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"
12 #if defined(GHCI) && defined(BREAKPOINT)
13 import Foreign.StablePtr
32 -- Template Haskell stuff iff bootstrapped
39 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
40 -- 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 -> matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, rhs) ->
116 ASSERT( null args ) -- Functions aren't lifted
117 ASSERT( isIdHsWrapper co_fn )
118 returnDs (bindNonRec fun rhs body_w_exports)
120 PatBind {pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }
121 -> -- let C x# y# = rhs in body
122 -- ==> case rhs of C x# y# -> body
124 do { rhs <- dsGuarded grhss ty
125 ; let upat = unLoc pat
126 eqn = EqnInfo { eqn_pats = [upat],
127 eqn_rhs = cantFailMatchResult body_w_exports }
128 ; var <- selectMatchVar upat
129 ; result <- matchEquations PatBindRhs [var] [eqn] (exprType body)
130 ; return (scrungleMatch var rhs result) }
132 other -> pprPanic "dsLet: unlifted" (pprLHsBinds hsbinds $$ ppr body)
135 -- Ordinary case for bindings; none should be unlifted
136 ds_val_bind (is_rec, binds) body
137 = do { prs <- dsLHsBinds binds
138 ; ASSERT( not (any (isUnLiftedType . idType . fst) prs) )
141 other -> return (Let (Rec prs) body) }
142 -- Use a Rec regardless of is_rec.
143 -- Why? Because it allows the binds to be all
144 -- mixed up, which is what happens in one rare case
145 -- Namely, for an AbsBind with no tyvars and no dicts,
146 -- but which does have dictionary bindings.
147 -- See notes with TcSimplify.inferLoop [NO TYVARS]
148 -- It turned out that wrapping a Rec here was the easiest solution
150 -- NB The previous case dealt with unlifted bindings, so we
151 -- only have to deal with lifted ones now; so Rec is ok
153 isUnboxedTupleBind :: HsBind Id -> Bool
154 isUnboxedTupleBind (PatBind { pat_rhs_ty = ty }) = isUnboxedTupleType ty
155 isUnboxedTupleBind other = False
157 scrungleMatch :: Id -> CoreExpr -> CoreExpr -> CoreExpr
158 -- Returns something like (let var = scrut in body)
159 -- but if var is an unboxed-tuple type, it inlines it in a fragile way
160 -- Special case to handle unboxed tuple patterns; they can't appear nested
162 -- case e of (# p1, p2 #) -> rhs
164 -- case e of (# x1, x2 #) -> ... match p1, p2 ...
166 -- let x = e in case x of ....
168 -- But there may be a big
169 -- let fail = ... in case e of ...
170 -- wrapping the whole case, which complicates matters slightly
171 -- It all seems a bit fragile. Test is dsrun013.
173 scrungleMatch var scrut body
174 | isUnboxedTupleType (idType var) = scrungle body
175 | otherwise = bindNonRec var scrut body
177 scrungle (Case (Var x) bndr ty alts)
178 | x == var = Case scrut bndr ty alts
179 scrungle (Let binds body) = Let binds (scrungle body)
180 scrungle other = panic ("scrungleMatch: tuple pattern:\n" ++ showSDoc (ppr other))
183 %************************************************************************
185 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
187 %************************************************************************
190 dsLExpr :: LHsExpr Id -> DsM CoreExpr
191 dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e
193 dsExpr :: HsExpr Id -> DsM CoreExpr
195 dsExpr (HsPar e) = dsLExpr e
196 dsExpr (ExprWithTySigOut e _) = dsLExpr e
197 dsExpr (HsVar var) = returnDs (Var var)
198 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
199 dsExpr (HsLit lit) = dsLit lit
200 dsExpr (HsOverLit lit) = dsOverLit lit
201 dsExpr (HsWrap co_fn e) = dsCoercion co_fn (dsExpr e)
203 dsExpr (NegApp expr neg_expr)
204 = do { core_expr <- dsLExpr expr
205 ; core_neg <- dsExpr neg_expr
206 ; return (core_neg `App` core_expr) }
208 dsExpr expr@(HsLam a_Match)
209 = matchWrapper LambdaExpr a_Match `thenDs` \ (binders, matching_code) ->
210 returnDs (mkLams binders matching_code)
212 #if defined(GHCI) && defined(BREAKPOINT)
213 dsExpr (HsApp (L _ (HsApp realFun@(L _ (HsWrap _ fun)) (L loc arg))) _)
215 , idName funId `elem` [breakpointJumpName, breakpointCondJumpName]
216 , ids <- filter (isValidType . idType) (extractIds arg)
217 = do warnDs (text "Extracted ids:" <+> ppr ids <+> ppr (map idType ids))
218 stablePtr <- ioToIOEnv $ newStablePtr ids
219 -- Yes, I know... I'm gonna burn in hell.
220 let Ptr addr# = castStablePtrToPtr stablePtr
221 funCore <- dsLExpr realFun
222 argCore <- dsLExpr (L loc (HsLit (HsInt (fromIntegral (I# (addr2Int# addr#))))))
223 hvalCore <- dsLExpr (L loc (extractHVals ids))
224 return ((funCore `App` argCore) `App` hvalCore)
225 where extractIds :: HsExpr Id -> [Id]
226 extractIds (HsApp fn arg)
227 | HsVar argId <- unLoc arg
228 = argId:extractIds (unLoc fn)
229 | HsWrap co_fn arg' <- unLoc arg
230 , HsVar argId <- arg' -- SLPJ: not sure what is going on here
231 = error (showSDoc (ppr co_fn)) -- argId:extractIds (unLoc fn)
233 extractHVals ids = ExplicitList unitTy (map (L loc . HsVar) ids)
234 -- checks for tyvars and unlifted kinds.
235 isValidType (TyVarTy _) = False
236 isValidType (FunTy a b) = isValidType a && isValidType b
237 isValidType (NoteTy _ t) = isValidType t
238 isValidType (AppTy a b) = isValidType a && isValidType b
239 isValidType (TyConApp con ts) = not (isUnLiftedTyCon con) && all isValidType ts
243 dsExpr expr@(HsApp fun arg)
244 = dsLExpr fun `thenDs` \ core_fun ->
245 dsLExpr arg `thenDs` \ core_arg ->
246 returnDs (core_fun `App` core_arg)
249 Operator sections. At first it looks as if we can convert
258 But no! expr might be a redex, and we can lose laziness badly this
263 for example. So we convert instead to
265 let y = expr in \x -> op y x
267 If \tr{expr} is actually just a variable, say, then the simplifier
271 dsExpr (OpApp e1 op _ e2)
272 = dsLExpr op `thenDs` \ core_op ->
273 -- for the type of y, we need the type of op's 2nd argument
274 dsLExpr e1 `thenDs` \ x_core ->
275 dsLExpr e2 `thenDs` \ y_core ->
276 returnDs (mkApps core_op [x_core, y_core])
278 dsExpr (SectionL expr op) -- Desugar (e !) to ((!) e)
279 = dsLExpr op `thenDs` \ core_op ->
280 dsLExpr expr `thenDs` \ x_core ->
281 returnDs (App core_op x_core)
283 -- dsLExpr (SectionR op expr) -- \ x -> op x expr
284 dsExpr (SectionR op expr)
285 = dsLExpr op `thenDs` \ core_op ->
286 -- for the type of x, we need the type of op's 2nd argument
288 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
289 -- See comment with SectionL
291 dsLExpr expr `thenDs` \ y_core ->
292 newSysLocalDs x_ty `thenDs` \ x_id ->
293 newSysLocalDs y_ty `thenDs` \ y_id ->
295 returnDs (bindNonRec y_id y_core $
296 Lam x_id (mkApps core_op [Var x_id, Var y_id]))
298 dsExpr (HsSCC cc expr)
299 = dsLExpr expr `thenDs` \ core_expr ->
300 getModuleDs `thenDs` \ mod_name ->
301 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
304 -- hdaume: core annotation
306 dsExpr (HsCoreAnn fs expr)
307 = dsLExpr expr `thenDs` \ core_expr ->
308 returnDs (Note (CoreNote $ unpackFS fs) core_expr)
310 dsExpr (HsCase discrim matches)
311 = dsLExpr discrim `thenDs` \ core_discrim ->
312 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
313 returnDs (scrungleMatch discrim_var core_discrim matching_code)
315 dsExpr (HsLet binds body)
316 = dsLExpr body `thenDs` \ body' ->
317 dsLocalBinds binds body'
319 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
320 -- because the interpretation of `stmts' depends on what sort of thing it is.
322 dsExpr (HsDo ListComp stmts body result_ty)
323 = -- Special case for list comprehensions
324 dsListComp stmts body elt_ty
326 [elt_ty] = tcTyConAppArgs result_ty
328 dsExpr (HsDo DoExpr stmts body result_ty)
329 = dsDo stmts body result_ty
331 dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
332 = dsMDo tbl stmts body result_ty
334 dsExpr (HsDo PArrComp stmts body result_ty)
335 = -- Special case for array comprehensions
336 dsPArrComp (map unLoc stmts) body elt_ty
338 [elt_ty] = tcTyConAppArgs result_ty
340 dsExpr (HsIf guard_expr then_expr else_expr)
341 = dsLExpr guard_expr `thenDs` \ core_guard ->
342 dsLExpr then_expr `thenDs` \ core_then ->
343 dsLExpr else_expr `thenDs` \ core_else ->
344 returnDs (mkIfThenElse core_guard core_then core_else)
349 \underline{\bf Various data construction things}
350 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
352 dsExpr (ExplicitList ty xs)
355 go [] = returnDs (mkNilExpr ty)
356 go (x:xs) = dsLExpr x `thenDs` \ core_x ->
357 go xs `thenDs` \ core_xs ->
358 returnDs (mkConsExpr ty core_x core_xs)
360 -- we create a list from the array elements and convert them into a list using
363 -- * the main disadvantage to this scheme is that `toP' traverses the list
364 -- twice: once to determine the length and a second time to put to elements
365 -- into the array; this inefficiency could be avoided by exposing some of
366 -- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
367 -- that we can exploit the fact that we already know the length of the array
368 -- here at compile time
370 dsExpr (ExplicitPArr ty xs)
371 = dsLookupGlobalId toPName `thenDs` \toP ->
372 dsExpr (ExplicitList ty xs) `thenDs` \coreList ->
373 returnDs (mkApps (Var toP) [Type ty, coreList])
375 dsExpr (ExplicitTuple expr_list boxity)
376 = mappM dsLExpr expr_list `thenDs` \ core_exprs ->
377 returnDs (mkConApp (tupleCon boxity (length expr_list))
378 (map (Type . exprType) core_exprs ++ core_exprs))
380 dsExpr (ArithSeq expr (From from))
381 = dsExpr expr `thenDs` \ expr2 ->
382 dsLExpr from `thenDs` \ from2 ->
383 returnDs (App expr2 from2)
385 dsExpr (ArithSeq expr (FromTo from two))
386 = dsExpr expr `thenDs` \ expr2 ->
387 dsLExpr from `thenDs` \ from2 ->
388 dsLExpr two `thenDs` \ two2 ->
389 returnDs (mkApps expr2 [from2, two2])
391 dsExpr (ArithSeq expr (FromThen from thn))
392 = dsExpr expr `thenDs` \ expr2 ->
393 dsLExpr from `thenDs` \ from2 ->
394 dsLExpr thn `thenDs` \ thn2 ->
395 returnDs (mkApps expr2 [from2, thn2])
397 dsExpr (ArithSeq expr (FromThenTo from thn two))
398 = dsExpr expr `thenDs` \ expr2 ->
399 dsLExpr from `thenDs` \ from2 ->
400 dsLExpr thn `thenDs` \ thn2 ->
401 dsLExpr two `thenDs` \ two2 ->
402 returnDs (mkApps expr2 [from2, thn2, two2])
404 dsExpr (PArrSeq expr (FromTo from two))
405 = dsExpr expr `thenDs` \ expr2 ->
406 dsLExpr from `thenDs` \ from2 ->
407 dsLExpr two `thenDs` \ two2 ->
408 returnDs (mkApps expr2 [from2, two2])
410 dsExpr (PArrSeq expr (FromThenTo from thn two))
411 = dsExpr expr `thenDs` \ expr2 ->
412 dsLExpr from `thenDs` \ from2 ->
413 dsLExpr thn `thenDs` \ thn2 ->
414 dsLExpr two `thenDs` \ two2 ->
415 returnDs (mkApps expr2 [from2, thn2, two2])
417 dsExpr (PArrSeq expr _)
418 = panic "DsExpr.dsExpr: Infinite parallel array!"
419 -- the parser shouldn't have generated it and the renamer and typechecker
420 -- shouldn't have let it through
424 \underline{\bf Record construction and update}
425 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
426 For record construction we do this (assuming T has three arguments)
430 let err = /\a -> recConErr a
431 T (recConErr t1 "M.lhs/230/op1")
433 (recConErr t1 "M.lhs/230/op3")
435 @recConErr@ then converts its arugment string into a proper message
436 before printing it as
438 M.lhs, line 230: missing field op1 was evaluated
441 We also handle @C{}@ as valid construction syntax for an unlabelled
442 constructor @C@, setting all of @C@'s fields to bottom.
445 dsExpr (RecordCon (L _ data_con_id) con_expr rbinds)
446 = dsExpr con_expr `thenDs` \ con_expr' ->
448 (arg_tys, _) = tcSplitFunTys (exprType con_expr')
449 -- A newtype in the corner should be opaque;
450 -- hence TcType.tcSplitFunTys
452 mk_arg (arg_ty, lbl) -- Selector id has the field label as its name
453 = case [rhs | (L _ sel_id, rhs) <- rbinds, lbl == idName sel_id] of
454 (rhs:rhss) -> ASSERT( null rhss )
456 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
457 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
459 labels = dataConFieldLabels (idDataCon data_con_id)
460 -- The data_con_id is guaranteed to be the wrapper id of the constructor
464 then mappM unlabelled_bottom arg_tys
465 else mappM mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels))
466 `thenDs` \ con_args ->
468 returnDs (mkApps con_expr' con_args)
471 Record update is a little harder. Suppose we have the decl:
473 data T = T1 {op1, op2, op3 :: Int}
474 | T2 {op4, op2 :: Int}
477 Then we translate as follows:
483 T1 op1 _ op3 -> T1 op1 op2 op3
484 T2 op4 _ -> T2 op4 op2
485 other -> recUpdError "M.lhs/230"
487 It's important that we use the constructor Ids for @T1@, @T2@ etc on the
488 RHSs, and do not generate a Core constructor application directly, because the constructor
489 might do some argument-evaluation first; and may have to throw away some
493 dsExpr (RecordUpd record_expr [] record_in_ty record_out_ty)
494 = dsLExpr record_expr
496 dsExpr expr@(RecordUpd record_expr rbinds record_in_ty record_out_ty)
497 = dsLExpr record_expr `thenDs` \ record_expr' ->
499 -- Desugar the rbinds, and generate let-bindings if
500 -- necessary so that we don't lose sharing
503 in_inst_tys = tcTyConAppArgs record_in_ty -- Newtype opaque
504 out_inst_tys = tcTyConAppArgs record_out_ty -- Newtype opaque
505 in_out_ty = mkFunTy record_in_ty record_out_ty
507 mk_val_arg field old_arg_id
508 = case [rhs | (L _ sel_id, rhs) <- rbinds, field == idName sel_id] of
509 (rhs:rest) -> ASSERT(null rest) rhs
510 [] -> nlHsVar old_arg_id
513 = ASSERT( isVanillaDataCon con )
514 newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids ->
515 -- This call to dataConInstOrigArgTys won't work for existentials
516 -- but existentials don't have record types anyway
518 val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
519 (dataConFieldLabels con) arg_ids
520 rhs = foldl (\a b -> nlHsApp a b)
521 (nlHsTyApp (dataConWrapId con) out_inst_tys)
524 returnDs (mkSimpleMatch [mkPrefixConPat con (map nlVarPat arg_ids) record_in_ty] rhs)
526 -- Record stuff doesn't work for existentials
527 -- The type checker checks for this, but we need
528 -- worry only about the constructors that are to be updated
529 ASSERT2( all isVanillaDataCon cons_to_upd, ppr expr )
531 -- It's important to generate the match with matchWrapper,
532 -- and the right hand sides with applications of the wrapper Id
533 -- so that everything works when we are doing fancy unboxing on the
534 -- constructor aguments.
535 mappM mk_alt cons_to_upd `thenDs` \ alts ->
536 matchWrapper RecUpd (MatchGroup alts in_out_ty) `thenDs` \ ([discrim_var], matching_code) ->
538 returnDs (bindNonRec discrim_var record_expr' matching_code)
541 updated_fields :: [FieldLabel]
542 updated_fields = [ idName sel_id | (L _ sel_id,_) <- rbinds]
544 -- Get the type constructor from the record_in_ty
545 -- so that we are sure it'll have all its DataCons
546 -- (In GHCI, it's possible that some TyCons may not have all
547 -- their constructors, in a module-loop situation.)
548 tycon = tcTyConAppTyCon record_in_ty
549 data_cons = tyConDataCons tycon
550 cons_to_upd = filter has_all_fields data_cons
552 has_all_fields :: DataCon -> Bool
553 has_all_fields con_id
554 = all (`elem` con_fields) updated_fields
556 con_fields = dataConFieldLabels con_id
559 Here is where we desugar the Template Haskell brackets and escapes
562 -- Template Haskell stuff
564 #ifdef GHCI /* Only if bootstrapping */
565 dsExpr (HsBracketOut x ps) = dsBracket x ps
566 dsExpr (HsSpliceE s) = pprPanic "dsExpr:splice" (ppr s)
569 -- Arrow notation extension
570 dsExpr (HsProc pat cmd) = dsProcExpr pat cmd
577 -- HsSyn constructs that just shouldn't be here:
578 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
583 %--------------------------------------------------------------------
585 Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
586 handled in DsListComp). Basically does the translation given in the
592 -> Type -- Type of the whole expression
595 dsDo stmts body result_ty
596 = go (map unLoc stmts)
600 go (ExprStmt rhs then_expr _ : stmts)
601 = do { rhs2 <- dsLExpr rhs
602 ; then_expr2 <- dsExpr then_expr
604 ; returnDs (mkApps then_expr2 [rhs2, rest]) }
606 go (LetStmt binds : stmts)
607 = do { rest <- go stmts
608 ; dsLocalBinds binds rest }
610 go (BindStmt pat rhs bind_op fail_op : stmts)
611 = do { body <- go stmts
612 ; var <- selectSimpleMatchVarL pat
613 ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
614 result_ty (cantFailMatchResult body)
615 ; match_code <- handle_failure pat match fail_op
616 ; rhs' <- dsLExpr rhs
617 ; bind_op' <- dsExpr bind_op
618 ; returnDs (mkApps bind_op' [rhs', Lam var match_code]) }
620 -- In a do expression, pattern-match failure just calls
621 -- the monadic 'fail' rather than throwing an exception
622 handle_failure pat match fail_op
624 = do { fail_op' <- dsExpr fail_op
625 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
626 ; extractMatchResult match (App fail_op' fail_msg) }
628 = extractMatchResult match (error "It can't fail")
630 mk_fail_msg pat = "Pattern match failure in do expression at " ++
631 showSDoc (ppr (getLoc pat))
634 Translation for RecStmt's:
635 -----------------------------
636 We turn (RecStmt [v1,..vn] stmts) into:
638 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
645 -> Type -- Type of the whole expression
648 dsMDo tbl stmts body result_ty
649 = go (map unLoc stmts)
651 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
652 mfix_id = lookupEvidence tbl mfixName
653 return_id = lookupEvidence tbl returnMName
654 bind_id = lookupEvidence tbl bindMName
655 then_id = lookupEvidence tbl thenMName
656 fail_id = lookupEvidence tbl failMName
661 go (LetStmt binds : stmts)
662 = do { rest <- go stmts
663 ; dsLocalBinds binds rest }
665 go (ExprStmt rhs _ rhs_ty : stmts)
666 = do { rhs2 <- dsLExpr rhs
668 ; returnDs (mkApps (Var then_id) [Type rhs_ty, Type b_ty, rhs2, rest]) }
670 go (BindStmt pat rhs _ _ : stmts)
671 = do { body <- go stmts
672 ; var <- selectSimpleMatchVarL pat
673 ; match <- matchSinglePat (Var var) (StmtCtxt ctxt) pat
674 result_ty (cantFailMatchResult body)
675 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
676 ; let fail_expr = mkApps (Var fail_id) [Type b_ty, fail_msg]
677 ; match_code <- extractMatchResult match fail_expr
679 ; rhs' <- dsLExpr rhs
680 ; returnDs (mkApps (Var bind_id) [Type (hsLPatType pat), Type b_ty,
681 rhs', Lam var match_code]) }
683 go (RecStmt rec_stmts later_ids rec_ids rec_rets binds : stmts)
684 = ASSERT( length rec_ids > 0 )
685 ASSERT( length rec_ids == length rec_rets )
686 go (new_bind_stmt : let_stmt : stmts)
688 new_bind_stmt = mkBindStmt (mk_tup_pat later_pats) mfix_app
689 let_stmt = LetStmt (HsValBinds (ValBindsOut [(Recursive, binds)] []))
692 -- Remove the later_ids that appear (without fancy coercions)
693 -- in rec_rets, because there's no need to knot-tie them separately
694 -- See Note [RecStmt] in HsExpr
695 later_ids' = filter (`notElem` mono_rec_ids) later_ids
696 mono_rec_ids = [ id | HsVar id <- rec_rets ]
698 mfix_app = nlHsApp (nlHsTyApp mfix_id [tup_ty]) mfix_arg
699 mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [mfix_pat] body]
700 (mkFunTy tup_ty body_ty))
702 -- The rec_tup_pat must bind the rec_ids only; remember that the
703 -- trimmed_laters may share the same Names
704 -- Meanwhile, the later_pats must bind the later_vars
705 rec_tup_pats = map mk_wild_pat later_ids' ++ map nlVarPat rec_ids
706 later_pats = map nlVarPat later_ids' ++ map mk_later_pat rec_ids
707 rets = map nlHsVar later_ids' ++ map noLoc rec_rets
709 mfix_pat = noLoc $ LazyPat $ mk_tup_pat rec_tup_pats
710 body = noLoc $ HsDo ctxt rec_stmts return_app body_ty
711 body_ty = mkAppTy m_ty tup_ty
712 tup_ty = mkCoreTupTy (map idType (later_ids' ++ rec_ids))
713 -- mkCoreTupTy deals with singleton case
715 return_app = nlHsApp (nlHsTyApp return_id [tup_ty])
718 mk_wild_pat :: Id -> LPat Id
719 mk_wild_pat v = noLoc $ WildPat $ idType v
721 mk_later_pat :: Id -> LPat Id
722 mk_later_pat v | v `elem` later_ids' = mk_wild_pat v
723 | otherwise = nlVarPat v
725 mk_tup_pat :: [LPat Id] -> LPat Id
727 mk_tup_pat ps = noLoc $ mkVanillaTuplePat ps Boxed
729 mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id
731 mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed