpr e)
206 dsExpr (NegApp expr neg_expr)
207 = do { core_expr <- dsLExpr expr
208 ; core_neg <- dsExpr neg_expr
209 ; return (core_neg `App` core_expr) }
211 dsExpr expr@(HsLam a_Match)
212 = matchWrapper LambdaExpr a_Match `thenDs` \ (binders, matching_code) ->
213 returnDs (mkLams binders matching_code)
215 dsExpr expr@(HsApp fun arg)
216 = dsLExpr fun `thenDs` \ core_fun ->
217 dsLExpr arg `thenDs` \ core_arg ->
218 returnDs (core_fun `mkDsApp` core_arg)
221 Operator sections. At first it looks as if we can convert
230 But no! expr might be a redex, and we can lose laziness badly this
235 for example. So we convert instead to
237 let y = expr in \x -> op y x
239 If \tr{expr} is actually just a variable, say, then the simplifier
243 dsExpr (OpApp e1 op _ e2)
244 = dsLExpr op `thenDs` \ core_op ->
245 -- for the type of y, we need the type of op's 2nd argument
246 dsLExpr e1 `thenDs` \ x_core ->
247 dsLExpr e2 `thenDs` \ y_core ->
248 returnDs (mkDsApps core_op [x_core, y_core])
250 dsExpr (SectionL expr op) -- Desugar (e !) to ((!) e)
251 = dsLExpr op `thenDs` \ core_op ->
252 dsLExpr expr `thenDs` \ x_core ->
253 returnDs (mkDsApp core_op x_core)
255 -- dsLExpr (SectionR op expr) -- \ x -> op x expr
256 dsExpr (SectionR op expr)
257 = dsLExpr op `thenDs` \ core_op ->
258 -- for the type of x, we need the type of op's 2nd argument
260 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
261 -- See comment with SectionL
263 dsLExpr expr `thenDs` \ y_core ->
264 newSysLocalDs x_ty `thenDs` \ x_id ->
265 newSysLocalDs y_ty `thenDs` \ y_id ->
267 returnDs (bindNonRec y_id y_core $
268 Lam x_id (mkDsApps core_op [Var x_id, Var y_id]))
270 dsExpr (HsSCC cc expr)
271 = dsLExpr expr `thenDs` \ core_expr ->
272 getModuleDs `thenDs` \ mod_name ->
273 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
276 -- hdaume: core annotation
278 dsExpr (HsCoreAnn fs expr)
279 = dsLExpr expr `thenDs` \ core_expr ->
280 returnDs (Note (CoreNote $ unpackFS fs) core_expr)
282 dsExpr (HsCase discrim matches)
283 = dsLExpr discrim `thenDs` \ core_discrim ->
284 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
285 returnDs (scrungleMatch discrim_var core_discrim matching_code)
287 -- Pepe: The binds are in scope in the body but NOT in the binding group
288 -- This is to avoid silliness in breakpoints
289 dsExpr (HsLet binds body)
290 = dsLExpr body `thenDs` \ body' ->
291 dsLocalBinds binds body'
293 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
294 -- because the interpretation of `stmts' depends on what sort of thing it is.
296 dsExpr (HsDo ListComp stmts body result_ty)
297 = -- Special case for list comprehensions
298 dsListComp stmts body elt_ty
300 [elt_ty] = tcTyConAppArgs result_ty
302 dsExpr (HsDo DoExpr stmts body result_ty)
303 = dsDo stmts body result_ty
305 dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
306 = dsMDo tbl stmts body result_ty
308 dsExpr (HsDo PArrComp stmts body result_ty)
309 = -- Special case for array comprehensions
310 dsPArrComp (map unLoc stmts) body elt_ty
312 [elt_ty] = tcTyConAppArgs result_ty
314 dsExpr (HsIf guard_expr then_expr else_expr)
315 = dsLExpr guard_expr `thenDs` \ core_guard ->
316 dsLExpr then_expr `thenDs` \ core_then ->
317 dsLExpr else_expr `thenDs` \ core_else ->
318 returnDs (mkIfThenElse core_guard core_then core_else)
323 \underline{\bf Various data construction things}
324 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
326 dsExpr (ExplicitList ty xs)
329 go [] = returnDs (mkNilExpr ty)
330 go (x:xs) = dsLExpr x `thenDs` \ core_x ->
331 go xs `thenDs` \ core_xs ->
332 returnDs (mkConsExpr ty core_x core_xs)
334 -- we create a list from the array elements and convert them into a list using
337 -- * the main disadvantage to this scheme is that `toP' traverses the list
338 -- twice: once to determine the length and a second time to put to elements
339 -- into the array; this inefficiency could be avoided by exposing some of
340 -- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
341 -- that we can exploit the fact that we already know the length of the array
342 -- here at compile time
344 dsExpr (ExplicitPArr ty xs)
345 = dsLookupGlobalId toPName `thenDs` \toP ->
346 dsExpr (ExplicitList ty xs) `thenDs` \coreList ->
347 returnDs (mkApps (Var toP) [Type ty, coreList])
349 dsExpr (ExplicitTuple expr_list boxity)
350 = mappM dsLExpr expr_list `thenDs` \ core_exprs ->
351 returnDs (mkConApp (tupleCon boxity (length expr_list))
352 (map (Type . exprType) core_exprs ++ core_exprs))
354 dsExpr (ArithSeq expr (From from))
355 = dsExpr expr `thenDs` \ expr2 ->
356 dsLExpr from `thenDs` \ from2 ->
357 returnDs (App expr2 from2)
359 dsExpr (ArithSeq expr (FromTo from two))
360 = dsExpr expr `thenDs` \ expr2 ->
361 dsLExpr from `thenDs` \ from2 ->
362 dsLExpr two `thenDs` \ two2 ->
363 returnDs (mkApps expr2 [from2, two2])
365 dsExpr (ArithSeq expr (FromThen from thn))
366 = dsExpr expr `thenDs` \ expr2 ->
367 dsLExpr from `thenDs` \ from2 ->
368 dsLExpr thn `thenDs` \ thn2 ->
369 returnDs (mkApps expr2 [from2, thn2])
371 dsExpr (ArithSeq expr (FromThenTo from thn two))
372 = dsExpr expr `thenDs` \ expr2 ->
373 dsLExpr from `thenDs` \ from2 ->
374 dsLExpr thn `thenDs` \ thn2 ->
375 dsLExpr two `thenDs` \ two2 ->
376 returnDs (mkApps expr2 [from2, thn2, two2])
378 dsExpr (PArrSeq expr (FromTo from two))
379 = dsExpr expr `thenDs` \ expr2 ->
380 dsLExpr from `thenDs` \ from2 ->
381 dsLExpr two `thenDs` \ two2 ->
382 returnDs (mkApps expr2 [from2, two2])
384 dsExpr (PArrSeq expr (FromThenTo from thn two))
385 = dsExpr expr `thenDs` \ expr2 ->
386 dsLExpr from `thenDs` \ from2 ->
387 dsLExpr thn `thenDs` \ thn2 ->
388 dsLExpr two `thenDs` \ two2 ->
389 returnDs (mkApps expr2 [from2, thn2, two2])
391 dsExpr (PArrSeq expr _)
392 = panic "DsExpr.dsExpr: Infinite parallel array!"
393 -- the parser shouldn't have generated it and the renamer and typechecker
394 -- shouldn't have let it through
398 \underline{\bf Record construction and update}
399 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
400 For record construction we do this (assuming T has three arguments)
404 let err = /\a -> recConErr a
405 T (recConErr t1 "M.lhs/230/op1")
407 (recConErr t1 "M.lhs/230/op3")
409 @recConErr@ then converts its arugment string into a proper message
410 before printing it as
412 M.lhs, line 230: missing field op1 was evaluated
415 We also handle @C{}@ as valid construction syntax for an unlabelled
416 constructor @C@, setting all of @C@'s fields to bottom.
419 dsExpr (RecordCon (L _ data_con_id) con_expr rbinds)
420 = dsExpr con_expr `thenDs` \ con_expr' ->
422 (arg_tys, _) = tcSplitFunTys (exprType con_expr')
423 -- A newtype in the corner should be opaque;
424 -- hence TcType.tcSplitFunTys
426 mk_arg (arg_ty, lbl) -- Selector id has the field label as its name
427 = case findField (rec_flds rbinds) lbl of
428 (rhs:rhss) -> ASSERT( null rhss )
430 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
431 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
433 labels = dataConFieldLabels (idDataCon data_con_id)
434 -- The data_con_id is guaranteed to be the wrapper id of the constructor
438 then mappM unlabelled_bottom arg_tys
439 else mappM mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels))
440 `thenDs` \ con_args ->
442 returnDs (mkApps con_expr' con_args)
445 Record update is a little harder. Suppose we have the decl:
447 data T = T1 {op1, op2, op3 :: Int}
448 | T2 {op4, op2 :: Int}
451 Then we translate as follows:
457 T1 op1 _ op3 -> T1 op1 op2 op3
458 T2 op4 _ -> T2 op4 op2
459 other -> recUpdError "M.lhs/230"
461 It's important that we use the constructor Ids for @T1@, @T2@ etc on the
462 RHSs, and do not generate a Core constructor application directly, because the constructor
463 might do some argument-evaluation first; and may have to throw away some
467 dsExpr expr@(RecordUpd record_expr (HsRecFields { rec_flds = fields })
468 cons_to_upd in_inst_tys out_inst_tys)
470 = dsLExpr record_expr
472 = -- Record stuff doesn't work for existentials
473 -- The type checker checks for this, but we need
474 -- worry only about the constructors that are to be updated
475 ASSERT2( notNull cons_to_upd && all isVanillaDataCon cons_to_upd, ppr expr )
477 do { record_expr' <- dsLExpr record_expr
478 ; let -- Awkwardly, for families, the match goes
479 -- from instance type to family type
480 tycon = dataConTyCon (head cons_to_upd)
481 in_ty = mkTyConApp tycon in_inst_tys
482 in_out_ty = mkFunTy in_ty
483 (mkFamilyTyConApp tycon out_inst_tys)
485 mk_val_arg field old_arg_id
486 = case findField fields field of
487 (rhs:rest) -> ASSERT(null rest) rhs
488 [] -> nlHsVar old_arg_id
491 = ASSERT( isVanillaDataCon con )
492 do { arg_ids <- newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys)
493 -- This call to dataConInstOrigArgTys won't work for existentials
494 -- but existentials don't have record types anyway
495 ; let val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
496 (dataConFieldLabels con) arg_ids
497 rhs = foldl (\a b -> nlHsApp a b)
498 (nlHsTyApp (dataConWrapId con) out_inst_tys)
500 pat = mkPrefixConPat con (map nlVarPat arg_ids) in_ty
502 ; return (mkSimpleMatch [pat] rhs) }
504 -- It's important to generate the match with matchWrapper,
505 -- and the right hand sides with applications of the wrapper Id
506 -- so that everything works when we are doing fancy unboxing on the
507 -- constructor aguments.
508 ; alts <- mapM mk_alt cons_to_upd
509 ; ([discrim_var], matching_code) <- matchWrapper RecUpd (MatchGroup alts in_out_ty)
511 ; return (bindNonRec discrim_var record_expr' matching_code) }
514 Here is where we desugar the Template Haskell brackets and escapes
517 -- Template Haskell stuff
519 #ifdef GHCI /* Only if bootstrapping */
520 dsExpr (HsBracketOut x ps) = dsBracket x ps
521 dsExpr (HsSpliceE s) = pprPanic "dsExpr:splice" (ppr s)
524 -- Arrow notation extension
525 dsExpr (HsProc pat cmd) = dsProcExpr pat cmd
531 dsExpr (HsTick ix vars e) = do
535 -- There is a problem here. The then and else branches
536 -- have no free variables, so they are open to lifting.
537 -- We need someway of stopping this.
538 -- This will make no difference to binary coverage
539 -- (did you go here: YES or NO), but will effect accurate
542 dsExpr (HsBinTick ixT ixF e) = do
544 do { ASSERT(exprType e2 `coreEqType` boolTy)
545 mkBinaryTickBox ixT ixF e2
552 -- HsSyn constructs that just shouldn't be here:
553 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
557 findField :: [HsRecField Id arg] -> Name -> [arg]
559 = [rhs | HsRecField { hsRecFieldId = id, hsRecFieldArg = rhs } <- rbinds
560 , lbl == idName (unLoc id) ]
563 %--------------------------------------------------------------------
565 Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
566 handled in DsListComp). Basically does the translation given in the
572 -> Type -- Type of the whole expression
575 dsDo stmts body result_ty
576 = go (map unLoc stmts)
580 go (ExprStmt rhs then_expr _ : stmts)
581 = do { rhs2 <- dsLExpr rhs
582 ; then_expr2 <- dsExpr then_expr
584 ; returnDs (mkApps then_expr2 [rhs2, rest]) }
586 go (LetStmt binds : stmts)
587 = do { rest <- go stmts
588 ; dsLocalBinds binds rest }
590 go (BindStmt pat rhs bind_op fail_op : stmts)
592 do { body <- go stmts
593 ; var <- selectSimpleMatchVarL pat
594 ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
595 result_ty (cantFailMatchResult body)
596 ; match_code <- handle_failure pat match fail_op
597 ; rhs' <- dsLExpr rhs
598 ; bind_op' <- dsExpr bind_op
599 ; returnDs (mkApps bind_op' [rhs', Lam var match_code]) }
601 -- In a do expression, pattern-match failure just calls
602 -- the monadic 'fail' rather than throwing an exception
603 handle_failure pat match fail_op
605 = do { fail_op' <- dsExpr fail_op
606 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
607 ; extractMatchResult match (App fail_op' fail_msg) }
609 = extractMatchResult match (error "It can't fail")
611 mk_fail_msg pat = "Pattern match failure in do expression at " ++
612 showSDoc (ppr (getLoc pat))
615 Translation for RecStmt's:
616 -----------------------------
617 We turn (RecStmt [v1,..vn] stmts) into:
619 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
626 -> Type -- Type of the whole expression
629 dsMDo tbl stmts body result_ty
630 = go (map unLoc stmts)
632 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
633 mfix_id = lookupEvidence tbl mfixName
634 return_id = lookupEvidence tbl returnMName
635 bind_id = lookupEvidence tbl bindMName
636 then_id = lookupEvidence tbl thenMName
637 fail_id = lookupEvidence tbl failMName
642 go (LetStmt binds : stmts)
643 = do { rest <- go stmts
644 ; dsLocalBinds binds rest }
646 go (ExprStmt rhs _ rhs_ty : stmts)
647 = do { rhs2 <- dsLExpr rhs
649 ; returnDs (mkApps (Var then_id) [Type rhs_ty, Type b_ty, rhs2, rest]) }
651 go (BindStmt pat rhs _ _ : stmts)
652 = do { body <- go stmts
653 ; var <- selectSimpleMatchVarL pat
654 ; match <- matchSinglePat (Var var) (StmtCtxt ctxt) pat
655 result_ty (cantFailMatchResult body)
656 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
657 ; let fail_expr = mkApps (Var fail_id) [Type b_ty, fail_msg]
658 ; match_code <- extractMatchResult match fail_expr
660 ; rhs' <- dsLExpr rhs
661 ; returnDs (mkApps (Var bind_id) [Type (hsLPatType pat), Type b_ty,
662 rhs', Lam var match_code]) }
664 go (RecStmt rec_stmts later_ids rec_ids rec_rets binds : stmts)
665 = ASSERT( length rec_ids > 0 )
666 ASSERT( length rec_ids == length rec_rets )
667 go (new_bind_stmt : let_stmt : stmts)
669 new_bind_stmt = mkBindStmt (mk_tup_pat later_pats) mfix_app
670 let_stmt = LetStmt (HsValBinds (ValBindsOut [(Recursive, binds)] []))
673 -- Remove the later_ids that appear (without fancy coercions)
674 -- in rec_rets, because there's no need to knot-tie them separately
675 -- See Note [RecStmt] in HsExpr
676 later_ids' = filter (`notElem` mono_rec_ids) later_ids
677 mono_rec_ids = [ id | HsVar id <- rec_rets ]
679 mfix_app = nlHsApp (nlHsTyApp mfix_id [tup_ty]) mfix_arg
680 mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [mfix_pat] body]
681 (mkFunTy tup_ty body_ty))
683 -- The rec_tup_pat must bind the rec_ids only; remember that the
684 -- trimmed_laters may share the same Names
685 -- Meanwhile, the later_pats must bind the later_vars
686 rec_tup_pats = map mk_wild_pat later_ids' ++ map nlVarPat rec_ids
687 later_pats = map nlVarPat later_ids' ++ map mk_later_pat rec_ids
688 rets = map nlHsVar later_ids' ++ map noLoc rec_rets
690 mfix_pat = noLoc $ LazyPat $ mk_tup_pat rec_tup_pats
691 body = noLoc $ HsDo ctxt rec_stmts return_app body_ty
692 body_ty = mkAppTy m_ty tup_ty
693 tup_ty = mkCoreTupTy (map idType (later_ids' ++ rec_ids))
694 -- mkCoreTupTy deals with singleton case
696 return_app = nlHsApp (nlHsTyApp return_id [tup_ty])
699 mk_wild_pat :: Id -> LPat Id
700 mk_wild_pat v = noLoc $ WildPat $ idType v
702 mk_later_pat :: Id -> LPat Id
703 mk_later_pat v | v `elem` later_ids' = mk_wild_pat v
704 | otherwise = nlVarPat v
706 mk_tup_pat :: [LPat Id] -> LPat Id
708 mk_tup_pat ps = noLoc $ mkVanillaTuplePat ps Boxed
710 mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id
712 mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed