2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcExpr]{Typecheck an expression}
9 -- The above warning supression flag is a temporary kludge.
10 -- While working on this module you are encouraged to remove it and fix
11 -- any warnings in the module. See
12 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
15 module TcExpr ( tcPolyExpr, tcPolyExprNC,
16 tcMonoExpr, tcInferRho, tcSyntaxOp ) where
18 #include "HsVersions.h"
20 #ifdef GHCI /* Only if bootstrapped */
21 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
22 import qualified DsMeta
39 import TcIface ( checkWiredInTyCon )
63 %************************************************************************
65 \subsection{Main wrappers}
67 %************************************************************************
70 tcPolyExpr, tcPolyExprNC
71 :: LHsExpr Name -- Expession to type check
72 -> BoxySigmaType -- Expected type (could be a polytpye)
73 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
75 -- tcPolyExpr is a convenient place (frequent but not too frequent) place
76 -- to add context information.
77 -- The NC version does not do so, usually because the caller wants
80 tcPolyExpr expr res_ty
81 = addErrCtxt (exprCtxt (unLoc expr)) $
82 (do {traceTc (text "tcPolyExpr") ; tcPolyExprNC expr res_ty })
84 tcPolyExprNC expr res_ty
86 = do { traceTc (text "tcPolyExprNC" <+> ppr res_ty)
87 ; (gen_fn, expr') <- tcGen res_ty emptyVarSet (\_ -> tcPolyExprNC expr)
88 -- Note the recursive call to tcPolyExpr, because the
89 -- type may have multiple layers of for-alls
90 -- E.g. forall a. Eq a => forall b. Ord b => ....
91 ; return (mkLHsWrap gen_fn expr') }
94 = tcMonoExpr expr res_ty
97 tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
98 tcPolyExprs [] [] = returnM []
99 tcPolyExprs (expr:exprs) (ty:tys)
100 = do { expr' <- tcPolyExpr expr ty
101 ; exprs' <- tcPolyExprs exprs tys
102 ; returnM (expr':exprs') }
103 tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
106 tcMonoExpr :: LHsExpr Name -- Expression to type check
107 -> BoxyRhoType -- Expected type (could be a type variable)
108 -- Definitely no foralls at the top
109 -- Can contain boxes, which will be filled in
110 -> TcM (LHsExpr TcId)
112 tcMonoExpr (L loc expr) res_ty
113 = ASSERT( not (isSigmaTy res_ty) )
115 do { expr' <- tcExpr expr res_ty
116 ; return (L loc expr') }
119 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
120 tcInferRho expr = tcInfer (tcMonoExpr expr)
124 %************************************************************************
126 tcExpr: the main expression typechecker
128 %************************************************************************
131 tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
132 tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
134 tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
135 ; coi <- boxyUnify lit_ty res_ty
136 ; return $ mkHsWrapCoI coi (HsLit lit)
139 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
140 ; return (HsPar expr') }
142 tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
143 ; returnM (HsSCC lbl expr') }
144 tcExpr (HsTickPragma info expr) res_ty
145 = do { expr' <- tcMonoExpr expr res_ty
146 ; returnM (HsTickPragma info expr') }
148 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
149 = do { expr' <- tcMonoExpr expr res_ty
150 ; return (HsCoreAnn lbl expr') }
152 tcExpr (HsOverLit lit) res_ty
153 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
154 ; return (HsOverLit lit') }
156 tcExpr (NegApp expr neg_expr) res_ty
157 = do { neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
158 (mkFunTy res_ty res_ty)
159 ; expr' <- tcMonoExpr expr res_ty
160 ; return (NegApp expr' neg_expr') }
162 tcExpr (HsIPVar ip) res_ty
163 = do { -- Implicit parameters must have a *tau-type* not a
164 -- type scheme. We enforce this by creating a fresh
165 -- type variable as its type. (Because res_ty may not
167 ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
168 ; co_fn <- tcSubExp ip_ty res_ty
169 ; (ip', inst) <- newIPDict (IPOccOrigin ip) ip ip_ty
171 ; return (mkHsWrap co_fn (HsIPVar ip')) }
173 tcExpr (HsApp e1 e2) res_ty
176 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
177 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
178 go lfun@(L loc fun) args
179 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
180 tcApp fun (length args) (tcArgs lfun args) res_ty
181 ; traceTc (text "tcExpr args': " <+> ppr args')
182 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
184 tcExpr (HsLam match) res_ty
185 = do { (co_fn, match') <- tcMatchLambda match res_ty
186 ; return (mkHsWrap co_fn (HsLam match')) }
188 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
189 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
191 -- Remember to extend the lexical type-variable environment
192 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (\ skol_tvs res_ty ->
193 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
194 tcPolyExprNC expr res_ty)
196 ; co_fn <- tcSubExp sig_tc_ty res_ty
197 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
199 tcExpr (HsType ty) res_ty
200 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
201 -- This is the syntax for type applications that I was planning
202 -- but there are difficulties (e.g. what order for type args)
203 -- so it's not enabled yet.
204 -- Can't eliminate it altogether from the parser, because the
205 -- same parser parses *patterns*.
209 %************************************************************************
211 Infix operators and sections
213 %************************************************************************
216 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
217 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
218 ; return (OpApp arg1' (L loc op') fix arg2') }
220 -- Left sections, equivalent to
227 -- We treat it as similar to the latter, so we don't
228 -- actually require the function to take two arguments
229 -- at all. For example, (x `not`) means (not x);
230 -- you get postfix operators! Not really Haskell 98
231 -- I suppose, but it's less work and kind of useful.
233 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
234 = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
235 ; return (SectionL arg1' (L loc op')) }
237 -- Right sections, equivalent to \ x -> x `op` expr, or
240 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
241 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
242 tcApp op 2 (tc_args arg1_ty') res_ty'
243 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
245 doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
246 <+> ptext SLIT("takes one argument")
247 tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
248 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
249 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
250 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
251 ; return (qtys', arg2') }
252 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
256 tcExpr (HsLet binds expr) res_ty
257 = do { (binds', expr') <- tcLocalBinds binds $
258 tcMonoExpr expr res_ty
259 ; return (HsLet binds' expr') }
261 tcExpr (HsCase scrut matches) exp_ty
262 = do { -- We used to typecheck the case alternatives first.
263 -- The case patterns tend to give good type info to use
264 -- when typechecking the scrutinee. For example
267 -- will report that map is applied to too few arguments
269 -- But now, in the GADT world, we need to typecheck the scrutinee
270 -- first, to get type info that may be refined in the case alternatives
271 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
274 ; traceTc (text "HsCase" <+> ppr scrut_ty)
275 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
276 ; return (HsCase scrut' matches') }
278 match_ctxt = MC { mc_what = CaseAlt,
281 tcExpr (HsIf pred b1 b2) res_ty
282 = do { pred' <- addErrCtxt (predCtxt pred) $
283 tcMonoExpr pred boolTy
284 ; b1' <- tcMonoExpr b1 res_ty
285 ; b2' <- tcMonoExpr b2 res_ty
286 ; return (HsIf pred' b1' b2') }
288 tcExpr (HsDo do_or_lc stmts body _) res_ty
289 = tcDoStmts do_or_lc stmts body res_ty
291 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
292 = do { (elt_ty, coi) <- boxySplitListTy res_ty
293 ; exprs' <- mappM (tc_elt elt_ty) exprs
294 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
296 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
298 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
299 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
300 ; exprs' <- mappM (tc_elt elt_ty) exprs
301 ; ifM (null exprs) (zapToMonotype elt_ty)
302 -- If there are no expressions in the comprehension
303 -- we must still fill in the box
304 -- (Not needed for [] and () becuase they happen
305 -- to parse as data constructors.)
306 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
308 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
310 -- For tuples, take care to preserve rigidity
311 -- E.g. case (x,y) of ....
312 -- The scrutinee should have a rigid type if x,y do
313 -- The general scheme is the same as in tcIdApp
314 tcExpr (ExplicitTuple exprs boxity) res_ty
315 = do { tvs <- newBoxyTyVars [argTypeKind | e <- exprs]
316 ; let tup_tc = tupleTyCon boxity (length exprs)
317 tup_res_ty = mkTyConApp tup_tc (mkTyVarTys tvs)
318 ; checkWiredInTyCon tup_tc -- Ensure instances are available
319 ; arg_tys <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
320 ; exprs' <- tcPolyExprs exprs arg_tys
321 ; arg_tys' <- mapM refineBox arg_tys
322 ; co_fn <- tcFunResTy (tyConName tup_tc) (mkTyConApp tup_tc arg_tys') res_ty
323 ; return (mkHsWrap co_fn (ExplicitTuple exprs' boxity)) }
325 tcExpr (HsProc pat cmd) res_ty
326 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
327 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
329 tcExpr e@(HsArrApp _ _ _ _ _) _
330 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
331 ptext SLIT("was found where an expression was expected")])
333 tcExpr e@(HsArrForm _ _ _) _
334 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
335 ptext SLIT("was found where an expression was expected")])
338 %************************************************************************
340 Record construction and update
342 %************************************************************************
345 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
346 = do { data_con <- tcLookupDataCon con_name
348 -- Check for missing fields
349 ; checkMissingFields data_con rbinds
351 ; let arity = dataConSourceArity data_con
352 check_fields qtvs qtys arg_tys
353 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
354 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
355 ; qtys' <- mapM refineBoxToTau qtys
356 ; return (qtys', rbinds') }
357 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
358 -- filled, which is the invariant expected by tcIdApp
359 -- How could this not be the case? Consider a record construction
360 -- that does not mention all the fields.
362 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
364 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
366 -- The main complication with RecordUpd is that we need to explicitly
367 -- handle the *non-updated* fields. Consider:
369 -- data T a b = MkT1 { fa :: a, fb :: b }
370 -- | MkT2 { fa :: a, fc :: Int -> Int }
371 -- | MkT3 { fd :: a }
373 -- upd :: T a b -> c -> T a c
374 -- upd t x = t { fb = x}
376 -- The type signature on upd is correct (i.e. the result should not be (T a b))
377 -- because upd should be equivalent to:
379 -- upd t x = case t of
380 -- MkT1 p q -> MkT1 p x
381 -- MkT2 a b -> MkT2 p b
382 -- MkT3 d -> error ...
384 -- So we need to give a completely fresh type to the result record,
385 -- and then constrain it by the fields that are *not* updated ("p" above).
387 -- Note that because MkT3 doesn't contain all the fields being updated,
388 -- its RHS is simply an error, so it doesn't impose any type constraints
390 -- All this is done in STEP 4 below.
394 -- For record update we require that every constructor involved in the
395 -- update (i.e. that has all the specified fields) is "vanilla". I
396 -- don't know how to do the update otherwise.
399 tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
401 -- Check that the field names are really field names
403 field_names = hsRecFields rbinds
405 ASSERT( notNull field_names )
406 mappM tcLookupField field_names `thenM` \ sel_ids ->
407 -- The renamer has already checked that they
410 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
411 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
412 not (isRecordSelector sel_id), -- Excludes class ops
413 let L loc field_name = hsRecFieldId fld
416 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
419 -- Figure out the tycon and data cons from the first field name
421 -- It's OK to use the non-tc splitters here (for a selector)
423 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
424 data_cons = tyConDataCons tycon -- it's not a field label
425 -- NB: for a data type family, the tycon is the instance tycon
427 relevant_cons = filter is_relevant data_cons
428 is_relevant con = all (`elem` dataConFieldLabels con) field_names
432 -- Check that at least one constructor has all the named fields
433 -- i.e. has an empty set of bad fields returned by badFields
434 checkTc (not (null relevant_cons))
435 (badFieldsUpd rbinds) `thenM_`
437 -- Check that all relevant data cons are vanilla. Doing record updates on
438 -- GADTs and/or existentials is more than my tiny brain can cope with today
439 checkTc (all isVanillaDataCon relevant_cons)
440 (nonVanillaUpd tycon) `thenM_`
443 -- Use the un-updated fields to find a vector of booleans saying
444 -- which type arguments must be the same in updatee and result.
446 -- WARNING: this code assumes that all data_cons in a common tycon
447 -- have FieldLabels abstracted over the same tyvars.
449 -- A constructor is only relevant to this process if
450 -- it contains *all* the fields that are being updated
451 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons -- A representative constructor
452 (con1_tyvars, theta, con1_arg_tys, con1_res_ty) = dataConSig con1
453 con1_flds = dataConFieldLabels con1
454 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
455 , not (fld `elem` field_names) ]
457 is_common_tv tv = tv `elemVarSet` common_tyvars
459 mk_inst_ty tv result_inst_ty
460 | is_common_tv tv = returnM result_inst_ty -- Same as result type
461 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
463 ASSERT( null theta ) -- Vanilla datacon
464 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, result_inst_env) ->
465 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ scrut_inst_tys ->
467 -- STEP 3: Typecheck the update bindings.
468 -- Do this after checking for bad fields in case
469 -- there's a field that doesn't match the constructor.
471 result_ty = substTy result_inst_env con1_res_ty
472 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
474 tcSubExp result_ty res_ty `thenM` \ co_fn ->
475 tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
477 -- STEP 5: Typecheck the expression to be updated
479 scrut_inst_env = zipTopTvSubst con1_tyvars scrut_inst_tys
480 scrut_ty = substTy scrut_inst_env con1_res_ty
481 -- This is one place where the isVanilla check is important
482 -- So that inst_tys matches the con1_tyvars
484 tcMonoExpr record_expr scrut_ty `thenM` \ record_expr' ->
486 -- STEP 6: Figure out the LIE we need.
487 -- We have to generate some dictionaries for the data type context,
488 -- since we are going to do pattern matching over the data cons.
490 -- What dictionaries do we need? The dataConStupidTheta tells us.
492 theta' = substTheta scrut_inst_env (dataConStupidTheta con1)
494 instStupidTheta RecordUpdOrigin theta' `thenM_`
496 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
497 let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
498 = WpCo $ mkTyConApp co_con scrut_inst_tys
503 returnM (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
504 relevant_cons scrut_inst_tys result_inst_tys))
508 %************************************************************************
510 Arithmetic sequences e.g. [a,b..]
511 and their parallel-array counterparts e.g. [: a,b.. :]
514 %************************************************************************
517 tcExpr (ArithSeq _ seq@(From expr)) res_ty
518 = do { (elt_ty, coi) <- boxySplitListTy res_ty
519 ; expr' <- tcPolyExpr expr elt_ty
520 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
522 ; return $ mkHsWrapCoI coi (ArithSeq (HsVar enum_from) (From expr')) }
524 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
525 = do { (elt_ty, coi) <- boxySplitListTy res_ty
526 ; expr1' <- tcPolyExpr expr1 elt_ty
527 ; expr2' <- tcPolyExpr expr2 elt_ty
528 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
529 elt_ty enumFromThenName
530 ; return $ mkHsWrapCoI coi
531 (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
533 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
534 = do { (elt_ty, coi) <- boxySplitListTy res_ty
535 ; expr1' <- tcPolyExpr expr1 elt_ty
536 ; expr2' <- tcPolyExpr expr2 elt_ty
537 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
538 elt_ty enumFromToName
539 ; return $ mkHsWrapCoI coi
540 (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
542 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
543 = do { (elt_ty, coi) <- boxySplitListTy res_ty
544 ; expr1' <- tcPolyExpr expr1 elt_ty
545 ; expr2' <- tcPolyExpr expr2 elt_ty
546 ; expr3' <- tcPolyExpr expr3 elt_ty
547 ; eft <- newMethodFromName (ArithSeqOrigin seq)
548 elt_ty enumFromThenToName
549 ; return $ mkHsWrapCoI coi
550 (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
552 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
553 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
554 ; expr1' <- tcPolyExpr expr1 elt_ty
555 ; expr2' <- tcPolyExpr expr2 elt_ty
556 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
557 elt_ty enumFromToPName
558 ; return $ mkHsWrapCoI coi
559 (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
561 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
562 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
563 ; expr1' <- tcPolyExpr expr1 elt_ty
564 ; expr2' <- tcPolyExpr expr2 elt_ty
565 ; expr3' <- tcPolyExpr expr3 elt_ty
566 ; eft <- newMethodFromName (PArrSeqOrigin seq)
567 elt_ty enumFromThenToPName
568 ; return $ mkHsWrapCoI coi
569 (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
571 tcExpr (PArrSeq _ _) _
572 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
573 -- the parser shouldn't have generated it and the renamer shouldn't have
578 %************************************************************************
582 %************************************************************************
585 #ifdef GHCI /* Only if bootstrapped */
586 -- Rename excludes these cases otherwise
587 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
588 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
594 %************************************************************************
598 %************************************************************************
601 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
605 %************************************************************************
609 %************************************************************************
612 ---------------------------
613 tcApp :: HsExpr Name -- Function
614 -> Arity -- Number of args reqd
615 -> ArgChecker results
616 -> BoxyRhoType -- Result type
617 -> TcM (HsExpr TcId, results)
619 -- (tcFun fun n_args arg_checker res_ty)
620 -- The argument type checker, arg_checker, will be passed exactly n_args types
622 tcApp (HsVar fun_name) n_args arg_checker res_ty
623 = tcIdApp fun_name n_args arg_checker res_ty
625 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
626 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
627 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
628 ; arg_tys' <- mapM readFilledBox arg_boxes
629 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
630 ; return (fun', args') }
632 ---------------------------
633 tcIdApp :: Name -- Function
634 -> Arity -- Number of args reqd
635 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
636 -> BoxyRhoType -- Result type
637 -> TcM (HsExpr TcId, results)
639 -- Call (f e1 ... en) :: res_ty
640 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
641 -- (where k <= n; fres has the rest)
642 -- NB: if k < n then the function doesn't have enough args, and
643 -- presumably fres is a type variable that we are going to
644 -- instantiate with a function type
646 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
648 tcIdApp fun_name n_args arg_checker res_ty
649 = do { let orig = OccurrenceOf fun_name
650 ; (fun, fun_ty) <- lookupFun orig fun_name
652 -- Split up the function type
653 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
654 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
656 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
657 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
658 res_qtvs = exactTyVarsOfType fun_res_ty
659 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
660 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
661 k = length fun_arg_tys -- k <= n_args
662 n_missing_args = n_args - k -- Always >= 0
664 -- Match the result type of the function with the
665 -- result type of the context, to get an inital substitution
666 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
667 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
668 res_ty' = mkFunTys extra_arg_tys' res_ty
669 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
671 -- Typecheck the arguments!
672 -- Doing so will fill arg_qtvs and extra_arg_tys'
673 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
675 -- Strip boxes from the qtvs that have been filled in by the arg checking
676 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
678 -- Result subsumption
679 -- This fills in res_qtvs
680 ; let res_subst = zipOpenTvSubst qtvs qtys''
681 fun_res_ty'' = substTy res_subst fun_res_ty
682 res_ty'' = mkFunTys extra_arg_tys'' res_ty
683 ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
685 -- And pack up the results
686 -- By applying the coercion just to the *function* we can make
687 -- tcFun work nicely for OpApp and Sections too
688 ; fun' <- instFun orig fun res_subst tv_theta_prs
689 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
690 ; traceTc (text "tcIdApp: " <+> ppr (mkHsWrap co_fn' fun') <+> ppr tv_theta_prs <+> ppr co_fn' <+> ppr fun')
691 ; return (mkHsWrap co_fn' fun', args') }
694 Note [Silly type synonyms in smart-app]
695 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
696 When we call sripBoxyType, all of the boxes should be filled
697 in. But we need to be careful about type synonyms:
701 In the call (f x) we'll typecheck x, expecting it to have type
702 (T box). Usually that would fill in the box, but in this case not;
703 because 'a' is discarded by the silly type synonym T. So we must
704 use exactTyVarsOfType to figure out which type variables are free
705 in the argument type.
708 -- tcId is a specialisation of tcIdApp when there are no arguments
709 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
714 -> BoxyRhoType -- Result type
716 tcId orig fun_name res_ty
717 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
718 ; (fun, fun_ty) <- lookupFun orig fun_name
720 -- Split up the function type
721 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
722 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
723 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
724 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
726 -- Do the subsumption check wrt the result type
727 ; let res_subst = zipTopTvSubst qtvs qtv_tys
728 fun_tau' = substTy res_subst fun_tau
730 ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
732 -- And pack up the results
733 ; fun' <- instFun orig fun res_subst tv_theta_prs
734 ; traceTc (text "tcId yields" <+> ppr (mkHsWrap co_fn fun'))
735 ; return (mkHsWrap co_fn fun') }
737 -- Note [Push result type in]
739 -- Unify with expected result before (was: after) type-checking the args
740 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
741 -- This is when we might detect a too-few args situation.
742 -- (One can think of cases when the opposite order would give
743 -- a better error message.)
744 -- [March 2003: I'm experimenting with putting this first. Here's an
745 -- example where it actually makes a real difference
746 -- class C t a b | t a -> b
747 -- instance C Char a Bool
749 -- data P t a = forall b. (C t a b) => MkP b
750 -- data Q t = MkQ (forall a. P t a)
753 -- f1 = MkQ (MkP True)
754 -- f2 = MkQ (MkP True :: forall a. P Char a)
756 -- With the change, f1 will type-check, because the 'Char' info from
757 -- the signature is propagated into MkQ's argument. With the check
758 -- in the other order, the extra signature in f2 is reqd.]
760 ---------------------------
761 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
762 -- Typecheck a syntax operator, checking that it has the specified type
763 -- The operator is always a variable at this stage (i.e. renamer output)
764 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
765 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
767 ---------------------------
768 instFun :: InstOrigin
770 -> TvSubst -- The instantiating substitution
771 -> [([TyVar], ThetaType)] -- Stuff to instantiate
774 instFun orig fun subst []
775 = return fun -- Common short cut
777 instFun orig fun subst tv_theta_prs
778 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
779 ; traceTc (text "instFun" <+> ppr ty_theta_prs')
780 -- Make two ad-hoc checks
781 ; doStupidChecks fun ty_theta_prs'
783 -- Now do normal instantiation
784 ; result <- go True fun ty_theta_prs'
785 ; traceTc (text "instFun result" <+> ppr result)
789 subst_pr (tvs, theta)
790 = (substTyVars subst tvs, substTheta subst theta)
792 go _ fun [] = do {traceTc (text "go _ fun [] returns" <+> ppr fun) ; return fun }
794 go True (HsVar fun_id) ((tys,theta) : prs)
795 | want_method_inst theta
796 = do { traceTc (text "go (HsVar fun_id) ((tys,theta) : prs) | want_method_inst theta")
797 ; meth_id <- newMethodWithGivenTy orig fun_id tys
798 ; go False (HsVar meth_id) prs }
799 -- Go round with 'False' to prevent further use
800 -- of newMethod: see Note [Multiple instantiation]
802 go _ fun ((tys, theta) : prs)
803 = do { co_fn <- instCall orig tys theta
804 ; traceTc (text "go yields co_fn" <+> ppr co_fn)
805 ; go False (HsWrap co_fn fun) prs }
807 -- See Note [No method sharing]
808 want_method_inst theta = not (null theta) -- Overloaded
809 && not opt_NoMethodSharing
812 Note [Multiple instantiation]
813 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
814 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
815 For example, consider
816 f :: forall a. Eq a => forall b. Ord b => a -> b
817 At a call to f, at say [Int, Bool], it's tempting to translate the call to
821 f_m1 :: forall b. Ord b => Int -> b
825 f_m2 = f_m1 Bool dOrdBool
827 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
828 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
830 But it's entirely possible that f_m2 will continue to float out, because it
831 mentions no type variables. Result, f_m1 isn't in scope.
833 Here's a concrete example that does this (test tc200):
836 f :: Eq b => b -> a -> Int
837 baz :: Eq a => Int -> a -> Int
842 Current solution: only do the "method sharing" thing for the first type/dict
843 application, not for the iterated ones. A horribly subtle point.
845 Note [No method sharing]
846 ~~~~~~~~~~~~~~~~~~~~~~~~
847 The -fno-method-sharing flag controls what happens so far as the LIE
848 is concerned. The default case is that for an overloaded function we
849 generate a "method" Id, and add the Method Inst to the LIE. So you get
852 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
853 If you specify -fno-method-sharing, the dictionary application
854 isn't shared, so we get
856 f = /\a (d:Num a) (x:a) -> (+) a d x x
857 This gets a bit less sharing, but
858 a) it's better for RULEs involving overloaded functions
859 b) perhaps fewer separated lambdas
863 tcArgs implements a left-to-right order, which goes beyond what is described in the
864 impredicative type inference paper. In particular, it allows
866 where runST :: (forall s. ST s a) -> a
867 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
868 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
869 before checking foo. The left-to-right order really helps here.
872 tcArgs :: LHsExpr Name -- The function (for error messages)
873 -> [LHsExpr Name] -- Actual args
874 -> ArgChecker [LHsExpr TcId]
876 type ArgChecker results
877 = [TyVar] -> [TcSigmaType] -- Current instantiation
878 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
879 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
881 tcArgs fun args qtvs qtys arg_tys
882 = go 1 qtys args arg_tys
884 go n qtys [] [] = return (qtys, [])
885 go n qtys (arg:args) (arg_ty:arg_tys)
886 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
887 ; qtys' <- mapM refineBox qtys -- Exploit new info
888 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
889 ; return (qtys'', arg':args') }
890 go n qtys args arg_tys = panic "tcArgs"
892 tcArg :: LHsExpr Name -- The function
893 -> Int -- and arg number (for error messages)
895 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
897 -> TcM (LHsExpr TcId) -- Resulting argument
898 tcArg fun arg_no arg qtvs qtys ty
899 = addErrCtxt (funAppCtxt fun arg arg_no) $
900 tcPolyExprNC arg (substTyWith qtvs qtys ty)
906 Nasty check to ensure that tagToEnum# is applied to a type that is an
907 enumeration TyCon. Unification may refine the type later, but this
908 check won't see that, alas. It's crude but it works.
910 Here's are two cases that should fail
912 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
915 g = tagToEnum# 0 -- Int is not an enumeration
919 doStupidChecks :: HsExpr TcId
920 -> [([TcType], ThetaType)]
922 -- Check two tiresome and ad-hoc cases
923 -- (a) the "stupid theta" for a data con; add the constraints
924 -- from the "stupid theta" of a data constructor (sigh)
925 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
927 doStupidChecks (HsVar fun_id) ((tys,_):_)
928 | Just con <- isDataConId_maybe fun_id -- (a)
929 = addDataConStupidTheta con tys
931 | fun_id `hasKey` tagToEnumKey -- (b)
932 = do { tys' <- zonkTcTypes tys
933 ; checkTc (ok tys') (tagToEnumError tys')
937 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
938 Just (tc,_) -> isEnumerationTyCon tc
941 doStupidChecks fun tv_theta_prs
942 = return () -- The common case
946 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
947 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
948 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
950 at_type | null tys = empty -- Probably never happens
951 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
954 %************************************************************************
956 \subsection{@tcId@ typechecks an identifier occurrence}
958 %************************************************************************
961 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
962 lookupFun orig id_name
963 = do { thing <- tcLookup id_name
965 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
967 wrap_id = dataConWrapId con
970 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
971 | otherwise -> return (HsVar id, idType id)
972 -- A global cannot possibly be ill-staged
973 -- nor does it need the 'lifting' treatment
975 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
976 -> do { thLocalId orig id ty lvl
978 Unrefineable -> return (HsVar id, ty)
979 Rigid co -> return (mkHsWrap co (HsVar id), ty)
980 Wobbly -> traceTc (text "lookupFun" <+> ppr id) >> return (HsVar id, ty) -- Wobbly, or no free vars
981 WobblyInvisible -> failWithTc (ppr id_name <+> ptext SLIT(" not in scope because it has a wobbly type (solution: add a type annotation)"))
984 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
987 #ifndef GHCI /* GHCI and TH is off */
988 --------------------------------------
989 -- thLocalId : Check for cross-stage lifting
990 thLocalId orig id id_ty th_bind_lvl
993 #else /* GHCI and TH is on */
994 thLocalId orig id id_ty th_bind_lvl
995 = do { use_stage <- getStage -- TH case
997 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
998 -> thBrackId orig id ps_var lie_var
999 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
1003 --------------------------------------
1004 thBrackId orig id ps_var lie_var
1005 | isExternalName id_name
1006 = -- Top-level identifiers in this module,
1007 -- (which have External Names)
1008 -- are just like the imported case:
1009 -- no need for the 'lifting' treatment
1010 -- E.g. this is fine:
1013 -- But we do need to put f into the keep-alive
1014 -- set, because after desugaring the code will
1015 -- only mention f's *name*, not f itself.
1016 do { keepAliveTc id_name; return id }
1019 = -- Nested identifiers, such as 'x' in
1020 -- E.g. \x -> [| h x |]
1021 -- We must behave as if the reference to x was
1023 -- We use 'x' itself as the splice proxy, used by
1024 -- the desugarer to stitch it all back together.
1025 -- If 'x' occurs many times we may get many identical
1026 -- bindings of the same splice proxy, but that doesn't
1027 -- matter, although it's a mite untidy.
1028 do { let id_ty = idType id
1029 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1030 -- If x is polymorphic, its occurrence sites might
1031 -- have different instantiations, so we can't use plain
1032 -- 'x' as the splice proxy name. I don't know how to
1033 -- solve this, and it's probably unimportant, so I'm
1034 -- just going to flag an error for now
1036 ; id_ty' <- zapToMonotype id_ty
1037 -- The id_ty might have an OpenTypeKind, but we
1038 -- can't instantiate the Lift class at that kind,
1039 -- so we zap it to a LiftedTypeKind monotype
1040 -- C.f. the call in TcPat.newLitInst
1042 ; setLIEVar lie_var $ do
1043 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
1044 -- Put the 'lift' constraint into the right LIE
1046 -- Update the pending splices
1047 ; ps <- readMutVar ps_var
1048 ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1057 %************************************************************************
1059 \subsection{Record bindings}
1061 %************************************************************************
1063 Game plan for record bindings
1064 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1065 1. Find the TyCon for the bindings, from the first field label.
1067 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1069 For each binding field = value
1071 3. Instantiate the field type (from the field label) using the type
1074 4 Type check the value using tcArg, passing the field type as
1075 the expected argument type.
1077 This extends OK when the field types are universally quantified.
1083 -> [TcType] -- Expected type for each field
1084 -> HsRecordBinds Name
1085 -> TcM (HsRecordBinds TcId)
1087 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1088 = do { mb_binds <- mappM do_bind rbinds
1089 ; return (HsRecFields (catMaybes mb_binds) dd) }
1091 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1092 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1093 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1094 = addErrCtxt (fieldCtxt field_lbl) $
1095 do { rhs' <- tcPolyExprNC rhs field_ty
1096 ; sel_id <- tcLookupField field_lbl
1097 ; ASSERT( isRecordSelector sel_id )
1098 return (Just (fld { hsRecFieldId = L loc sel_id, hsRecFieldArg = rhs' })) }
1100 = do { addErrTc (badFieldCon data_con field_lbl)
1103 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1104 checkMissingFields data_con rbinds
1105 | null field_labels -- Not declared as a record;
1106 -- But C{} is still valid if no strict fields
1107 = if any isMarkedStrict field_strs then
1108 -- Illegal if any arg is strict
1109 addErrTc (missingStrictFields data_con [])
1113 | otherwise -- A record
1114 = checkM (null missing_s_fields)
1115 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1117 doptM Opt_WarnMissingFields `thenM` \ warn ->
1118 checkM (not (warn && notNull missing_ns_fields))
1119 (warnTc True (missingFields data_con missing_ns_fields))
1123 = [ fl | (fl, str) <- field_info,
1125 not (fl `elem` field_names_used)
1128 = [ fl | (fl, str) <- field_info,
1129 not (isMarkedStrict str),
1130 not (fl `elem` field_names_used)
1133 field_names_used = hsRecFields rbinds
1134 field_labels = dataConFieldLabels data_con
1136 field_info = zipEqual "missingFields"
1140 field_strs = dataConStrictMarks data_con
1143 %************************************************************************
1145 \subsection{Errors and contexts}
1147 %************************************************************************
1149 Boring and alphabetical:
1152 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1155 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1157 fieldCtxt field_name
1158 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1160 funAppCtxt fun arg arg_no
1161 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1162 quotes (ppr fun) <> text ", namely"])
1163 4 (quotes (ppr arg))
1166 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1169 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type")
1170 <+> quotes (pprSourceTyCon tycon)
1171 <+> ptext SLIT("is not (yet) supported"),
1172 ptext SLIT("Use pattern-matching instead")]
1174 = hang (ptext SLIT("No constructor has all these fields:"))
1175 4 (pprQuotedList (hsRecFields rbinds))
1177 naughtyRecordSel sel_id
1178 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1179 ptext SLIT("as a function due to escaped type variables") $$
1180 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1183 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1185 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1186 missingStrictFields con fields
1189 rest | null fields = empty -- Happens for non-record constructors
1190 -- with strict fields
1191 | otherwise = colon <+> pprWithCommas ppr fields
1193 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1194 ptext SLIT("does not have the required strict field(s)")
1196 missingFields :: DataCon -> [FieldLabel] -> SDoc
1197 missingFields con fields
1198 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1199 <+> pprWithCommas ppr fields
1201 -- callCtxt fun args = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1204 polySpliceErr :: Id -> SDoc
1206 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)