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, tcMonoExpr, tcInferRho, tcSyntaxOp) where
17 #include "HsVersions.h"
19 #ifdef GHCI /* Only if bootstrapped */
20 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
21 import qualified DsMeta
38 import TcIface ( checkWiredInTyCon )
62 %************************************************************************
64 \subsection{Main wrappers}
66 %************************************************************************
69 tcPolyExpr, tcPolyExprNC
70 :: LHsExpr Name -- Expession to type check
71 -> BoxySigmaType -- Expected type (could be a polytpye)
72 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
74 -- tcPolyExpr is a convenient place (frequent but not too frequent) place
75 -- to add context information.
76 -- The NC version does not do so, usually because the caller wants
79 tcPolyExpr expr res_ty
80 = addErrCtxt (exprCtxt (unLoc expr)) $
81 (do {traceTc (text "tcPolyExpr") ; tcPolyExprNC expr res_ty })
83 tcPolyExprNC expr res_ty
85 = do { traceTc (text "tcPolyExprNC" <+> ppr res_ty)
86 ; (gen_fn, expr') <- tcGen res_ty emptyVarSet (\_ -> tcPolyExprNC expr)
87 -- Note the recursive call to tcPolyExpr, because the
88 -- type may have multiple layers of for-alls
89 -- E.g. forall a. Eq a => forall b. Ord b => ....
90 ; return (mkLHsWrap gen_fn expr') }
93 = tcMonoExpr expr res_ty
96 tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
97 tcPolyExprs [] [] = returnM []
98 tcPolyExprs (expr:exprs) (ty:tys)
99 = do { expr' <- tcPolyExpr expr ty
100 ; exprs' <- tcPolyExprs exprs tys
101 ; returnM (expr':exprs') }
102 tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
105 tcMonoExpr :: LHsExpr Name -- Expression to type check
106 -> BoxyRhoType -- Expected type (could be a type variable)
107 -- Definitely no foralls at the top
108 -- Can contain boxes, which will be filled in
109 -> TcM (LHsExpr TcId)
111 tcMonoExpr (L loc expr) res_ty
112 = ASSERT( not (isSigmaTy res_ty) )
114 do { expr' <- tcExpr expr res_ty
115 ; return (L loc expr') }
118 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
119 tcInferRho expr = tcInfer (tcMonoExpr expr)
123 %************************************************************************
125 tcExpr: the main expression typechecker
127 %************************************************************************
130 tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
131 tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
133 tcExpr (HsLit lit) res_ty = do { let lit_ty = hsLitType lit
134 ; coi <- boxyUnify lit_ty res_ty
135 ; return $ mkHsWrapCoI coi (HsLit lit)
138 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
139 ; return (HsPar expr') }
141 tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
142 ; returnM (HsSCC lbl expr') }
143 tcExpr (HsTickPragma info expr) res_ty
144 = do { expr' <- tcMonoExpr expr res_ty
145 ; returnM (HsTickPragma info expr') }
147 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
148 = do { expr' <- tcMonoExpr expr res_ty
149 ; return (HsCoreAnn lbl expr') }
151 tcExpr (HsOverLit lit) res_ty
152 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
153 ; return (HsOverLit lit') }
155 tcExpr (NegApp expr neg_expr) res_ty
156 = do { neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
157 (mkFunTy res_ty res_ty)
158 ; expr' <- tcMonoExpr expr res_ty
159 ; return (NegApp expr' neg_expr') }
161 tcExpr (HsIPVar ip) res_ty
162 = do { -- Implicit parameters must have a *tau-type* not a
163 -- type scheme. We enforce this by creating a fresh
164 -- type variable as its type. (Because res_ty may not
166 ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
167 ; co_fn <- tcSubExp ip_ty res_ty
168 ; (ip', inst) <- newIPDict (IPOccOrigin ip) ip ip_ty
170 ; return (mkHsWrap co_fn (HsIPVar ip')) }
172 tcExpr (HsApp e1 e2) res_ty
175 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
176 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
177 go lfun@(L loc fun) args
178 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
179 tcApp fun (length args) (tcArgs lfun args) res_ty
180 ; traceTc (text "tcExpr args': " <+> ppr args')
181 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
183 tcExpr (HsLam match) res_ty
184 = do { (co_fn, match') <- tcMatchLambda match res_ty
185 ; return (mkHsWrap co_fn (HsLam match')) }
187 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
188 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
190 -- Remember to extend the lexical type-variable environment
191 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (\ skol_tvs res_ty ->
192 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
193 tcPolyExprNC expr res_ty)
195 ; co_fn <- tcSubExp sig_tc_ty res_ty
196 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
198 tcExpr (HsType ty) res_ty
199 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
200 -- This is the syntax for type applications that I was planning
201 -- but there are difficulties (e.g. what order for type args)
202 -- so it's not enabled yet.
203 -- Can't eliminate it altogether from the parser, because the
204 -- same parser parses *patterns*.
208 %************************************************************************
210 Infix operators and sections
212 %************************************************************************
215 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
216 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
217 ; return (OpApp arg1' (L loc op') fix arg2') }
219 -- Left sections, equivalent to
226 -- We treat it as similar to the latter, so we don't
227 -- actually require the function to take two arguments
228 -- at all. For example, (x `not`) means (not x);
229 -- you get postfix operators! Not really Haskell 98
230 -- I suppose, but it's less work and kind of useful.
232 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
233 = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
234 ; return (SectionL arg1' (L loc op')) }
236 -- Right sections, equivalent to \ x -> x `op` expr, or
239 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
240 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
241 tcApp op 2 (tc_args arg1_ty') res_ty'
242 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
244 doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
245 <+> ptext SLIT("takes one argument")
246 tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
247 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
248 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
249 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
250 ; return (qtys', arg2') }
251 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
255 tcExpr (HsLet binds expr) res_ty
256 = do { (binds', expr') <- tcLocalBinds binds $
257 tcMonoExpr expr res_ty
258 ; return (HsLet binds' expr') }
260 tcExpr (HsCase scrut matches) exp_ty
261 = do { -- We used to typecheck the case alternatives first.
262 -- The case patterns tend to give good type info to use
263 -- when typechecking the scrutinee. For example
266 -- will report that map is applied to too few arguments
268 -- But now, in the GADT world, we need to typecheck the scrutinee
269 -- first, to get type info that may be refined in the case alternatives
270 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
273 ; traceTc (text "HsCase" <+> ppr scrut_ty)
274 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
275 ; return (HsCase scrut' matches') }
277 match_ctxt = MC { mc_what = CaseAlt,
280 tcExpr (HsIf pred b1 b2) res_ty
281 = do { pred' <- addErrCtxt (predCtxt pred) $
282 tcMonoExpr pred boolTy
283 ; b1' <- tcMonoExpr b1 res_ty
284 ; b2' <- tcMonoExpr b2 res_ty
285 ; return (HsIf pred' b1' b2') }
287 tcExpr (HsDo do_or_lc stmts body _) res_ty
288 = tcDoStmts do_or_lc stmts body res_ty
290 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
291 = do { (elt_ty, coi) <- boxySplitListTy res_ty
292 ; exprs' <- mappM (tc_elt elt_ty) exprs
293 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
295 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
297 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
298 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
299 ; exprs' <- mappM (tc_elt elt_ty) exprs
300 ; ifM (null exprs) (zapToMonotype elt_ty)
301 -- If there are no expressions in the comprehension
302 -- we must still fill in the box
303 -- (Not needed for [] and () becuase they happen
304 -- to parse as data constructors.)
305 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
307 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
309 -- For tuples, take care to preserve rigidity
310 -- E.g. case (x,y) of ....
311 -- The scrutinee should have a rigid type if x,y do
312 -- The general scheme is the same as in tcIdApp
313 tcExpr (ExplicitTuple exprs boxity) res_ty
314 = do { tvs <- newBoxyTyVars [argTypeKind | e <- exprs]
315 ; let tup_tc = tupleTyCon boxity (length exprs)
316 tup_res_ty = mkTyConApp tup_tc (mkTyVarTys tvs)
317 ; checkWiredInTyCon tup_tc -- Ensure instances are available
318 ; arg_tys <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
319 ; exprs' <- tcPolyExprs exprs arg_tys
320 ; arg_tys' <- mapM refineBox arg_tys
321 ; co_fn <- tcFunResTy (tyConName tup_tc) (mkTyConApp tup_tc arg_tys') res_ty
322 ; return (mkHsWrap co_fn (ExplicitTuple exprs' boxity)) }
324 tcExpr (HsProc pat cmd) res_ty
325 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
326 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
328 tcExpr e@(HsArrApp _ _ _ _ _) _
329 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
330 ptext SLIT("was found where an expression was expected")])
332 tcExpr e@(HsArrForm _ _ _) _
333 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
334 ptext SLIT("was found where an expression was expected")])
337 %************************************************************************
339 Record construction and update
341 %************************************************************************
344 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
345 = do { data_con <- tcLookupDataCon con_name
347 -- Check for missing fields
348 ; checkMissingFields data_con rbinds
350 ; let arity = dataConSourceArity data_con
351 check_fields qtvs qtys arg_tys
352 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
353 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
354 ; qtys' <- mapM refineBoxToTau qtys
355 ; return (qtys', rbinds') }
356 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
357 -- filled, which is the invariant expected by tcIdApp
358 -- How could this not be the case? Consider a record construction
359 -- that does not mention all the fields.
361 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
363 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
365 -- The main complication with RecordUpd is that we need to explicitly
366 -- handle the *non-updated* fields. Consider:
368 -- data T a b = MkT1 { fa :: a, fb :: b }
369 -- | MkT2 { fa :: a, fc :: Int -> Int }
370 -- | MkT3 { fd :: a }
372 -- upd :: T a b -> c -> T a c
373 -- upd t x = t { fb = x}
375 -- The type signature on upd is correct (i.e. the result should not be (T a b))
376 -- because upd should be equivalent to:
378 -- upd t x = case t of
379 -- MkT1 p q -> MkT1 p x
380 -- MkT2 a b -> MkT2 p b
381 -- MkT3 d -> error ...
383 -- So we need to give a completely fresh type to the result record,
384 -- and then constrain it by the fields that are *not* updated ("p" above).
386 -- Note that because MkT3 doesn't contain all the fields being updated,
387 -- its RHS is simply an error, so it doesn't impose any type constraints
389 -- All this is done in STEP 4 below.
393 -- For record update we require that every constructor involved in the
394 -- update (i.e. that has all the specified fields) is "vanilla". I
395 -- don't know how to do the update otherwise.
398 tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
400 -- Check that the field names are really field names
402 field_names = hsRecFields rbinds
404 ASSERT( notNull field_names )
405 mappM tcLookupField field_names `thenM` \ sel_ids ->
406 -- The renamer has already checked that they
409 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
410 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
411 not (isRecordSelector sel_id), -- Excludes class ops
412 let L loc field_name = hsRecFieldId fld
415 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
418 -- Figure out the tycon and data cons from the first field name
420 -- It's OK to use the non-tc splitters here (for a selector)
422 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
423 data_cons = tyConDataCons tycon -- it's not a field label
424 -- NB: for a data type family, the tycon is the instance tycon
426 relevant_cons = filter is_relevant data_cons
427 is_relevant con = all (`elem` dataConFieldLabels con) field_names
431 -- Check that at least one constructor has all the named fields
432 -- i.e. has an empty set of bad fields returned by badFields
433 checkTc (not (null relevant_cons))
434 (badFieldsUpd rbinds) `thenM_`
436 -- Check that all relevant data cons are vanilla. Doing record updates on
437 -- GADTs and/or existentials is more than my tiny brain can cope with today
438 checkTc (all isVanillaDataCon relevant_cons)
439 (nonVanillaUpd tycon) `thenM_`
442 -- Use the un-updated fields to find a vector of booleans saying
443 -- which type arguments must be the same in updatee and result.
445 -- WARNING: this code assumes that all data_cons in a common tycon
446 -- have FieldLabels abstracted over the same tyvars.
448 -- A constructor is only relevant to this process if
449 -- it contains *all* the fields that are being updated
450 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons -- A representative constructor
451 (con1_tyvars, theta, con1_arg_tys, con1_res_ty) = dataConSig con1
452 con1_flds = dataConFieldLabels con1
453 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
454 , not (fld `elem` field_names) ]
456 is_common_tv tv = tv `elemVarSet` common_tyvars
458 mk_inst_ty tv result_inst_ty
459 | is_common_tv tv = returnM result_inst_ty -- Same as result type
460 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
462 ASSERT( null theta ) -- Vanilla datacon
463 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, result_inst_env) ->
464 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ scrut_inst_tys ->
466 -- STEP 3: Typecheck the update bindings.
467 -- Do this after checking for bad fields in case
468 -- there's a field that doesn't match the constructor.
470 result_ty = substTy result_inst_env con1_res_ty
471 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
473 tcSubExp result_ty res_ty `thenM` \ co_fn ->
474 tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
476 -- STEP 5: Typecheck the expression to be updated
478 scrut_inst_env = zipTopTvSubst con1_tyvars scrut_inst_tys
479 scrut_ty = substTy scrut_inst_env con1_res_ty
480 -- This is one place where the isVanilla check is important
481 -- So that inst_tys matches the con1_tyvars
483 tcMonoExpr record_expr scrut_ty `thenM` \ record_expr' ->
485 -- STEP 6: Figure out the LIE we need.
486 -- We have to generate some dictionaries for the data type context,
487 -- since we are going to do pattern matching over the data cons.
489 -- What dictionaries do we need? The dataConStupidTheta tells us.
491 theta' = substTheta scrut_inst_env (dataConStupidTheta con1)
493 instStupidTheta RecordUpdOrigin theta' `thenM_`
495 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
496 let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
497 = WpCo $ mkTyConApp co_con scrut_inst_tys
502 returnM (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
503 relevant_cons scrut_inst_tys result_inst_tys))
507 %************************************************************************
509 Arithmetic sequences e.g. [a,b..]
510 and their parallel-array counterparts e.g. [: a,b.. :]
513 %************************************************************************
516 tcExpr (ArithSeq _ seq@(From expr)) res_ty
517 = do { (elt_ty, coi) <- boxySplitListTy res_ty
518 ; expr' <- tcPolyExpr expr elt_ty
519 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
521 ; return $ mkHsWrapCoI coi (ArithSeq (HsVar enum_from) (From expr')) }
523 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
524 = do { (elt_ty, coi) <- boxySplitListTy res_ty
525 ; expr1' <- tcPolyExpr expr1 elt_ty
526 ; expr2' <- tcPolyExpr expr2 elt_ty
527 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
528 elt_ty enumFromThenName
529 ; return $ mkHsWrapCoI coi
530 (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
532 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
533 = do { (elt_ty, coi) <- boxySplitListTy res_ty
534 ; expr1' <- tcPolyExpr expr1 elt_ty
535 ; expr2' <- tcPolyExpr expr2 elt_ty
536 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
537 elt_ty enumFromToName
538 ; return $ mkHsWrapCoI coi
539 (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
541 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
542 = do { (elt_ty, coi) <- boxySplitListTy res_ty
543 ; expr1' <- tcPolyExpr expr1 elt_ty
544 ; expr2' <- tcPolyExpr expr2 elt_ty
545 ; expr3' <- tcPolyExpr expr3 elt_ty
546 ; eft <- newMethodFromName (ArithSeqOrigin seq)
547 elt_ty enumFromThenToName
548 ; return $ mkHsWrapCoI coi
549 (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
551 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
552 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
553 ; expr1' <- tcPolyExpr expr1 elt_ty
554 ; expr2' <- tcPolyExpr expr2 elt_ty
555 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
556 elt_ty enumFromToPName
557 ; return $ mkHsWrapCoI coi
558 (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
560 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
561 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
562 ; expr1' <- tcPolyExpr expr1 elt_ty
563 ; expr2' <- tcPolyExpr expr2 elt_ty
564 ; expr3' <- tcPolyExpr expr3 elt_ty
565 ; eft <- newMethodFromName (PArrSeqOrigin seq)
566 elt_ty enumFromThenToPName
567 ; return $ mkHsWrapCoI coi
568 (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
570 tcExpr (PArrSeq _ _) _
571 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
572 -- the parser shouldn't have generated it and the renamer shouldn't have
577 %************************************************************************
581 %************************************************************************
584 #ifdef GHCI /* Only if bootstrapped */
585 -- Rename excludes these cases otherwise
586 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
587 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
593 %************************************************************************
597 %************************************************************************
600 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
604 %************************************************************************
608 %************************************************************************
611 ---------------------------
612 tcApp :: HsExpr Name -- Function
613 -> Arity -- Number of args reqd
614 -> ArgChecker results
615 -> BoxyRhoType -- Result type
616 -> TcM (HsExpr TcId, results)
618 -- (tcFun fun n_args arg_checker res_ty)
619 -- The argument type checker, arg_checker, will be passed exactly n_args types
621 tcApp (HsVar fun_name) n_args arg_checker res_ty
622 = tcIdApp fun_name n_args arg_checker res_ty
624 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
625 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
626 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
627 ; arg_tys' <- mapM readFilledBox arg_boxes
628 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
629 ; return (fun', args') }
631 ---------------------------
632 tcIdApp :: Name -- Function
633 -> Arity -- Number of args reqd
634 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
635 -> BoxyRhoType -- Result type
636 -> TcM (HsExpr TcId, results)
638 -- Call (f e1 ... en) :: res_ty
639 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
640 -- (where k <= n; fres has the rest)
641 -- NB: if k < n then the function doesn't have enough args, and
642 -- presumably fres is a type variable that we are going to
643 -- instantiate with a function type
645 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
647 tcIdApp fun_name n_args arg_checker res_ty
648 = do { let orig = OccurrenceOf fun_name
649 ; (fun, fun_ty) <- lookupFun orig fun_name
651 -- Split up the function type
652 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
653 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
655 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
656 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
657 res_qtvs = exactTyVarsOfType fun_res_ty
658 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
659 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
660 k = length fun_arg_tys -- k <= n_args
661 n_missing_args = n_args - k -- Always >= 0
663 -- Match the result type of the function with the
664 -- result type of the context, to get an inital substitution
665 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
666 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
667 res_ty' = mkFunTys extra_arg_tys' res_ty
668 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
670 -- Typecheck the arguments!
671 -- Doing so will fill arg_qtvs and extra_arg_tys'
672 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
674 -- Strip boxes from the qtvs that have been filled in by the arg checking
675 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
677 -- Result subsumption
678 -- This fills in res_qtvs
679 ; let res_subst = zipOpenTvSubst qtvs qtys''
680 fun_res_ty'' = substTy res_subst fun_res_ty
681 res_ty'' = mkFunTys extra_arg_tys'' res_ty
682 ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
684 -- And pack up the results
685 -- By applying the coercion just to the *function* we can make
686 -- tcFun work nicely for OpApp and Sections too
687 ; fun' <- instFun orig fun res_subst tv_theta_prs
688 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
689 ; traceTc (text "tcIdApp: " <+> ppr (mkHsWrap co_fn' fun') <+> ppr tv_theta_prs <+> ppr co_fn' <+> ppr fun')
690 ; return (mkHsWrap co_fn' fun', args') }
693 Note [Silly type synonyms in smart-app]
694 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
695 When we call sripBoxyType, all of the boxes should be filled
696 in. But we need to be careful about type synonyms:
700 In the call (f x) we'll typecheck x, expecting it to have type
701 (T box). Usually that would fill in the box, but in this case not;
702 because 'a' is discarded by the silly type synonym T. So we must
703 use exactTyVarsOfType to figure out which type variables are free
704 in the argument type.
707 -- tcId is a specialisation of tcIdApp when there are no arguments
708 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
713 -> BoxyRhoType -- Result type
715 tcId orig fun_name res_ty
716 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
717 ; (fun, fun_ty) <- lookupFun orig fun_name
719 -- Split up the function type
720 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
721 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
722 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
723 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
725 -- Do the subsumption check wrt the result type
726 ; let res_subst = zipTopTvSubst qtvs qtv_tys
727 fun_tau' = substTy res_subst fun_tau
729 ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
731 -- And pack up the results
732 ; fun' <- instFun orig fun res_subst tv_theta_prs
733 ; traceTc (text "tcId yields" <+> ppr (mkHsWrap co_fn fun'))
734 ; return (mkHsWrap co_fn fun') }
736 -- Note [Push result type in]
738 -- Unify with expected result before (was: after) type-checking the args
739 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
740 -- This is when we might detect a too-few args situation.
741 -- (One can think of cases when the opposite order would give
742 -- a better error message.)
743 -- [March 2003: I'm experimenting with putting this first. Here's an
744 -- example where it actually makes a real difference
745 -- class C t a b | t a -> b
746 -- instance C Char a Bool
748 -- data P t a = forall b. (C t a b) => MkP b
749 -- data Q t = MkQ (forall a. P t a)
752 -- f1 = MkQ (MkP True)
753 -- f2 = MkQ (MkP True :: forall a. P Char a)
755 -- With the change, f1 will type-check, because the 'Char' info from
756 -- the signature is propagated into MkQ's argument. With the check
757 -- in the other order, the extra signature in f2 is reqd.]
759 ---------------------------
760 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
761 -- Typecheck a syntax operator, checking that it has the specified type
762 -- The operator is always a variable at this stage (i.e. renamer output)
763 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
764 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
766 ---------------------------
767 instFun :: InstOrigin
769 -> TvSubst -- The instantiating substitution
770 -> [([TyVar], ThetaType)] -- Stuff to instantiate
773 instFun orig fun subst []
774 = return fun -- Common short cut
776 instFun orig fun subst tv_theta_prs
777 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
778 ; traceTc (text "instFun" <+> ppr ty_theta_prs')
779 -- Make two ad-hoc checks
780 ; doStupidChecks fun ty_theta_prs'
782 -- Now do normal instantiation
783 ; result <- go True fun ty_theta_prs'
784 ; traceTc (text "instFun result" <+> ppr result)
788 subst_pr (tvs, theta)
789 = (substTyVars subst tvs, substTheta subst theta)
791 go _ fun [] = do {traceTc (text "go _ fun [] returns" <+> ppr fun) ; return fun }
793 go True (HsVar fun_id) ((tys,theta) : prs)
794 | want_method_inst theta
795 = do { traceTc (text "go (HsVar fun_id) ((tys,theta) : prs) | want_method_inst theta")
796 ; meth_id <- newMethodWithGivenTy orig fun_id tys
797 ; go False (HsVar meth_id) prs }
798 -- Go round with 'False' to prevent further use
799 -- of newMethod: see Note [Multiple instantiation]
801 go _ fun ((tys, theta) : prs)
802 = do { co_fn <- instCall orig tys theta
803 ; traceTc (text "go yields co_fn" <+> ppr co_fn)
804 ; go False (HsWrap co_fn fun) prs }
806 -- See Note [No method sharing]
807 want_method_inst theta = not (null theta) -- Overloaded
808 && not opt_NoMethodSharing
811 Note [Multiple instantiation]
812 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
813 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
814 For example, consider
815 f :: forall a. Eq a => forall b. Ord b => a -> b
816 At a call to f, at say [Int, Bool], it's tempting to translate the call to
820 f_m1 :: forall b. Ord b => Int -> b
824 f_m2 = f_m1 Bool dOrdBool
826 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
827 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
829 But it's entirely possible that f_m2 will continue to float out, because it
830 mentions no type variables. Result, f_m1 isn't in scope.
832 Here's a concrete example that does this (test tc200):
835 f :: Eq b => b -> a -> Int
836 baz :: Eq a => Int -> a -> Int
841 Current solution: only do the "method sharing" thing for the first type/dict
842 application, not for the iterated ones. A horribly subtle point.
844 Note [No method sharing]
845 ~~~~~~~~~~~~~~~~~~~~~~~~
846 The -fno-method-sharing flag controls what happens so far as the LIE
847 is concerned. The default case is that for an overloaded function we
848 generate a "method" Id, and add the Method Inst to the LIE. So you get
851 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
852 If you specify -fno-method-sharing, the dictionary application
853 isn't shared, so we get
855 f = /\a (d:Num a) (x:a) -> (+) a d x x
856 This gets a bit less sharing, but
857 a) it's better for RULEs involving overloaded functions
858 b) perhaps fewer separated lambdas
862 tcArgs implements a left-to-right order, which goes beyond what is described in the
863 impredicative type inference paper. In particular, it allows
865 where runST :: (forall s. ST s a) -> a
866 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
867 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
868 before checking foo. The left-to-right order really helps here.
871 tcArgs :: LHsExpr Name -- The function (for error messages)
872 -> [LHsExpr Name] -- Actual args
873 -> ArgChecker [LHsExpr TcId]
875 type ArgChecker results
876 = [TyVar] -> [TcSigmaType] -- Current instantiation
877 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
878 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
880 tcArgs fun args qtvs qtys arg_tys
881 = go 1 qtys args arg_tys
883 go n qtys [] [] = return (qtys, [])
884 go n qtys (arg:args) (arg_ty:arg_tys)
885 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
886 ; qtys' <- mapM refineBox qtys -- Exploit new info
887 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
888 ; return (qtys'', arg':args') }
889 go n qtys args arg_tys = panic "tcArgs"
891 tcArg :: LHsExpr Name -- The function
892 -> Int -- and arg number (for error messages)
894 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
896 -> TcM (LHsExpr TcId) -- Resulting argument
897 tcArg fun arg_no arg qtvs qtys ty
898 = addErrCtxt (funAppCtxt fun arg arg_no) $
899 tcPolyExprNC arg (substTyWith qtvs qtys ty)
905 Nasty check to ensure that tagToEnum# is applied to a type that is an
906 enumeration TyCon. Unification may refine the type later, but this
907 check won't see that, alas. It's crude but it works.
909 Here's are two cases that should fail
911 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
914 g = tagToEnum# 0 -- Int is not an enumeration
918 doStupidChecks :: HsExpr TcId
919 -> [([TcType], ThetaType)]
921 -- Check two tiresome and ad-hoc cases
922 -- (a) the "stupid theta" for a data con; add the constraints
923 -- from the "stupid theta" of a data constructor (sigh)
924 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
926 doStupidChecks (HsVar fun_id) ((tys,_):_)
927 | Just con <- isDataConId_maybe fun_id -- (a)
928 = addDataConStupidTheta con tys
930 | fun_id `hasKey` tagToEnumKey -- (b)
931 = do { tys' <- zonkTcTypes tys
932 ; checkTc (ok tys') (tagToEnumError tys')
936 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
937 Just (tc,_) -> isEnumerationTyCon tc
940 doStupidChecks fun tv_theta_prs
941 = return () -- The common case
945 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
946 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
947 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
949 at_type | null tys = empty -- Probably never happens
950 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
953 %************************************************************************
955 \subsection{@tcId@ typechecks an identifier occurrence}
957 %************************************************************************
960 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
961 lookupFun orig id_name
962 = do { thing <- tcLookup id_name
964 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
966 wrap_id = dataConWrapId con
969 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
970 | otherwise -> return (HsVar id, idType id)
971 -- A global cannot possibly be ill-staged
972 -- nor does it need the 'lifting' treatment
974 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
975 -> do { thLocalId orig id ty lvl
977 Unrefineable -> return (HsVar id, ty)
978 Rigid co -> return (mkHsWrap co (HsVar id), ty)
979 Wobbly -> traceTc (text "lookupFun" <+> ppr id) >> return (HsVar id, ty) -- Wobbly, or no free vars
980 WobblyInvisible -> failWithTc (ppr id_name <+> ptext SLIT(" not in scope because it has a wobbly type (solution: add a type annotation)"))
983 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
986 #ifndef GHCI /* GHCI and TH is off */
987 --------------------------------------
988 -- thLocalId : Check for cross-stage lifting
989 thLocalId orig id id_ty th_bind_lvl
992 #else /* GHCI and TH is on */
993 thLocalId orig id id_ty th_bind_lvl
994 = do { use_stage <- getStage -- TH case
996 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
997 -> thBrackId orig id ps_var lie_var
998 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
1002 --------------------------------------
1003 thBrackId orig id ps_var lie_var
1005 = -- Top-level identifiers in this module,
1006 -- (which have External Names)
1007 -- are just like the imported case:
1008 -- no need for the 'lifting' treatment
1009 -- E.g. this is fine:
1012 -- But we do need to put f into the keep-alive
1013 -- set, because after desugaring the code will
1014 -- only mention f's *name*, not f itself.
1015 do { keepAliveTc id; return id }
1018 = -- Nested identifiers, such as 'x' in
1019 -- E.g. \x -> [| h x |]
1020 -- We must behave as if the reference to x was
1022 -- We use 'x' itself as the splice proxy, used by
1023 -- the desugarer to stitch it all back together.
1024 -- If 'x' occurs many times we may get many identical
1025 -- bindings of the same splice proxy, but that doesn't
1026 -- matter, although it's a mite untidy.
1027 do { let id_ty = idType id
1028 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1029 -- If x is polymorphic, its occurrence sites might
1030 -- have different instantiations, so we can't use plain
1031 -- 'x' as the splice proxy name. I don't know how to
1032 -- solve this, and it's probably unimportant, so I'm
1033 -- just going to flag an error for now
1035 ; id_ty' <- zapToMonotype id_ty
1036 -- The id_ty might have an OpenTypeKind, but we
1037 -- can't instantiate the Lift class at that kind,
1038 -- so we zap it to a LiftedTypeKind monotype
1039 -- C.f. the call in TcPat.newLitInst
1041 ; setLIEVar lie_var $ do
1042 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
1043 -- Put the 'lift' constraint into the right LIE
1045 -- Update the pending splices
1046 ; ps <- readMutVar ps_var
1047 ; writeMutVar ps_var ((idName id, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1054 %************************************************************************
1056 \subsection{Record bindings}
1058 %************************************************************************
1060 Game plan for record bindings
1061 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1062 1. Find the TyCon for the bindings, from the first field label.
1064 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1066 For each binding field = value
1068 3. Instantiate the field type (from the field label) using the type
1071 4 Type check the value using tcArg, passing the field type as
1072 the expected argument type.
1074 This extends OK when the field types are universally quantified.
1080 -> [TcType] -- Expected type for each field
1081 -> HsRecordBinds Name
1082 -> TcM (HsRecordBinds TcId)
1084 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1085 = do { mb_binds <- mappM do_bind rbinds
1086 ; return (HsRecFields (catMaybes mb_binds) dd) }
1088 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1089 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1090 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1091 = addErrCtxt (fieldCtxt field_lbl) $
1092 do { rhs' <- tcPolyExprNC rhs field_ty
1093 ; sel_id <- tcLookupField field_lbl
1094 ; ASSERT( isRecordSelector sel_id )
1095 return (Just (fld { hsRecFieldId = L loc sel_id, hsRecFieldArg = rhs' })) }
1097 = do { addErrTc (badFieldCon data_con field_lbl)
1100 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1101 checkMissingFields data_con rbinds
1102 | null field_labels -- Not declared as a record;
1103 -- But C{} is still valid if no strict fields
1104 = if any isMarkedStrict field_strs then
1105 -- Illegal if any arg is strict
1106 addErrTc (missingStrictFields data_con [])
1110 | otherwise -- A record
1111 = checkM (null missing_s_fields)
1112 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1114 doptM Opt_WarnMissingFields `thenM` \ warn ->
1115 checkM (not (warn && notNull missing_ns_fields))
1116 (warnTc True (missingFields data_con missing_ns_fields))
1120 = [ fl | (fl, str) <- field_info,
1122 not (fl `elem` field_names_used)
1125 = [ fl | (fl, str) <- field_info,
1126 not (isMarkedStrict str),
1127 not (fl `elem` field_names_used)
1130 field_names_used = hsRecFields rbinds
1131 field_labels = dataConFieldLabels data_con
1133 field_info = zipEqual "missingFields"
1137 field_strs = dataConStrictMarks data_con
1140 %************************************************************************
1142 \subsection{Errors and contexts}
1144 %************************************************************************
1146 Boring and alphabetical:
1149 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1152 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1154 fieldCtxt field_name
1155 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1157 funAppCtxt fun arg arg_no
1158 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1159 quotes (ppr fun) <> text ", namely"])
1160 4 (quotes (ppr arg))
1163 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1166 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type")
1167 <+> quotes (pprSourceTyCon tycon)
1168 <+> ptext SLIT("is not (yet) supported"),
1169 ptext SLIT("Use pattern-matching instead")]
1171 = hang (ptext SLIT("No constructor has all these fields:"))
1172 4 (pprQuotedList (hsRecFields rbinds))
1174 naughtyRecordSel sel_id
1175 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1176 ptext SLIT("as a function due to escaped type variables") $$
1177 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1180 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1182 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1183 missingStrictFields con fields
1186 rest | null fields = empty -- Happens for non-record constructors
1187 -- with strict fields
1188 | otherwise = colon <+> pprWithCommas ppr fields
1190 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1191 ptext SLIT("does not have the required strict field(s)")
1193 missingFields :: DataCon -> [FieldLabel] -> SDoc
1194 missingFields con fields
1195 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1196 <+> pprWithCommas ppr fields
1198 -- callCtxt fun args = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1201 polySpliceErr :: Id -> SDoc
1203 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)