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 relevant_cons = filter is_relevant data_cons
412 is_relevant con = all (`elem` dataConFieldLabels con) upd_field_lbls
416 -- Check that at least one constructor has all the named fields
417 -- i.e. has an empty set of bad fields returned by badFields
418 checkTc (not (null relevant_cons))
419 (badFieldsUpd hrbinds) `thenM_`
421 -- Check that all relevant data cons are vanilla. Doing record updates on
422 -- GADTs and/or existentials is more than my tiny brain can cope with today
423 checkTc (all isVanillaDataCon relevant_cons)
424 (nonVanillaUpd tycon) `thenM_`
427 -- Use the un-updated fields to find a vector of booleans saying
428 -- which type arguments must be the same in updatee and result.
430 -- WARNING: this code assumes that all data_cons in a common tycon
431 -- have FieldLabels abstracted over the same tyvars.
433 -- A constructor is only relevant to this process if
434 -- it contains *all* the fields that are being updated
435 con1 = head relevant_cons -- A representative constructor
436 con1_tyvars = dataConUnivTyVars con1
437 con1_flds = dataConFieldLabels con1
438 con1_arg_tys = dataConOrigArgTys con1
439 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
440 , not (fld `elem` upd_field_lbls) ]
442 is_common_tv tv = tv `elemVarSet` common_tyvars
444 mk_inst_ty tv result_inst_ty
445 | is_common_tv tv = returnM result_inst_ty -- Same as result type
446 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
448 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
449 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ inst_tys ->
452 -- Typecheck the update bindings.
453 -- (Do this after checking for bad fields in case there's a field that
454 -- doesn't match the constructor.)
456 result_record_ty = mkTyConApp tycon result_inst_tys
457 con1_arg_tys' = map (substTy inst_env) con1_arg_tys
459 tcSubExp result_record_ty res_ty `thenM` \ co_fn ->
460 tcRecordBinds con1 con1_arg_tys' hrbinds `thenM` \ rbinds' ->
463 -- Typecheck the expression to be updated
465 record_ty = ASSERT( length inst_tys == tyConArity tycon )
466 mkTyConApp tycon inst_tys
467 -- This is one place where the isVanilla check is important
468 -- So that inst_tys matches the tycon
470 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
473 -- Figure out the LIE we need. We have to generate some
474 -- dictionaries for the data type context, since we are going to
475 -- do pattern matching over the data cons.
477 -- What dictionaries do we need? The tyConStupidTheta tells us.
479 theta' = substTheta inst_env (tyConStupidTheta tycon)
481 instStupidTheta RecordUpdOrigin theta' `thenM_`
484 returnM (mkHsWrap co_fn (RecordUpd record_expr' rbinds' record_ty result_record_ty))
488 %************************************************************************
490 Arithmetic sequences e.g. [a,b..]
491 and their parallel-array counterparts e.g. [: a,b.. :]
494 %************************************************************************
497 tcExpr (ArithSeq _ seq@(From expr)) res_ty
498 = do { elt_ty <- boxySplitListTy res_ty
499 ; expr' <- tcPolyExpr expr elt_ty
500 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
502 ; return (ArithSeq (HsVar enum_from) (From expr')) }
504 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
505 = do { elt_ty <- boxySplitListTy res_ty
506 ; expr1' <- tcPolyExpr expr1 elt_ty
507 ; expr2' <- tcPolyExpr expr2 elt_ty
508 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
509 elt_ty enumFromThenName
510 ; return (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
513 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
514 = do { elt_ty <- boxySplitListTy res_ty
515 ; expr1' <- tcPolyExpr expr1 elt_ty
516 ; expr2' <- tcPolyExpr expr2 elt_ty
517 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
518 elt_ty enumFromToName
519 ; return (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
521 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
522 = do { elt_ty <- boxySplitListTy res_ty
523 ; expr1' <- tcPolyExpr expr1 elt_ty
524 ; expr2' <- tcPolyExpr expr2 elt_ty
525 ; expr3' <- tcPolyExpr expr3 elt_ty
526 ; eft <- newMethodFromName (ArithSeqOrigin seq)
527 elt_ty enumFromThenToName
528 ; return (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
530 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
531 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
532 ; expr1' <- tcPolyExpr expr1 elt_ty
533 ; expr2' <- tcPolyExpr expr2 elt_ty
534 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
535 elt_ty enumFromToPName
536 ; return (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
538 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
539 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
540 ; expr1' <- tcPolyExpr expr1 elt_ty
541 ; expr2' <- tcPolyExpr expr2 elt_ty
542 ; expr3' <- tcPolyExpr expr3 elt_ty
543 ; eft <- newMethodFromName (PArrSeqOrigin seq)
544 elt_ty enumFromThenToPName
545 ; return (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
547 tcExpr (PArrSeq _ _) _
548 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
549 -- the parser shouldn't have generated it and the renamer shouldn't have
554 %************************************************************************
558 %************************************************************************
561 #ifdef GHCI /* Only if bootstrapped */
562 -- Rename excludes these cases otherwise
563 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
564 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
570 %************************************************************************
574 %************************************************************************
577 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
581 %************************************************************************
585 %************************************************************************
588 ---------------------------
589 tcApp :: HsExpr Name -- Function
590 -> Arity -- Number of args reqd
591 -> ArgChecker results
592 -> BoxyRhoType -- Result type
593 -> TcM (HsExpr TcId, results)
595 -- (tcFun fun n_args arg_checker res_ty)
596 -- The argument type checker, arg_checker, will be passed exactly n_args types
598 tcApp (HsVar fun_name) n_args arg_checker res_ty
599 = tcIdApp fun_name n_args arg_checker res_ty
601 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
602 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
603 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
604 ; arg_tys' <- mapM readFilledBox arg_boxes
605 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
606 ; return (fun', args') }
608 ---------------------------
609 tcIdApp :: Name -- Function
610 -> Arity -- Number of args reqd
611 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
612 -> BoxyRhoType -- Result type
613 -> TcM (HsExpr TcId, results)
615 -- Call (f e1 ... en) :: res_ty
616 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
617 -- (where k <= n; fres has the rest)
618 -- NB: if k < n then the function doesn't have enough args, and
619 -- presumably fres is a type variable that we are going to
620 -- instantiate with a function type
622 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
624 tcIdApp fun_name n_args arg_checker res_ty
625 = do { let orig = OccurrenceOf fun_name
626 ; (fun, fun_ty) <- lookupFun orig fun_name
628 -- Split up the function type
629 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
630 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
632 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
633 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
634 res_qtvs = exactTyVarsOfType fun_res_ty
635 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
636 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
637 k = length fun_arg_tys -- k <= n_args
638 n_missing_args = n_args - k -- Always >= 0
640 -- Match the result type of the function with the
641 -- result type of the context, to get an inital substitution
642 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
643 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
644 res_ty' = mkFunTys extra_arg_tys' res_ty
645 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
647 -- Typecheck the arguments!
648 -- Doing so will fill arg_qtvs and extra_arg_tys'
649 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
651 -- Strip boxes from the qtvs that have been filled in by the arg checking
652 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
654 -- Result subsumption
655 -- This fills in res_qtvs
656 ; let res_subst = zipOpenTvSubst qtvs qtys''
657 fun_res_ty'' = substTy res_subst fun_res_ty
658 res_ty'' = mkFunTys extra_arg_tys'' res_ty
659 ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
661 -- And pack up the results
662 -- By applying the coercion just to the *function* we can make
663 -- tcFun work nicely for OpApp and Sections too
664 ; fun' <- instFun orig fun res_subst tv_theta_prs
665 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
666 ; return (mkHsWrap co_fn' fun', args') }
669 Note [Silly type synonyms in smart-app]
670 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
671 When we call sripBoxyType, all of the boxes should be filled
672 in. But we need to be careful about type synonyms:
676 In the call (f x) we'll typecheck x, expecting it to have type
677 (T box). Usually that would fill in the box, but in this case not;
678 because 'a' is discarded by the silly type synonym T. So we must
679 use exactTyVarsOfType to figure out which type variables are free
680 in the argument type.
683 -- tcId is a specialisation of tcIdApp when there are no arguments
684 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
689 -> BoxyRhoType -- Result type
691 tcId orig fun_name res_ty
692 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
693 ; (fun, fun_ty) <- lookupFun orig fun_name
695 -- Split up the function type
696 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
697 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
698 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
699 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
701 -- Do the subsumption check wrt the result type
702 ; let res_subst = zipTopTvSubst qtvs qtv_tys
703 fun_tau' = substTy res_subst fun_tau
705 ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
707 -- And pack up the results
708 ; fun' <- instFun orig fun res_subst tv_theta_prs
709 ; return (mkHsWrap co_fn fun') }
711 -- Note [Push result type in]
713 -- Unify with expected result before (was: after) type-checking the args
714 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
715 -- This is when we might detect a too-few args situation.
716 -- (One can think of cases when the opposite order would give
717 -- a better error message.)
718 -- [March 2003: I'm experimenting with putting this first. Here's an
719 -- example where it actually makes a real difference
720 -- class C t a b | t a -> b
721 -- instance C Char a Bool
723 -- data P t a = forall b. (C t a b) => MkP b
724 -- data Q t = MkQ (forall a. P t a)
727 -- f1 = MkQ (MkP True)
728 -- f2 = MkQ (MkP True :: forall a. P Char a)
730 -- With the change, f1 will type-check, because the 'Char' info from
731 -- the signature is propagated into MkQ's argument. With the check
732 -- in the other order, the extra signature in f2 is reqd.]
734 ---------------------------
735 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
736 -- Typecheck a syntax operator, checking that it has the specified type
737 -- The operator is always a variable at this stage (i.e. renamer output)
738 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
739 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
741 ---------------------------
742 instFun :: InstOrigin
744 -> TvSubst -- The instantiating substitution
745 -> [([TyVar], ThetaType)] -- Stuff to instantiate
748 instFun orig fun subst []
749 = return fun -- Common short cut
751 instFun orig fun subst tv_theta_prs
752 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
754 -- Make two ad-hoc checks
755 ; doStupidChecks fun ty_theta_prs'
757 -- Now do normal instantiation
758 ; go True fun ty_theta_prs' }
760 subst_pr (tvs, theta)
761 = (substTyVars subst tvs, substTheta subst theta)
763 go _ fun [] = return fun
765 go True (HsVar fun_id) ((tys,theta) : prs)
766 | want_method_inst theta
767 = do { meth_id <- newMethodWithGivenTy orig fun_id tys
768 ; go False (HsVar meth_id) prs }
769 -- Go round with 'False' to prevent further use
770 -- of newMethod: see Note [Multiple instantiation]
772 go _ fun ((tys, theta) : prs)
773 = do { co_fn <- instCall orig tys theta
774 ; go False (HsWrap co_fn fun) prs }
776 -- See Note [No method sharing]
777 want_method_inst theta = not (null theta) -- Overloaded
778 && not opt_NoMethodSharing
781 Note [Multiple instantiation]
782 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
783 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
784 For example, consider
785 f :: forall a. Eq a => forall b. Ord b => a -> b
786 At a call to f, at say [Int, Bool], it's tempting to translate the call to
790 f_m1 :: forall b. Ord b => Int -> b
794 f_m2 = f_m1 Bool dOrdBool
796 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
797 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
799 But it's entirely possible that f_m2 will continue to float out, because it
800 mentions no type variables. Result, f_m1 isn't in scope.
802 Here's a concrete example that does this (test tc200):
805 f :: Eq b => b -> a -> Int
806 baz :: Eq a => Int -> a -> Int
811 Current solution: only do the "method sharing" thing for the first type/dict
812 application, not for the iterated ones. A horribly subtle point.
814 Note [No method sharing]
815 ~~~~~~~~~~~~~~~~~~~~~~~~
816 The -fno-method-sharing flag controls what happens so far as the LIE
817 is concerned. The default case is that for an overloaded function we
818 generate a "method" Id, and add the Method Inst to the LIE. So you get
821 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
822 If you specify -fno-method-sharing, the dictionary application
823 isn't shared, so we get
825 f = /\a (d:Num a) (x:a) -> (+) a d x x
826 This gets a bit less sharing, but
827 a) it's better for RULEs involving overloaded functions
828 b) perhaps fewer separated lambdas
832 tcArgs implements a left-to-right order, which goes beyond what is described in the
833 impredicative type inference paper. In particular, it allows
835 where runST :: (forall s. ST s a) -> a
836 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
837 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
838 before checking foo. The left-to-right order really helps here.
841 tcArgs :: LHsExpr Name -- The function (for error messages)
842 -> [LHsExpr Name] -- Actual args
843 -> ArgChecker [LHsExpr TcId]
845 type ArgChecker results
846 = [TyVar] -> [TcSigmaType] -- Current instantiation
847 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
848 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
850 tcArgs fun args qtvs qtys arg_tys
851 = go 1 qtys args arg_tys
853 go n qtys [] [] = return (qtys, [])
854 go n qtys (arg:args) (arg_ty:arg_tys)
855 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
856 ; qtys' <- mapM refineBox qtys -- Exploit new info
857 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
858 ; return (qtys'', arg':args') }
860 tcArg :: LHsExpr Name -- The function
861 -> Int -- and arg number (for error messages)
863 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
865 -> TcM (LHsExpr TcId) -- Resulting argument
866 tcArg fun arg_no arg qtvs qtys ty
867 = addErrCtxt (funAppCtxt fun arg arg_no) $
868 tcPolyExprNC arg (substTyWith qtvs qtys ty)
874 Nasty check to ensure that tagToEnum# is applied to a type that is an
875 enumeration TyCon. Unification may refine the type later, but this
876 check won't see that, alas. It's crude but it works.
878 Here's are two cases that should fail
880 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
883 g = tagToEnum# 0 -- Int is not an enumeration
887 doStupidChecks :: HsExpr TcId
888 -> [([TcType], ThetaType)]
890 -- Check two tiresome and ad-hoc cases
891 -- (a) the "stupid theta" for a data con; add the constraints
892 -- from the "stupid theta" of a data constructor (sigh)
893 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
895 doStupidChecks (HsVar fun_id) ((tys,_):_)
896 | Just con <- isDataConId_maybe fun_id -- (a)
897 = addDataConStupidTheta con tys
899 | fun_id `hasKey` tagToEnumKey -- (b)
900 = do { tys' <- zonkTcTypes tys
901 ; checkTc (ok tys') (tagToEnumError tys')
905 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
906 Just (tc,_) -> isEnumerationTyCon tc
909 doStupidChecks fun tv_theta_prs
910 = return () -- The common case
914 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
915 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
916 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
918 at_type | null tys = empty -- Probably never happens
919 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
922 %************************************************************************
924 \subsection{@tcId@ typechecks an identifier occurrence}
926 %************************************************************************
929 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
930 lookupFun orig id_name
931 = do { thing <- tcLookup id_name
933 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
935 wrap_id = dataConWrapId con
938 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
939 | otherwise -> return (HsVar id, idType id)
940 -- A global cannot possibly be ill-staged
941 -- nor does it need the 'lifting' treatment
943 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
944 -> do { thLocalId orig id ty lvl
946 Nothing -> return (HsVar id, ty) -- Wobbly, or no free vars
947 Just co -> return (mkHsWrap co (HsVar id), ty) }
949 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
952 #ifndef GHCI /* GHCI and TH is off */
953 --------------------------------------
954 -- thLocalId : Check for cross-stage lifting
955 thLocalId orig id id_ty th_bind_lvl
958 #else /* GHCI and TH is on */
959 thLocalId orig id id_ty th_bind_lvl
960 = do { use_stage <- getStage -- TH case
962 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
963 -> thBrackId orig id ps_var lie_var
964 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
968 --------------------------------------
969 thBrackId orig id ps_var lie_var
970 | isExternalName id_name
971 = -- Top-level identifiers in this module,
972 -- (which have External Names)
973 -- are just like the imported case:
974 -- no need for the 'lifting' treatment
975 -- E.g. this is fine:
978 -- But we do need to put f into the keep-alive
979 -- set, because after desugaring the code will
980 -- only mention f's *name*, not f itself.
981 do { keepAliveTc id_name; return id }
984 = -- Nested identifiers, such as 'x' in
985 -- E.g. \x -> [| h x |]
986 -- We must behave as if the reference to x was
988 -- We use 'x' itself as the splice proxy, used by
989 -- the desugarer to stitch it all back together.
990 -- If 'x' occurs many times we may get many identical
991 -- bindings of the same splice proxy, but that doesn't
992 -- matter, although it's a mite untidy.
993 do { let id_ty = idType id
994 ; checkTc (isTauTy id_ty) (polySpliceErr id)
995 -- If x is polymorphic, its occurrence sites might
996 -- have different instantiations, so we can't use plain
997 -- 'x' as the splice proxy name. I don't know how to
998 -- solve this, and it's probably unimportant, so I'm
999 -- just going to flag an error for now
1001 ; id_ty' <- zapToMonotype id_ty
1002 -- The id_ty might have an OpenTypeKind, but we
1003 -- can't instantiate the Lift class at that kind,
1004 -- so we zap it to a LiftedTypeKind monotype
1005 -- C.f. the call in TcPat.newLitInst
1007 ; setLIEVar lie_var $ do
1008 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
1009 -- Put the 'lift' constraint into the right LIE
1011 -- Update the pending splices
1012 ; ps <- readMutVar ps_var
1013 ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1022 %************************************************************************
1024 \subsection{Record bindings}
1026 %************************************************************************
1028 Game plan for record bindings
1029 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1030 1. Find the TyCon for the bindings, from the first field label.
1032 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1034 For each binding field = value
1036 3. Instantiate the field type (from the field label) using the type
1039 4 Type check the value using tcArg, passing the field type as
1040 the expected argument type.
1042 This extends OK when the field types are universally quantified.
1048 -> [TcType] -- Expected type for each field
1049 -> HsRecordBinds Name
1050 -> TcM (HsRecordBinds TcId)
1052 tcRecordBinds data_con arg_tys (HsRecordBinds rbinds)
1053 = do { mb_binds <- mappM do_bind rbinds
1054 ; return (HsRecordBinds (catMaybes mb_binds)) }
1056 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1057 do_bind (L loc field_lbl, rhs)
1058 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1059 = addErrCtxt (fieldCtxt field_lbl) $
1060 do { rhs' <- tcPolyExprNC rhs field_ty
1061 ; sel_id <- tcLookupField field_lbl
1062 ; ASSERT( isRecordSelector sel_id )
1063 return (Just (L loc sel_id, rhs')) }
1065 = do { addErrTc (badFieldCon data_con field_lbl)
1068 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1069 checkMissingFields data_con rbinds
1070 | null field_labels -- Not declared as a record;
1071 -- But C{} is still valid if no strict fields
1072 = if any isMarkedStrict field_strs then
1073 -- Illegal if any arg is strict
1074 addErrTc (missingStrictFields data_con [])
1078 | otherwise -- A record
1079 = checkM (null missing_s_fields)
1080 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1082 doptM Opt_WarnMissingFields `thenM` \ warn ->
1083 checkM (not (warn && notNull missing_ns_fields))
1084 (warnTc True (missingFields data_con missing_ns_fields))
1088 = [ fl | (fl, str) <- field_info,
1090 not (fl `elem` field_names_used)
1093 = [ fl | (fl, str) <- field_info,
1094 not (isMarkedStrict str),
1095 not (fl `elem` field_names_used)
1098 field_names_used = recBindFields rbinds
1099 field_labels = dataConFieldLabels data_con
1101 field_info = zipEqual "missingFields"
1105 field_strs = dataConStrictMarks data_con
1108 %************************************************************************
1110 \subsection{Errors and contexts}
1112 %************************************************************************
1114 Boring and alphabetical:
1117 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1120 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1122 fieldCtxt field_name
1123 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1125 funAppCtxt fun arg arg_no
1126 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1127 quotes (ppr fun) <> text ", namely"])
1128 4 (quotes (ppr arg))
1131 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1134 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type") <+> quotes (ppr tycon)
1135 <+> ptext SLIT("is not (yet) supported"),
1136 ptext SLIT("Use pattern-matching instead")]
1138 = hang (ptext SLIT("No constructor has all these fields:"))
1139 4 (pprQuotedList (recBindFields rbinds))
1141 naughtyRecordSel sel_id
1142 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1143 ptext SLIT("as a function due to escaped type variables") $$
1144 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1147 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1149 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1150 missingStrictFields con fields
1153 rest | null fields = empty -- Happens for non-record constructors
1154 -- with strict fields
1155 | otherwise = colon <+> pprWithCommas ppr fields
1157 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1158 ptext SLIT("does not have the required strict field(s)")
1160 missingFields :: DataCon -> [FieldLabel] -> SDoc
1161 missingFields con fields
1162 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1163 <+> pprWithCommas ppr fields
1166 = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1169 polySpliceErr :: Id -> SDoc
1171 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)