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, matchSinglePat )
13 import MatchLit ( dsLit, dsOverLit )
14 import DsBinds ( dsHsNestedBinds )
15 import DsGRHSs ( dsGuarded )
16 import DsListComp ( dsListComp, dsPArrComp )
17 import DsUtils ( mkErrorAppDs, mkStringExpr, mkConsExpr, mkNilExpr,
18 extractMatchResult, cantFailMatchResult, matchCanFail,
19 mkCoreTupTy, selectSimpleMatchVarL, lookupEvidence )
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, tcTyConAppTyCon, tcTyConAppArgs,
37 tcTyConAppArgs, isUnLiftedType, Type, mkAppTy )
38 import Type ( funArgTy, splitFunTys, isUnboxedTupleType, mkFunTy )
40 import CoreUtils ( exprType, mkIfThenElse, bindNonRec )
42 import CostCentre ( mkUserCC )
43 import Id ( Id, idType, idName, idDataCon )
44 import PrelInfo ( rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID )
45 import DataCon ( DataCon, dataConWrapId, dataConFieldLabels, dataConInstOrigArgTys )
46 import DataCon ( isVanillaDataCon )
48 import TyCon ( FieldLabel, tyConDataCons )
49 import TysWiredIn ( tupleCon )
50 import BasicTypes ( RecFlag(..), Boxity(..), ipNameName )
51 import PrelNames ( toPName,
52 returnMName, bindMName, thenMName, failMName,
54 import SrcLoc ( Located(..), unLoc, getLoc, noLoc )
55 import Util ( zipEqual, zipWithEqual )
56 import Maybe ( fromJust )
57 import Bag ( bagToList )
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 :: [HsBindGroup Id] -> CoreExpr -> DsM CoreExpr
82 dsLet groups body = foldlDs dsBindGroup body (reverse groups)
84 dsBindGroup :: CoreExpr -> HsBindGroup Id -> DsM CoreExpr
85 dsBindGroup body (HsIPBinds binds)
86 = foldlDs dsIPBind body binds
88 dsIPBind body (L _ (IPBind n e))
89 = dsLExpr e `thenDs` \ e' ->
90 returnDs (Let (NonRec (ipNameName n) e') body)
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 pragmas...
96 dsBindGroup body bind@(HsBindGroup hsbinds sigs is_rec)
97 | [L _ (AbsBinds [] [] exports inlines binds)] <- bagToList hsbinds,
98 or [isUnLiftedType (idType g) | (_, g, l) <- exports]
99 = ASSERT (case is_rec of {NonRecursive -> True; other -> False})
100 -- Unlifted bindings are always non-recursive
101 -- and are always a Fun or Pat monobind
103 -- ToDo: in some bizarre case it's conceivable that there
104 -- could be dict binds in the 'binds'. (See the notes
105 -- below. Then pattern-match would fail. Urk.)
107 body_w_exports = foldr bind_export body exports
108 bind_export (tvs, g, l) body = ASSERT( null tvs )
109 bindNonRec g (Var l) body
111 mk_error_app pat = mkErrorAppDs iRREFUT_PAT_ERROR_ID
115 case bagToList binds of
116 [L loc (FunBind (L _ fun) _ matches)]
117 -> putSrcSpanDs loc $
118 matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, rhs) ->
119 ASSERT( null args ) -- Functions aren't lifted
120 returnDs (bindNonRec fun rhs body_w_exports)
122 [L loc (PatBind pat grhss ty)]
123 -> putSrcSpanDs loc $
124 dsGuarded grhss ty `thenDs` \ rhs ->
125 mk_error_app pat `thenDs` \ error_expr ->
126 matchSimply rhs PatBindRhs pat body_w_exports error_expr
128 other -> pprPanic "dsLet: unlifted" (ppr bind $$ ppr body)
130 -- Ordinary case for bindings
131 dsBindGroup body (HsBindGroup binds sigs is_rec)
132 = dsHsNestedBinds binds `thenDs` \ prs ->
133 returnDs (Let (Rec prs) body)
134 -- Use a Rec regardless of is_rec.
135 -- Why? Because it allows the binds to be all
136 -- mixed up, which is what happens in one rare case
137 -- Namely, for an AbsBind with no tyvars and no dicts,
138 -- but which does have dictionary bindings.
139 -- See notes with TcSimplify.inferLoop [NO TYVARS]
140 -- It turned out that wrapping a Rec here was the easiest solution
142 -- NB The previous case dealt with unlifted bindings, so we
143 -- only have to deal with lifted ones now; so Rec is ok
146 %************************************************************************
148 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
150 %************************************************************************
153 dsLExpr :: LHsExpr Id -> DsM CoreExpr
154 dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e
156 dsExpr :: HsExpr Id -> DsM CoreExpr
158 dsExpr (HsPar e) = dsLExpr e
159 dsExpr (ExprWithTySigOut e _) = dsLExpr e
160 dsExpr (HsVar var) = returnDs (Var var)
161 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
162 dsExpr (HsLit lit) = dsLit lit
163 dsExpr (HsOverLit lit) = dsOverLit lit
165 dsExpr (NegApp expr neg_expr)
166 = do { core_expr <- dsLExpr expr
167 ; core_neg <- dsExpr neg_expr
168 ; return (core_neg `App` core_expr) }
170 dsExpr expr@(HsLam a_Match)
171 = matchWrapper LambdaExpr a_Match `thenDs` \ (binders, matching_code) ->
172 returnDs (mkLams binders matching_code)
174 dsExpr expr@(HsApp fun arg)
175 = dsLExpr fun `thenDs` \ core_fun ->
176 dsLExpr arg `thenDs` \ core_arg ->
177 returnDs (core_fun `App` core_arg)
180 Operator sections. At first it looks as if we can convert
189 But no! expr might be a redex, and we can lose laziness badly this
194 for example. So we convert instead to
196 let y = expr in \x -> op y x
198 If \tr{expr} is actually just a variable, say, then the simplifier
202 dsExpr (OpApp e1 op _ e2)
203 = dsLExpr op `thenDs` \ core_op ->
204 -- for the type of y, we need the type of op's 2nd argument
205 dsLExpr e1 `thenDs` \ x_core ->
206 dsLExpr e2 `thenDs` \ y_core ->
207 returnDs (mkApps core_op [x_core, y_core])
209 dsExpr (SectionL expr op)
210 = dsLExpr op `thenDs` \ core_op ->
211 -- for the type of y, we need the type of op's 2nd argument
213 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
214 -- Must look through an implicit-parameter type;
215 -- newtype impossible; hence Type.splitFunTys
217 dsLExpr expr `thenDs` \ x_core ->
218 newSysLocalDs x_ty `thenDs` \ x_id ->
219 newSysLocalDs y_ty `thenDs` \ y_id ->
221 returnDs (bindNonRec x_id x_core $
222 Lam y_id (mkApps core_op [Var x_id, Var y_id]))
224 -- dsLExpr (SectionR op expr) -- \ x -> op x expr
225 dsExpr (SectionR op expr)
226 = dsLExpr op `thenDs` \ core_op ->
227 -- for the type of x, we need the type of op's 2nd argument
229 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
230 -- See comment with SectionL
232 dsLExpr expr `thenDs` \ y_core ->
233 newSysLocalDs x_ty `thenDs` \ x_id ->
234 newSysLocalDs y_ty `thenDs` \ y_id ->
236 returnDs (bindNonRec y_id y_core $
237 Lam x_id (mkApps core_op [Var x_id, Var y_id]))
239 dsExpr (HsSCC cc expr)
240 = dsLExpr expr `thenDs` \ core_expr ->
241 getModuleDs `thenDs` \ mod_name ->
242 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
245 -- hdaume: core annotation
247 dsExpr (HsCoreAnn fs expr)
248 = dsLExpr expr `thenDs` \ core_expr ->
249 returnDs (Note (CoreNote $ unpackFS fs) core_expr)
251 -- Special case to handle unboxed tuple patterns; they can't appear nested
252 dsExpr (HsCase discrim matches@(MatchGroup _ ty))
253 | isUnboxedTupleType (funArgTy ty)
254 = dsLExpr discrim `thenDs` \ core_discrim ->
255 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
256 case matching_code of
257 Case (Var x) bndr ty alts | x == discrim_var ->
258 returnDs (Case core_discrim bndr ty alts)
259 _ -> panic ("dsLExpr: tuple pattern:\n" ++ showSDoc (ppr matching_code))
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 body result_ty)
274 = -- Special case for list comprehensions
275 dsListComp stmts body elt_ty
277 [elt_ty] = tcTyConAppArgs result_ty
279 dsExpr (HsDo DoExpr stmts body result_ty)
280 = dsDo stmts body result_ty
282 dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
283 = dsMDo tbl stmts body result_ty
285 dsExpr (HsDo PArrComp stmts body result_ty)
286 = -- Special case for array comprehensions
287 dsPArrComp (map unLoc stmts) body elt_ty
289 [elt_ty] = tcTyConAppArgs result_ty
291 dsExpr (HsIf guard_expr then_expr else_expr)
292 = dsLExpr guard_expr `thenDs` \ core_guard ->
293 dsLExpr then_expr `thenDs` \ core_then ->
294 dsLExpr else_expr `thenDs` \ core_else ->
295 returnDs (mkIfThenElse core_guard core_then core_else)
300 \underline{\bf Type lambda and application}
301 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~
303 dsExpr (TyLam tyvars expr)
304 = dsLExpr expr `thenDs` \ core_expr ->
305 returnDs (mkLams tyvars core_expr)
307 dsExpr (TyApp expr tys)
308 = dsLExpr expr `thenDs` \ core_expr ->
309 returnDs (mkTyApps core_expr tys)
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 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 [] record_in_ty record_out_ty)
459 = dsLExpr record_expr
461 dsExpr expr@(RecordUpd record_expr rbinds record_in_ty record_out_ty)
462 = dsLExpr record_expr `thenDs` \ record_expr' ->
464 -- Desugar the rbinds, and generate let-bindings if
465 -- necessary so that we don't lose sharing
468 in_inst_tys = tcTyConAppArgs record_in_ty -- Newtype opaque
469 out_inst_tys = tcTyConAppArgs record_out_ty -- Newtype opaque
470 in_out_ty = mkFunTy record_in_ty record_out_ty
472 mk_val_arg field old_arg_id
473 = case [rhs | (L _ sel_id, rhs) <- rbinds, field == idName sel_id] of
474 (rhs:rest) -> ASSERT(null rest) rhs
475 [] -> nlHsVar old_arg_id
478 = newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids ->
479 -- This call to dataConArgTys won't work for existentials
480 -- but existentials don't have record types anyway
482 val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
483 (dataConFieldLabels con) arg_ids
484 rhs = foldl (\a b -> nlHsApp a b)
485 (noLoc $ TyApp (nlHsVar (dataConWrapId con))
489 returnDs (mkSimpleMatch [noLoc $ ConPatOut (noLoc con) [] [] emptyLHsBinds
490 (PrefixCon (map nlVarPat 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 isVanillaDataCon 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 mappM mk_alt cons_to_upd `thenDs` \ alts ->
503 matchWrapper RecUpd (MatchGroup alts in_out_ty) `thenDs` \ ([discrim_var], matching_code) ->
505 returnDs (bindNonRec discrim_var record_expr' matching_code)
508 updated_fields :: [FieldLabel]
509 updated_fields = [ idName sel_id | (L _ sel_id,_) <- rbinds]
511 -- Get the type constructor from the record_in_ty
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 = tcTyConAppTyCon record_in_ty
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 = dsLExpr expr `thenDs` \ core_expr ->
536 returnDs (mkLams dictvars core_expr)
540 dsExpr (DictApp expr dicts) -- becomes a curried application
541 = dsLExpr 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 (HsSpliceE s) = pprPanic "dsExpr:splice" (ppr s)
555 -- Arrow notation extension
556 dsExpr (HsProc pat cmd) = dsProcExpr pat cmd
563 -- HsSyn constructs that just shouldn't be here:
564 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
569 %--------------------------------------------------------------------
571 Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
572 handled in DsListComp). Basically does the translation given in the
578 -> Type -- Type of the whole expression
581 dsDo stmts body result_ty
582 = go (map unLoc stmts)
586 go (ExprStmt rhs then_expr _ : stmts)
587 = do { rhs2 <- dsLExpr rhs
588 ; then_expr2 <- dsExpr then_expr
590 ; returnDs (mkApps then_expr2 [rhs2, rest]) }
592 go (LetStmt binds : stmts)
593 = do { rest <- go stmts
596 go (BindStmt pat rhs bind_op fail_op : stmts)
597 = do { body <- go stmts
598 ; var <- selectSimpleMatchVarL pat
599 ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
600 result_ty (cantFailMatchResult body)
601 ; match_code <- handle_failure pat match fail_op
602 ; rhs' <- dsLExpr rhs
603 ; bind_op' <- dsExpr bind_op
604 ; returnDs (mkApps bind_op' [rhs', Lam var match_code]) }
606 -- In a do expression, pattern-match failure just calls
607 -- the monadic 'fail' rather than throwing an exception
608 handle_failure pat match fail_op
610 = do { fail_op' <- dsExpr fail_op
611 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
612 ; extractMatchResult match (App fail_op' fail_msg) }
614 = extractMatchResult match (error "It can't fail")
616 mk_fail_msg pat = "Pattern match failure in do expression at " ++
617 showSDoc (ppr (getLoc pat))
620 Translation for RecStmt's:
621 -----------------------------
622 We turn (RecStmt [v1,..vn] stmts) into:
624 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
631 -> Type -- Type of the whole expression
634 dsMDo tbl stmts body result_ty
635 = go (map unLoc stmts)
637 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
638 mfix_id = lookupEvidence tbl mfixName
639 return_id = lookupEvidence tbl returnMName
640 bind_id = lookupEvidence tbl bindMName
641 then_id = lookupEvidence tbl thenMName
642 fail_id = lookupEvidence tbl failMName
647 go (LetStmt binds : stmts)
648 = do { rest <- go stmts
651 go (ExprStmt rhs _ rhs_ty : stmts)
652 = do { rhs2 <- dsLExpr rhs
654 ; returnDs (mkApps (Var then_id) [Type rhs_ty, Type b_ty, rhs2, rest]) }
656 go (BindStmt pat rhs _ _ : stmts)
657 = do { body <- go stmts
658 ; var <- selectSimpleMatchVarL pat
659 ; match <- matchSinglePat (Var var) (StmtCtxt ctxt) pat
660 result_ty (cantFailMatchResult body)
661 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
662 ; let fail_expr = mkApps (Var fail_id) [Type b_ty, fail_msg]
663 ; match_code <- extractMatchResult match fail_expr
665 ; rhs' <- dsLExpr rhs
666 ; returnDs (mkApps (Var bind_id) [Type (hsPatType pat), Type b_ty,
667 rhs', Lam var match_code]) }
669 go (RecStmt rec_stmts later_ids rec_ids rec_rets binds : stmts)
670 = ASSERT( length rec_ids > 0 )
671 ASSERT( length rec_ids == length rec_rets )
672 go (new_bind_stmt : let_stmt : stmts)
674 new_bind_stmt = mkBindStmt (mk_tup_pat later_pats) mfix_app
675 let_stmt = LetStmt [HsBindGroup binds [] Recursive]
678 -- Remove the later_ids that appear (without fancy coercions)
679 -- in rec_rets, because there's no need to knot-tie them separately
680 -- See Note [RecStmt] in HsExpr
681 later_ids' = filter (`notElem` mono_rec_ids) later_ids
682 mono_rec_ids = [ id | HsVar id <- rec_rets ]
684 mfix_app = nlHsApp (noLoc $ TyApp (nlHsVar mfix_id) [tup_ty]) mfix_arg
685 mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [mfix_pat] body]
686 (mkFunTy tup_ty body_ty))
688 -- The rec_tup_pat must bind the rec_ids only; remember that the
689 -- trimmed_laters may share the same Names
690 -- Meanwhile, the later_pats must bind the later_vars
691 rec_tup_pats = map mk_wild_pat later_ids' ++ map nlVarPat rec_ids
692 later_pats = map nlVarPat later_ids' ++ map mk_later_pat rec_ids
693 rets = map nlHsVar later_ids' ++ map noLoc rec_rets
695 mfix_pat = noLoc $ LazyPat $ mk_tup_pat rec_tup_pats
696 body = noLoc $ HsDo ctxt rec_stmts return_app body_ty
697 body_ty = mkAppTy m_ty tup_ty
698 tup_ty = mkCoreTupTy (map idType (later_ids' ++ rec_ids))
699 -- mkCoreTupTy deals with singleton case
701 return_app = nlHsApp (noLoc $ TyApp (nlHsVar return_id) [tup_ty])
704 mk_wild_pat :: Id -> LPat Id
705 mk_wild_pat v = noLoc $ WildPat $ idType v
707 mk_later_pat :: Id -> LPat Id
708 mk_later_pat v | v `elem` later_ids' = mk_wild_pat v
709 | otherwise = nlVarPat v
711 mk_tup_pat :: [LPat Id] -> LPat Id
713 mk_tup_pat ps = noLoc $ TuplePat ps Boxed
715 mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id
717 mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed