2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcExpr]{Typecheck an expression}
8 module TcExpr ( tcPolyExpr, tcPolyExprNC,
9 tcMonoExpr, tcInferRho, tcSyntaxOp ) where
11 #include "HsVersions.h"
13 #ifdef GHCI /* Only if bootstrapped */
14 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
15 import qualified DsMeta
53 %************************************************************************
55 \subsection{Main wrappers}
57 %************************************************************************
60 tcPolyExpr, tcPolyExprNC
61 :: LHsExpr Name -- Expession to type check
62 -> BoxySigmaType -- Expected type (could be a polytpye)
63 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
65 -- tcPolyExpr is a convenient place (frequent but not too frequent) place
66 -- to add context information.
67 -- The NC version does not do so, usually because the caller wants
70 tcPolyExpr expr res_ty
71 = addErrCtxt (exprCtxt (unLoc expr)) $
72 tcPolyExprNC expr res_ty
74 tcPolyExprNC expr res_ty
76 = do { (gen_fn, expr') <- tcGen res_ty emptyVarSet (\_ -> tcPolyExprNC expr)
77 -- Note the recursive call to tcPolyExpr, because the
78 -- type may have multiple layers of for-alls
79 -- E.g. forall a. Eq a => forall b. Ord b => ....
80 ; return (mkLHsWrap gen_fn expr') }
83 = tcMonoExpr expr res_ty
86 tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
87 tcPolyExprs [] [] = returnM []
88 tcPolyExprs (expr:exprs) (ty:tys)
89 = do { expr' <- tcPolyExpr expr ty
90 ; exprs' <- tcPolyExprs exprs tys
91 ; returnM (expr':exprs') }
92 tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
95 tcMonoExpr :: LHsExpr Name -- Expression to type check
96 -> BoxyRhoType -- Expected type (could be a type variable)
97 -- Definitely no foralls at the top
98 -- Can contain boxes, which will be filled in
101 tcMonoExpr (L loc expr) res_ty
102 = ASSERT( not (isSigmaTy res_ty) )
104 do { expr' <- tcExpr expr res_ty
105 ; return (L loc expr') }
108 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
109 tcInferRho expr = tcInfer (tcMonoExpr expr)
114 %************************************************************************
116 tcExpr: the main expression typechecker
118 %************************************************************************
121 tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
122 tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
124 tcExpr (HsLit lit) res_ty = do { boxyUnify (hsLitType lit) res_ty
125 ; return (HsLit lit) }
127 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
128 ; return (HsPar expr') }
130 tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
131 ; returnM (HsSCC lbl expr') }
132 tcExpr (HsTickPragma info expr) res_ty
133 = do { expr' <- tcMonoExpr expr res_ty
134 ; returnM (HsTickPragma info expr') }
136 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
137 = do { expr' <- tcMonoExpr expr res_ty
138 ; return (HsCoreAnn lbl expr') }
140 tcExpr (HsOverLit lit) res_ty
141 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
142 ; return (HsOverLit lit') }
144 tcExpr (NegApp expr neg_expr) res_ty
145 = do { neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
146 (mkFunTy res_ty res_ty)
147 ; expr' <- tcMonoExpr expr res_ty
148 ; return (NegApp expr' neg_expr') }
150 tcExpr (HsIPVar ip) res_ty
151 = do { -- Implicit parameters must have a *tau-type* not a
152 -- type scheme. We enforce this by creating a fresh
153 -- type variable as its type. (Because res_ty may not
155 ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
156 ; co_fn <- tcSubExp ip_ty res_ty
157 ; (ip', inst) <- newIPDict (IPOccOrigin ip) ip ip_ty
159 ; return (mkHsWrap co_fn (HsIPVar ip')) }
161 tcExpr (HsApp e1 e2) res_ty
164 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
165 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
166 go lfun@(L loc fun) args
167 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
168 tcApp fun (length args) (tcArgs lfun args) res_ty
169 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
171 tcExpr (HsLam match) res_ty
172 = do { (co_fn, match') <- tcMatchLambda match res_ty
173 ; return (mkHsWrap co_fn (HsLam match')) }
175 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
176 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
178 -- Remember to extend the lexical type-variable environment
179 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (\ skol_tvs res_ty ->
180 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
181 tcPolyExprNC expr res_ty)
183 ; co_fn <- tcSubExp sig_tc_ty res_ty
184 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
186 tcExpr (HsType ty) res_ty
187 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
188 -- This is the syntax for type applications that I was planning
189 -- but there are difficulties (e.g. what order for type args)
190 -- so it's not enabled yet.
191 -- Can't eliminate it altogether from the parser, because the
192 -- same parser parses *patterns*.
196 %************************************************************************
198 Infix operators and sections
200 %************************************************************************
203 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
204 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
205 ; return (OpApp arg1' (L loc op') fix arg2') }
207 -- Left sections, equivalent to
214 -- We treat it as similar to the latter, so we don't
215 -- actually require the function to take two arguments
216 -- at all. For example, (x `not`) means (not x);
217 -- you get postfix operators! Not really Haskell 98
218 -- I suppose, but it's less work and kind of useful.
220 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
221 = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
222 ; return (SectionL arg1' (L loc op')) }
224 -- Right sections, equivalent to \ x -> x `op` expr, or
227 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
228 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
229 tcApp op 2 (tc_args arg1_ty') res_ty'
230 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
232 doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
233 <+> ptext SLIT("takes one argument")
234 tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
235 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
236 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
237 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
238 ; return (qtys', arg2') }
239 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
243 tcExpr (HsLet binds expr) res_ty
244 = do { (binds', expr') <- tcLocalBinds binds $
245 tcMonoExpr expr res_ty
246 ; return (HsLet binds' expr') }
248 tcExpr (HsCase scrut matches) exp_ty
249 = do { -- We used to typecheck the case alternatives first.
250 -- The case patterns tend to give good type info to use
251 -- when typechecking the scrutinee. For example
254 -- will report that map is applied to too few arguments
256 -- But now, in the GADT world, we need to typecheck the scrutinee
257 -- first, to get type info that may be refined in the case alternatives
258 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
261 ; traceTc (text "HsCase" <+> ppr scrut_ty)
262 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
263 ; return (HsCase scrut' matches') }
265 match_ctxt = MC { mc_what = CaseAlt,
268 tcExpr (HsIf pred b1 b2) res_ty
269 = do { pred' <- addErrCtxt (predCtxt pred) $
270 tcMonoExpr pred boolTy
271 ; b1' <- tcMonoExpr b1 res_ty
272 ; b2' <- tcMonoExpr b2 res_ty
273 ; return (HsIf pred' b1' b2') }
275 tcExpr (HsDo do_or_lc stmts body _) res_ty
276 = tcDoStmts do_or_lc stmts body res_ty
278 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
279 = do { elt_ty <- boxySplitListTy res_ty
280 ; exprs' <- mappM (tc_elt elt_ty) exprs
281 ; return (ExplicitList elt_ty exprs') }
283 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
285 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
286 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
287 ; exprs' <- mappM (tc_elt elt_ty) exprs
288 ; ifM (null exprs) (zapToMonotype elt_ty)
289 -- If there are no expressions in the comprehension
290 -- we must still fill in the box
291 -- (Not needed for [] and () becuase they happen
292 -- to parse as data constructors.)
293 ; return (ExplicitPArr elt_ty exprs') }
295 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
297 -- For tuples, take care to preserve rigidity
298 -- E.g. case (x,y) of ....
299 -- The scrutinee should have a rigid type if x,y do
300 -- The general scheme is the same as in tcIdApp
301 tcExpr (ExplicitTuple exprs boxity) res_ty
302 = do { tvs <- newBoxyTyVars [argTypeKind | e <- exprs]
303 ; let tup_tc = tupleTyCon boxity (length exprs)
304 tup_res_ty = mkTyConApp tup_tc (mkTyVarTys tvs)
305 ; arg_tys <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
306 ; exprs' <- tcPolyExprs exprs arg_tys
307 ; arg_tys' <- mapM refineBox arg_tys
308 ; co_fn <- tcFunResTy (tyConName tup_tc) (mkTyConApp tup_tc arg_tys') res_ty
309 ; return (mkHsWrap co_fn (ExplicitTuple exprs' boxity)) }
311 tcExpr (HsProc pat cmd) res_ty
312 = do { (pat', cmd') <- tcProc pat cmd res_ty
313 ; return (HsProc pat' cmd') }
315 tcExpr e@(HsArrApp _ _ _ _ _) _
316 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
317 ptext SLIT("was found where an expression was expected")])
319 tcExpr e@(HsArrForm _ _ _) _
320 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
321 ptext SLIT("was found where an expression was expected")])
324 %************************************************************************
326 Record construction and update
328 %************************************************************************
331 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
332 = do { data_con <- tcLookupDataCon con_name
334 -- Check for missing fields
335 ; checkMissingFields data_con rbinds
337 ; let arity = dataConSourceArity data_con
338 check_fields qtvs qtys arg_tys
339 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
340 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
341 ; qtys' <- mapM refineBoxToTau qtys
342 ; return (qtys', rbinds') }
343 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
344 -- filled, which is the invariant expected by tcIdApp
345 -- How could this not be the case? Consider a record construction
346 -- that does not mention all the fields.
348 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
350 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
352 -- The main complication with RecordUpd is that we need to explicitly
353 -- handle the *non-updated* fields. Consider:
355 -- data T a b = MkT1 { fa :: a, fb :: b }
356 -- | MkT2 { fa :: a, fc :: Int -> Int }
357 -- | MkT3 { fd :: a }
359 -- upd :: T a b -> c -> T a c
360 -- upd t x = t { fb = x}
362 -- The type signature on upd is correct (i.e. the result should not be (T a b))
363 -- because upd should be equivalent to:
365 -- upd t x = case t of
366 -- MkT1 p q -> MkT1 p x
367 -- MkT2 a b -> MkT2 p b
368 -- MkT3 d -> error ...
370 -- So we need to give a completely fresh type to the result record,
371 -- and then constrain it by the fields that are *not* updated ("p" above).
373 -- Note that because MkT3 doesn't contain all the fields being updated,
374 -- its RHS is simply an error, so it doesn't impose any type constraints
376 -- All this is done in STEP 4 below.
380 -- For record update we require that every constructor involved in the
381 -- update (i.e. that has all the specified fields) is "vanilla". I
382 -- don't know how to do the update otherwise.
385 tcExpr expr@(RecordUpd record_expr hrbinds@(HsRecordBinds rbinds) _ _ _) res_ty
387 -- Check that the field names are really field names
388 ASSERT( notNull rbinds )
390 field_names = map fst rbinds
392 mappM (tcLookupField . unLoc) field_names `thenM` \ sel_ids ->
393 -- The renamer has already checked that they
396 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
397 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
398 not (isRecordSelector sel_id) -- Excludes class ops
401 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
404 -- Figure out the tycon and data cons from the first field name
406 -- It's OK to use the non-tc splitters here (for a selector)
407 upd_field_lbls = recBindFields hrbinds
409 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
410 data_cons = tyConDataCons tycon -- it's not a field label
411 -- NB: for a data type family, the tycon is the instance tycon
413 relevant_cons = filter is_relevant data_cons
414 is_relevant con = all (`elem` dataConFieldLabels con) upd_field_lbls
418 -- Check that at least one constructor has all the named fields
419 -- i.e. has an empty set of bad fields returned by badFields
420 checkTc (not (null relevant_cons))
421 (badFieldsUpd hrbinds) `thenM_`
423 -- Check that all relevant data cons are vanilla. Doing record updates on
424 -- GADTs and/or existentials is more than my tiny brain can cope with today
425 checkTc (all isVanillaDataCon relevant_cons)
426 (nonVanillaUpd tycon) `thenM_`
429 -- Use the un-updated fields to find a vector of booleans saying
430 -- which type arguments must be the same in updatee and result.
432 -- WARNING: this code assumes that all data_cons in a common tycon
433 -- have FieldLabels abstracted over the same tyvars.
435 -- A constructor is only relevant to this process if
436 -- it contains *all* the fields that are being updated
437 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons -- A representative constructor
438 (con1_tyvars, theta, con1_arg_tys, con1_res_ty) = dataConSig con1
439 con1_flds = dataConFieldLabels con1
440 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
441 , not (fld `elem` upd_field_lbls) ]
443 is_common_tv tv = tv `elemVarSet` common_tyvars
445 mk_inst_ty tv result_inst_ty
446 | is_common_tv tv = returnM result_inst_ty -- Same as result type
447 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
449 ASSERT( null theta ) -- Vanilla datacon
450 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, result_inst_env) ->
451 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ scrut_inst_tys ->
453 -- STEP 3: Typecheck the update bindings.
454 -- Do this after checking for bad fields in case
455 -- there's a field that doesn't match the constructor.
457 result_ty = substTy result_inst_env con1_res_ty
458 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
460 tcSubExp result_ty res_ty `thenM` \ co_fn ->
461 tcRecordBinds con1 con1_arg_tys' hrbinds `thenM` \ rbinds' ->
463 -- STEP 5: Typecheck the expression to be updated
465 scrut_inst_env = zipTopTvSubst con1_tyvars scrut_inst_tys
466 scrut_ty = substTy scrut_inst_env con1_res_ty
467 -- This is one place where the isVanilla check is important
468 -- So that inst_tys matches the con1_tyvars
470 tcMonoExpr record_expr scrut_ty `thenM` \ record_expr' ->
472 -- STEP 6: Figure out the LIE we need.
473 -- We have to generate some dictionaries for the data type context,
474 -- since we are going to do pattern matching over the data cons.
476 -- What dictionaries do we need? The dataConStupidTheta tells us.
478 theta' = substTheta scrut_inst_env (dataConStupidTheta con1)
480 instStupidTheta RecordUpdOrigin theta' `thenM_`
482 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
483 let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
484 = WpCo $ mkTyConApp co_con scrut_inst_tys
487 scrut_ty = mkTyConApp tycon scrut_inst_tys -- Type of pattern, the result of the cast
490 returnM (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
491 relevant_cons scrut_inst_tys result_inst_tys))
495 %************************************************************************
497 Arithmetic sequences e.g. [a,b..]
498 and their parallel-array counterparts e.g. [: a,b.. :]
501 %************************************************************************
504 tcExpr (ArithSeq _ seq@(From expr)) res_ty
505 = do { elt_ty <- boxySplitListTy res_ty
506 ; expr' <- tcPolyExpr expr elt_ty
507 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
509 ; return (ArithSeq (HsVar enum_from) (From expr')) }
511 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
512 = do { elt_ty <- boxySplitListTy res_ty
513 ; expr1' <- tcPolyExpr expr1 elt_ty
514 ; expr2' <- tcPolyExpr expr2 elt_ty
515 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
516 elt_ty enumFromThenName
517 ; return (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
520 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
521 = do { elt_ty <- boxySplitListTy res_ty
522 ; expr1' <- tcPolyExpr expr1 elt_ty
523 ; expr2' <- tcPolyExpr expr2 elt_ty
524 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
525 elt_ty enumFromToName
526 ; return (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
528 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
529 = do { elt_ty <- boxySplitListTy res_ty
530 ; expr1' <- tcPolyExpr expr1 elt_ty
531 ; expr2' <- tcPolyExpr expr2 elt_ty
532 ; expr3' <- tcPolyExpr expr3 elt_ty
533 ; eft <- newMethodFromName (ArithSeqOrigin seq)
534 elt_ty enumFromThenToName
535 ; return (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
537 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
538 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
539 ; expr1' <- tcPolyExpr expr1 elt_ty
540 ; expr2' <- tcPolyExpr expr2 elt_ty
541 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
542 elt_ty enumFromToPName
543 ; return (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
545 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
546 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
547 ; expr1' <- tcPolyExpr expr1 elt_ty
548 ; expr2' <- tcPolyExpr expr2 elt_ty
549 ; expr3' <- tcPolyExpr expr3 elt_ty
550 ; eft <- newMethodFromName (PArrSeqOrigin seq)
551 elt_ty enumFromThenToPName
552 ; return (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
554 tcExpr (PArrSeq _ _) _
555 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
556 -- the parser shouldn't have generated it and the renamer shouldn't have
561 %************************************************************************
565 %************************************************************************
568 #ifdef GHCI /* Only if bootstrapped */
569 -- Rename excludes these cases otherwise
570 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
571 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
577 %************************************************************************
581 %************************************************************************
584 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
588 %************************************************************************
592 %************************************************************************
595 ---------------------------
596 tcApp :: HsExpr Name -- Function
597 -> Arity -- Number of args reqd
598 -> ArgChecker results
599 -> BoxyRhoType -- Result type
600 -> TcM (HsExpr TcId, results)
602 -- (tcFun fun n_args arg_checker res_ty)
603 -- The argument type checker, arg_checker, will be passed exactly n_args types
605 tcApp (HsVar fun_name) n_args arg_checker res_ty
606 = tcIdApp fun_name n_args arg_checker res_ty
608 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
609 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
610 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
611 ; arg_tys' <- mapM readFilledBox arg_boxes
612 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
613 ; return (fun', args') }
615 ---------------------------
616 tcIdApp :: Name -- Function
617 -> Arity -- Number of args reqd
618 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
619 -> BoxyRhoType -- Result type
620 -> TcM (HsExpr TcId, results)
622 -- Call (f e1 ... en) :: res_ty
623 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
624 -- (where k <= n; fres has the rest)
625 -- NB: if k < n then the function doesn't have enough args, and
626 -- presumably fres is a type variable that we are going to
627 -- instantiate with a function type
629 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
631 tcIdApp fun_name n_args arg_checker res_ty
632 = do { let orig = OccurrenceOf fun_name
633 ; (fun, fun_ty) <- lookupFun orig fun_name
635 -- Split up the function type
636 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
637 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
639 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
640 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
641 res_qtvs = exactTyVarsOfType fun_res_ty
642 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
643 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
644 k = length fun_arg_tys -- k <= n_args
645 n_missing_args = n_args - k -- Always >= 0
647 -- Match the result type of the function with the
648 -- result type of the context, to get an inital substitution
649 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
650 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
651 res_ty' = mkFunTys extra_arg_tys' res_ty
652 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
654 -- Typecheck the arguments!
655 -- Doing so will fill arg_qtvs and extra_arg_tys'
656 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
658 -- Strip boxes from the qtvs that have been filled in by the arg checking
659 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
661 -- Result subsumption
662 -- This fills in res_qtvs
663 ; let res_subst = zipOpenTvSubst qtvs qtys''
664 fun_res_ty'' = substTy res_subst fun_res_ty
665 res_ty'' = mkFunTys extra_arg_tys'' res_ty
666 ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
668 -- And pack up the results
669 -- By applying the coercion just to the *function* we can make
670 -- tcFun work nicely for OpApp and Sections too
671 ; fun' <- instFun orig fun res_subst tv_theta_prs
672 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
673 ; return (mkHsWrap co_fn' fun', args') }
676 Note [Silly type synonyms in smart-app]
677 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
678 When we call sripBoxyType, all of the boxes should be filled
679 in. But we need to be careful about type synonyms:
683 In the call (f x) we'll typecheck x, expecting it to have type
684 (T box). Usually that would fill in the box, but in this case not;
685 because 'a' is discarded by the silly type synonym T. So we must
686 use exactTyVarsOfType to figure out which type variables are free
687 in the argument type.
690 -- tcId is a specialisation of tcIdApp when there are no arguments
691 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
696 -> BoxyRhoType -- Result type
698 tcId orig fun_name res_ty
699 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
700 ; (fun, fun_ty) <- lookupFun orig fun_name
702 -- Split up the function type
703 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
704 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
705 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
706 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
708 -- Do the subsumption check wrt the result type
709 ; let res_subst = zipTopTvSubst qtvs qtv_tys
710 fun_tau' = substTy res_subst fun_tau
712 ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
714 -- And pack up the results
715 ; fun' <- instFun orig fun res_subst tv_theta_prs
716 ; return (mkHsWrap co_fn fun') }
718 -- Note [Push result type in]
720 -- Unify with expected result before (was: after) type-checking the args
721 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
722 -- This is when we might detect a too-few args situation.
723 -- (One can think of cases when the opposite order would give
724 -- a better error message.)
725 -- [March 2003: I'm experimenting with putting this first. Here's an
726 -- example where it actually makes a real difference
727 -- class C t a b | t a -> b
728 -- instance C Char a Bool
730 -- data P t a = forall b. (C t a b) => MkP b
731 -- data Q t = MkQ (forall a. P t a)
734 -- f1 = MkQ (MkP True)
735 -- f2 = MkQ (MkP True :: forall a. P Char a)
737 -- With the change, f1 will type-check, because the 'Char' info from
738 -- the signature is propagated into MkQ's argument. With the check
739 -- in the other order, the extra signature in f2 is reqd.]
741 ---------------------------
742 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
743 -- Typecheck a syntax operator, checking that it has the specified type
744 -- The operator is always a variable at this stage (i.e. renamer output)
745 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
746 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
748 ---------------------------
749 instFun :: InstOrigin
751 -> TvSubst -- The instantiating substitution
752 -> [([TyVar], ThetaType)] -- Stuff to instantiate
755 instFun orig fun subst []
756 = return fun -- Common short cut
758 instFun orig fun subst tv_theta_prs
759 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
761 -- Make two ad-hoc checks
762 ; doStupidChecks fun ty_theta_prs'
764 -- Now do normal instantiation
765 ; go True fun ty_theta_prs' }
767 subst_pr (tvs, theta)
768 = (substTyVars subst tvs, substTheta subst theta)
770 go _ fun [] = return fun
772 go True (HsVar fun_id) ((tys,theta) : prs)
773 | want_method_inst theta
774 = do { meth_id <- newMethodWithGivenTy orig fun_id tys
775 ; go False (HsVar meth_id) prs }
776 -- Go round with 'False' to prevent further use
777 -- of newMethod: see Note [Multiple instantiation]
779 go _ fun ((tys, theta) : prs)
780 = do { co_fn <- instCall orig tys theta
781 ; go False (HsWrap co_fn fun) prs }
783 -- See Note [No method sharing]
784 want_method_inst theta = not (null theta) -- Overloaded
785 && not opt_NoMethodSharing
788 Note [Multiple instantiation]
789 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
790 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
791 For example, consider
792 f :: forall a. Eq a => forall b. Ord b => a -> b
793 At a call to f, at say [Int, Bool], it's tempting to translate the call to
797 f_m1 :: forall b. Ord b => Int -> b
801 f_m2 = f_m1 Bool dOrdBool
803 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
804 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
806 But it's entirely possible that f_m2 will continue to float out, because it
807 mentions no type variables. Result, f_m1 isn't in scope.
809 Here's a concrete example that does this (test tc200):
812 f :: Eq b => b -> a -> Int
813 baz :: Eq a => Int -> a -> Int
818 Current solution: only do the "method sharing" thing for the first type/dict
819 application, not for the iterated ones. A horribly subtle point.
821 Note [No method sharing]
822 ~~~~~~~~~~~~~~~~~~~~~~~~
823 The -fno-method-sharing flag controls what happens so far as the LIE
824 is concerned. The default case is that for an overloaded function we
825 generate a "method" Id, and add the Method Inst to the LIE. So you get
828 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
829 If you specify -fno-method-sharing, the dictionary application
830 isn't shared, so we get
832 f = /\a (d:Num a) (x:a) -> (+) a d x x
833 This gets a bit less sharing, but
834 a) it's better for RULEs involving overloaded functions
835 b) perhaps fewer separated lambdas
839 tcArgs implements a left-to-right order, which goes beyond what is described in the
840 impredicative type inference paper. In particular, it allows
842 where runST :: (forall s. ST s a) -> a
843 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
844 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
845 before checking foo. The left-to-right order really helps here.
848 tcArgs :: LHsExpr Name -- The function (for error messages)
849 -> [LHsExpr Name] -- Actual args
850 -> ArgChecker [LHsExpr TcId]
852 type ArgChecker results
853 = [TyVar] -> [TcSigmaType] -- Current instantiation
854 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
855 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
857 tcArgs fun args qtvs qtys arg_tys
858 = go 1 qtys args arg_tys
860 go n qtys [] [] = return (qtys, [])
861 go n qtys (arg:args) (arg_ty:arg_tys)
862 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
863 ; qtys' <- mapM refineBox qtys -- Exploit new info
864 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
865 ; return (qtys'', arg':args') }
866 go n qtys args arg_tys = panic "tcArgs"
868 tcArg :: LHsExpr Name -- The function
869 -> Int -- and arg number (for error messages)
871 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
873 -> TcM (LHsExpr TcId) -- Resulting argument
874 tcArg fun arg_no arg qtvs qtys ty
875 = addErrCtxt (funAppCtxt fun arg arg_no) $
876 tcPolyExprNC arg (substTyWith qtvs qtys ty)
882 Nasty check to ensure that tagToEnum# is applied to a type that is an
883 enumeration TyCon. Unification may refine the type later, but this
884 check won't see that, alas. It's crude but it works.
886 Here's are two cases that should fail
888 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
891 g = tagToEnum# 0 -- Int is not an enumeration
895 doStupidChecks :: HsExpr TcId
896 -> [([TcType], ThetaType)]
898 -- Check two tiresome and ad-hoc cases
899 -- (a) the "stupid theta" for a data con; add the constraints
900 -- from the "stupid theta" of a data constructor (sigh)
901 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
903 doStupidChecks (HsVar fun_id) ((tys,_):_)
904 | Just con <- isDataConId_maybe fun_id -- (a)
905 = addDataConStupidTheta con tys
907 | fun_id `hasKey` tagToEnumKey -- (b)
908 = do { tys' <- zonkTcTypes tys
909 ; checkTc (ok tys') (tagToEnumError tys')
913 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
914 Just (tc,_) -> isEnumerationTyCon tc
917 doStupidChecks fun tv_theta_prs
918 = return () -- The common case
922 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
923 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
924 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
926 at_type | null tys = empty -- Probably never happens
927 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
930 %************************************************************************
932 \subsection{@tcId@ typechecks an identifier occurrence}
934 %************************************************************************
937 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
938 lookupFun orig id_name
939 = do { thing <- tcLookup id_name
941 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
943 wrap_id = dataConWrapId con
946 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
947 | otherwise -> return (HsVar id, idType id)
948 -- A global cannot possibly be ill-staged
949 -- nor does it need the 'lifting' treatment
951 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
952 -> do { thLocalId orig id ty lvl
954 Nothing -> return (HsVar id, ty) -- Wobbly, or no free vars
955 Just co -> return (mkHsWrap co (HsVar id), ty) }
957 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
960 #ifndef GHCI /* GHCI and TH is off */
961 --------------------------------------
962 -- thLocalId : Check for cross-stage lifting
963 thLocalId orig id id_ty th_bind_lvl
966 #else /* GHCI and TH is on */
967 thLocalId orig id id_ty th_bind_lvl
968 = do { use_stage <- getStage -- TH case
970 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
971 -> thBrackId orig id ps_var lie_var
972 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
976 --------------------------------------
977 thBrackId orig id ps_var lie_var
978 | isExternalName id_name
979 = -- Top-level identifiers in this module,
980 -- (which have External Names)
981 -- are just like the imported case:
982 -- no need for the 'lifting' treatment
983 -- E.g. this is fine:
986 -- But we do need to put f into the keep-alive
987 -- set, because after desugaring the code will
988 -- only mention f's *name*, not f itself.
989 do { keepAliveTc id_name; return id }
992 = -- Nested identifiers, such as 'x' in
993 -- E.g. \x -> [| h x |]
994 -- We must behave as if the reference to x was
996 -- We use 'x' itself as the splice proxy, used by
997 -- the desugarer to stitch it all back together.
998 -- If 'x' occurs many times we may get many identical
999 -- bindings of the same splice proxy, but that doesn't
1000 -- matter, although it's a mite untidy.
1001 do { let id_ty = idType id
1002 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1003 -- If x is polymorphic, its occurrence sites might
1004 -- have different instantiations, so we can't use plain
1005 -- 'x' as the splice proxy name. I don't know how to
1006 -- solve this, and it's probably unimportant, so I'm
1007 -- just going to flag an error for now
1009 ; id_ty' <- zapToMonotype id_ty
1010 -- The id_ty might have an OpenTypeKind, but we
1011 -- can't instantiate the Lift class at that kind,
1012 -- so we zap it to a LiftedTypeKind monotype
1013 -- C.f. the call in TcPat.newLitInst
1015 ; setLIEVar lie_var $ do
1016 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
1017 -- Put the 'lift' constraint into the right LIE
1019 -- Update the pending splices
1020 ; ps <- readMutVar ps_var
1021 ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1030 %************************************************************************
1032 \subsection{Record bindings}
1034 %************************************************************************
1036 Game plan for record bindings
1037 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1038 1. Find the TyCon for the bindings, from the first field label.
1040 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1042 For each binding field = value
1044 3. Instantiate the field type (from the field label) using the type
1047 4 Type check the value using tcArg, passing the field type as
1048 the expected argument type.
1050 This extends OK when the field types are universally quantified.
1056 -> [TcType] -- Expected type for each field
1057 -> HsRecordBinds Name
1058 -> TcM (HsRecordBinds TcId)
1060 tcRecordBinds data_con arg_tys (HsRecordBinds rbinds)
1061 = do { mb_binds <- mappM do_bind rbinds
1062 ; return (HsRecordBinds (catMaybes mb_binds)) }
1064 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1065 do_bind (L loc field_lbl, rhs)
1066 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1067 = addErrCtxt (fieldCtxt field_lbl) $
1068 do { rhs' <- tcPolyExprNC rhs field_ty
1069 ; sel_id <- tcLookupField field_lbl
1070 ; ASSERT( isRecordSelector sel_id )
1071 return (Just (L loc sel_id, rhs')) }
1073 = do { addErrTc (badFieldCon data_con field_lbl)
1076 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1077 checkMissingFields data_con rbinds
1078 | null field_labels -- Not declared as a record;
1079 -- But C{} is still valid if no strict fields
1080 = if any isMarkedStrict field_strs then
1081 -- Illegal if any arg is strict
1082 addErrTc (missingStrictFields data_con [])
1086 | otherwise -- A record
1087 = checkM (null missing_s_fields)
1088 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1090 doptM Opt_WarnMissingFields `thenM` \ warn ->
1091 checkM (not (warn && notNull missing_ns_fields))
1092 (warnTc True (missingFields data_con missing_ns_fields))
1096 = [ fl | (fl, str) <- field_info,
1098 not (fl `elem` field_names_used)
1101 = [ fl | (fl, str) <- field_info,
1102 not (isMarkedStrict str),
1103 not (fl `elem` field_names_used)
1106 field_names_used = recBindFields rbinds
1107 field_labels = dataConFieldLabels data_con
1109 field_info = zipEqual "missingFields"
1113 field_strs = dataConStrictMarks data_con
1116 %************************************************************************
1118 \subsection{Errors and contexts}
1120 %************************************************************************
1122 Boring and alphabetical:
1125 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1128 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1130 fieldCtxt field_name
1131 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1133 funAppCtxt fun arg arg_no
1134 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1135 quotes (ppr fun) <> text ", namely"])
1136 4 (quotes (ppr arg))
1139 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1142 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type")
1143 <+> quotes (pprSourceTyCon tycon)
1144 <+> ptext SLIT("is not (yet) supported"),
1145 ptext SLIT("Use pattern-matching instead")]
1147 = hang (ptext SLIT("No constructor has all these fields:"))
1148 4 (pprQuotedList (recBindFields rbinds))
1150 naughtyRecordSel sel_id
1151 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1152 ptext SLIT("as a function due to escaped type variables") $$
1153 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1156 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1158 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1159 missingStrictFields con fields
1162 rest | null fields = empty -- Happens for non-record constructors
1163 -- with strict fields
1164 | otherwise = colon <+> pprWithCommas ppr fields
1166 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1167 ptext SLIT("does not have the required strict field(s)")
1169 missingFields :: DataCon -> [FieldLabel] -> SDoc
1170 missingFields con fields
1171 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1172 <+> pprWithCommas ppr fields
1174 -- callCtxt fun args = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1177 polySpliceErr :: Id -> SDoc
1179 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)