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,
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 )
47 import TyCon ( FieldLabel, tyConDataCons )
48 import TysWiredIn ( tupleCon )
49 import BasicTypes ( RecFlag(..), Boxity(..), ipNameName )
50 import PrelNames ( toPName,
51 returnMName, bindMName, thenMName, failMName,
53 import SrcLoc ( Located(..), unLoc, getLoc, noLoc )
54 import Util ( zipEqual, zipWithEqual )
55 import Bag ( bagToList )
61 %************************************************************************
65 %************************************************************************
67 @dsLet@ is a match-result transformer, taking the @MatchResult@ for the body
68 and transforming it into one for the let-bindings enclosing the body.
70 This may seem a bit odd, but (source) let bindings can contain unboxed
75 This must be transformed to a case expression and, if the type has
76 more than one constructor, may fail.
79 dsLet :: [HsBindGroup Id] -> CoreExpr -> DsM CoreExpr
80 dsLet groups body = foldlDs dsBindGroup body (reverse groups)
82 dsBindGroup :: CoreExpr -> HsBindGroup Id -> DsM CoreExpr
83 dsBindGroup body (HsIPBinds binds)
84 = foldlDs dsIPBind body binds
86 dsIPBind body (L _ (IPBind n e))
87 = dsLExpr e `thenDs` \ e' ->
88 returnDs (Let (NonRec (ipNameName n) e') body)
90 -- Special case for bindings which bind unlifted variables
91 -- We need to do a case right away, rather than building
92 -- a tuple and doing selections.
93 -- Silently ignore INLINE pragmas...
94 dsBindGroup body bind@(HsBindGroup hsbinds sigs is_rec)
95 | [L _ (AbsBinds [] [] exports inlines binds)] <- bagToList hsbinds,
96 or [isUnLiftedType (idType g) | (_, g, l) <- exports]
97 = ASSERT (case is_rec of {NonRecursive -> True; other -> False})
98 -- Unlifted bindings are always non-recursive
99 -- and are always a Fun or Pat monobind
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.)
105 body_w_exports = foldr bind_export body exports
106 bind_export (tvs, g, l) body = ASSERT( null tvs )
107 bindNonRec g (Var l) body
109 mk_error_app pat = mkErrorAppDs iRREFUT_PAT_ERROR_ID
113 case bagToList binds of
114 [L loc (FunBind (L _ fun) _ matches)]
115 -> putSrcSpanDs loc $
116 matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, rhs) ->
117 ASSERT( null args ) -- Functions aren't lifted
118 returnDs (bindNonRec fun rhs body_w_exports)
120 [L loc (PatBind pat grhss ty)]
121 -> putSrcSpanDs loc $
122 dsGuarded grhss ty `thenDs` \ rhs ->
123 mk_error_app pat `thenDs` \ error_expr ->
124 matchSimply rhs PatBindRhs pat body_w_exports error_expr
126 other -> pprPanic "dsLet: unlifted" (ppr bind $$ ppr body)
128 -- Ordinary case for bindings
129 dsBindGroup body (HsBindGroup binds sigs is_rec)
130 = dsHsNestedBinds binds `thenDs` \ prs ->
131 returnDs (Let (Rec prs) body)
132 -- Use a Rec regardless of is_rec.
133 -- Why? Because it allows the binds to be all
134 -- mixed up, which is what happens in one rare case
135 -- Namely, for an AbsBind with no tyvars and no dicts,
136 -- but which does have dictionary bindings.
137 -- See notes with TcSimplify.inferLoop [NO TYVARS]
138 -- It turned out that wrapping a Rec here was the easiest solution
140 -- NB The previous case dealt with unlifted bindings, so we
141 -- only have to deal with lifted ones now; so Rec is ok
144 %************************************************************************
146 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
148 %************************************************************************
151 dsLExpr :: LHsExpr Id -> DsM CoreExpr
152 dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e
154 dsExpr :: HsExpr Id -> DsM CoreExpr
156 dsExpr (HsPar e) = dsLExpr e
157 dsExpr (ExprWithTySigOut e _) = dsLExpr e
158 dsExpr (HsVar var) = returnDs (Var var)
159 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
160 dsExpr (HsLit lit) = dsLit lit
161 dsExpr (HsOverLit lit) = dsOverLit lit
163 dsExpr (NegApp expr neg_expr)
164 = do { core_expr <- dsLExpr expr
165 ; core_neg <- dsExpr neg_expr
166 ; return (core_neg `App` core_expr) }
168 dsExpr expr@(HsLam a_Match)
169 = matchWrapper LambdaExpr a_Match `thenDs` \ (binders, matching_code) ->
170 returnDs (mkLams binders matching_code)
172 dsExpr expr@(HsApp fun arg)
173 = dsLExpr fun `thenDs` \ core_fun ->
174 dsLExpr arg `thenDs` \ core_arg ->
175 returnDs (core_fun `App` core_arg)
178 Operator sections. At first it looks as if we can convert
187 But no! expr might be a redex, and we can lose laziness badly this
192 for example. So we convert instead to
194 let y = expr in \x -> op y x
196 If \tr{expr} is actually just a variable, say, then the simplifier
200 dsExpr (OpApp e1 op _ e2)
201 = dsLExpr op `thenDs` \ core_op ->
202 -- for the type of y, we need the type of op's 2nd argument
203 dsLExpr e1 `thenDs` \ x_core ->
204 dsLExpr e2 `thenDs` \ y_core ->
205 returnDs (mkApps core_op [x_core, y_core])
207 dsExpr (SectionL expr op)
208 = dsLExpr op `thenDs` \ core_op ->
209 -- for the type of y, we need the type of op's 2nd argument
211 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
212 -- Must look through an implicit-parameter type;
213 -- newtype impossible; hence Type.splitFunTys
215 dsLExpr expr `thenDs` \ x_core ->
216 newSysLocalDs x_ty `thenDs` \ x_id ->
217 newSysLocalDs y_ty `thenDs` \ y_id ->
219 returnDs (bindNonRec x_id x_core $
220 Lam y_id (mkApps core_op [Var x_id, Var y_id]))
222 -- dsLExpr (SectionR op expr) -- \ x -> op x expr
223 dsExpr (SectionR op expr)
224 = dsLExpr op `thenDs` \ core_op ->
225 -- for the type of x, we need the type of op's 2nd argument
227 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
228 -- See comment with SectionL
230 dsLExpr expr `thenDs` \ y_core ->
231 newSysLocalDs x_ty `thenDs` \ x_id ->
232 newSysLocalDs y_ty `thenDs` \ y_id ->
234 returnDs (bindNonRec y_id y_core $
235 Lam x_id (mkApps core_op [Var x_id, Var y_id]))
237 dsExpr (HsSCC cc expr)
238 = dsLExpr expr `thenDs` \ core_expr ->
239 getModuleDs `thenDs` \ mod_name ->
240 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
243 -- hdaume: core annotation
245 dsExpr (HsCoreAnn fs expr)
246 = dsLExpr expr `thenDs` \ core_expr ->
247 returnDs (Note (CoreNote $ unpackFS fs) core_expr)
249 -- Special case to handle unboxed tuple patterns; they can't appear nested
250 dsExpr (HsCase discrim matches@(MatchGroup _ ty))
251 | isUnboxedTupleType (funArgTy ty)
252 = dsLExpr discrim `thenDs` \ core_discrim ->
253 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
254 case matching_code of
255 Case (Var x) bndr ty alts | x == discrim_var ->
256 returnDs (Case core_discrim bndr ty alts)
257 _ -> panic ("dsLExpr: tuple pattern:\n" ++ showSDoc (ppr matching_code))
259 dsExpr (HsCase discrim matches)
260 = dsLExpr discrim `thenDs` \ core_discrim ->
261 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
262 returnDs (bindNonRec discrim_var core_discrim matching_code)
264 dsExpr (HsLet binds body)
265 = dsLExpr body `thenDs` \ body' ->
268 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
269 -- because the interpretation of `stmts' depends on what sort of thing it is.
271 dsExpr (HsDo ListComp stmts body result_ty)
272 = -- Special case for list comprehensions
273 dsListComp stmts body elt_ty
275 [elt_ty] = tcTyConAppArgs result_ty
277 dsExpr (HsDo DoExpr stmts body result_ty)
278 = dsDo stmts body result_ty
280 dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
281 = dsMDo tbl stmts body result_ty
283 dsExpr (HsDo PArrComp stmts body result_ty)
284 = -- Special case for array comprehensions
285 dsPArrComp (map unLoc stmts) body elt_ty
287 [elt_ty] = tcTyConAppArgs 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 (ArithSeq expr (From from))
344 = dsExpr expr `thenDs` \ expr2 ->
345 dsLExpr from `thenDs` \ from2 ->
346 returnDs (App expr2 from2)
348 dsExpr (ArithSeq expr (FromTo from two))
349 = dsExpr expr `thenDs` \ expr2 ->
350 dsLExpr from `thenDs` \ from2 ->
351 dsLExpr two `thenDs` \ two2 ->
352 returnDs (mkApps expr2 [from2, two2])
354 dsExpr (ArithSeq expr (FromThen from thn))
355 = dsExpr expr `thenDs` \ expr2 ->
356 dsLExpr from `thenDs` \ from2 ->
357 dsLExpr thn `thenDs` \ thn2 ->
358 returnDs (mkApps expr2 [from2, thn2])
360 dsExpr (ArithSeq expr (FromThenTo from thn two))
361 = dsExpr 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 (PArrSeq expr (FromTo from two))
368 = dsExpr expr `thenDs` \ expr2 ->
369 dsLExpr from `thenDs` \ from2 ->
370 dsLExpr two `thenDs` \ two2 ->
371 returnDs (mkApps expr2 [from2, two2])
373 dsExpr (PArrSeq expr (FromThenTo from thn two))
374 = dsExpr 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 (PArrSeq 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 (RecordCon (L _ data_con_id) con_expr rbinds)
409 = dsExpr 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
415 mk_arg (arg_ty, lbl) -- Selector id has the field label as its name
416 = case [rhs | (L _ sel_id, rhs) <- rbinds, lbl == idName sel_id] of
417 (rhs:rhss) -> ASSERT( null rhss )
419 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
420 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
422 labels = dataConFieldLabels (idDataCon data_con_id)
423 -- The data_con_id is guaranteed to be the wrapper id of the constructor
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 (RecordUpd record_expr [] record_in_ty record_out_ty)
457 = dsLExpr record_expr
459 dsExpr expr@(RecordUpd record_expr rbinds record_in_ty record_out_ty)
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
468 in_out_ty = mkFunTy record_in_ty record_out_ty
470 mk_val_arg field old_arg_id
471 = case [rhs | (L _ sel_id, rhs) <- rbinds, field == idName 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
478 -- but existentials don't have record types anyway
480 val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
481 (dataConFieldLabels con) arg_ids
482 rhs = foldl (\a b -> nlHsApp a b)
483 (noLoc $ TyApp (nlHsVar (dataConWrapId con))
487 returnDs (mkSimpleMatch [noLoc $ ConPatOut (noLoc con) [] [] emptyLHsBinds
488 (PrefixCon (map nlVarPat arg_ids)) record_in_ty]
491 -- Record stuff doesn't work for existentials
492 -- The type checker checks for this, but we need
493 -- worry only about the constructors that are to be updated
494 ASSERT2( all isVanillaDataCon cons_to_upd, ppr expr )
496 -- It's important to generate the match with matchWrapper,
497 -- and the right hand sides with applications of the wrapper Id
498 -- so that everything works when we are doing fancy unboxing on the
499 -- constructor aguments.
500 mappM mk_alt cons_to_upd `thenDs` \ alts ->
501 matchWrapper RecUpd (MatchGroup alts in_out_ty) `thenDs` \ ([discrim_var], matching_code) ->
503 returnDs (bindNonRec discrim_var record_expr' matching_code)
506 updated_fields :: [FieldLabel]
507 updated_fields = [ idName sel_id | (L _ sel_id,_) <- rbinds]
509 -- Get the type constructor from the record_in_ty
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 = tcTyConAppTyCon record_in_ty
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"
567 %--------------------------------------------------------------------
569 Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
570 handled in DsListComp). Basically does the translation given in the
576 -> Type -- Type of the whole expression
579 dsDo stmts body result_ty
580 = go (map unLoc stmts)
584 go (ExprStmt rhs then_expr _ : stmts)
585 = do { rhs2 <- dsLExpr rhs
586 ; then_expr2 <- dsExpr then_expr
588 ; returnDs (mkApps then_expr2 [rhs2, rest]) }
590 go (LetStmt binds : stmts)
591 = do { rest <- go stmts
594 go (BindStmt pat rhs bind_op fail_op : stmts)
595 = do { body <- go stmts
596 ; var <- selectSimpleMatchVarL pat
597 ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
598 result_ty (cantFailMatchResult body)
599 ; match_code <- handle_failure pat match fail_op
600 ; rhs' <- dsLExpr rhs
601 ; bind_op' <- dsExpr bind_op
602 ; returnDs (mkApps bind_op' [rhs', Lam var match_code]) }
604 -- In a do expression, pattern-match failure just calls
605 -- the monadic 'fail' rather than throwing an exception
606 handle_failure pat match fail_op
608 = do { fail_op' <- dsExpr fail_op
609 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
610 ; extractMatchResult match (App fail_op' fail_msg) }
612 = extractMatchResult match (error "It can't fail")
614 mk_fail_msg pat = "Pattern match failure in do expression at " ++
615 showSDoc (ppr (getLoc pat))
618 Translation for RecStmt's:
619 -----------------------------
620 We turn (RecStmt [v1,..vn] stmts) into:
622 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
629 -> Type -- Type of the whole expression
632 dsMDo tbl stmts body result_ty
633 = go (map unLoc stmts)
635 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
636 mfix_id = lookupEvidence tbl mfixName
637 return_id = lookupEvidence tbl returnMName
638 bind_id = lookupEvidence tbl bindMName
639 then_id = lookupEvidence tbl thenMName
640 fail_id = lookupEvidence tbl failMName
645 go (LetStmt binds : stmts)
646 = do { rest <- go stmts
649 go (ExprStmt rhs _ rhs_ty : stmts)
650 = do { rhs2 <- dsLExpr rhs
652 ; returnDs (mkApps (Var then_id) [Type rhs_ty, Type b_ty, rhs2, rest]) }
654 go (BindStmt pat rhs _ _ : stmts)
655 = do { body <- go stmts
656 ; var <- selectSimpleMatchVarL pat
657 ; match <- matchSinglePat (Var var) (StmtCtxt ctxt) pat
658 result_ty (cantFailMatchResult body)
659 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
660 ; let fail_expr = mkApps (Var fail_id) [Type b_ty, fail_msg]
661 ; match_code <- extractMatchResult match fail_expr
663 ; rhs' <- dsLExpr rhs
664 ; returnDs (mkApps (Var bind_id) [Type (hsPatType pat), Type b_ty,
665 rhs', Lam var match_code]) }
667 go (RecStmt rec_stmts later_ids rec_ids rec_rets binds : stmts)
668 = ASSERT( length rec_ids > 0 )
669 ASSERT( length rec_ids == length rec_rets )
670 go (new_bind_stmt : let_stmt : stmts)
672 new_bind_stmt = mkBindStmt (mk_tup_pat later_pats) mfix_app
673 let_stmt = LetStmt [HsBindGroup binds [] Recursive]
676 -- Remove the later_ids that appear (without fancy coercions)
677 -- in rec_rets, because there's no need to knot-tie them separately
678 -- See Note [RecStmt] in HsExpr
679 later_ids' = filter (`notElem` mono_rec_ids) later_ids
680 mono_rec_ids = [ id | HsVar id <- rec_rets ]
682 mfix_app = nlHsApp (noLoc $ TyApp (nlHsVar mfix_id) [tup_ty]) mfix_arg
683 mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [mfix_pat] body]
684 (mkFunTy tup_ty body_ty))
686 -- The rec_tup_pat must bind the rec_ids only; remember that the
687 -- trimmed_laters may share the same Names
688 -- Meanwhile, the later_pats must bind the later_vars
689 rec_tup_pats = map mk_wild_pat later_ids' ++ map nlVarPat rec_ids
690 later_pats = map nlVarPat later_ids' ++ map mk_later_pat rec_ids
691 rets = map nlHsVar later_ids' ++ map noLoc rec_rets
693 mfix_pat = noLoc $ LazyPat $ mk_tup_pat rec_tup_pats
694 body = noLoc $ HsDo ctxt rec_stmts return_app body_ty
695 body_ty = mkAppTy m_ty tup_ty
696 tup_ty = mkCoreTupTy (map idType (later_ids' ++ rec_ids))
697 -- mkCoreTupTy deals with singleton case
699 return_app = nlHsApp (noLoc $ TyApp (nlHsVar return_id) [tup_ty])
702 mk_wild_pat :: Id -> LPat Id
703 mk_wild_pat v = noLoc $ WildPat $ idType v
705 mk_later_pat :: Id -> LPat Id
706 mk_later_pat v | v `elem` later_ids' = mk_wild_pat v
707 | otherwise = nlVarPat v
709 mk_tup_pat :: [LPat Id] -> LPat Id
711 mk_tup_pat ps = noLoc $ TuplePat ps Boxed
713 mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id
715 mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed