2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsExpr]{Matching expressions (Exprs)}
7 module DsExpr ( dsExpr, dsLExpr, dsLocalBinds, dsValBinds, dsLit ) where
9 #include "HsVersions.h"
10 #if defined(GHCI) && defined(BREAKPOINT)
11 import Foreign.StablePtr ( newStablePtr, castStablePtrToPtr )
12 import GHC.Exts ( Ptr(..), Int(..), addr2Int# )
13 import IOEnv ( ioToIOEnv )
14 import PrelNames ( breakpointJumpName, breakpointCondJumpName )
15 import TysWiredIn ( unitTy )
16 import TypeRep ( Type(..) )
17 import TyCon ( isUnLiftedTyCon )
20 import Match ( matchWrapper, matchSinglePat, matchEquations )
21 import MatchLit ( dsLit, dsOverLit )
22 import DsBinds ( dsLHsBinds, dsCoercion )
23 import DsGRHSs ( dsGuarded )
24 import DsListComp ( dsListComp, dsPArrComp )
25 import DsUtils ( mkErrorAppDs, mkStringExpr, mkConsExpr, mkNilExpr,
26 extractMatchResult, cantFailMatchResult, matchCanFail,
27 mkCoreTupTy, selectSimpleMatchVarL, lookupEvidence, selectMatchVar )
28 import DsArrows ( dsProcExpr )
32 -- Template Haskell stuff iff bootstrapped
33 import DsMeta ( dsBracket )
37 import TcHsSyn ( hsPatType, mkVanillaTuplePat )
39 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
40 -- needs to see source types (newtypes etc), and sometimes not
41 -- So WATCH OUT; check each use of split*Ty functions.
42 -- Sigh. This is a pain.
44 import TcType ( tcSplitAppTy, tcSplitFunTys, tcTyConAppTyCon,
45 tcTyConAppArgs, isUnLiftedType, Type, mkAppTy )
46 import Type ( splitFunTys, isUnboxedTupleType, mkFunTy )
48 import CoreUtils ( exprType, mkIfThenElse, bindNonRec )
50 import CostCentre ( mkUserCC )
51 import Id ( Id, idType, idName, idDataCon )
52 import PrelInfo ( rEC_CON_ERROR_ID )
53 import DataCon ( DataCon, dataConWrapId, dataConFieldLabels, dataConInstOrigArgTys )
54 import DataCon ( isVanillaDataCon )
55 import TyCon ( FieldLabel, tyConDataCons )
56 import TysWiredIn ( tupleCon )
57 import BasicTypes ( RecFlag(..), Boxity(..), ipNameName )
58 import PrelNames ( toPName,
59 returnMName, bindMName, thenMName, failMName,
61 import SrcLoc ( Located(..), unLoc, getLoc, noLoc )
62 import Util ( zipEqual, zipWithEqual )
63 import Bag ( bagToList )
69 %************************************************************************
71 dsLocalBinds, dsValBinds
73 %************************************************************************
76 dsLocalBinds :: HsLocalBinds Id -> CoreExpr -> DsM CoreExpr
77 dsLocalBinds EmptyLocalBinds body = return body
78 dsLocalBinds (HsValBinds binds) body = dsValBinds binds body
79 dsLocalBinds (HsIPBinds binds) body = dsIPBinds binds body
81 -------------------------
82 dsValBinds :: HsValBinds Id -> CoreExpr -> DsM CoreExpr
83 dsValBinds (ValBindsOut binds _) body = foldrDs ds_val_bind body binds
85 -------------------------
86 dsIPBinds (IPBinds ip_binds dict_binds) body
87 = do { prs <- dsLHsBinds dict_binds
88 ; let inner = foldr (\(x,r) e -> Let (NonRec x r) e) body prs
89 ; foldrDs ds_ip_bind inner ip_binds }
91 ds_ip_bind (L _ (IPBind n e)) body
92 = dsLExpr e `thenDs` \ e' ->
93 returnDs (Let (NonRec (ipNameName n) e') body)
95 -------------------------
96 ds_val_bind :: (RecFlag, LHsBinds Id) -> CoreExpr -> DsM CoreExpr
97 -- Special case for bindings which bind unlifted variables
98 -- We need to do a case right away, rather than building
99 -- a tuple and doing selections.
100 -- Silently ignore INLINE and SPECIALISE pragmas...
101 ds_val_bind (NonRecursive, hsbinds) body
102 | [L _ (AbsBinds [] [] exports binds)] <- bagToList hsbinds,
103 (L loc bind : null_binds) <- bagToList binds,
105 || isUnboxedTupleBind bind
106 || or [isUnLiftedType (idType g) | (_, g, _, _) <- exports]
108 body_w_exports = foldr bind_export body exports
109 bind_export (tvs, g, l, _) body = ASSERT( null tvs )
110 bindNonRec g (Var l) body
112 ASSERT (null null_binds)
113 -- Non-recursive, non-overloaded bindings only come in ones
114 -- ToDo: in some bizarre case it's conceivable that there
115 -- could be dict binds in the 'binds'. (See the notes
116 -- below. Then pattern-match would fail. Urk.)
119 FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn }
120 -> matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, rhs) ->
121 ASSERT( null args ) -- Functions aren't lifted
122 ASSERT( isIdCoercion co_fn )
123 returnDs (bindNonRec fun rhs body_w_exports)
125 PatBind {pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }
126 -> -- let C x# y# = rhs in body
127 -- ==> case rhs of C x# y# -> body
129 do { rhs <- dsGuarded grhss ty
130 ; let upat = unLoc pat
131 eqn = EqnInfo { eqn_wrap = idWrapper, eqn_pats = [upat],
132 eqn_rhs = cantFailMatchResult body_w_exports }
133 ; var <- selectMatchVar upat ty
134 ; result <- matchEquations PatBindRhs [var] [eqn] (exprType body)
135 ; return (scrungleMatch var rhs result) }
137 other -> pprPanic "dsLet: unlifted" (pprLHsBinds hsbinds $$ ppr body)
140 -- Ordinary case for bindings; none should be unlifted
141 ds_val_bind (is_rec, binds) body
142 = do { prs <- dsLHsBinds binds
143 ; ASSERT( not (any (isUnLiftedType . idType . fst) prs) )
146 other -> return (Let (Rec prs) body) }
147 -- Use a Rec regardless of is_rec.
148 -- Why? Because it allows the binds to be all
149 -- mixed up, which is what happens in one rare case
150 -- Namely, for an AbsBind with no tyvars and no dicts,
151 -- but which does have dictionary bindings.
152 -- See notes with TcSimplify.inferLoop [NO TYVARS]
153 -- It turned out that wrapping a Rec here was the easiest solution
155 -- NB The previous case dealt with unlifted bindings, so we
156 -- only have to deal with lifted ones now; so Rec is ok
158 isUnboxedTupleBind :: HsBind Id -> Bool
159 isUnboxedTupleBind (PatBind { pat_rhs_ty = ty }) = isUnboxedTupleType ty
160 isUnboxedTupleBind other = False
162 scrungleMatch :: Id -> CoreExpr -> CoreExpr -> CoreExpr
163 -- Returns something like (let var = scrut in body)
164 -- but if var is an unboxed-tuple type, it inlines it in a fragile way
165 -- Special case to handle unboxed tuple patterns; they can't appear nested
167 -- case e of (# p1, p2 #) -> rhs
169 -- case e of (# x1, x2 #) -> ... match p1, p2 ...
171 -- let x = e in case x of ....
173 -- But there may be a big
174 -- let fail = ... in case e of ...
175 -- wrapping the whole case, which complicates matters slightly
176 -- It all seems a bit fragile. Test is dsrun013.
178 scrungleMatch var scrut body
179 | isUnboxedTupleType (idType var) = scrungle body
180 | otherwise = bindNonRec var scrut body
182 scrungle (Case (Var x) bndr ty alts)
183 | x == var = Case scrut bndr ty alts
184 scrungle (Let binds body) = Let binds (scrungle body)
185 scrungle other = panic ("scrungleMatch: tuple pattern:\n" ++ showSDoc (ppr other))
188 %************************************************************************
190 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
192 %************************************************************************
195 dsLExpr :: LHsExpr Id -> DsM CoreExpr
196 dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e
198 dsExpr :: HsExpr Id -> DsM CoreExpr
200 dsExpr (HsPar e) = dsLExpr e
201 dsExpr (ExprWithTySigOut e _) = dsLExpr e
202 dsExpr (HsVar var) = returnDs (Var var)
203 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
204 dsExpr (HsLit lit) = dsLit lit
205 dsExpr (HsOverLit lit) = dsOverLit lit
207 dsExpr (NegApp expr neg_expr)
208 = do { core_expr <- dsLExpr expr
209 ; core_neg <- dsExpr neg_expr
210 ; return (core_neg `App` core_expr) }
212 dsExpr expr@(HsLam a_Match)
213 = matchWrapper LambdaExpr a_Match `thenDs` \ (binders, matching_code) ->
214 returnDs (mkLams binders matching_code)
216 #if defined(GHCI) && defined(BREAKPOINT)
217 dsExpr (HsApp (L _ (HsApp realFun@(L _ (HsCoerce _ fun)) (L loc arg))) _)
219 , idName funId `elem` [breakpointJumpName, breakpointCondJumpName]
220 , ids <- filter (isValidType . idType) (extractIds arg)
221 = do dsWarn (text "Extracted ids:" <+> ppr ids <+> ppr (map idType ids))
222 stablePtr <- ioToIOEnv $ newStablePtr ids
223 -- Yes, I know... I'm gonna burn in hell.
224 let Ptr addr# = castStablePtrToPtr stablePtr
225 funCore <- dsLExpr realFun
226 argCore <- dsLExpr (L loc (HsLit (HsInt (fromIntegral (I# (addr2Int# addr#))))))
227 hvalCore <- dsLExpr (L loc (extractHVals ids))
228 return ((funCore `App` argCore) `App` hvalCore)
229 where extractIds :: HsExpr Id -> [Id]
230 extractIds (HsApp fn arg)
231 | HsVar argId <- unLoc arg
232 = argId:extractIds (unLoc fn)
233 | TyApp arg' ts <- unLoc arg
234 , HsVar argId <- unLoc arg'
235 = error (showSDoc (ppr ts)) -- argId:extractIds (unLoc fn)
237 extractHVals ids = ExplicitList unitTy (map (L loc . HsVar) ids)
238 -- checks for tyvars and unlifted kinds.
239 isValidType (TyVarTy _) = False
240 isValidType (FunTy a b) = isValidType a && isValidType b
241 isValidType (NoteTy _ t) = isValidType t
242 isValidType (AppTy a b) = isValidType a && isValidType b
243 isValidType (TyConApp con ts) = not (isUnLiftedTyCon con) && all isValidType ts
247 dsExpr expr@(HsApp fun arg)
248 = dsLExpr fun `thenDs` \ core_fun ->
249 dsLExpr arg `thenDs` \ core_arg ->
250 returnDs (core_fun `App` core_arg)
253 Operator sections. At first it looks as if we can convert
262 But no! expr might be a redex, and we can lose laziness badly this
267 for example. So we convert instead to
269 let y = expr in \x -> op y x
271 If \tr{expr} is actually just a variable, say, then the simplifier
275 dsExpr (OpApp e1 op _ e2)
276 = dsLExpr op `thenDs` \ core_op ->
277 -- for the type of y, we need the type of op's 2nd argument
278 dsLExpr e1 `thenDs` \ x_core ->
279 dsLExpr e2 `thenDs` \ y_core ->
280 returnDs (mkApps core_op [x_core, y_core])
282 dsExpr (SectionL expr op)
283 = dsLExpr op `thenDs` \ core_op ->
284 -- for the type of y, we need the type of op's 2nd argument
286 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
287 -- Must look through an implicit-parameter type;
288 -- newtype impossible; hence Type.splitFunTys
290 dsLExpr expr `thenDs` \ x_core ->
291 newSysLocalDs x_ty `thenDs` \ x_id ->
292 newSysLocalDs y_ty `thenDs` \ y_id ->
294 returnDs (bindNonRec x_id x_core $
295 Lam y_id (mkApps core_op [Var x_id, Var y_id]))
297 -- dsLExpr (SectionR op expr) -- \ x -> op x expr
298 dsExpr (SectionR op expr)
299 = dsLExpr op `thenDs` \ core_op ->
300 -- for the type of x, we need the type of op's 2nd argument
302 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
303 -- See comment with SectionL
305 dsLExpr expr `thenDs` \ y_core ->
306 newSysLocalDs x_ty `thenDs` \ x_id ->
307 newSysLocalDs y_ty `thenDs` \ y_id ->
309 returnDs (bindNonRec y_id y_core $
310 Lam x_id (mkApps core_op [Var x_id, Var y_id]))
312 dsExpr (HsSCC cc expr)
313 = dsLExpr expr `thenDs` \ core_expr ->
314 getModuleDs `thenDs` \ mod_name ->
315 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
318 -- hdaume: core annotation
320 dsExpr (HsCoreAnn fs expr)
321 = dsLExpr expr `thenDs` \ core_expr ->
322 returnDs (Note (CoreNote $ unpackFS fs) core_expr)
324 dsExpr (HsCase discrim matches)
325 = dsLExpr discrim `thenDs` \ core_discrim ->
326 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
327 returnDs (scrungleMatch discrim_var core_discrim matching_code)
329 dsExpr (HsLet binds body)
330 = dsLExpr body `thenDs` \ body' ->
331 dsLocalBinds binds body'
333 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
334 -- because the interpretation of `stmts' depends on what sort of thing it is.
336 dsExpr (HsDo ListComp stmts body result_ty)
337 = -- Special case for list comprehensions
338 dsListComp stmts body elt_ty
340 [elt_ty] = tcTyConAppArgs result_ty
342 dsExpr (HsDo DoExpr stmts body result_ty)
343 = dsDo stmts body result_ty
345 dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
346 = dsMDo tbl stmts body result_ty
348 dsExpr (HsDo PArrComp stmts body result_ty)
349 = -- Special case for array comprehensions
350 dsPArrComp (map unLoc stmts) body elt_ty
352 [elt_ty] = tcTyConAppArgs result_ty
354 dsExpr (HsIf guard_expr then_expr else_expr)
355 = dsLExpr guard_expr `thenDs` \ core_guard ->
356 dsLExpr then_expr `thenDs` \ core_then ->
357 dsLExpr else_expr `thenDs` \ core_else ->
358 returnDs (mkIfThenElse core_guard core_then core_else)
363 \underline{\bf Type lambda and application}
364 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~
366 dsExpr (TyLam tyvars expr)
367 = dsLExpr expr `thenDs` \ core_expr ->
368 returnDs (mkLams tyvars core_expr)
370 dsExpr (TyApp expr tys)
371 = dsLExpr expr `thenDs` \ core_expr ->
372 returnDs (mkTyApps core_expr tys)
377 \underline{\bf Various data construction things}
378 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
380 dsExpr (ExplicitList ty xs)
383 go [] = returnDs (mkNilExpr ty)
384 go (x:xs) = dsLExpr x `thenDs` \ core_x ->
385 go xs `thenDs` \ core_xs ->
386 returnDs (mkConsExpr ty core_x core_xs)
388 -- we create a list from the array elements and convert them into a list using
391 -- * the main disadvantage to this scheme is that `toP' traverses the list
392 -- twice: once to determine the length and a second time to put to elements
393 -- into the array; this inefficiency could be avoided by exposing some of
394 -- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
395 -- that we can exploit the fact that we already know the length of the array
396 -- here at compile time
398 dsExpr (ExplicitPArr ty xs)
399 = dsLookupGlobalId toPName `thenDs` \toP ->
400 dsExpr (ExplicitList ty xs) `thenDs` \coreList ->
401 returnDs (mkApps (Var toP) [Type ty, coreList])
403 dsExpr (ExplicitTuple expr_list boxity)
404 = mappM dsLExpr expr_list `thenDs` \ core_exprs ->
405 returnDs (mkConApp (tupleCon boxity (length expr_list))
406 (map (Type . exprType) core_exprs ++ core_exprs))
408 dsExpr (ArithSeq expr (From from))
409 = dsExpr expr `thenDs` \ expr2 ->
410 dsLExpr from `thenDs` \ from2 ->
411 returnDs (App expr2 from2)
413 dsExpr (ArithSeq expr (FromTo from two))
414 = dsExpr expr `thenDs` \ expr2 ->
415 dsLExpr from `thenDs` \ from2 ->
416 dsLExpr two `thenDs` \ two2 ->
417 returnDs (mkApps expr2 [from2, two2])
419 dsExpr (ArithSeq expr (FromThen from thn))
420 = dsExpr expr `thenDs` \ expr2 ->
421 dsLExpr from `thenDs` \ from2 ->
422 dsLExpr thn `thenDs` \ thn2 ->
423 returnDs (mkApps expr2 [from2, thn2])
425 dsExpr (ArithSeq expr (FromThenTo from thn two))
426 = dsExpr expr `thenDs` \ expr2 ->
427 dsLExpr from `thenDs` \ from2 ->
428 dsLExpr thn `thenDs` \ thn2 ->
429 dsLExpr two `thenDs` \ two2 ->
430 returnDs (mkApps expr2 [from2, thn2, two2])
432 dsExpr (PArrSeq expr (FromTo from two))
433 = dsExpr expr `thenDs` \ expr2 ->
434 dsLExpr from `thenDs` \ from2 ->
435 dsLExpr two `thenDs` \ two2 ->
436 returnDs (mkApps expr2 [from2, two2])
438 dsExpr (PArrSeq expr (FromThenTo from thn two))
439 = dsExpr expr `thenDs` \ expr2 ->
440 dsLExpr from `thenDs` \ from2 ->
441 dsLExpr thn `thenDs` \ thn2 ->
442 dsLExpr two `thenDs` \ two2 ->
443 returnDs (mkApps expr2 [from2, thn2, two2])
445 dsExpr (PArrSeq expr _)
446 = panic "DsExpr.dsExpr: Infinite parallel array!"
447 -- the parser shouldn't have generated it and the renamer and typechecker
448 -- shouldn't have let it through
452 \underline{\bf Record construction and update}
453 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
454 For record construction we do this (assuming T has three arguments)
458 let err = /\a -> recConErr a
459 T (recConErr t1 "M.lhs/230/op1")
461 (recConErr t1 "M.lhs/230/op3")
463 @recConErr@ then converts its arugment string into a proper message
464 before printing it as
466 M.lhs, line 230: missing field op1 was evaluated
469 We also handle @C{}@ as valid construction syntax for an unlabelled
470 constructor @C@, setting all of @C@'s fields to bottom.
473 dsExpr (RecordCon (L _ data_con_id) con_expr rbinds)
474 = dsExpr con_expr `thenDs` \ con_expr' ->
476 (arg_tys, _) = tcSplitFunTys (exprType con_expr')
477 -- A newtype in the corner should be opaque;
478 -- hence TcType.tcSplitFunTys
480 mk_arg (arg_ty, lbl) -- Selector id has the field label as its name
481 = case [rhs | (L _ sel_id, rhs) <- rbinds, lbl == idName sel_id] of
482 (rhs:rhss) -> ASSERT( null rhss )
484 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
485 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
487 labels = dataConFieldLabels (idDataCon data_con_id)
488 -- The data_con_id is guaranteed to be the wrapper id of the constructor
492 then mappM unlabelled_bottom arg_tys
493 else mappM mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels))
494 `thenDs` \ con_args ->
496 returnDs (mkApps con_expr' con_args)
499 Record update is a little harder. Suppose we have the decl:
501 data T = T1 {op1, op2, op3 :: Int}
502 | T2 {op4, op2 :: Int}
505 Then we translate as follows:
511 T1 op1 _ op3 -> T1 op1 op2 op3
512 T2 op4 _ -> T2 op4 op2
513 other -> recUpdError "M.lhs/230"
515 It's important that we use the constructor Ids for @T1@, @T2@ etc on the
516 RHSs, and do not generate a Core constructor application directly, because the constructor
517 might do some argument-evaluation first; and may have to throw away some
521 dsExpr (RecordUpd record_expr [] record_in_ty record_out_ty)
522 = dsLExpr record_expr
524 dsExpr expr@(RecordUpd record_expr rbinds record_in_ty record_out_ty)
525 = dsLExpr record_expr `thenDs` \ record_expr' ->
527 -- Desugar the rbinds, and generate let-bindings if
528 -- necessary so that we don't lose sharing
531 in_inst_tys = tcTyConAppArgs record_in_ty -- Newtype opaque
532 out_inst_tys = tcTyConAppArgs record_out_ty -- Newtype opaque
533 in_out_ty = mkFunTy record_in_ty record_out_ty
535 mk_val_arg field old_arg_id
536 = case [rhs | (L _ sel_id, rhs) <- rbinds, field == idName sel_id] of
537 (rhs:rest) -> ASSERT(null rest) rhs
538 [] -> nlHsVar old_arg_id
541 = newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids ->
542 -- This call to dataConInstOrigArgTys won't work for existentials
543 -- but existentials don't have record types anyway
545 val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
546 (dataConFieldLabels con) arg_ids
547 rhs = foldl (\a b -> nlHsApp a b)
548 (noLoc $ TyApp (nlHsVar (dataConWrapId con))
552 returnDs (mkSimpleMatch [noLoc $ ConPatOut (noLoc con) [] [] emptyLHsBinds
553 (PrefixCon (map nlVarPat arg_ids)) record_in_ty]
556 -- Record stuff doesn't work for existentials
557 -- The type checker checks for this, but we need
558 -- worry only about the constructors that are to be updated
559 ASSERT2( all isVanillaDataCon cons_to_upd, ppr expr )
561 -- It's important to generate the match with matchWrapper,
562 -- and the right hand sides with applications of the wrapper Id
563 -- so that everything works when we are doing fancy unboxing on the
564 -- constructor aguments.
565 mappM mk_alt cons_to_upd `thenDs` \ alts ->
566 matchWrapper RecUpd (MatchGroup alts in_out_ty) `thenDs` \ ([discrim_var], matching_code) ->
568 returnDs (bindNonRec discrim_var record_expr' matching_code)
571 updated_fields :: [FieldLabel]
572 updated_fields = [ idName sel_id | (L _ sel_id,_) <- rbinds]
574 -- Get the type constructor from the record_in_ty
575 -- so that we are sure it'll have all its DataCons
576 -- (In GHCI, it's possible that some TyCons may not have all
577 -- their constructors, in a module-loop situation.)
578 tycon = tcTyConAppTyCon record_in_ty
579 data_cons = tyConDataCons tycon
580 cons_to_upd = filter has_all_fields data_cons
582 has_all_fields :: DataCon -> Bool
583 has_all_fields con_id
584 = all (`elem` con_fields) updated_fields
586 con_fields = dataConFieldLabels con_id
591 \underline{\bf Dictionary lambda and application}
592 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
593 @DictLam@ and @DictApp@ turn into the regular old things.
594 (OLD:) @DictFunApp@ also becomes a curried application, albeit slightly more
595 complicated; reminiscent of fully-applied constructors.
597 dsExpr (DictLam dictvars expr)
598 = dsLExpr expr `thenDs` \ core_expr ->
599 returnDs (mkLams dictvars core_expr)
603 dsExpr (DictApp expr dicts) -- becomes a curried application
604 = dsLExpr expr `thenDs` \ core_expr ->
605 returnDs (foldl (\f d -> f `App` (Var d)) core_expr dicts)
607 dsExpr (HsCoerce co_fn e) = dsCoercion co_fn (dsExpr e)
610 Here is where we desugar the Template Haskell brackets and escapes
613 -- Template Haskell stuff
615 #ifdef GHCI /* Only if bootstrapping */
616 dsExpr (HsBracketOut x ps) = dsBracket x ps
617 dsExpr (HsSpliceE s) = pprPanic "dsExpr:splice" (ppr s)
620 -- Arrow notation extension
621 dsExpr (HsProc pat cmd) = dsProcExpr pat cmd
628 -- HsSyn constructs that just shouldn't be here:
629 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
634 %--------------------------------------------------------------------
636 Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
637 handled in DsListComp). Basically does the translation given in the
643 -> Type -- Type of the whole expression
646 dsDo stmts body result_ty
647 = go (map unLoc stmts)
651 go (ExprStmt rhs then_expr _ : stmts)
652 = do { rhs2 <- dsLExpr rhs
653 ; then_expr2 <- dsExpr then_expr
655 ; returnDs (mkApps then_expr2 [rhs2, rest]) }
657 go (LetStmt binds : stmts)
658 = do { rest <- go stmts
659 ; dsLocalBinds binds rest }
661 go (BindStmt pat rhs bind_op fail_op : stmts)
662 = do { body <- go stmts
663 ; var <- selectSimpleMatchVarL pat
664 ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
665 result_ty (cantFailMatchResult body)
666 ; match_code <- handle_failure pat match fail_op
667 ; rhs' <- dsLExpr rhs
668 ; bind_op' <- dsExpr bind_op
669 ; returnDs (mkApps bind_op' [rhs', Lam var match_code]) }
671 -- In a do expression, pattern-match failure just calls
672 -- the monadic 'fail' rather than throwing an exception
673 handle_failure pat match fail_op
675 = do { fail_op' <- dsExpr fail_op
676 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
677 ; extractMatchResult match (App fail_op' fail_msg) }
679 = extractMatchResult match (error "It can't fail")
681 mk_fail_msg pat = "Pattern match failure in do expression at " ++
682 showSDoc (ppr (getLoc pat))
685 Translation for RecStmt's:
686 -----------------------------
687 We turn (RecStmt [v1,..vn] stmts) into:
689 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
696 -> Type -- Type of the whole expression
699 dsMDo tbl stmts body result_ty
700 = go (map unLoc stmts)
702 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
703 mfix_id = lookupEvidence tbl mfixName
704 return_id = lookupEvidence tbl returnMName
705 bind_id = lookupEvidence tbl bindMName
706 then_id = lookupEvidence tbl thenMName
707 fail_id = lookupEvidence tbl failMName
712 go (LetStmt binds : stmts)
713 = do { rest <- go stmts
714 ; dsLocalBinds binds rest }
716 go (ExprStmt rhs _ rhs_ty : stmts)
717 = do { rhs2 <- dsLExpr rhs
719 ; returnDs (mkApps (Var then_id) [Type rhs_ty, Type b_ty, rhs2, rest]) }
721 go (BindStmt pat rhs _ _ : stmts)
722 = do { body <- go stmts
723 ; var <- selectSimpleMatchVarL pat
724 ; match <- matchSinglePat (Var var) (StmtCtxt ctxt) pat
725 result_ty (cantFailMatchResult body)
726 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
727 ; let fail_expr = mkApps (Var fail_id) [Type b_ty, fail_msg]
728 ; match_code <- extractMatchResult match fail_expr
730 ; rhs' <- dsLExpr rhs
731 ; returnDs (mkApps (Var bind_id) [Type (hsPatType pat), Type b_ty,
732 rhs', Lam var match_code]) }
734 go (RecStmt rec_stmts later_ids rec_ids rec_rets binds : stmts)
735 = ASSERT( length rec_ids > 0 )
736 ASSERT( length rec_ids == length rec_rets )
737 go (new_bind_stmt : let_stmt : stmts)
739 new_bind_stmt = mkBindStmt (mk_tup_pat later_pats) mfix_app
740 let_stmt = LetStmt (HsValBinds (ValBindsOut [(Recursive, binds)] []))
743 -- Remove the later_ids that appear (without fancy coercions)
744 -- in rec_rets, because there's no need to knot-tie them separately
745 -- See Note [RecStmt] in HsExpr
746 later_ids' = filter (`notElem` mono_rec_ids) later_ids
747 mono_rec_ids = [ id | HsVar id <- rec_rets ]
749 mfix_app = nlHsApp (noLoc $ TyApp (nlHsVar mfix_id) [tup_ty]) mfix_arg
750 mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [mfix_pat] body]
751 (mkFunTy tup_ty body_ty))
753 -- The rec_tup_pat must bind the rec_ids only; remember that the
754 -- trimmed_laters may share the same Names
755 -- Meanwhile, the later_pats must bind the later_vars
756 rec_tup_pats = map mk_wild_pat later_ids' ++ map nlVarPat rec_ids
757 later_pats = map nlVarPat later_ids' ++ map mk_later_pat rec_ids
758 rets = map nlHsVar later_ids' ++ map noLoc rec_rets
760 mfix_pat = noLoc $ LazyPat $ mk_tup_pat rec_tup_pats
761 body = noLoc $ HsDo ctxt rec_stmts return_app body_ty
762 body_ty = mkAppTy m_ty tup_ty
763 tup_ty = mkCoreTupTy (map idType (later_ids' ++ rec_ids))
764 -- mkCoreTupTy deals with singleton case
766 return_app = nlHsApp (noLoc $ TyApp (nlHsVar return_id) [tup_ty])
769 mk_wild_pat :: Id -> LPat Id
770 mk_wild_pat v = noLoc $ WildPat $ idType v
772 mk_later_pat :: Id -> LPat Id
773 mk_later_pat v | v `elem` later_ids' = mk_wild_pat v
774 | otherwise = nlVarPat v
776 mk_tup_pat :: [LPat Id] -> LPat Id
778 mk_tup_pat ps = noLoc $ mkVanillaTuplePat ps Boxed
780 mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id
782 mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed