2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Desugaring exporessions.
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 module DsExpr ( dsExpr, dsLExpr, dsLocalBinds, dsValBinds, dsLit ) where
18 #include "HsVersions.h"
33 -- Template Haskell stuff iff bootstrapped
40 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
41 -- needs to see source types
62 %************************************************************************
64 dsLocalBinds, dsValBinds
66 %************************************************************************
69 dsLocalBinds :: HsLocalBinds Id -> CoreExpr -> DsM CoreExpr
70 dsLocalBinds EmptyLocalBinds body = return body
71 dsLocalBinds (HsValBinds binds) body = dsValBinds binds body
72 dsLocalBinds (HsIPBinds binds) body = dsIPBinds binds body
74 -------------------------
75 dsValBinds :: HsValBinds Id -> CoreExpr -> DsM CoreExpr
76 dsValBinds (ValBindsOut binds _) body = foldrM ds_val_bind body binds
78 -------------------------
79 dsIPBinds (IPBinds ip_binds dict_binds) body
80 = do { prs <- dsLHsBinds dict_binds
81 ; let inner = Let (Rec prs) body
82 -- The dict bindings may not be in
83 -- dependency order; hence Rec
84 ; foldrM ds_ip_bind inner ip_binds }
86 ds_ip_bind (L _ (IPBind n e)) body
88 return (Let (NonRec (ipNameName n) e') body)
90 -------------------------
91 ds_val_bind :: (RecFlag, LHsBinds Id) -> CoreExpr -> DsM CoreExpr
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 and SPECIALISE pragmas...
96 ds_val_bind (NonRecursive, hsbinds) body
97 | [L _ (AbsBinds [] [] exports binds)] <- bagToList hsbinds,
98 (L loc bind : null_binds) <- bagToList binds,
100 || isUnboxedTupleBind bind
101 || or [isUnLiftedType (idType g) | (_, g, _, _) <- exports]
103 body_w_exports = foldr bind_export body exports
104 bind_export (tvs, g, l, _) body = ASSERT( null tvs )
105 bindNonRec g (Var l) body
107 ASSERT (null null_binds)
108 -- Non-recursive, non-overloaded bindings only come in ones
109 -- ToDo: in some bizarre case it's conceivable that there
110 -- could be dict binds in the 'binds'. (See the notes
111 -- below. Then pattern-match would fail. Urk.)
114 FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn,
115 fun_tick = tick, fun_infix = inf }
116 -> do (args, rhs) <- matchWrapper (FunRhs (idName fun ) inf) matches
117 MASSERT( null args ) -- Functions aren't lifted
118 MASSERT( isIdHsWrapper co_fn )
119 rhs' <- mkOptTickBox tick rhs
120 return (bindNonRec fun rhs' body_w_exports)
122 PatBind {pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }
123 -> -- let C x# y# = rhs in body
124 -- ==> case rhs of C x# y# -> body
126 do { rhs <- dsGuarded grhss ty
127 ; let upat = unLoc pat
128 eqn = EqnInfo { eqn_pats = [upat],
129 eqn_rhs = cantFailMatchResult body_w_exports }
130 ; var <- selectMatchVar upat
131 ; result <- matchEquations PatBindRhs [var] [eqn] (exprType body)
132 ; return (scrungleMatch var rhs result) }
134 other -> pprPanic "dsLet: unlifted" (pprLHsBinds hsbinds $$ ppr body)
137 -- Ordinary case for bindings; none should be unlifted
138 ds_val_bind (is_rec, binds) body
139 = do { prs <- dsLHsBinds binds
140 ; ASSERT( not (any (isUnLiftedType . idType . fst) prs) )
143 other -> return (Let (Rec prs) body) }
144 -- Use a Rec regardless of is_rec.
145 -- Why? Because it allows the binds to be all
146 -- mixed up, which is what happens in one rare case
147 -- Namely, for an AbsBind with no tyvars and no dicts,
148 -- but which does have dictionary bindings.
149 -- See notes with TcSimplify.inferLoop [NO TYVARS]
150 -- It turned out that wrapping a Rec here was the easiest solution
152 -- NB The previous case dealt with unlifted bindings, so we
153 -- only have to deal with lifted ones now; so Rec is ok
155 isUnboxedTupleBind :: HsBind Id -> Bool
156 isUnboxedTupleBind (PatBind { pat_rhs_ty = ty }) = isUnboxedTupleType ty
157 isUnboxedTupleBind other = False
159 scrungleMatch :: Id -> CoreExpr -> CoreExpr -> CoreExpr
160 -- Returns something like (let var = scrut in body)
161 -- but if var is an unboxed-tuple type, it inlines it in a fragile way
162 -- Special case to handle unboxed tuple patterns; they can't appear nested
164 -- case e of (# p1, p2 #) -> rhs
166 -- case e of (# x1, x2 #) -> ... match p1, p2 ...
168 -- let x = e in case x of ....
170 -- But there may be a big
171 -- let fail = ... in case e of ...
172 -- wrapping the whole case, which complicates matters slightly
173 -- It all seems a bit fragile. Test is dsrun013.
175 scrungleMatch var scrut body
176 | isUnboxedTupleType (idType var) = scrungle body
177 | otherwise = bindNonRec var scrut body
179 scrungle (Case (Var x) bndr ty alts)
180 | x == var = Case scrut bndr ty alts
181 scrungle (Let binds body) = Let binds (scrungle body)
182 scrungle other = panic ("scrungleMatch: tuple pattern:\n" ++ showSDoc (ppr other))
186 %************************************************************************
188 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
190 %************************************************************************
193 dsLExpr :: LHsExpr Id -> DsM CoreExpr
195 dsLExpr (L loc e) = putSrcSpanDs loc $ dsExpr e
197 dsExpr :: HsExpr Id -> DsM CoreExpr
198 dsExpr (HsPar e) = dsLExpr e
199 dsExpr (ExprWithTySigOut e _) = dsLExpr e
200 dsExpr (HsVar var) = return (Var var)
201 dsExpr (HsIPVar ip) = return (Var (ipNameName ip))
202 dsExpr (HsLit lit) = dsLit lit
203 dsExpr (HsOverLit lit) = dsOverLit lit
204 dsExpr (HsWrap co_fn e) = dsCoercion co_fn (dsExpr e)
206 dsExpr (NegApp expr neg_expr)
207 = App <$> dsExpr neg_expr <*> dsLExpr expr
209 dsExpr expr@(HsLam a_Match)
210 = uncurry mkLams <$> matchWrapper LambdaExpr a_Match
212 dsExpr expr@(HsApp fun arg)
213 = mkDsApp <$> dsLExpr fun <*> dsLExpr arg
216 Operator sections. At first it looks as if we can convert
225 But no! expr might be a redex, and we can lose laziness badly this
230 for example. So we convert instead to
232 let y = expr in \x -> op y x
234 If \tr{expr} is actually just a variable, say, then the simplifier
238 dsExpr (OpApp e1 op _ e2)
239 = -- for the type of y, we need the type of op's 2nd argument
240 mkDsApps <$> dsLExpr op <*> mapM dsLExpr [e1, e2]
242 dsExpr (SectionL expr op) -- Desugar (e !) to ((!) e)
243 = mkDsApp <$> dsLExpr op <*> dsLExpr expr
245 -- dsLExpr (SectionR op expr) -- \ x -> op x expr
246 dsExpr (SectionR op expr) = do
247 core_op <- dsLExpr op
248 -- for the type of x, we need the type of op's 2nd argument
249 let (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
250 -- See comment with SectionL
251 y_core <- dsLExpr expr
252 x_id <- newSysLocalDs x_ty
253 y_id <- newSysLocalDs y_ty
254 return (bindNonRec y_id y_core $
255 Lam x_id (mkDsApps core_op [Var x_id, Var y_id]))
257 dsExpr (HsSCC cc expr) = do
258 mod_name <- getModuleDs
259 Note (SCC (mkUserCC cc mod_name)) <$> dsLExpr expr
262 -- hdaume: core annotation
264 dsExpr (HsCoreAnn fs expr)
265 = Note (CoreNote $ unpackFS fs) <$> dsLExpr expr
267 dsExpr (HsCase discrim matches) = do
268 core_discrim <- dsLExpr discrim
269 ([discrim_var], matching_code) <- matchWrapper CaseAlt matches
270 return (scrungleMatch discrim_var core_discrim matching_code)
272 -- Pepe: The binds are in scope in the body but NOT in the binding group
273 -- This is to avoid silliness in breakpoints
274 dsExpr (HsLet binds body) = do
275 body' <- dsLExpr body
276 dsLocalBinds binds body'
278 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
279 -- because the interpretation of `stmts' depends on what sort of thing it is.
281 dsExpr (HsDo ListComp stmts body result_ty)
282 = -- Special case for list comprehensions
283 dsListComp stmts body elt_ty
285 [elt_ty] = tcTyConAppArgs result_ty
287 dsExpr (HsDo DoExpr stmts body result_ty)
288 = dsDo stmts body result_ty
290 dsExpr (HsDo (MDoExpr tbl) stmts body result_ty)
291 = dsMDo tbl stmts body result_ty
293 dsExpr (HsDo PArrComp stmts body result_ty)
294 = -- Special case for array comprehensions
295 dsPArrComp (map unLoc stmts) body elt_ty
297 [elt_ty] = tcTyConAppArgs result_ty
299 dsExpr (HsIf guard_expr then_expr else_expr)
300 = mkIfThenElse <$> dsLExpr guard_expr <*> dsLExpr then_expr <*> dsLExpr else_expr
305 \underline{\bf Various data construction things}
306 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
308 dsExpr (ExplicitList ty xs)
311 go [] = return (mkNilExpr ty)
312 go (x:xs) = mkConsExpr ty <$> dsLExpr x <*> go xs
314 -- we create a list from the array elements and convert them into a list using
317 -- * the main disadvantage to this scheme is that `toP' traverses the list
318 -- twice: once to determine the length and a second time to put to elements
319 -- into the array; this inefficiency could be avoided by exposing some of
320 -- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
321 -- that we can exploit the fact that we already know the length of the array
322 -- here at compile time
324 dsExpr (ExplicitPArr ty xs) = do
325 toP <- dsLookupGlobalId toPName
326 coreList <- dsExpr (ExplicitList ty xs)
327 return (mkApps (Var toP) [Type ty, coreList])
329 dsExpr (ExplicitTuple expr_list boxity) = do
330 core_exprs <- mapM dsLExpr expr_list
331 return (mkConApp (tupleCon boxity (length expr_list))
332 (map (Type . exprType) core_exprs ++ core_exprs))
334 dsExpr (ArithSeq expr (From from))
335 = App <$> dsExpr expr <*> dsLExpr from
337 dsExpr (ArithSeq expr (FromTo from to))
338 = mkApps <$> dsExpr expr <*> mapM dsLExpr [from, to]
340 dsExpr (ArithSeq expr (FromThen from thn))
341 = mkApps <$> dsExpr expr <*> mapM dsLExpr [from, thn]
343 dsExpr (ArithSeq expr (FromThenTo from thn to))
344 = mkApps <$> dsExpr expr <*> mapM dsLExpr [from, thn, to]
346 dsExpr (PArrSeq expr (FromTo from to))
347 = mkApps <$> dsExpr expr <*> mapM dsLExpr [from, to]
349 dsExpr (PArrSeq expr (FromThenTo from thn to))
350 = mkApps <$> dsExpr expr <*> mapM dsLExpr [from, thn, to]
352 dsExpr (PArrSeq expr _)
353 = panic "DsExpr.dsExpr: Infinite parallel array!"
354 -- the parser shouldn't have generated it and the renamer and typechecker
355 -- shouldn't have let it through
359 \underline{\bf Record construction and update}
360 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
361 For record construction we do this (assuming T has three arguments)
365 let err = /\a -> recConErr a
366 T (recConErr t1 "M.lhs/230/op1")
368 (recConErr t1 "M.lhs/230/op3")
370 @recConErr@ then converts its arugment string into a proper message
371 before printing it as
373 M.lhs, line 230: missing field op1 was evaluated
376 We also handle @C{}@ as valid construction syntax for an unlabelled
377 constructor @C@, setting all of @C@'s fields to bottom.
380 dsExpr (RecordCon (L _ data_con_id) con_expr rbinds) = do
381 con_expr' <- dsExpr con_expr
383 (arg_tys, _) = tcSplitFunTys (exprType con_expr')
384 -- A newtype in the corner should be opaque;
385 -- hence TcType.tcSplitFunTys
387 mk_arg (arg_ty, lbl) -- Selector id has the field label as its name
388 = case findField (rec_flds rbinds) lbl of
389 (rhs:rhss) -> ASSERT( null rhss )
391 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
392 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
394 labels = dataConFieldLabels (idDataCon data_con_id)
395 -- The data_con_id is guaranteed to be the wrapper id of the constructor
397 con_args <- if null labels
398 then mapM unlabelled_bottom arg_tys
399 else mapM mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels)
401 return (mkApps con_expr' con_args)
404 Record update is a little harder. Suppose we have the decl:
406 data T = T1 {op1, op2, op3 :: Int}
407 | T2 {op4, op2 :: Int}
410 Then we translate as follows:
416 T1 op1 _ op3 -> T1 op1 op2 op3
417 T2 op4 _ -> T2 op4 op2
418 other -> recUpdError "M.lhs/230"
420 It's important that we use the constructor Ids for @T1@, @T2@ etc on the
421 RHSs, and do not generate a Core constructor application directly, because the constructor
422 might do some argument-evaluation first; and may have to throw away some
426 dsExpr expr@(RecordUpd record_expr (HsRecFields { rec_flds = fields })
427 cons_to_upd in_inst_tys out_inst_tys)
429 = dsLExpr record_expr
431 = -- Record stuff doesn't work for existentials
432 -- The type checker checks for this, but we need
433 -- worry only about the constructors that are to be updated
434 ASSERT2( notNull cons_to_upd && all isVanillaDataCon cons_to_upd, ppr expr )
436 do { record_expr' <- dsLExpr record_expr
437 ; let -- Awkwardly, for families, the match goes
438 -- from instance type to family type
439 tycon = dataConTyCon (head cons_to_upd)
440 in_ty = mkTyConApp tycon in_inst_tys
441 in_out_ty = mkFunTy in_ty
442 (mkFamilyTyConApp tycon out_inst_tys)
444 mk_val_arg field old_arg_id
445 = case findField fields field of
446 (rhs:rest) -> ASSERT(null rest) rhs
447 [] -> nlHsVar old_arg_id
450 = ASSERT( isVanillaDataCon con )
451 do { arg_ids <- newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys)
452 -- This call to dataConInstOrigArgTys won't work for existentials
453 -- but existentials don't have record types anyway
454 ; let val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
455 (dataConFieldLabels con) arg_ids
456 rhs = foldl (\a b -> nlHsApp a b)
457 (nlHsTyApp (dataConWrapId con) out_inst_tys)
459 pat = mkPrefixConPat con (map nlVarPat arg_ids) in_ty
461 ; return (mkSimpleMatch [pat] rhs) }
463 -- It's important to generate the match with matchWrapper,
464 -- and the right hand sides with applications of the wrapper Id
465 -- so that everything works when we are doing fancy unboxing on the
466 -- constructor aguments.
467 ; alts <- mapM mk_alt cons_to_upd
468 ; ([discrim_var], matching_code) <- matchWrapper RecUpd (MatchGroup alts in_out_ty)
470 ; return (bindNonRec discrim_var record_expr' matching_code) }
473 Here is where we desugar the Template Haskell brackets and escapes
476 -- Template Haskell stuff
478 #ifdef GHCI /* Only if bootstrapping */
479 dsExpr (HsBracketOut x ps) = dsBracket x ps
480 dsExpr (HsSpliceE s) = pprPanic "dsExpr:splice" (ppr s)
483 -- Arrow notation extension
484 dsExpr (HsProc pat cmd) = dsProcExpr pat cmd
490 dsExpr (HsTick ix vars e) = do
494 -- There is a problem here. The then and else branches
495 -- have no free variables, so they are open to lifting.
496 -- We need someway of stopping this.
497 -- This will make no difference to binary coverage
498 -- (did you go here: YES or NO), but will effect accurate
501 dsExpr (HsBinTick ixT ixF e) = do
503 do { ASSERT(exprType e2 `coreEqType` boolTy)
504 mkBinaryTickBox ixT ixF e2
511 -- HsSyn constructs that just shouldn't be here:
512 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
516 findField :: [HsRecField Id arg] -> Name -> [arg]
518 = [rhs | HsRecField { hsRecFieldId = id, hsRecFieldArg = rhs } <- rbinds
519 , lbl == idName (unLoc id) ]
522 %--------------------------------------------------------------------
524 Desugar 'do' and 'mdo' expressions (NOT list comprehensions, they're
525 handled in DsListComp). Basically does the translation given in the
531 -> Type -- Type of the whole expression
534 dsDo stmts body result_ty
535 = go (map unLoc stmts)
539 go (ExprStmt rhs then_expr _ : stmts)
540 = do { rhs2 <- dsLExpr rhs
541 ; then_expr2 <- dsExpr then_expr
543 ; return (mkApps then_expr2 [rhs2, rest]) }
545 go (LetStmt binds : stmts)
546 = do { rest <- go stmts
547 ; dsLocalBinds binds rest }
549 go (BindStmt pat rhs bind_op fail_op : stmts)
551 do { body <- go stmts
552 ; var <- selectSimpleMatchVarL pat
553 ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
554 result_ty (cantFailMatchResult body)
555 ; match_code <- handle_failure pat match fail_op
556 ; rhs' <- dsLExpr rhs
557 ; bind_op' <- dsExpr bind_op
558 ; return (mkApps bind_op' [rhs', Lam var match_code]) }
560 -- In a do expression, pattern-match failure just calls
561 -- the monadic 'fail' rather than throwing an exception
562 handle_failure pat match fail_op
564 = do { fail_op' <- dsExpr fail_op
565 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
566 ; extractMatchResult match (App fail_op' fail_msg) }
568 = extractMatchResult match (error "It can't fail")
570 mk_fail_msg pat = "Pattern match failure in do expression at " ++
571 showSDoc (ppr (getLoc pat))
574 Translation for RecStmt's:
575 -----------------------------
576 We turn (RecStmt [v1,..vn] stmts) into:
578 (v1,..,vn) <- mfix (\~(v1,..vn). do stmts
585 -> Type -- Type of the whole expression
588 dsMDo tbl stmts body result_ty
589 = go (map unLoc stmts)
591 (m_ty, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
592 mfix_id = lookupEvidence tbl mfixName
593 return_id = lookupEvidence tbl returnMName
594 bind_id = lookupEvidence tbl bindMName
595 then_id = lookupEvidence tbl thenMName
596 fail_id = lookupEvidence tbl failMName
601 go (LetStmt binds : stmts)
602 = do { rest <- go stmts
603 ; dsLocalBinds binds rest }
605 go (ExprStmt rhs _ rhs_ty : stmts)
606 = do { rhs2 <- dsLExpr rhs
608 ; return (mkApps (Var then_id) [Type rhs_ty, Type b_ty, rhs2, rest]) }
610 go (BindStmt pat rhs _ _ : stmts)
611 = do { body <- go stmts
612 ; var <- selectSimpleMatchVarL pat
613 ; match <- matchSinglePat (Var var) (StmtCtxt ctxt) pat
614 result_ty (cantFailMatchResult body)
615 ; fail_msg <- mkStringExpr (mk_fail_msg pat)
616 ; let fail_expr = mkApps (Var fail_id) [Type b_ty, fail_msg]
617 ; match_code <- extractMatchResult match fail_expr
619 ; rhs' <- dsLExpr rhs
620 ; return (mkApps (Var bind_id) [Type (hsLPatType pat), Type b_ty,
621 rhs', Lam var match_code]) }
623 go (RecStmt rec_stmts later_ids rec_ids rec_rets binds : stmts)
624 = ASSERT( length rec_ids > 0 )
625 ASSERT( length rec_ids == length rec_rets )
626 go (new_bind_stmt : let_stmt : stmts)
628 new_bind_stmt = mkBindStmt (mk_tup_pat later_pats) mfix_app
629 let_stmt = LetStmt (HsValBinds (ValBindsOut [(Recursive, binds)] []))
632 -- Remove the later_ids that appear (without fancy coercions)
633 -- in rec_rets, because there's no need to knot-tie them separately
634 -- See Note [RecStmt] in HsExpr
635 later_ids' = filter (`notElem` mono_rec_ids) later_ids
636 mono_rec_ids = [ id | HsVar id <- rec_rets ]
638 mfix_app = nlHsApp (nlHsTyApp mfix_id [tup_ty]) mfix_arg
639 mfix_arg = noLoc $ HsLam (MatchGroup [mkSimpleMatch [mfix_pat] body]
640 (mkFunTy tup_ty body_ty))
642 -- The rec_tup_pat must bind the rec_ids only; remember that the
643 -- trimmed_laters may share the same Names
644 -- Meanwhile, the later_pats must bind the later_vars
645 rec_tup_pats = map mk_wild_pat later_ids' ++ map nlVarPat rec_ids
646 later_pats = map nlVarPat later_ids' ++ map mk_later_pat rec_ids
647 rets = map nlHsVar later_ids' ++ map noLoc rec_rets
649 mfix_pat = noLoc $ LazyPat $ mk_tup_pat rec_tup_pats
650 body = noLoc $ HsDo ctxt rec_stmts return_app body_ty
651 body_ty = mkAppTy m_ty tup_ty
652 tup_ty = mkCoreTupTy (map idType (later_ids' ++ rec_ids))
653 -- mkCoreTupTy deals with singleton case
655 return_app = nlHsApp (nlHsTyApp return_id [tup_ty])
658 mk_wild_pat :: Id -> LPat Id
659 mk_wild_pat v = noLoc $ WildPat $ idType v
661 mk_later_pat :: Id -> LPat Id
662 mk_later_pat v | v `elem` later_ids' = mk_wild_pat v
663 | otherwise = nlVarPat v
665 mk_tup_pat :: [LPat Id] -> LPat Id
667 mk_tup_pat ps = noLoc $ mkVanillaTuplePat ps Boxed
669 mk_ret_tup :: [LHsExpr Id] -> LHsExpr Id
671 mk_ret_tup rs = noLoc $ ExplicitTuple rs Boxed