2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsExpr]{Matching expressions (Exprs)}
7 module DsExpr ( dsExpr, dsLet, dsLit ) where
9 #include "HsVersions.h"
12 import Match ( matchWrapper, matchSimply )
13 import MatchLit ( dsLit )
14 import DsBinds ( dsMonoBinds, AutoScc(..) )
15 import DsGRHSs ( dsGuarded )
16 import DsCCall ( dsCCall )
17 import DsListComp ( dsListComp, dsPArrComp )
18 import DsUtils ( mkErrorAppDs, mkStringLit, mkConsExpr, mkNilExpr)
22 -- Template Haskell stuff iff bootstrapped
23 import DsMeta ( dsBracket )
26 import HsSyn ( failureFreePat,
27 HsExpr(..), Pat(..), HsLit(..), ArithSeqInfo(..),
28 Stmt(..), HsMatchContext(..), HsDoContext(..),
29 Match(..), HsBinds(..), MonoBinds(..), HsConDetails(..),
32 import TcHsSyn ( TypecheckedHsExpr, TypecheckedHsBinds, TypecheckedStmt, hsPatType )
34 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
35 -- needs to see source types (newtypes etc), and sometimes not
36 -- So WATCH OUT; check each use of split*Ty functions.
37 -- Sigh. This is a pain.
39 import TcType ( tcSplitAppTy, tcSplitFunTys, tcTyConAppArgs,
40 tcSplitTyConApp, isUnLiftedType, Type )
41 import Type ( splitFunTys )
43 import CoreUtils ( exprType, mkIfThenElse, bindNonRec )
45 import FieldLabel ( FieldLabel, fieldLabelTyCon )
46 import CostCentre ( mkUserCC )
47 import Id ( Id, idType, recordSelectorFieldLabel )
48 import PrelInfo ( rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID )
49 import DataCon ( DataCon, dataConWrapId, dataConFieldLabels, dataConInstOrigArgTys )
50 import DataCon ( isExistentialDataCon )
51 import TyCon ( tyConDataCons )
52 import TysWiredIn ( tupleCon )
53 import BasicTypes ( RecFlag(..), Boxity(..), ipNameName )
54 import PrelNames ( toPName )
55 import Util ( zipEqual, zipWithEqual )
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 :: TypecheckedHsBinds -> CoreExpr -> DsM CoreExpr
84 dsLet (ThenBinds b1 b2) body
85 = dsLet b2 body `thenDs` \ body' ->
88 -- Special case for bindings which bind unlifted variables
89 -- We need to do a case right away, rather than building
90 -- a tuple and doing selections.
91 -- Silently ignore INLINE pragmas...
92 dsLet bind@(MonoBind (AbsBinds [] [] exports inlines binds) sigs is_rec) body
93 | or [isUnLiftedType (idType g) | (_, g, l) <- exports]
94 = ASSERT (case is_rec of {NonRecursive -> True; other -> False})
95 -- Unlifted bindings are always non-recursive
96 -- and are always a Fun or Pat monobind
98 -- ToDo: in some bizarre case it's conceivable that there
99 -- could be dict binds in the 'binds'. (See the notes
100 -- below. Then pattern-match would fail. Urk.)
102 FunMonoBind fun _ matches loc
104 matchWrapper (FunRhs fun) matches `thenDs` \ (args, rhs) ->
105 ASSERT( null args ) -- Functions aren't lifted
106 returnDs (bindNonRec fun rhs body_w_exports)
108 PatMonoBind pat grhss loc
110 dsGuarded grhss `thenDs` \ rhs ->
111 mk_error_app pat `thenDs` \ error_expr ->
112 matchSimply rhs PatBindRhs pat body_w_exports error_expr
114 other -> pprPanic "dsLet: unlifted" (ppr bind $$ ppr body)
116 body_w_exports = foldr bind_export body exports
117 bind_export (tvs, g, l) body = ASSERT( null tvs )
118 bindNonRec g (Var l) body
120 mk_error_app pat = mkErrorAppDs iRREFUT_PAT_ERROR_ID
124 -- Ordinary case for bindings
125 dsLet (MonoBind binds sigs is_rec) body
126 = dsMonoBinds NoSccs binds [] `thenDs` \ prs ->
127 returnDs (Let (Rec prs) body)
128 -- Use a Rec regardless of is_rec.
129 -- Why? Because it allows the MonoBinds to be all
130 -- mixed up, which is what happens in one rare case
131 -- Namely, for an AbsBind with no tyvars and no dicts,
132 -- but which does have dictionary bindings.
133 -- See notes with TcSimplify.inferLoop [NO TYVARS]
134 -- It turned out that wrapping a Rec here was the easiest solution
136 -- NB The previous case dealt with unlifted bindings, so we
137 -- only have to deal with lifted ones now; so Rec is ok
140 %************************************************************************
142 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
144 %************************************************************************
147 dsExpr :: TypecheckedHsExpr -> DsM CoreExpr
149 dsExpr (HsPar x) = dsExpr x
150 dsExpr (HsVar var) = returnDs (Var var)
151 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
152 dsExpr (HsLit lit) = dsLit lit
153 -- HsOverLit has been gotten rid of by the type checker
155 dsExpr expr@(HsLam a_Match)
156 = matchWrapper LambdaExpr [a_Match] `thenDs` \ (binders, matching_code) ->
157 returnDs (mkLams binders matching_code)
159 dsExpr expr@(HsApp fun arg)
160 = dsExpr fun `thenDs` \ core_fun ->
161 dsExpr arg `thenDs` \ core_arg ->
162 returnDs (core_fun `App` core_arg)
165 Operator sections. At first it looks as if we can convert
174 But no! expr might be a redex, and we can lose laziness badly this
179 for example. So we convert instead to
181 let y = expr in \x -> op y x
183 If \tr{expr} is actually just a variable, say, then the simplifier
187 dsExpr (OpApp e1 op _ e2)
188 = dsExpr op `thenDs` \ core_op ->
189 -- for the type of y, we need the type of op's 2nd argument
190 dsExpr e1 `thenDs` \ x_core ->
191 dsExpr e2 `thenDs` \ y_core ->
192 returnDs (mkApps core_op [x_core, y_core])
194 dsExpr (SectionL expr op)
195 = dsExpr op `thenDs` \ core_op ->
196 -- for the type of y, we need the type of op's 2nd argument
198 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
199 -- Must look through an implicit-parameter type;
200 -- newtype impossible; hence Type.splitFunTys
202 dsExpr expr `thenDs` \ x_core ->
203 newSysLocalDs x_ty `thenDs` \ x_id ->
204 newSysLocalDs y_ty `thenDs` \ y_id ->
206 returnDs (bindNonRec x_id x_core $
207 Lam y_id (mkApps core_op [Var x_id, Var y_id]))
209 -- dsExpr (SectionR op expr) -- \ x -> op x expr
210 dsExpr (SectionR op expr)
211 = dsExpr op `thenDs` \ core_op ->
212 -- for the type of x, we need the type of op's 2nd argument
214 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
215 -- See comment with SectionL
217 dsExpr expr `thenDs` \ y_core ->
218 newSysLocalDs x_ty `thenDs` \ x_id ->
219 newSysLocalDs y_ty `thenDs` \ y_id ->
221 returnDs (bindNonRec y_id y_core $
222 Lam x_id (mkApps core_op [Var x_id, Var y_id]))
224 dsExpr (HsCCall lbl args may_gc is_asm result_ty)
225 = mapDs dsExpr args `thenDs` \ core_args ->
226 dsCCall lbl core_args may_gc is_asm result_ty
227 -- dsCCall does all the unboxification, etc.
229 dsExpr (HsSCC cc expr)
230 = dsExpr expr `thenDs` \ core_expr ->
231 getModuleDs `thenDs` \ mod_name ->
232 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
234 -- special case to handle unboxed tuple patterns.
236 dsExpr (HsCase discrim matches src_loc)
237 | all ubx_tuple_match matches
238 = putSrcLocDs src_loc $
239 dsExpr discrim `thenDs` \ core_discrim ->
240 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
241 case matching_code of
242 Case (Var x) bndr alts | x == discrim_var ->
243 returnDs (Case core_discrim bndr alts)
244 _ -> panic ("dsExpr: tuple pattern:\n" ++ showSDoc (ppr matching_code))
246 ubx_tuple_match (Match [TuplePat ps Unboxed] _ _) = True
247 ubx_tuple_match _ = False
249 dsExpr (HsCase discrim matches src_loc)
250 = putSrcLocDs src_loc $
251 dsExpr discrim `thenDs` \ core_discrim ->
252 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
253 returnDs (bindNonRec discrim_var core_discrim matching_code)
255 dsExpr (HsLet binds body)
256 = dsExpr body `thenDs` \ body' ->
259 dsExpr (HsWith expr binds is_with)
260 = dsExpr expr `thenDs` \ expr' ->
261 foldlDs dsIPBind expr' binds
264 = dsExpr e `thenDs` \ e' ->
265 returnDs (Let (NonRec (ipNameName n) e') body)
267 -- We need the `ListComp' form to use `deListComp' (rather than the "do" form)
268 -- because the interpretation of `stmts' depends on what sort of thing it is.
270 dsExpr (HsDo ListComp stmts _ result_ty src_loc)
271 = -- Special case for list comprehensions
272 putSrcLocDs src_loc $
273 dsListComp stmts elt_ty
275 (_, [elt_ty]) = tcSplitTyConApp result_ty
277 dsExpr (HsDo DoExpr stmts ids result_ty src_loc)
278 = putSrcLocDs src_loc $
279 dsDo DoExpr stmts ids result_ty
281 dsExpr (HsDo PArrComp stmts _ result_ty src_loc)
282 = -- Special case for array comprehensions
283 putSrcLocDs src_loc $
284 dsPArrComp stmts elt_ty
286 (_, [elt_ty]) = tcSplitTyConApp result_ty
288 dsExpr (HsIf guard_expr then_expr else_expr src_loc)
289 = putSrcLocDs src_loc $
290 dsExpr guard_expr `thenDs` \ core_guard ->
291 dsExpr then_expr `thenDs` \ core_then ->
292 dsExpr 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 = dsExpr expr `thenDs` \ core_expr ->
303 returnDs (mkLams tyvars core_expr)
305 dsExpr (TyApp expr tys)
306 = dsExpr 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) = dsExpr 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 = mapDs dsExpr expr_list `thenDs` \ core_exprs ->
340 returnDs (mkConApp (tupleCon boxity (length expr_list))
341 (map (Type . exprType) core_exprs ++ core_exprs))
343 dsExpr (ArithSeqOut expr (From from))
344 = dsExpr expr `thenDs` \ expr2 ->
345 dsExpr from `thenDs` \ from2 ->
346 returnDs (App expr2 from2)
348 dsExpr (ArithSeqOut expr (FromTo from two))
349 = dsExpr expr `thenDs` \ expr2 ->
350 dsExpr from `thenDs` \ from2 ->
351 dsExpr two `thenDs` \ two2 ->
352 returnDs (mkApps expr2 [from2, two2])
354 dsExpr (ArithSeqOut expr (FromThen from thn))
355 = dsExpr expr `thenDs` \ expr2 ->
356 dsExpr from `thenDs` \ from2 ->
357 dsExpr thn `thenDs` \ thn2 ->
358 returnDs (mkApps expr2 [from2, thn2])
360 dsExpr (ArithSeqOut expr (FromThenTo from thn two))
361 = dsExpr expr `thenDs` \ expr2 ->
362 dsExpr from `thenDs` \ from2 ->
363 dsExpr thn `thenDs` \ thn2 ->
364 dsExpr two `thenDs` \ two2 ->
365 returnDs (mkApps expr2 [from2, thn2, two2])
367 dsExpr (PArrSeqOut expr (FromTo from two))
368 = dsExpr expr `thenDs` \ expr2 ->
369 dsExpr from `thenDs` \ from2 ->
370 dsExpr two `thenDs` \ two2 ->
371 returnDs (mkApps expr2 [from2, two2])
373 dsExpr (PArrSeqOut expr (FromThenTo from thn two))
374 = dsExpr expr `thenDs` \ expr2 ->
375 dsExpr from `thenDs` \ from2 ->
376 dsExpr thn `thenDs` \ thn2 ->
377 dsExpr two `thenDs` \ two2 ->
378 returnDs (mkApps expr2 [from2, thn2, two2])
380 dsExpr (PArrSeqOut 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 (RecordConOut data_con 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
416 = case [rhs | (sel_id,rhs) <- rbinds,
417 lbl == recordSelectorFieldLabel sel_id] of
418 (rhs:rhss) -> ASSERT( null rhss )
420 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
421 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
423 labels = dataConFieldLabels data_con
427 then mapDs unlabelled_bottom arg_tys
428 else mapDs 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 (RecordUpdOut record_expr record_in_ty record_out_ty [])
459 dsExpr expr@(RecordUpdOut record_expr record_in_ty record_out_ty rbinds)
460 = getSrcLocDs `thenDs` \ src_loc ->
461 dsExpr record_expr `thenDs` \ record_expr' ->
463 -- Desugar the rbinds, and generate let-bindings if
464 -- necessary so that we don't lose sharing
467 in_inst_tys = tcTyConAppArgs record_in_ty -- Newtype opaque
468 out_inst_tys = tcTyConAppArgs record_out_ty -- Newtype opaque
470 mk_val_arg field old_arg_id
471 = case [rhs | (sel_id, rhs) <- rbinds,
472 field == recordSelectorFieldLabel sel_id] of
473 (rhs:rest) -> ASSERT(null rest) rhs
474 [] -> HsVar old_arg_id
477 = newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids ->
478 -- This call to dataConArgTys won't work for existentials
480 val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
481 (dataConFieldLabels con) arg_ids
482 rhs = foldl HsApp (TyApp (HsVar (dataConWrapId con)) out_inst_tys)
485 returnDs (mkSimpleMatch [ConPatOut con (PrefixCon (map VarPat arg_ids)) record_in_ty [] []]
490 -- Record stuff doesn't work for existentials
491 -- The type checker checks for this, but we need
492 -- worry only about the constructors that are to be updated
493 ASSERT2( all (not . isExistentialDataCon) cons_to_upd, ppr expr )
495 -- It's important to generate the match with matchWrapper,
496 -- and the right hand sides with applications of the wrapper Id
497 -- so that everything works when we are doing fancy unboxing on the
498 -- constructor aguments.
499 mapDs mk_alt cons_to_upd `thenDs` \ alts ->
500 matchWrapper RecUpd alts `thenDs` \ ([discrim_var], matching_code) ->
502 returnDs (bindNonRec discrim_var record_expr' matching_code)
505 updated_fields :: [FieldLabel]
506 updated_fields = [recordSelectorFieldLabel sel_id | (sel_id,_) <- rbinds]
508 -- Get the type constructor from the first field label,
509 -- so that we are sure it'll have all its DataCons
510 -- (In GHCI, it's possible that some TyCons may not have all
511 -- their constructors, in a module-loop situation.)
512 tycon = fieldLabelTyCon (head updated_fields)
513 data_cons = tyConDataCons tycon
514 cons_to_upd = filter has_all_fields data_cons
516 has_all_fields :: DataCon -> Bool
517 has_all_fields con_id
518 = all (`elem` con_fields) updated_fields
520 con_fields = dataConFieldLabels con_id
525 \underline{\bf Dictionary lambda and application}
526 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
527 @DictLam@ and @DictApp@ turn into the regular old things.
528 (OLD:) @DictFunApp@ also becomes a curried application, albeit slightly more
529 complicated; reminiscent of fully-applied constructors.
531 dsExpr (DictLam dictvars expr)
532 = dsExpr expr `thenDs` \ core_expr ->
533 returnDs (mkLams dictvars core_expr)
537 dsExpr (DictApp expr dicts) -- becomes a curried application
538 = dsExpr expr `thenDs` \ core_expr ->
539 returnDs (foldl (\f d -> f `App` (Var d)) core_expr dicts)
542 Here is where we desugar the Template Haskell brackets and escapes
545 -- Template Haskell stuff
547 #ifdef GHCI /* Only if bootstrapping */
548 dsExpr (HsBracketOut x ps) = dsBracket x ps
549 dsExpr (HsSplice n e) = pprPanic "dsExpr:splice" (ppr e)
558 -- HsSyn constructs that just shouldn't be here:
559 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
560 dsExpr (ArithSeqIn _) = panic "dsExpr:ArithSeqIn"
561 dsExpr (PArrSeqIn _) = panic "dsExpr:PArrSeqIn"
566 %--------------------------------------------------------------------
568 Basically does the translation given in the Haskell~1.3 report:
573 -> [Id] -- id for: [return,fail,>>=,>>]
574 -> Type -- Element type; the whole expression has type (m t)
577 dsDo do_or_lc stmts ids@[return_id, fail_id, bind_id, then_id] result_ty
579 (_, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
580 is_do = case do_or_lc of
584 -- For ExprStmt, see the comments near HsExpr.Stmt about
585 -- exactly what ExprStmts mean!
587 -- In dsDo we can only see DoStmt and ListComp (no guards)
589 go [ResultStmt expr locn]
590 | is_do = do_expr expr locn
591 | otherwise = do_expr expr locn `thenDs` \ expr2 ->
592 returnDs (mkApps (Var return_id) [Type b_ty, expr2])
594 go (ExprStmt expr a_ty locn : stmts)
595 | is_do -- Do expression
596 = do_expr expr locn `thenDs` \ expr2 ->
597 go stmts `thenDs` \ rest ->
598 returnDs (mkApps (Var then_id) [Type a_ty, Type b_ty, expr2, rest])
600 | otherwise -- List comprehension
601 = do_expr expr locn `thenDs` \ expr2 ->
602 go stmts `thenDs` \ rest ->
604 msg = "Pattern match failure in do expression, " ++ showSDoc (ppr locn)
606 mkStringLit msg `thenDs` \ core_msg ->
607 returnDs (mkIfThenElse expr2 rest
608 (App (App (Var fail_id) (Type b_ty)) core_msg))
610 go (LetStmt binds : stmts )
611 = go stmts `thenDs` \ rest ->
614 go (BindStmt pat expr locn : stmts)
616 dsExpr expr `thenDs` \ expr2 ->
619 fail_expr = HsApp (TyApp (HsVar fail_id) [b_ty])
620 (HsLit (HsString (mkFastString msg)))
621 msg = "Pattern match failure in do expression, " ++ showSDoc (ppr locn)
622 main_match = mkSimpleMatch [pat]
623 (HsDo do_or_lc stmts ids result_ty locn)
626 | failureFreePat pat = [main_match]
629 , mkSimpleMatch [WildPat a_ty] fail_expr result_ty locn
632 matchWrapper (DoCtxt do_or_lc) the_matches `thenDs` \ (binders, matching_code) ->
633 returnDs (mkApps (Var bind_id) [Type a_ty, Type b_ty, expr2,
634 mkLams binders matching_code])
639 do_expr expr locn = putSrcLocDs locn (dsExpr expr)