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 #if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ <= 201
13 IMPORT_DELOOPER(DsLoop) -- partly to get dsBinds, partly to chk dsExpr
15 import {-# SOURCE #-} DsBinds (dsBinds )
18 import HsSyn ( failureFreePat,
19 HsExpr(..), OutPat(..), HsLit(..), ArithSeqInfo(..),
20 Stmt(..), DoOrListComp(..), Match(..), HsBinds, HsType, Fixity,
23 import TcHsSyn ( SYN_IE(TypecheckedHsExpr), SYN_IE(TypecheckedHsBinds),
24 SYN_IE(TypecheckedRecordBinds), SYN_IE(TypecheckedPat),
25 SYN_IE(TypecheckedStmt)
30 import DsCCall ( dsCCall )
31 import DsHsSyn ( outPatType )
32 import DsListComp ( dsListComp )
33 import DsUtils ( mkAppDs, mkConDs, mkPrimDs, dsExprToAtom, mkTupleExpr,
34 mkErrorAppDs, showForErr, EquationInfo,
35 MatchResult, SYN_IE(DsCoreArg)
37 import Match ( matchWrapper )
39 import CoreUtils ( coreExprType, substCoreExpr, argToExpr,
40 mkCoreIfThenElse, unTagBinders )
41 import CostCentre ( mkUserCC )
42 import FieldLabel ( fieldLabelType, FieldLabel )
43 import Id ( idType, nullIdEnv, addOneToIdEnv,
44 dataConArgTys, dataConFieldLabels,
45 recordSelectorFieldLabel, SYN_IE(Id)
47 import Literal ( mkMachInt, Literal(..) )
48 import Name ( Name{--O only-} )
49 import Outputable ( PprStyle(..), Outputable(..) )
50 import PprType ( GenType )
51 import PrelVals ( rEC_CON_ERROR_ID, rEC_UPD_ERROR_ID, voidId )
52 import Pretty ( Doc, hcat, ptext, text )
53 import Type ( splitSigmaTy, splitFunTy, typePrimRep,
54 getAppDataTyConExpandingDicts, maybeAppTyCon, getAppTyCon, applyTy,
55 maybeBoxedPrimType, splitAppTy, SYN_IE(Type)
57 import TysPrim ( voidTy )
58 import TysWiredIn ( mkTupleTy, tupleCon, nilDataCon, consDataCon, listTyCon,
61 import TyVar ( nullTyVarEnv, addOneToTyVarEnv, GenTyVar{-instance Eq-} )
62 import Usage ( SYN_IE(UVar) )
63 import Maybes ( maybeToBool )
64 import Util ( zipEqual, pprError, panic, assertPanic )
66 mk_nil_con ty = mkCon nilDataCon [] [ty] [] -- micro utility...
69 The funny business to do with variables is that we look them up in the
70 Id-to-Id and Id-to-Id maps that the monadery is carrying
71 around; if we get hits, we use the value accordingly.
73 %************************************************************************
75 \subsection[DsExpr-vars-and-cons]{Variables and constructors}
77 %************************************************************************
80 dsExpr :: TypecheckedHsExpr -> DsM CoreExpr
82 dsExpr e@(HsVar var) = dsId var
85 %************************************************************************
87 \subsection[DsExpr-literals]{Literals}
89 %************************************************************************
91 We give int/float literals type Integer and Rational, respectively.
92 The typechecker will (presumably) have put \tr{from{Integer,Rational}s}
95 ToDo: put in range checks for when converting "i"
96 (or should that be in the typechecker?)
98 For numeric literals, we try to detect there use at a standard type
99 (Int, Float, etc.) are directly put in the right constructor.
100 [NB: down with the @App@ conversion.]
101 Otherwise, we punt, putting in a "NoRep" Core literal (where the
102 representation decisions are delayed)...
104 See also below where we look for @DictApps@ for \tr{plusInt}, etc.
107 dsExpr (HsLitOut (HsString s) _)
109 = returnDs (mk_nil_con charTy)
113 the_char = mkCon charDataCon [] [] [LitArg (MachChar (_HEAD_ s))]
114 the_nil = mk_nil_con charTy
116 mkConDs consDataCon [TyArg charTy, VarArg the_char, VarArg the_nil]
118 -- "_" => build (\ c n -> c 'c' n) -- LATER
120 -- "str" ==> build (\ c n -> foldr charTy T c n "str")
123 dsExpr (HsLitOut (HsString str) _)
124 = newTyVarsDs [alphaTyVar] `thenDs` \ [new_tyvar] ->
126 new_ty = mkTyVarTy new_tyvar
129 charTy `mkFunTy` (new_ty `mkFunTy` new_ty),
131 mkForallTy [alphaTyVar]
132 ((charTy `mkFunTy` (alphaTy `mkFunTy` alphaTy))
133 `mkFunTy` (alphaTy `mkFunTy` alphaTy))
134 ] `thenDs` \ [c,n,g] ->
135 returnDs (mkBuild charTy new_tyvar c n g (
137 (CoTyApp (CoTyApp (Var foldrId) charTy) new_ty) *** ensure non-prim type ***
138 [VarArg c,VarArg n,LitArg (NoRepStr str)]))
141 -- otherwise, leave it as a NoRepStr;
142 -- the Core-to-STG pass will wrap it in an application of "unpackCStringId".
144 dsExpr (HsLitOut (HsString str) _)
145 = returnDs (Lit (NoRepStr str))
147 dsExpr (HsLitOut (HsLitLit s) ty)
148 = returnDs ( mkCon data_con [] [] [LitArg (MachLitLit s kind)] )
151 = case (maybeBoxedPrimType ty) of
152 Just (boxing_data_con, prim_ty)
153 -> (boxing_data_con, typePrimRep prim_ty)
155 -> pprError "ERROR: ``literal-literal'' not a single-constructor type: "
156 (hcat [ptext s, text "; type: ", ppr PprDebug ty])
158 dsExpr (HsLitOut (HsInt i) ty)
159 = returnDs (Lit (NoRepInteger i ty))
161 dsExpr (HsLitOut (HsFrac r) ty)
162 = returnDs (Lit (NoRepRational r ty))
164 -- others where we know what to do:
166 dsExpr (HsLitOut (HsIntPrim i) _)
167 = if (i >= toInteger minInt && i <= toInteger maxInt) then
168 returnDs (Lit (mkMachInt i))
170 error ("ERROR: Int constant " ++ show i ++ out_of_range_msg)
172 dsExpr (HsLitOut (HsFloatPrim f) _)
173 = returnDs (Lit (MachFloat f))
174 -- ToDo: range checking needed!
176 dsExpr (HsLitOut (HsDoublePrim d) _)
177 = returnDs (Lit (MachDouble d))
178 -- ToDo: range checking needed!
180 dsExpr (HsLitOut (HsChar c) _)
181 = returnDs ( mkCon charDataCon [] [] [LitArg (MachChar c)] )
183 dsExpr (HsLitOut (HsCharPrim c) _)
184 = returnDs (Lit (MachChar c))
186 dsExpr (HsLitOut (HsStringPrim s) _)
187 = returnDs (Lit (MachStr s))
189 -- end of literals magic. --
191 dsExpr expr@(HsLam a_Match)
192 = matchWrapper LambdaMatch [a_Match] "lambda" `thenDs` \ (binders, matching_code) ->
193 returnDs ( mkValLam binders matching_code )
195 dsExpr expr@(HsApp e1 e2) = dsApp expr []
196 dsExpr expr@(OpApp e1 op _ e2) = dsApp expr []
199 Operator sections. At first it looks as if we can convert
208 But no! expr might be a redex, and we can lose laziness badly this
213 for example. So we convert instead to
215 let y = expr in \x -> op y x
217 If \tr{expr} is actually just a variable, say, then the simplifier
221 dsExpr (SectionL expr op)
222 = dsExpr op `thenDs` \ core_op ->
223 dsExpr expr `thenDs` \ core_expr ->
224 dsExprToAtom (VarArg core_expr) $ \ y_atom ->
226 -- for the type of x, we need the type of op's 2nd argument
228 x_ty = case (splitSigmaTy (coreExprType core_op)) of { (_, _, tau_ty) ->
229 case (splitFunTy tau_ty) of {
230 ((_:arg2_ty:_), _) -> arg2_ty;
231 _ -> panic "dsExpr:SectionL:arg 2 ty" }}
233 newSysLocalDs x_ty `thenDs` \ x_id ->
234 returnDs (mkValLam [x_id] (core_op `App` y_atom `App` VarArg x_id))
236 -- dsExpr (SectionR op expr) -- \ x -> op x expr
237 dsExpr (SectionR op expr)
238 = dsExpr op `thenDs` \ core_op ->
239 dsExpr expr `thenDs` \ core_expr ->
240 dsExprToAtom (VarArg core_expr) $ \ y_atom ->
242 -- for the type of x, we need the type of op's 1st argument
244 x_ty = case (splitSigmaTy (coreExprType core_op)) of { (_, _, tau_ty) ->
245 case (splitFunTy tau_ty) of {
246 ((arg1_ty:_), _) -> arg1_ty;
247 _ -> panic "dsExpr:SectionR:arg 1 ty" }}
249 newSysLocalDs x_ty `thenDs` \ x_id ->
250 returnDs (mkValLam [x_id] (core_op `App` VarArg x_id `App` y_atom))
252 dsExpr (CCall label args may_gc is_asm result_ty)
253 = mapDs dsExpr args `thenDs` \ core_args ->
254 dsCCall label core_args may_gc is_asm result_ty
255 -- dsCCall does all the unboxification, etc.
257 dsExpr (HsSCC cc expr)
258 = dsExpr expr `thenDs` \ core_expr ->
259 getModuleAndGroupDs `thenDs` \ (mod_name, group_name) ->
260 returnDs ( SCC (mkUserCC cc mod_name group_name) core_expr)
262 dsExpr expr@(HsCase discrim matches src_loc)
263 = putSrcLocDs src_loc $
264 dsExpr discrim `thenDs` \ core_discrim ->
265 matchWrapper CaseMatch matches "case" `thenDs` \ ([discrim_var], matching_code) ->
266 returnDs ( mkCoLetAny (NonRec discrim_var core_discrim) matching_code )
268 dsExpr (HsLet binds expr)
269 = dsBinds Nothing binds `thenDs` \ core_binds ->
270 dsExpr expr `thenDs` \ core_expr ->
271 returnDs ( mkCoLetsAny core_binds core_expr )
273 dsExpr (HsDoOut do_or_lc stmts return_id then_id zero_id result_ty src_loc)
274 | maybeToBool maybe_list_comp
275 = -- Special case for list comprehensions
276 putSrcLocDs src_loc $
277 dsListComp stmts elt_ty
280 = putSrcLocDs src_loc $
281 dsDo do_or_lc stmts return_id then_id zero_id result_ty
284 = case (do_or_lc, maybeAppTyCon result_ty) of
285 (ListComp, Just (tycon, [elt_ty]))
289 -- We need the ListComp form to use deListComp (rather than the "do" form)
290 -- because the "return" in a do block is a call to "PrelBase.return", and
291 -- not a ReturnStmt. Only the ListComp form has ReturnStmts
293 Just elt_ty = maybe_list_comp
295 dsExpr (HsIf guard_expr then_expr else_expr src_loc)
296 = putSrcLocDs src_loc $
297 dsExpr guard_expr `thenDs` \ core_guard ->
298 dsExpr then_expr `thenDs` \ core_then ->
299 dsExpr else_expr `thenDs` \ core_else ->
300 returnDs (mkCoreIfThenElse core_guard core_then core_else)
304 Type lambda and application
305 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
307 dsExpr (TyLam tyvars expr)
308 = dsExpr expr `thenDs` \ core_expr ->
309 returnDs (mkTyLam tyvars core_expr)
311 dsExpr expr@(TyApp e tys) = dsApp expr []
315 Various data construction things
316 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
318 dsExpr (ExplicitListOut ty xs)
320 [] -> returnDs (mk_nil_con ty)
322 dsExpr y `thenDs` \ core_hd ->
323 dsExpr (ExplicitListOut ty ys) `thenDs` \ core_tl ->
324 mkConDs consDataCon [TyArg ty, VarArg core_hd, VarArg core_tl]
326 dsExpr (ExplicitTuple expr_list)
327 = mapDs dsExpr expr_list `thenDs` \ core_exprs ->
328 mkConDs (tupleCon (length expr_list))
329 (map (TyArg . coreExprType) core_exprs ++ map VarArg core_exprs)
331 dsExpr (ArithSeqOut expr (From from))
332 = dsExpr expr `thenDs` \ expr2 ->
333 dsExpr from `thenDs` \ from2 ->
334 mkAppDs expr2 [VarArg from2]
336 dsExpr (ArithSeqOut expr (FromTo from two))
337 = dsExpr expr `thenDs` \ expr2 ->
338 dsExpr from `thenDs` \ from2 ->
339 dsExpr two `thenDs` \ two2 ->
340 mkAppDs expr2 [VarArg from2, VarArg two2]
342 dsExpr (ArithSeqOut expr (FromThen from thn))
343 = dsExpr expr `thenDs` \ expr2 ->
344 dsExpr from `thenDs` \ from2 ->
345 dsExpr thn `thenDs` \ thn2 ->
346 mkAppDs expr2 [VarArg from2, VarArg thn2]
348 dsExpr (ArithSeqOut expr (FromThenTo from thn two))
349 = dsExpr expr `thenDs` \ expr2 ->
350 dsExpr from `thenDs` \ from2 ->
351 dsExpr thn `thenDs` \ thn2 ->
352 dsExpr two `thenDs` \ two2 ->
353 mkAppDs expr2 [VarArg from2, VarArg thn2, VarArg two2]
356 Record construction and update
357 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
358 For record construction we do this (assuming T has three arguments)
362 let err = /\a -> recConErr a
363 T (recConErr t1 "M.lhs/230/op1")
365 (recConErr t1 "M.lhs/230/op3")
367 recConErr then converts its arugment string into a proper message
368 before printing it as
370 M.lhs, line 230: missing field op1 was evaluated
374 dsExpr (RecordCon con_expr rbinds)
375 = dsExpr con_expr `thenDs` \ con_expr' ->
377 con_id = get_con con_expr'
378 (arg_tys, _) = splitFunTy (coreExprType con_expr')
381 = case [rhs | (sel_id,rhs,_) <- rbinds,
382 lbl == recordSelectorFieldLabel sel_id] of
383 (rhs:rhss) -> ASSERT( null rhss )
385 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showForErr lbl)
387 mapDs mk_arg (zipEqual "dsExpr:RecordCon" arg_tys (dataConFieldLabels con_id)) `thenDs` \ con_args ->
388 mkAppDs con_expr' (map VarArg con_args)
390 -- "con_expr'" is simply an application of the constructor Id
391 -- to types and (perhaps) dictionaries. This gets the constructor...
392 get_con (Var con) = con
393 get_con (App fun _) = get_con fun
396 Record update is a little harder. Suppose we have the decl:
398 data T = T1 {op1, op2, op3 :: Int}
399 | T2 {op4, op2 :: Int}
402 Then we translate as follows:
408 T1 op1 _ op3 -> T1 op1 op2 op3
409 T2 op4 _ -> T2 op4 op2
410 other -> recUpdError "M.lhs/230"
412 It's important that we use the constructor Ids for T1, T2 etc on the
413 RHSs, and do not generate a Core Con directly, because the constructor
414 might do some argument-evaluation first; and may have to throw away some
418 dsExpr (RecordUpdOut record_expr record_out_ty dicts rbinds)
419 = dsExpr record_expr `thenDs` \ record_expr' ->
421 -- Desugar the rbinds, and generate let-bindings if
422 -- necessary so that we don't lose sharing
423 dsRbinds rbinds $ \ rbinds' ->
425 record_in_ty = coreExprType record_expr'
426 (tycon, in_inst_tys, cons) = getAppDataTyConExpandingDicts record_in_ty
427 (_, out_inst_tys, _) = getAppDataTyConExpandingDicts record_out_ty
428 cons_to_upd = filter has_all_fields cons
430 -- initial_args are passed to every constructor
431 initial_args = map TyArg out_inst_tys ++ map VarArg dicts
433 mk_val_arg (field, arg_id)
434 = case [arg | (f, arg) <- rbinds',
435 field == recordSelectorFieldLabel f] of
436 (arg:args) -> ASSERT(null args)
441 = newSysLocalsDs (dataConArgTys con in_inst_tys) `thenDs` \ arg_ids ->
443 val_args = map mk_val_arg (zipEqual "dsExpr:RecordUpd" (dataConFieldLabels con) arg_ids)
445 returnDs (con, arg_ids, mkGenApp (mkGenApp (Var con) initial_args) val_args)
448 | length cons_to_upd == length cons
451 = newSysLocalDs record_in_ty `thenDs` \ deflt_id ->
452 mkErrorAppDs rEC_UPD_ERROR_ID record_out_ty "" `thenDs` \ err ->
453 returnDs (BindDefault deflt_id err)
455 mapDs mk_alt cons_to_upd `thenDs` \ alts ->
456 mk_default `thenDs` \ deflt ->
458 returnDs (Case record_expr' (AlgAlts alts deflt))
461 has_all_fields :: Id -> Bool
462 has_all_fields con_id
465 con_fields = dataConFieldLabels con_id
466 ok (sel_id, _, _) = recordSelectorFieldLabel sel_id `elem` con_fields
469 Dictionary lambda and application
470 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
471 @DictLam@ and @DictApp@ turn into the regular old things.
472 (OLD:) @DictFunApp@ also becomes a curried application, albeit slightly more
473 complicated; reminiscent of fully-applied constructors.
475 dsExpr (DictLam dictvars expr)
476 = dsExpr expr `thenDs` \ core_expr ->
477 returnDs( mkValLam dictvars core_expr )
481 dsExpr expr@(DictApp e dicts) -- becomes a curried application
485 @SingleDicts@ become @Locals@; @Dicts@ turn into tuples, unless
487 @ClassDictLam dictvars methods expr@ is ``the opposite'':
489 \ x -> case x of ( dictvars-and-methods-tuple ) -> expr
492 dsExpr (SingleDict dict) -- just a local
493 = lookupEnvDs dict `thenDs` \ dict' ->
496 dsExpr (Dictionary [] []) -- Empty dictionary represented by void,
497 = returnDs (Var voidId) -- (not, as would happen if we took the next case, by ())
499 dsExpr (Dictionary dicts methods)
500 = mapDs lookupEnvDs (dicts ++ methods) `thenDs` \ d_and_ms' ->
501 returnDs (mkTupleExpr d_and_ms')
503 dsExpr (ClassDictLam dicts methods expr)
504 = dsExpr expr `thenDs` \ core_expr ->
505 case num_of_d_and_ms of
506 0 -> newSysLocalDs voidTy `thenDs` \ new_x ->
507 returnDs (mkValLam [new_x] core_expr)
510 returnDs (mkValLam dicts_and_methods core_expr)
513 newSysLocalDs tuple_ty `thenDs` \ new_x ->
515 Lam (ValBinder new_x)
518 [(tuple_con, dicts_and_methods, core_expr)]
521 num_of_d_and_ms = length dicts + length methods
522 dicts_and_methods = dicts ++ methods
523 tuple_ty = mkTupleTy num_of_d_and_ms (map idType dicts_and_methods)
524 tuple_con = tupleCon num_of_d_and_ms
527 -- HsSyn constructs that just shouldn't be here:
528 dsExpr (HsDo _ _ _) = panic "dsExpr:HsDo"
529 dsExpr (ExplicitList _) = panic "dsExpr:ExplicitList"
530 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
531 dsExpr (ArithSeqIn _) = panic "dsExpr:ArithSeqIn"
534 out_of_range_msg -- ditto
535 = " out of range: [" ++ show minInt ++ ", " ++ show maxInt ++ "]\n"
538 %--------------------------------------------------------------------
540 @(dsApp e [t_1,..,t_n, e_1,..,e_n])@ returns something with the same
543 e t_1 ... t_n e_1 .. e_n
546 We're doing all this so we can saturate constructors (as painlessly as
550 dsApp :: TypecheckedHsExpr -- expr to desugar
551 -> [DsCoreArg] -- accumulated ty/val args: NB:
552 -> DsM CoreExpr -- final result
554 dsApp (HsApp e1 e2) args
555 = dsExpr e2 `thenDs` \ core_e2 ->
556 dsApp e1 (VarArg core_e2 : args)
558 dsApp (OpApp e1 op _ e2) args
559 = dsExpr e1 `thenDs` \ core_e1 ->
560 dsExpr e2 `thenDs` \ core_e2 ->
561 dsApp op (VarArg core_e1 : VarArg core_e2 : args)
563 dsApp (DictApp expr dicts) args
564 = mapDs lookupEnvDs dicts `thenDs` \ core_dicts ->
565 dsApp expr (map (VarArg . Var) core_dicts ++ args)
567 dsApp (TyApp expr tys) args
568 = dsApp expr (map TyArg tys ++ args)
570 -- we might should look out for SectionLs, etc., here, but we don't
572 dsApp anything_else args
573 = dsExpr anything_else `thenDs` \ core_expr ->
574 mkAppDs core_expr args
577 = lookupEnvDs v `thenDs` \ v' ->
582 dsRbinds :: TypecheckedRecordBinds -- The field bindings supplied
583 -> ([(Id, CoreArg)] -> DsM CoreExpr) -- A continuation taking the field
584 -- bindings with atomic rhss
585 -> DsM CoreExpr -- The result of the continuation,
586 -- wrapped in suitable Lets
588 dsRbinds [] continue_with
591 dsRbinds ((sel_id, rhs, pun_flag) : rbinds) continue_with
592 = dsExpr rhs `thenDs` \ rhs' ->
593 dsExprToAtom (VarArg rhs') $ \ rhs_atom ->
594 dsRbinds rbinds $ \ rbinds' ->
595 continue_with ((sel_id, rhs_atom) : rbinds')
599 -- do_unfold ty_env val_env (Lam (TyBinder tyvar) body) (TyArg ty : args)
600 -- = do_unfold (addOneToTyVarEnv ty_env tyvar ty) val_env body args
602 -- do_unfold ty_env val_env (Lam (ValBinder binder) body) (arg@(VarArg expr) : args)
603 -- = dsExprToAtom arg $ \ arg_atom ->
605 -- (addOneToIdEnv val_env binder (argToExpr arg_atom))
608 -- do_unfold ty_env val_env body args
609 -- = -- Clone the remaining part of the template
610 -- uniqSMtoDsM (substCoreExpr val_env ty_env body) `thenDs` \ body' ->
612 -- -- Apply result to remaining arguments
613 -- mkAppDs body' args
616 Basically does the translation given in the Haskell~1.3 report:
620 -> Id -- id for: return m
621 -> Id -- id for: (>>=) m
622 -> Id -- id for: zero m
623 -> Type -- Element type; the whole expression has type (m t)
626 dsDo do_or_lc stmts return_id then_id zero_id result_ty
627 = dsId return_id `thenDs` \ return_ds ->
628 dsId then_id `thenDs` \ then_ds ->
629 dsId zero_id `thenDs` \ zero_ds ->
631 (_, b_ty) = splitAppTy result_ty -- result_ty must be of the form (m b)
634 = dsExpr expr `thenDs` \ expr2 ->
635 mkAppDs return_ds [TyArg b_ty, VarArg expr2]
637 go (GuardStmt expr locn : stmts)
638 = do_expr expr locn `thenDs` \ expr2 ->
639 go stmts `thenDs` \ rest ->
640 mkAppDs zero_ds [TyArg b_ty] `thenDs` \ zero_expr ->
641 returnDs (mkCoreIfThenElse expr2 rest zero_expr)
643 go (ExprStmt expr locn : stmts)
644 = do_expr expr locn `thenDs` \ expr2 ->
646 (_, a_ty) = splitAppTy (coreExprType expr2) -- Must be of form (m a)
651 go stmts `thenDs` \ rest ->
652 newSysLocalDs a_ty `thenDs` \ ignored_result_id ->
653 mkAppDs then_ds [TyArg a_ty, TyArg b_ty, VarArg expr2,
654 VarArg (mkValLam [ignored_result_id] rest)]
656 go (LetStmt binds : stmts )
657 = dsBinds Nothing binds `thenDs` \ binds2 ->
658 go stmts `thenDs` \ rest ->
659 returnDs (mkCoLetsAny binds2 rest)
661 go (BindStmt pat expr locn : stmts)
663 dsExpr expr `thenDs` \ expr2 ->
665 (_, a_ty) = splitAppTy (coreExprType expr2) -- Must be of form (m a)
666 zero_expr = TyApp (HsVar zero_id) [b_ty]
667 main_match = PatMatch pat (SimpleMatch (
668 HsDoOut do_or_lc stmts return_id then_id zero_id result_ty locn))
670 = if failureFreePat pat
672 else [main_match, PatMatch (WildPat a_ty) (SimpleMatch zero_expr)]
674 matchWrapper DoBindMatch the_matches match_msg
675 `thenDs` \ (binders, matching_code) ->
676 mkAppDs then_ds [TyArg a_ty, TyArg b_ty,
677 VarArg expr2, VarArg (mkValLam binders matching_code)]
682 do_expr expr locn = putSrcLocDs locn (dsExpr expr)
684 match_msg = case do_or_lc of
685 DoStmt -> "`do' statement"
686 ListComp -> "comprehension"