2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[DsExpr]{Matching expressions (Exprs)}
7 #include "HsVersions.h"
9 module DsExpr ( dsExpr ) where
12 IMPORT_DELOOPER(DsLoop) -- partly to get dsBinds, partly to chk dsExpr
14 import HsSyn ( failureFreePat,
15 HsExpr(..), OutPat(..), HsLit(..), ArithSeqInfo(..),
16 Stmt(..), Match(..), Qual, HsBinds, PolyType,
19 import TcHsSyn ( TypecheckedHsExpr(..), TypecheckedHsBinds(..),
20 TypecheckedRecordBinds(..), TypecheckedPat(..),
26 import DsCCall ( dsCCall )
27 import DsHsSyn ( outPatType )
28 import DsListComp ( dsListComp )
29 import DsUtils ( mkAppDs, mkConDs, mkPrimDs, dsExprToAtom,
30 mkErrorAppDs, showForErr, EquationInfo,
33 import Match ( matchWrapper )
35 import CoreUnfold ( UnfoldingDetails(..), UnfoldingGuidance(..),
37 import CoreUtils ( coreExprType, substCoreExpr, argToExpr,
38 mkCoreIfThenElse, unTagBinders )
39 import CostCentre ( mkUserCC )
40 import FieldLabel ( fieldLabelType, FieldLabel )
41 import Id ( mkTupleCon, idType, nullIdEnv, addOneToIdEnv,
42 getIdUnfolding, dataConArgTys, dataConFieldLabels,
43 recordSelectorFieldLabel
45 import Literal ( mkMachInt, Literal(..) )
46 import MagicUFs ( MagicUnfoldingFun )
47 import Name ( Name{--O only-} )
48 import PprStyle ( PprStyle(..) )
49 import PprType ( GenType )
50 import PrelVals ( rEC_CON_ERROR_ID, rEC_UPD_ERROR_ID, voidId )
51 import Pretty ( ppShow, ppBesides, ppPStr, ppStr )
52 import TyCon ( isDataTyCon, isNewTyCon )
53 import Type ( splitSigmaTy, splitFunTy, typePrimRep,
54 getAppDataTyConExpandingDicts, getAppTyCon, applyTy,
57 import TysWiredIn ( mkTupleTy, voidTy, nilDataCon, consDataCon,
60 import TyVar ( nullTyVarEnv, addOneToTyVarEnv, GenTyVar{-instance Eq-} )
61 import Usage ( UVar(..) )
62 import Util ( zipEqual, pprError, panic, assertPanic )
64 mk_nil_con ty = mkCon nilDataCon [] [ty] [] -- micro utility...
67 The funny business to do with variables is that we look them up in the
68 Id-to-Id and Id-to-Id maps that the monadery is carrying
69 around; if we get hits, we use the value accordingly.
71 %************************************************************************
73 \subsection[DsExpr-vars-and-cons]{Variables and constructors}
75 %************************************************************************
78 dsExpr :: TypecheckedHsExpr -> DsM CoreExpr
80 dsExpr (HsVar var) = dsApp (HsVar var) []
83 %************************************************************************
85 \subsection[DsExpr-literals]{Literals}
87 %************************************************************************
89 We give int/float literals type Integer and Rational, respectively.
90 The typechecker will (presumably) have put \tr{from{Integer,Rational}s}
93 ToDo: put in range checks for when converting "i"
94 (or should that be in the typechecker?)
96 For numeric literals, we try to detect there use at a standard type
97 (Int, Float, etc.) are directly put in the right constructor.
98 [NB: down with the @App@ conversion.]
99 Otherwise, we punt, putting in a "NoRep" Core literal (where the
100 representation decisions are delayed)...
102 See also below where we look for @DictApps@ for \tr{plusInt}, etc.
105 dsExpr (HsLitOut (HsString s) _)
107 = returnDs (mk_nil_con charTy)
111 the_char = mkCon charDataCon [] [] [LitArg (MachChar (_HEAD_ s))]
112 the_nil = mk_nil_con charTy
114 mkConDs consDataCon [charTy] [the_char, the_nil]
116 -- "_" => build (\ c n -> c 'c' n) -- LATER
118 -- "str" ==> build (\ c n -> foldr charTy T c n "str")
121 dsExpr (HsLitOut (HsString str) _)
122 = newTyVarsDs [alphaTyVar] `thenDs` \ [new_tyvar] ->
124 new_ty = mkTyVarTy new_tyvar
127 charTy `mkFunTy` (new_ty `mkFunTy` new_ty),
129 mkForallTy [alphaTyVar]
130 ((charTy `mkFunTy` (alphaTy `mkFunTy` alphaTy))
131 `mkFunTy` (alphaTy `mkFunTy` alphaTy))
132 ] `thenDs` \ [c,n,g] ->
133 returnDs (mkBuild charTy new_tyvar c n g (
135 (CoTyApp (CoTyApp (Var foldrId) charTy) new_ty) *** ensure non-prim type ***
136 [VarArg c,VarArg n,LitArg (NoRepStr str)]))
139 -- otherwise, leave it as a NoRepStr;
140 -- the Core-to-STG pass will wrap it in an application of "unpackCStringId".
142 dsExpr (HsLitOut (HsString str) _)
143 = returnDs (Lit (NoRepStr str))
145 dsExpr (HsLitOut (HsLitLit s) ty)
146 = returnDs ( mkCon data_con [] [] [LitArg (MachLitLit s kind)] )
149 = case (maybeBoxedPrimType ty) of
150 Just (boxing_data_con, prim_ty)
151 -> (boxing_data_con, typePrimRep prim_ty)
153 -> pprError "ERROR: ``literal-literal'' not a single-constructor type: "
154 (ppBesides [ppPStr s, ppStr "; type: ", ppr PprDebug ty])
156 dsExpr (HsLitOut (HsInt i) ty)
157 = returnDs (Lit (NoRepInteger i ty))
159 dsExpr (HsLitOut (HsFrac r) ty)
160 = returnDs (Lit (NoRepRational r ty))
162 -- others where we know what to do:
164 dsExpr (HsLitOut (HsIntPrim i) _)
165 = if (i >= toInteger minInt && i <= toInteger maxInt) then
166 returnDs (Lit (mkMachInt i))
168 error ("ERROR: Int constant " ++ show i ++ out_of_range_msg)
170 dsExpr (HsLitOut (HsFloatPrim f) _)
171 = returnDs (Lit (MachFloat f))
172 -- ToDo: range checking needed!
174 dsExpr (HsLitOut (HsDoublePrim d) _)
175 = returnDs (Lit (MachDouble d))
176 -- ToDo: range checking needed!
178 dsExpr (HsLitOut (HsChar c) _)
179 = returnDs ( mkCon charDataCon [] [] [LitArg (MachChar c)] )
181 dsExpr (HsLitOut (HsCharPrim c) _)
182 = returnDs (Lit (MachChar c))
184 dsExpr (HsLitOut (HsStringPrim s) _)
185 = returnDs (Lit (MachStr s))
187 -- end of literals magic. --
189 dsExpr expr@(HsLam a_Match)
190 = matchWrapper LambdaMatch [a_Match] "lambda" `thenDs` \ (binders, matching_code) ->
191 returnDs ( mkValLam binders matching_code )
193 dsExpr expr@(HsApp e1 e2) = dsApp expr []
194 dsExpr expr@(OpApp e1 op e2) = dsApp expr []
197 Operator sections. At first it looks as if we can convert
206 But no! expr might be a redex, and we can lose laziness badly this
211 for example. So we convert instead to
213 let y = expr in \x -> op y x
215 If \tr{expr} is actually just a variable, say, then the simplifier
219 dsExpr (SectionL expr op)
220 = dsExpr op `thenDs` \ core_op ->
221 dsExpr expr `thenDs` \ core_expr ->
222 dsExprToAtom core_expr $ \ y_atom ->
224 -- for the type of x, we need the type of op's 2nd argument
226 x_ty = case (splitSigmaTy (coreExprType core_op)) of { (_, _, tau_ty) ->
227 case (splitFunTy tau_ty) of {
228 ((_:arg2_ty:_), _) -> arg2_ty;
229 _ -> panic "dsExpr:SectionL:arg 2 ty" }}
231 newSysLocalDs x_ty `thenDs` \ x_id ->
232 returnDs (mkValLam [x_id] (core_op `App` y_atom `App` VarArg x_id))
234 -- dsExpr (SectionR op expr) -- \ x -> op x expr
235 dsExpr (SectionR op expr)
236 = dsExpr op `thenDs` \ core_op ->
237 dsExpr expr `thenDs` \ core_expr ->
238 dsExprToAtom core_expr $ \ y_atom ->
240 -- for the type of x, we need the type of op's 1st argument
242 x_ty = case (splitSigmaTy (coreExprType core_op)) of { (_, _, tau_ty) ->
243 case (splitFunTy tau_ty) of {
244 ((arg1_ty:_), _) -> arg1_ty;
245 _ -> panic "dsExpr:SectionR:arg 1 ty" }}
247 newSysLocalDs x_ty `thenDs` \ x_id ->
248 returnDs (mkValLam [x_id] (core_op `App` VarArg x_id `App` y_atom))
250 dsExpr (CCall label args may_gc is_asm result_ty)
251 = mapDs dsExpr args `thenDs` \ core_args ->
252 dsCCall label core_args may_gc is_asm result_ty
253 -- dsCCall does all the unboxification, etc.
255 dsExpr (HsSCC cc expr)
256 = dsExpr expr `thenDs` \ core_expr ->
257 getModuleAndGroupDs `thenDs` \ (mod_name, group_name) ->
258 returnDs ( SCC (mkUserCC cc mod_name group_name) core_expr)
260 dsExpr expr@(HsCase discrim matches src_loc)
261 = putSrcLocDs src_loc $
262 dsExpr discrim `thenDs` \ core_discrim ->
263 matchWrapper CaseMatch matches "case" `thenDs` \ ([discrim_var], matching_code) ->
264 returnDs ( mkCoLetAny (NonRec discrim_var core_discrim) matching_code )
266 dsExpr (ListComp expr quals)
267 = dsExpr expr `thenDs` \ core_expr ->
268 dsListComp core_expr quals
270 dsExpr (HsLet binds expr)
271 = dsBinds binds `thenDs` \ core_binds ->
272 dsExpr expr `thenDs` \ core_expr ->
273 returnDs ( mkCoLetsAny core_binds core_expr )
275 dsExpr (HsDoOut stmts then_id zero_id src_loc)
276 = putSrcLocDs src_loc $
277 dsDo then_id zero_id stmts
279 dsExpr (HsIf guard_expr then_expr else_expr src_loc)
280 = putSrcLocDs src_loc $
281 dsExpr guard_expr `thenDs` \ core_guard ->
282 dsExpr then_expr `thenDs` \ core_then ->
283 dsExpr else_expr `thenDs` \ core_else ->
284 returnDs (mkCoreIfThenElse core_guard core_then core_else)
288 Type lambda and application
289 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
291 dsExpr (TyLam tyvars expr)
292 = dsExpr expr `thenDs` \ core_expr ->
293 returnDs (mkTyLam tyvars core_expr)
295 dsExpr expr@(TyApp e tys) = dsApp expr []
299 Various data construction things
300 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
302 dsExpr (ExplicitListOut ty xs)
304 [] -> returnDs (mk_nil_con ty)
306 dsExpr y `thenDs` \ core_hd ->
307 dsExpr (ExplicitListOut ty ys) `thenDs` \ core_tl ->
308 mkConDs consDataCon [ty] [core_hd, core_tl]
310 dsExpr (ExplicitTuple expr_list)
311 = mapDs dsExpr expr_list `thenDs` \ core_exprs ->
312 mkConDs (mkTupleCon (length expr_list))
313 (map coreExprType core_exprs)
316 -- Two cases, one for ordinary constructors and one for newtype constructors
317 dsExpr (HsCon con tys args)
318 | isDataTyCon tycon -- The usual datatype case
319 = mapDs dsExpr args `thenDs` \ args_exprs ->
320 mkConDs con tys args_exprs
322 | otherwise -- The newtype case
323 = ASSERT( isNewTyCon tycon )
324 ASSERT( null rest_args )
325 dsExpr first_arg `thenDs` \ arg_expr ->
326 returnDs (Coerce (CoerceIn con) result_ty arg_expr)
329 (first_arg:rest_args) = args
330 (args_tys, result_ty) = splitFunTy (foldl applyTy (idType con) tys)
331 (tycon,_) = getAppTyCon result_ty
333 dsExpr (ArithSeqOut expr (From from))
334 = dsExpr expr `thenDs` \ expr2 ->
335 dsExpr from `thenDs` \ from2 ->
336 mkAppDs expr2 [] [from2]
338 dsExpr (ArithSeqOut expr (FromTo from two))
339 = dsExpr expr `thenDs` \ expr2 ->
340 dsExpr from `thenDs` \ from2 ->
341 dsExpr two `thenDs` \ two2 ->
342 mkAppDs expr2 [] [from2, two2]
344 dsExpr (ArithSeqOut expr (FromThen from thn))
345 = dsExpr expr `thenDs` \ expr2 ->
346 dsExpr from `thenDs` \ from2 ->
347 dsExpr thn `thenDs` \ thn2 ->
348 mkAppDs expr2 [] [from2, thn2]
350 dsExpr (ArithSeqOut expr (FromThenTo from thn two))
351 = dsExpr expr `thenDs` \ expr2 ->
352 dsExpr from `thenDs` \ from2 ->
353 dsExpr thn `thenDs` \ thn2 ->
354 dsExpr two `thenDs` \ two2 ->
355 mkAppDs expr2 [] [from2, thn2, two2]
358 Record construction and update
359 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
360 For record construction we do this (assuming T has three arguments)
364 let err = /\a -> recConErr a
365 T (recConErr t1 "M.lhs/230/op1")
367 (recConErr t1 "M.lhs/230/op3")
369 recConErr then converts its arugment string into a proper message
370 before printing it as
372 M.lhs, line 230: missing field op1 was evaluated
376 dsExpr (RecordCon con_expr rbinds)
377 = dsExpr con_expr `thenDs` \ con_expr' ->
379 con_id = get_con con_expr'
380 (arg_tys, _) = splitFunTy (coreExprType con_expr')
383 = case [rhs | (sel_id,rhs,_) <- rbinds,
384 lbl == recordSelectorFieldLabel sel_id] of
385 (rhs:rhss) -> ASSERT( null rhss )
387 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showForErr lbl)
389 mapDs mk_arg (zipEqual "dsExpr:RecordCon" arg_tys (dataConFieldLabels con_id)) `thenDs` \ con_args ->
390 mkAppDs con_expr' [] con_args
392 -- "con_expr'" is simply an application of the constructor Id
393 -- to types and (perhaps) dictionaries. This gets the constructor...
394 get_con (Var con) = con
395 get_con (App fun _) = get_con fun
398 Record update is a little harder. Suppose we have the decl:
400 data T = T1 {op1, op2, op3 :: Int}
401 | T2 {op4, op2 :: Int}
404 Then we translate as follows:
410 T1 op1 _ op3 -> T1 op1 op2 op3
411 T2 op4 _ -> T2 op4 op2
412 other -> recUpdError "M.lhs/230"
414 It's important that we use the constructor Ids for T1, T2 etc on the
415 RHSs, and do not generate a Core Con directly, because the constructor
416 might do some argument-evaluation first; and may have to throw away some
420 dsExpr (RecordUpdOut record_expr dicts rbinds)
421 = dsExpr record_expr `thenDs` \ record_expr' ->
423 -- Desugar the rbinds, and generate let-bindings if
424 -- necessary so that we don't lose sharing
425 dsRbinds rbinds $ \ rbinds' ->
427 record_ty = coreExprType record_expr'
428 (tycon, inst_tys, cons) = _trace "DsExpr.getAppDataTyConExpandingDicts" $
429 getAppDataTyConExpandingDicts record_ty
430 cons_to_upd = filter has_all_fields cons
432 -- initial_args are passed to every constructor
433 initial_args = map TyArg inst_tys ++ map VarArg dicts
435 mk_val_arg (field, arg_id)
436 = case [arg | (f, arg) <- rbinds',
437 field == recordSelectorFieldLabel f] of
438 (arg:args) -> ASSERT(null args)
443 = newSysLocalsDs (dataConArgTys con inst_tys) `thenDs` \ arg_ids ->
445 val_args = map mk_val_arg (zipEqual "dsExpr:RecordUpd" (dataConFieldLabels con) arg_ids)
447 returnDs (con, arg_ids, mkGenApp (mkGenApp (Var con) initial_args) val_args)
450 | length cons_to_upd == length cons
453 = newSysLocalDs record_ty `thenDs` \ deflt_id ->
454 mkErrorAppDs rEC_UPD_ERROR_ID record_ty "" `thenDs` \ err ->
455 returnDs (BindDefault deflt_id err)
457 mapDs mk_alt cons_to_upd `thenDs` \ alts ->
458 mk_default `thenDs` \ deflt ->
460 returnDs (Case record_expr' (AlgAlts alts deflt))
463 has_all_fields :: Id -> Bool
464 has_all_fields con_id
467 con_fields = dataConFieldLabels con_id
468 ok (sel_id, _, _) = recordSelectorFieldLabel sel_id `elem` con_fields
471 Dictionary lambda and application
472 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
473 @DictLam@ and @DictApp@ turn into the regular old things.
474 (OLD:) @DictFunApp@ also becomes a curried application, albeit slightly more
475 complicated; reminiscent of fully-applied constructors.
477 dsExpr (DictLam dictvars expr)
478 = dsExpr expr `thenDs` \ core_expr ->
479 returnDs( mkValLam dictvars core_expr )
483 dsExpr expr@(DictApp e dicts) -- becomes a curried application
487 @SingleDicts@ become @Locals@; @Dicts@ turn into tuples, unless
489 @ClassDictLam dictvars methods expr@ is ``the opposite'':
491 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
494 dsExpr (SingleDict dict) -- just a local
495 = lookupEnvWithDefaultDs dict (Var dict)
497 dsExpr (Dictionary dicts methods)
498 = -- hey, these things may have been substituted away...
499 zipWithDs lookupEnvWithDefaultDs
500 dicts_and_methods dicts_and_methods_exprs
501 `thenDs` \ core_d_and_ms ->
503 (case num_of_d_and_ms of
504 0 -> returnDs (Var voidId)
506 1 -> returnDs (head core_d_and_ms) -- just a single Id
509 mkConDs (mkTupleCon num_of_d_and_ms)
510 (map coreExprType core_d_and_ms)
514 dicts_and_methods = dicts ++ methods
515 dicts_and_methods_exprs = map Var dicts_and_methods
516 num_of_d_and_ms = length dicts_and_methods
518 dsExpr (ClassDictLam dicts methods expr)
519 = dsExpr expr `thenDs` \ core_expr ->
520 case num_of_d_and_ms of
521 0 -> newSysLocalDs voidTy `thenDs` \ new_x ->
522 returnDs (mkValLam [new_x] core_expr)
525 returnDs (mkValLam dicts_and_methods core_expr)
528 newSysLocalDs tuple_ty `thenDs` \ new_x ->
530 Lam (ValBinder new_x)
533 [(tuple_con, dicts_and_methods, core_expr)]
536 num_of_d_and_ms = length dicts + length methods
537 dicts_and_methods = dicts ++ methods
538 tuple_ty = mkTupleTy num_of_d_and_ms (map idType dicts_and_methods)
539 tuple_con = mkTupleCon num_of_d_and_ms
542 -- HsSyn constructs that just shouldn't be here:
543 dsExpr (HsDo _ _) = panic "dsExpr:HsDo"
544 dsExpr (ExplicitList _) = panic "dsExpr:ExplicitList"
545 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
546 dsExpr (ArithSeqIn _) = panic "dsExpr:ArithSeqIn"
549 out_of_range_msg -- ditto
550 = " out of range: [" ++ show minInt ++ ", " ++ show maxInt ++ "]\n"
553 %--------------------------------------------------------------------
555 @(dsApp e [t_1,..,t_n, e_1,..,e_n])@ returns something with the same
558 e t_1 ... t_n e_1 .. e_n
561 We're doing all this so we can saturate constructors (as painlessly as
565 type DsCoreArg = GenCoreArg CoreExpr{-NB!-} TyVar UVar
567 dsApp :: TypecheckedHsExpr -- expr to desugar
568 -> [DsCoreArg] -- accumulated ty/val args: NB:
569 -> DsM CoreExpr -- final result
571 dsApp (HsApp e1 e2) args
572 = dsExpr e2 `thenDs` \ core_e2 ->
573 dsApp e1 (VarArg core_e2 : args)
575 dsApp (OpApp e1 op e2) args
576 = dsExpr e1 `thenDs` \ core_e1 ->
577 dsExpr e2 `thenDs` \ core_e2 ->
578 dsApp op (VarArg core_e1 : VarArg core_e2 : args)
580 dsApp (DictApp expr dicts) args
581 = -- now, those dicts may have been substituted away...
582 zipWithDs lookupEnvWithDefaultDs dicts (map Var dicts)
583 `thenDs` \ core_dicts ->
584 dsApp expr (map VarArg core_dicts ++ args)
586 dsApp (TyApp expr tys) args
587 = dsApp expr (map TyArg tys ++ args)
589 -- we might should look out for SectionLs, etc., here, but we don't
592 = lookupEnvDs v `thenDs` \ maybe_expr ->
594 Just expr -> apply_to_args expr args
596 Nothing -> -- we're only saturating constructors and PrimOps
597 case getIdUnfolding v of
598 GenForm _ the_unfolding EssentialUnfolding
599 -> do_unfold nullTyVarEnv nullIdEnv (unTagBinders the_unfolding) args
601 _ -> apply_to_args (Var v) args
604 dsApp anything_else args
605 = dsExpr anything_else `thenDs` \ core_expr ->
606 apply_to_args core_expr args
608 -- a DsM version of mkGenApp:
609 apply_to_args :: CoreExpr -> [DsCoreArg] -> DsM CoreExpr
611 apply_to_args fun args
613 (ty_args, val_args) = foldr sep ([],[]) args
615 mkAppDs fun ty_args val_args
617 sep a@(LitArg l) (tys,vals) = (tys, (Lit l):vals)
618 sep a@(VarArg e) (tys,vals) = (tys, e:vals)
619 sep a@(TyArg ty) (tys,vals) = (ty:tys, vals)
620 sep a@(UsageArg _) _ = panic "DsExpr:apply_to_args:UsageArg"
625 dsRbinds :: TypecheckedRecordBinds -- The field bindings supplied
626 -> ([(Id, CoreArg)] -> DsM CoreExpr) -- A continuation taking the field
627 -- bindings with atomic rhss
628 -> DsM CoreExpr -- The result of the continuation,
629 -- wrapped in suitable Lets
631 dsRbinds [] continue_with
634 dsRbinds ((sel_id, rhs, pun_flag) : rbinds) continue_with
635 = dsExpr rhs `thenDs` \ rhs' ->
636 dsExprToAtom rhs' $ \ rhs_atom ->
637 dsRbinds rbinds $ \ rbinds' ->
638 continue_with ((sel_id, rhs_atom) : rbinds')
642 do_unfold ty_env val_env (Lam (TyBinder tyvar) body) (TyArg ty : args)
643 = do_unfold (addOneToTyVarEnv ty_env tyvar ty) val_env body args
645 do_unfold ty_env val_env (Lam (ValBinder binder) body) (VarArg expr : args)
646 = dsExprToAtom expr $ \ arg_atom ->
648 (addOneToIdEnv val_env binder (argToExpr arg_atom))
651 do_unfold ty_env val_env body args
652 = -- Clone the remaining part of the template
653 uniqSMtoDsM (substCoreExpr val_env ty_env body) `thenDs` \ body' ->
655 -- Apply result to remaining arguments
656 apply_to_args body' args
659 Basically does the translation given in the Haskell~1.3 report:
661 dsDo :: Id -- id for: (>>=) m
662 -> Id -- id for: zero m
666 dsDo then_id zero_id (stmt:stmts)
668 ExprStmt expr locn -> ASSERT( null stmts ) do_expr expr locn
670 ExprStmtOut expr locn a b ->
671 do_expr expr locn `thenDs` \ expr2 ->
672 ds_rest `thenDs` \ rest ->
673 dsApp (HsVar then_id) [TyArg a, TyArg b, VarArg expr2, VarArg rest]
676 dsBinds binds `thenDs` \ binds2 ->
677 ds_rest `thenDs` \ rest ->
678 returnDs (mkCoLetsAny binds2 rest)
680 BindStmtOut pat expr locn a b ->
681 do_expr expr locn `thenDs` \ expr2 ->
683 zero_expr = TyApp (HsVar zero_id) [b]
685 = PatMatch pat (SimpleMatch (HsDoOut stmts then_id zero_id locn))
687 = if failureFreePat pat
689 else [main_match, PatMatch (WildPat a) (SimpleMatch zero_expr)]
691 matchWrapper DoBindMatch the_matches "`do' statement"
692 `thenDs` \ (binders, matching_code) ->
693 dsApp (HsVar then_id) [TyArg a, TyArg b,
694 VarArg expr2, VarArg (mkValLam binders matching_code)]
696 ds_rest = dsDo then_id zero_id stmts
697 do_expr expr locn = putSrcLocDs locn (dsExpr expr)
700 dsDo then_expr zero_expr [] = panic "dsDo:[]"