2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[DsExpr]{Matching expressions (Exprs)}
7 module DsExpr ( dsExpr, dsLet ) where
9 #include "HsVersions.h"
12 import HsSyn ( failureFreePat,
13 HsExpr(..), OutPat(..), HsLit(..), ArithSeqInfo(..),
14 Stmt(..), HsMatchContext(..), HsDoContext(..),
15 Match(..), HsBinds(..), MonoBinds(..),
18 import TcHsSyn ( TypecheckedHsExpr, TypecheckedHsBinds, TypecheckedStmt, outPatType )
20 -- NB: The desugarer, which straddles the source and Core worlds, sometimes
21 -- needs to see source types (newtypes etc), and sometimes not
22 -- So WATCH OUT; check each use of split*Ty functions.
23 -- Sigh. This is a pain.
25 import TcType ( tcSplitAppTy, tcSplitFunTys, tcSplitTyConApp_maybe, tcTyConAppArgs,
26 isIntegerTy, tcSplitTyConApp, isUnLiftedType, Type )
27 import Type ( splitFunTys )
29 import CoreUtils ( exprType, mkIfThenElse, bindNonRec )
32 import DsBinds ( dsMonoBinds, AutoScc(..) )
33 import DsGRHSs ( dsGuarded )
34 import DsCCall ( dsCCall, resultWrapper )
35 import DsListComp ( dsListComp )
36 import DsUtils ( mkErrorAppDs, mkStringLit, mkStringLitFS,
37 mkConsExpr, mkNilExpr, mkIntegerLit
39 import Match ( matchWrapper, matchSimply )
41 import FieldLabel ( FieldLabel, fieldLabelTyCon )
42 import CostCentre ( mkUserCC )
43 import Id ( Id, idType, recordSelectorFieldLabel )
44 import PrelInfo ( rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID )
45 import DataCon ( DataCon, dataConWrapId, dataConFieldLabels, dataConInstOrigArgTys )
46 import DataCon ( isExistentialDataCon )
47 import Literal ( Literal(..) )
48 import TyCon ( tyConDataCons )
49 import TysWiredIn ( tupleCon, listTyCon, charDataCon, intDataCon )
50 import BasicTypes ( RecFlag(..), Boxity(..), ipNameName )
51 import Maybes ( maybeToBool )
52 import PrelNames ( hasKey, ratioTyConKey )
53 import Util ( zipEqual, zipWithEqual )
56 import Ratio ( numerator, denominator )
60 %************************************************************************
64 %************************************************************************
66 @dsLet@ is a match-result transformer, taking the @MatchResult@ for the body
67 and transforming it into one for the let-bindings enclosing the body.
69 This may seem a bit odd, but (source) let bindings can contain unboxed
74 This must be transformed to a case expression and, if the type has
75 more than one constructor, may fail.
78 dsLet :: TypecheckedHsBinds -> CoreExpr -> DsM CoreExpr
83 dsLet (ThenBinds b1 b2) body
84 = dsLet b2 body `thenDs` \ body' ->
87 -- Special case for bindings which bind unlifted variables
88 -- We need to do a case right away, rather than building
89 -- a tuple and doing selections.
90 -- Silently ignore INLINE pragmas...
91 dsLet (MonoBind (AbsBinds [] [] exports inlines binds) sigs is_rec) body
92 | or [isUnLiftedType (idType g) | (_, g, l) <- exports]
93 = ASSERT (case is_rec of {NonRecursive -> True; other -> False})
94 -- Unlifted bindings are always non-recursive
95 -- and are always a Fun or Pat monobind
97 -- ToDo: in some bizarre case it's conceivable that there
98 -- could be dict binds in the 'binds'. (See the notes
99 -- below. Then pattern-match would fail. Urk.)
101 FunMonoBind fun _ matches loc
103 matchWrapper (FunRhs fun) matches `thenDs` \ (args, rhs) ->
104 ASSERT( null args ) -- Functions aren't lifted
105 returnDs (bindNonRec fun rhs body_w_exports)
107 PatMonoBind pat grhss loc
109 dsGuarded grhss `thenDs` \ rhs ->
110 mk_error_app pat `thenDs` \ error_expr ->
111 matchSimply rhs PatBindRhs pat body_w_exports error_expr
113 body_w_exports = foldr bind_export body exports
114 bind_export (tvs, g, l) body = ASSERT( null tvs )
115 bindNonRec g (Var l) body
117 mk_error_app pat = mkErrorAppDs iRREFUT_PAT_ERROR_ID
121 -- Ordinary case for bindings
122 dsLet (MonoBind binds sigs is_rec) body
123 = dsMonoBinds NoSccs binds [] `thenDs` \ prs ->
124 returnDs (Let (Rec prs) body)
125 -- Use a Rec regardless of is_rec.
126 -- Why? Because it allows the MonoBinds to be all
127 -- mixed up, which is what happens in one rare case
128 -- Namely, for an AbsBind with no tyvars and no dicts,
129 -- but which does have dictionary bindings.
130 -- See notes with TcSimplify.inferLoop [NO TYVARS]
131 -- It turned out that wrapping a Rec here was the easiest solution
133 -- NB The previous case dealt with unlifted bindings, so we
134 -- only have to deal with lifted ones now; so Rec is ok
137 %************************************************************************
139 \subsection[DsExpr-vars-and-cons]{Variables, constructors, literals}
141 %************************************************************************
144 dsExpr :: TypecheckedHsExpr -> DsM CoreExpr
146 dsExpr (HsVar var) = returnDs (Var var)
147 dsExpr (HsIPVar ip) = returnDs (Var (ipNameName ip))
148 dsExpr (HsLit lit) = dsLit lit
149 -- HsOverLit has been gotten rid of by the type checker
151 dsExpr expr@(HsLam a_Match)
152 = matchWrapper LambdaExpr [a_Match] `thenDs` \ (binders, matching_code) ->
153 returnDs (mkLams binders matching_code)
155 dsExpr expr@(HsApp fun arg)
156 = dsExpr fun `thenDs` \ core_fun ->
157 dsExpr arg `thenDs` \ core_arg ->
158 returnDs (core_fun `App` core_arg)
161 Operator sections. At first it looks as if we can convert
170 But no! expr might be a redex, and we can lose laziness badly this
175 for example. So we convert instead to
177 let y = expr in \x -> op y x
179 If \tr{expr} is actually just a variable, say, then the simplifier
183 dsExpr (OpApp e1 op _ e2)
184 = dsExpr op `thenDs` \ core_op ->
185 -- for the type of y, we need the type of op's 2nd argument
186 dsExpr e1 `thenDs` \ x_core ->
187 dsExpr e2 `thenDs` \ y_core ->
188 returnDs (mkApps core_op [x_core, y_core])
190 dsExpr (SectionL expr op)
191 = dsExpr op `thenDs` \ core_op ->
192 -- for the type of y, we need the type of op's 2nd argument
194 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
195 -- Must look through an implicit-parameter type;
196 -- newtype impossible; hence Type.splitFunTys
198 dsExpr expr `thenDs` \ x_core ->
199 newSysLocalDs x_ty `thenDs` \ x_id ->
200 newSysLocalDs y_ty `thenDs` \ y_id ->
202 returnDs (bindNonRec x_id x_core $
203 Lam y_id (mkApps core_op [Var x_id, Var y_id]))
205 -- dsExpr (SectionR op expr) -- \ x -> op x expr
206 dsExpr (SectionR op expr)
207 = dsExpr op `thenDs` \ core_op ->
208 -- for the type of x, we need the type of op's 2nd argument
210 (x_ty:y_ty:_, _) = splitFunTys (exprType core_op)
211 -- See comment with SectionL
213 dsExpr expr `thenDs` \ y_core ->
214 newSysLocalDs x_ty `thenDs` \ x_id ->
215 newSysLocalDs y_ty `thenDs` \ y_id ->
217 returnDs (bindNonRec y_id y_core $
218 Lam x_id (mkApps core_op [Var x_id, Var y_id]))
220 dsExpr (HsCCall lbl args may_gc is_asm result_ty)
221 = mapDs dsExpr args `thenDs` \ core_args ->
222 dsCCall lbl core_args may_gc is_asm result_ty
223 -- dsCCall does all the unboxification, etc.
225 dsExpr (HsSCC cc expr)
226 = dsExpr expr `thenDs` \ core_expr ->
227 getModuleDs `thenDs` \ mod_name ->
228 returnDs (Note (SCC (mkUserCC cc mod_name)) core_expr)
230 -- special case to handle unboxed tuple patterns.
232 dsExpr (HsCase discrim matches src_loc)
233 | all ubx_tuple_match matches
234 = putSrcLocDs src_loc $
235 dsExpr discrim `thenDs` \ core_discrim ->
236 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
237 case matching_code of
238 Case (Var x) bndr alts | x == discrim_var ->
239 returnDs (Case core_discrim bndr alts)
240 _ -> panic ("dsExpr: tuple pattern:\n" ++ showSDoc (ppr matching_code))
242 ubx_tuple_match (Match [TuplePat ps Unboxed] _ _) = True
243 ubx_tuple_match _ = False
245 dsExpr (HsCase discrim matches src_loc)
246 = putSrcLocDs src_loc $
247 dsExpr discrim `thenDs` \ core_discrim ->
248 matchWrapper CaseAlt matches `thenDs` \ ([discrim_var], matching_code) ->
249 returnDs (bindNonRec discrim_var core_discrim matching_code)
251 dsExpr (HsLet binds body)
252 = dsExpr body `thenDs` \ body' ->
255 dsExpr (HsWith expr binds)
256 = dsExpr expr `thenDs` \ expr' ->
257 foldlDs dsIPBind expr' binds
260 = dsExpr e `thenDs` \ e' ->
261 returnDs (Let (NonRec (ipNameName n) e') body)
263 dsExpr (HsDoOut do_or_lc stmts return_id then_id fail_id result_ty src_loc)
264 | maybeToBool maybe_list_comp
265 = -- Special case for list comprehensions
266 putSrcLocDs src_loc $
267 dsListComp stmts elt_ty
270 = putSrcLocDs src_loc $
271 dsDo do_or_lc stmts return_id then_id fail_id result_ty
274 = case (do_or_lc, tcSplitTyConApp_maybe result_ty) of
275 (ListComp, Just (tycon, [elt_ty]))
279 -- We need the ListComp form to use deListComp (rather than the "do" form)
280 -- because the interpretation of ExprStmt depends on what sort of thing
283 Just elt_ty = maybe_list_comp
285 dsExpr (HsIf guard_expr then_expr else_expr src_loc)
286 = putSrcLocDs src_loc $
287 dsExpr guard_expr `thenDs` \ core_guard ->
288 dsExpr then_expr `thenDs` \ core_then ->
289 dsExpr else_expr `thenDs` \ core_else ->
290 returnDs (mkIfThenElse core_guard core_then core_else)
295 \underline{\bf Type lambda and application}
296 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~
298 dsExpr (TyLam tyvars expr)
299 = dsExpr expr `thenDs` \ core_expr ->
300 returnDs (mkLams tyvars core_expr)
302 dsExpr (TyApp expr tys)
303 = dsExpr expr `thenDs` \ core_expr ->
304 returnDs (mkTyApps core_expr tys)
309 \underline{\bf Various data construction things}
310 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
312 dsExpr (ExplicitList ty xs)
315 go [] = returnDs (mkNilExpr ty)
316 go (x:xs) = dsExpr x `thenDs` \ core_x ->
317 go xs `thenDs` \ core_xs ->
318 returnDs (mkConsExpr ty core_x core_xs)
320 dsExpr (ExplicitTuple expr_list boxity)
321 = mapDs dsExpr expr_list `thenDs` \ core_exprs ->
322 returnDs (mkConApp (tupleCon boxity (length expr_list))
323 (map (Type . exprType) core_exprs ++ core_exprs))
325 dsExpr (ArithSeqOut expr (From from))
326 = dsExpr expr `thenDs` \ expr2 ->
327 dsExpr from `thenDs` \ from2 ->
328 returnDs (App expr2 from2)
330 dsExpr (ArithSeqOut expr (FromTo from two))
331 = dsExpr expr `thenDs` \ expr2 ->
332 dsExpr from `thenDs` \ from2 ->
333 dsExpr two `thenDs` \ two2 ->
334 returnDs (mkApps expr2 [from2, two2])
336 dsExpr (ArithSeqOut expr (FromThen from thn))
337 = dsExpr expr `thenDs` \ expr2 ->
338 dsExpr from `thenDs` \ from2 ->
339 dsExpr thn `thenDs` \ thn2 ->
340 returnDs (mkApps expr2 [from2, thn2])
342 dsExpr (ArithSeqOut expr (FromThenTo from thn two))
343 = dsExpr expr `thenDs` \ expr2 ->
344 dsExpr from `thenDs` \ from2 ->
345 dsExpr thn `thenDs` \ thn2 ->
346 dsExpr two `thenDs` \ two2 ->
347 returnDs (mkApps expr2 [from2, thn2, two2])
351 \underline{\bf Record construction and update}
352 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
353 For record construction we do this (assuming T has three arguments)
357 let err = /\a -> recConErr a
358 T (recConErr t1 "M.lhs/230/op1")
360 (recConErr t1 "M.lhs/230/op3")
362 @recConErr@ then converts its arugment string into a proper message
363 before printing it as
365 M.lhs, line 230: missing field op1 was evaluated
368 We also handle @C{}@ as valid construction syntax for an unlabelled
369 constructor @C@, setting all of @C@'s fields to bottom.
372 dsExpr (RecordConOut data_con con_expr rbinds)
373 = dsExpr con_expr `thenDs` \ con_expr' ->
375 (arg_tys, _) = tcSplitFunTys (exprType con_expr')
376 -- A newtype in the corner should be opaque;
377 -- hence TcType.tcSplitFunTys
380 = case [rhs | (sel_id,rhs,_) <- rbinds,
381 lbl == recordSelectorFieldLabel sel_id] of
382 (rhs:rhss) -> ASSERT( null rhss )
384 [] -> mkErrorAppDs rEC_CON_ERROR_ID arg_ty (showSDoc (ppr lbl))
385 unlabelled_bottom arg_ty = mkErrorAppDs rEC_CON_ERROR_ID arg_ty ""
387 labels = dataConFieldLabels data_con
391 then mapDs unlabelled_bottom arg_tys
392 else mapDs mk_arg (zipEqual "dsExpr:RecordCon" arg_tys labels))
393 `thenDs` \ con_args ->
395 returnDs (mkApps con_expr' con_args)
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 constructor application directly, because the constructor
416 might do some argument-evaluation first; and may have to throw away some
420 dsExpr (RecordUpdOut record_expr record_in_ty record_out_ty dicts [])
423 dsExpr (RecordUpdOut record_expr record_in_ty record_out_ty dicts rbinds)
424 = getSrcLocDs `thenDs` \ src_loc ->
425 dsExpr record_expr `thenDs` \ record_expr' ->
427 -- Desugar the rbinds, and generate let-bindings if
428 -- necessary so that we don't lose sharing
431 in_inst_tys = tcTyConAppArgs record_in_ty -- Newtype opaque
432 out_inst_tys = tcTyConAppArgs record_out_ty -- Newtype opaque
434 mk_val_arg field old_arg_id
435 = case [rhs | (sel_id, rhs, _) <- rbinds,
436 field == recordSelectorFieldLabel sel_id] of
437 (rhs:rest) -> ASSERT(null rest) rhs
438 [] -> HsVar old_arg_id
441 = newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys) `thenDs` \ arg_ids ->
442 -- This call to dataConArgTys won't work for existentials
444 val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
445 (dataConFieldLabels con) arg_ids
446 rhs = foldl HsApp (DictApp (TyApp (HsVar (dataConWrapId con))
451 returnDs (mkSimpleMatch [ConPat con record_in_ty [] [] (map VarPat arg_ids)]
456 -- Record stuff doesn't work for existentials
457 ASSERT( all (not . isExistentialDataCon) data_cons )
459 -- It's important to generate the match with matchWrapper,
460 -- and the right hand sides with applications of the wrapper Id
461 -- so that everything works when we are doing fancy unboxing on the
462 -- constructor aguments.
463 mapDs mk_alt cons_to_upd `thenDs` \ alts ->
464 matchWrapper RecUpd alts `thenDs` \ ([discrim_var], matching_code) ->
466 returnDs (bindNonRec discrim_var record_expr' matching_code)
469 updated_fields :: [FieldLabel]
470 updated_fields = [recordSelectorFieldLabel sel_id | (sel_id,_,_) <- rbinds]
472 -- Get the type constructor from the first field label,
473 -- so that we are sure it'll have all its DataCons
474 -- (In GHCI, it's possible that some TyCons may not have all
475 -- their constructors, in a module-loop situation.)
476 tycon = fieldLabelTyCon (head updated_fields)
477 data_cons = tyConDataCons tycon
478 cons_to_upd = filter has_all_fields data_cons
480 has_all_fields :: DataCon -> Bool
481 has_all_fields con_id
482 = all (`elem` con_fields) updated_fields
484 con_fields = dataConFieldLabels con_id
489 \underline{\bf Dictionary lambda and application}
490 % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
491 @DictLam@ and @DictApp@ turn into the regular old things.
492 (OLD:) @DictFunApp@ also becomes a curried application, albeit slightly more
493 complicated; reminiscent of fully-applied constructors.
495 dsExpr (DictLam dictvars expr)
496 = dsExpr expr `thenDs` \ core_expr ->
497 returnDs (mkLams dictvars core_expr)
501 dsExpr (DictApp expr dicts) -- becomes a curried application
502 = dsExpr expr `thenDs` \ core_expr ->
503 returnDs (foldl (\f d -> f `App` (Var d)) core_expr dicts)
509 -- HsSyn constructs that just shouldn't be here:
510 dsExpr (HsDo _ _ _) = panic "dsExpr:HsDo"
511 dsExpr (ExprWithTySig _ _) = panic "dsExpr:ExprWithTySig"
512 dsExpr (ArithSeqIn _) = panic "dsExpr:ArithSeqIn"
517 %--------------------------------------------------------------------
519 Basically does the translation given in the Haskell~1.3 report:
524 -> Id -- id for: return m
525 -> Id -- id for: (>>=) m
526 -> Id -- id for: fail m
527 -> Type -- Element type; the whole expression has type (m t)
530 dsDo do_or_lc stmts return_id then_id fail_id result_ty
532 (_, b_ty) = tcSplitAppTy result_ty -- result_ty must be of the form (m b)
533 is_do = case do_or_lc of
537 -- For ExprStmt, see the comments near HsExpr.Stmt about
538 -- exactly what ExprStmts mean!
540 -- In dsDo we can only see DoStmt and ListComp (no gaurds)
542 go [ResultStmt expr locn]
543 | is_do = do_expr expr locn
544 | otherwise = do_expr expr locn `thenDs` \ expr2 ->
545 returnDs (mkApps (Var return_id) [Type b_ty, expr2])
547 go (ExprStmt expr a_ty locn : stmts)
548 | is_do -- Do expression
549 = do_expr expr locn `thenDs` \ expr2 ->
550 go stmts `thenDs` \ rest ->
551 newSysLocalDs a_ty `thenDs` \ ignored_result_id ->
552 returnDs (mkApps (Var then_id) [Type a_ty, Type b_ty, expr2,
553 Lam ignored_result_id rest])
555 | otherwise -- List comprehension
556 = do_expr expr locn `thenDs` \ expr2 ->
557 go stmts `thenDs` \ rest ->
559 msg = "Pattern match failure in do expression, " ++ showSDoc (ppr locn)
561 mkStringLit msg `thenDs` \ core_msg ->
562 returnDs (mkIfThenElse expr2 rest
563 (App (App (Var fail_id) (Type b_ty)) core_msg))
565 go (LetStmt binds : stmts )
566 = go stmts `thenDs` \ rest ->
569 go (BindStmt pat expr locn : stmts)
571 dsExpr expr `thenDs` \ expr2 ->
573 a_ty = outPatType pat
574 fail_expr = HsApp (TyApp (HsVar fail_id) [b_ty])
575 (HsLit (HsString (_PK_ msg)))
576 msg = "Pattern match failure in do expression, " ++ showSDoc (ppr locn)
577 main_match = mkSimpleMatch [pat]
578 (HsDoOut do_or_lc stmts return_id then_id
579 fail_id result_ty locn)
582 | failureFreePat pat = [main_match]
585 , mkSimpleMatch [WildPat a_ty] fail_expr result_ty locn
588 matchWrapper (DoCtxt do_or_lc) the_matches `thenDs` \ (binders, matching_code) ->
589 returnDs (mkApps (Var then_id) [Type a_ty, Type b_ty, expr2,
590 mkLams binders matching_code])
595 do_expr expr locn = putSrcLocDs locn (dsExpr expr)
599 %************************************************************************
601 \subsection[DsExpr-literals]{Literals}
603 %************************************************************************
605 We give int/float literals type @Integer@ and @Rational@, respectively.
606 The typechecker will (presumably) have put \tr{from{Integer,Rational}s}
609 ToDo: put in range checks for when converting ``@i@''
610 (or should that be in the typechecker?)
612 For numeric literals, we try to detect there use at a standard type
613 (@Int@, @Float@, etc.) are directly put in the right constructor.
614 [NB: down with the @App@ conversion.]
616 See also below where we look for @DictApps@ for \tr{plusInt}, etc.
619 dsLit :: HsLit -> DsM CoreExpr
620 dsLit (HsChar c) = returnDs (mkConApp charDataCon [mkLit (MachChar c)])
621 dsLit (HsCharPrim c) = returnDs (mkLit (MachChar c))
622 dsLit (HsString str) = mkStringLitFS str
623 dsLit (HsStringPrim s) = returnDs (mkLit (MachStr s))
624 dsLit (HsInteger i) = mkIntegerLit i
625 dsLit (HsInt i) = returnDs (mkConApp intDataCon [mkIntLit i])
626 dsLit (HsIntPrim i) = returnDs (mkIntLit i)
627 dsLit (HsFloatPrim f) = returnDs (mkLit (MachFloat f))
628 dsLit (HsDoublePrim d) = returnDs (mkLit (MachDouble d))
629 dsLit (HsLitLit str ty)
630 = ASSERT( maybeToBool maybe_ty )
631 returnDs (wrap_fn (mkLit (MachLitLit str rep_ty)))
633 (maybe_ty, wrap_fn) = resultWrapper ty
634 Just rep_ty = maybe_ty
637 = mkIntegerLit (numerator r) `thenDs` \ num ->
638 mkIntegerLit (denominator r) `thenDs` \ denom ->
639 returnDs (mkConApp ratio_data_con [Type integer_ty, num, denom])
641 (ratio_data_con, integer_ty)
642 = case tcSplitTyConApp ty of
643 (tycon, [i_ty]) -> ASSERT(isIntegerTy i_ty && tycon `hasKey` ratioTyConKey)
644 (head (tyConDataCons tycon), i_ty)