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
32 import TcIface ( checkWiredInTyCon )
54 %************************************************************************
56 \subsection{Main wrappers}
58 %************************************************************************
61 tcPolyExpr, tcPolyExprNC
62 :: LHsExpr Name -- Expession to type check
63 -> BoxySigmaType -- Expected type (could be a polytpye)
64 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
66 -- tcPolyExpr is a convenient place (frequent but not too frequent) place
67 -- to add context information.
68 -- The NC version does not do so, usually because the caller wants
71 tcPolyExpr expr res_ty
72 = addErrCtxt (exprCtxt (unLoc expr)) $
73 tcPolyExprNC expr res_ty
75 tcPolyExprNC expr res_ty
77 = do { (gen_fn, expr') <- tcGen res_ty emptyVarSet (\_ -> tcPolyExprNC expr)
78 -- Note the recursive call to tcPolyExpr, because the
79 -- type may have multiple layers of for-alls
80 -- E.g. forall a. Eq a => forall b. Ord b => ....
81 ; return (mkLHsWrap gen_fn expr') }
84 = tcMonoExpr expr res_ty
87 tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
88 tcPolyExprs [] [] = returnM []
89 tcPolyExprs (expr:exprs) (ty:tys)
90 = do { expr' <- tcPolyExpr expr ty
91 ; exprs' <- tcPolyExprs exprs tys
92 ; returnM (expr':exprs') }
93 tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
96 tcMonoExpr :: LHsExpr Name -- Expression to type check
97 -> BoxyRhoType -- Expected type (could be a type variable)
98 -- Definitely no foralls at the top
99 -- Can contain boxes, which will be filled in
100 -> TcM (LHsExpr TcId)
102 tcMonoExpr (L loc expr) res_ty
103 = ASSERT( not (isSigmaTy res_ty) )
105 do { expr' <- tcExpr expr res_ty
106 ; return (L loc expr') }
109 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
110 tcInferRho expr = tcInfer (tcMonoExpr expr)
115 %************************************************************************
117 tcExpr: the main expression typechecker
119 %************************************************************************
122 tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
123 tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
125 tcExpr (HsLit lit) res_ty = do { boxyUnify (hsLitType lit) res_ty
126 ; return (HsLit lit) }
128 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
129 ; return (HsPar expr') }
131 tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
132 ; returnM (HsSCC lbl expr') }
133 tcExpr (HsTickPragma info expr) res_ty
134 = do { expr' <- tcMonoExpr expr res_ty
135 ; returnM (HsTickPragma info expr') }
137 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
138 = do { expr' <- tcMonoExpr expr res_ty
139 ; return (HsCoreAnn lbl expr') }
141 tcExpr (HsOverLit lit) res_ty
142 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
143 ; return (HsOverLit lit') }
145 tcExpr (NegApp expr neg_expr) res_ty
146 = do { neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
147 (mkFunTy res_ty res_ty)
148 ; expr' <- tcMonoExpr expr res_ty
149 ; return (NegApp expr' neg_expr') }
151 tcExpr (HsIPVar ip) res_ty
152 = do { -- Implicit parameters must have a *tau-type* not a
153 -- type scheme. We enforce this by creating a fresh
154 -- type variable as its type. (Because res_ty may not
156 ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
157 ; co_fn <- tcSubExp ip_ty res_ty
158 ; (ip', inst) <- newIPDict (IPOccOrigin ip) ip ip_ty
160 ; return (mkHsWrap co_fn (HsIPVar ip')) }
162 tcExpr (HsApp e1 e2) res_ty
165 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
166 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
167 go lfun@(L loc fun) args
168 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
169 tcApp fun (length args) (tcArgs lfun args) res_ty
170 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
172 tcExpr (HsLam match) res_ty
173 = do { (co_fn, match') <- tcMatchLambda match res_ty
174 ; return (mkHsWrap co_fn (HsLam match')) }
176 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
177 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
179 -- Remember to extend the lexical type-variable environment
180 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (\ skol_tvs res_ty ->
181 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
182 tcPolyExprNC expr res_ty)
184 ; co_fn <- tcSubExp sig_tc_ty res_ty
185 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
187 tcExpr (HsType ty) res_ty
188 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
189 -- This is the syntax for type applications that I was planning
190 -- but there are difficulties (e.g. what order for type args)
191 -- so it's not enabled yet.
192 -- Can't eliminate it altogether from the parser, because the
193 -- same parser parses *patterns*.
197 %************************************************************************
199 Infix operators and sections
201 %************************************************************************
204 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
205 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
206 ; return (OpApp arg1' (L loc op') fix arg2') }
208 -- Left sections, equivalent to
215 -- We treat it as similar to the latter, so we don't
216 -- actually require the function to take two arguments
217 -- at all. For example, (x `not`) means (not x);
218 -- you get postfix operators! Not really Haskell 98
219 -- I suppose, but it's less work and kind of useful.
221 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
222 = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
223 ; return (SectionL arg1' (L loc op')) }
225 -- Right sections, equivalent to \ x -> x `op` expr, or
228 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
229 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
230 tcApp op 2 (tc_args arg1_ty') res_ty'
231 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
233 doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
234 <+> ptext SLIT("takes one argument")
235 tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
236 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
237 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
238 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
239 ; return (qtys', arg2') }
240 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
244 tcExpr (HsLet binds expr) res_ty
245 = do { (binds', expr') <- tcLocalBinds binds $
246 tcMonoExpr expr res_ty
247 ; return (HsLet binds' expr') }
249 tcExpr (HsCase scrut matches) exp_ty
250 = do { -- We used to typecheck the case alternatives first.
251 -- The case patterns tend to give good type info to use
252 -- when typechecking the scrutinee. For example
255 -- will report that map is applied to too few arguments
257 -- But now, in the GADT world, we need to typecheck the scrutinee
258 -- first, to get type info that may be refined in the case alternatives
259 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
262 ; traceTc (text "HsCase" <+> ppr scrut_ty)
263 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
264 ; return (HsCase scrut' matches') }
266 match_ctxt = MC { mc_what = CaseAlt,
269 tcExpr (HsIf pred b1 b2) res_ty
270 = do { pred' <- addErrCtxt (predCtxt pred) $
271 tcMonoExpr pred boolTy
272 ; b1' <- tcMonoExpr b1 res_ty
273 ; b2' <- tcMonoExpr b2 res_ty
274 ; return (HsIf pred' b1' b2') }
276 tcExpr (HsDo do_or_lc stmts body _) res_ty
277 = tcDoStmts do_or_lc stmts body res_ty
279 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
280 = do { elt_ty <- boxySplitListTy res_ty
281 ; exprs' <- mappM (tc_elt elt_ty) exprs
282 ; return (ExplicitList elt_ty exprs') }
284 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
286 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
287 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
288 ; exprs' <- mappM (tc_elt elt_ty) exprs
289 ; ifM (null exprs) (zapToMonotype elt_ty)
290 -- If there are no expressions in the comprehension
291 -- we must still fill in the box
292 -- (Not needed for [] and () becuase they happen
293 -- to parse as data constructors.)
294 ; return (ExplicitPArr elt_ty exprs') }
296 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
298 -- For tuples, take care to preserve rigidity
299 -- E.g. case (x,y) of ....
300 -- The scrutinee should have a rigid type if x,y do
301 -- The general scheme is the same as in tcIdApp
302 tcExpr (ExplicitTuple exprs boxity) res_ty
303 = do { tvs <- newBoxyTyVars [argTypeKind | e <- exprs]
304 ; let tup_tc = tupleTyCon boxity (length exprs)
305 tup_res_ty = mkTyConApp tup_tc (mkTyVarTys tvs)
306 ; checkWiredInTyCon tup_tc -- Ensure instances are available
307 ; arg_tys <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
308 ; exprs' <- tcPolyExprs exprs arg_tys
309 ; arg_tys' <- mapM refineBox arg_tys
310 ; co_fn <- tcFunResTy (tyConName tup_tc) (mkTyConApp tup_tc arg_tys') res_ty
311 ; return (mkHsWrap co_fn (ExplicitTuple exprs' boxity)) }
313 tcExpr (HsProc pat cmd) res_ty
314 = do { (pat', cmd') <- tcProc pat cmd res_ty
315 ; return (HsProc pat' cmd') }
317 tcExpr e@(HsArrApp _ _ _ _ _) _
318 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
319 ptext SLIT("was found where an expression was expected")])
321 tcExpr e@(HsArrForm _ _ _) _
322 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
323 ptext SLIT("was found where an expression was expected")])
326 %************************************************************************
328 Record construction and update
330 %************************************************************************
333 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
334 = do { data_con <- tcLookupDataCon con_name
336 -- Check for missing fields
337 ; checkMissingFields data_con rbinds
339 ; let arity = dataConSourceArity data_con
340 check_fields qtvs qtys arg_tys
341 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
342 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
343 ; qtys' <- mapM refineBoxToTau qtys
344 ; return (qtys', rbinds') }
345 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
346 -- filled, which is the invariant expected by tcIdApp
347 -- How could this not be the case? Consider a record construction
348 -- that does not mention all the fields.
350 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
352 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
354 -- The main complication with RecordUpd is that we need to explicitly
355 -- handle the *non-updated* fields. Consider:
357 -- data T a b = MkT1 { fa :: a, fb :: b }
358 -- | MkT2 { fa :: a, fc :: Int -> Int }
359 -- | MkT3 { fd :: a }
361 -- upd :: T a b -> c -> T a c
362 -- upd t x = t { fb = x}
364 -- The type signature on upd is correct (i.e. the result should not be (T a b))
365 -- because upd should be equivalent to:
367 -- upd t x = case t of
368 -- MkT1 p q -> MkT1 p x
369 -- MkT2 a b -> MkT2 p b
370 -- MkT3 d -> error ...
372 -- So we need to give a completely fresh type to the result record,
373 -- and then constrain it by the fields that are *not* updated ("p" above).
375 -- Note that because MkT3 doesn't contain all the fields being updated,
376 -- its RHS is simply an error, so it doesn't impose any type constraints
378 -- All this is done in STEP 4 below.
382 -- For record update we require that every constructor involved in the
383 -- update (i.e. that has all the specified fields) is "vanilla". I
384 -- don't know how to do the update otherwise.
387 tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
389 -- Check that the field names are really field names
391 field_names = hsRecFields rbinds
393 ASSERT( notNull field_names )
394 mappM tcLookupField field_names `thenM` \ sel_ids ->
395 -- The renamer has already checked that they
398 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
399 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
400 not (isRecordSelector sel_id), -- Excludes class ops
401 let L loc field_name = hsRecFieldId fld
404 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
407 -- Figure out the tycon and data cons from the first field name
409 -- It's OK to use the non-tc splitters here (for a selector)
411 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
412 data_cons = tyConDataCons tycon -- it's not a field label
413 -- NB: for a data type family, the tycon is the instance tycon
415 relevant_cons = filter is_relevant data_cons
416 is_relevant con = all (`elem` dataConFieldLabels con) field_names
420 -- Check that at least one constructor has all the named fields
421 -- i.e. has an empty set of bad fields returned by badFields
422 checkTc (not (null relevant_cons))
423 (badFieldsUpd rbinds) `thenM_`
425 -- Check that all relevant data cons are vanilla. Doing record updates on
426 -- GADTs and/or existentials is more than my tiny brain can cope with today
427 checkTc (all isVanillaDataCon relevant_cons)
428 (nonVanillaUpd tycon) `thenM_`
431 -- Use the un-updated fields to find a vector of booleans saying
432 -- which type arguments must be the same in updatee and result.
434 -- WARNING: this code assumes that all data_cons in a common tycon
435 -- have FieldLabels abstracted over the same tyvars.
437 -- A constructor is only relevant to this process if
438 -- it contains *all* the fields that are being updated
439 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons -- A representative constructor
440 (con1_tyvars, theta, con1_arg_tys, con1_res_ty) = dataConSig con1
441 con1_flds = dataConFieldLabels con1
442 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
443 , not (fld `elem` field_names) ]
445 is_common_tv tv = tv `elemVarSet` common_tyvars
447 mk_inst_ty tv result_inst_ty
448 | is_common_tv tv = returnM result_inst_ty -- Same as result type
449 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
451 ASSERT( null theta ) -- Vanilla datacon
452 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, result_inst_env) ->
453 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ scrut_inst_tys ->
455 -- STEP 3: Typecheck the update bindings.
456 -- Do this after checking for bad fields in case
457 -- there's a field that doesn't match the constructor.
459 result_ty = substTy result_inst_env con1_res_ty
460 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
462 tcSubExp result_ty res_ty `thenM` \ co_fn ->
463 tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
465 -- STEP 5: Typecheck the expression to be updated
467 scrut_inst_env = zipTopTvSubst con1_tyvars scrut_inst_tys
468 scrut_ty = substTy scrut_inst_env con1_res_ty
469 -- This is one place where the isVanilla check is important
470 -- So that inst_tys matches the con1_tyvars
472 tcMonoExpr record_expr scrut_ty `thenM` \ record_expr' ->
474 -- STEP 6: Figure out the LIE we need.
475 -- We have to generate some dictionaries for the data type context,
476 -- since we are going to do pattern matching over the data cons.
478 -- What dictionaries do we need? The dataConStupidTheta tells us.
480 theta' = substTheta scrut_inst_env (dataConStupidTheta con1)
482 instStupidTheta RecordUpdOrigin theta' `thenM_`
484 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
485 let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
486 = WpCo $ mkTyConApp co_con scrut_inst_tys
491 returnM (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
492 relevant_cons scrut_inst_tys result_inst_tys))
496 %************************************************************************
498 Arithmetic sequences e.g. [a,b..]
499 and their parallel-array counterparts e.g. [: a,b.. :]
502 %************************************************************************
505 tcExpr (ArithSeq _ seq@(From expr)) res_ty
506 = do { elt_ty <- boxySplitListTy res_ty
507 ; expr' <- tcPolyExpr expr elt_ty
508 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
510 ; return (ArithSeq (HsVar enum_from) (From expr')) }
512 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
513 = do { elt_ty <- boxySplitListTy res_ty
514 ; expr1' <- tcPolyExpr expr1 elt_ty
515 ; expr2' <- tcPolyExpr expr2 elt_ty
516 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
517 elt_ty enumFromThenName
518 ; return (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
521 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
522 = do { elt_ty <- boxySplitListTy res_ty
523 ; expr1' <- tcPolyExpr expr1 elt_ty
524 ; expr2' <- tcPolyExpr expr2 elt_ty
525 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
526 elt_ty enumFromToName
527 ; return (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
529 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
530 = do { elt_ty <- boxySplitListTy res_ty
531 ; expr1' <- tcPolyExpr expr1 elt_ty
532 ; expr2' <- tcPolyExpr expr2 elt_ty
533 ; expr3' <- tcPolyExpr expr3 elt_ty
534 ; eft <- newMethodFromName (ArithSeqOrigin seq)
535 elt_ty enumFromThenToName
536 ; return (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
538 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
539 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
540 ; expr1' <- tcPolyExpr expr1 elt_ty
541 ; expr2' <- tcPolyExpr expr2 elt_ty
542 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
543 elt_ty enumFromToPName
544 ; return (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
546 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
547 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
548 ; expr1' <- tcPolyExpr expr1 elt_ty
549 ; expr2' <- tcPolyExpr expr2 elt_ty
550 ; expr3' <- tcPolyExpr expr3 elt_ty
551 ; eft <- newMethodFromName (PArrSeqOrigin seq)
552 elt_ty enumFromThenToPName
553 ; return (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
555 tcExpr (PArrSeq _ _) _
556 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
557 -- the parser shouldn't have generated it and the renamer shouldn't have
562 %************************************************************************
566 %************************************************************************
569 #ifdef GHCI /* Only if bootstrapped */
570 -- Rename excludes these cases otherwise
571 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
572 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
578 %************************************************************************
582 %************************************************************************
585 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
589 %************************************************************************
593 %************************************************************************
596 ---------------------------
597 tcApp :: HsExpr Name -- Function
598 -> Arity -- Number of args reqd
599 -> ArgChecker results
600 -> BoxyRhoType -- Result type
601 -> TcM (HsExpr TcId, results)
603 -- (tcFun fun n_args arg_checker res_ty)
604 -- The argument type checker, arg_checker, will be passed exactly n_args types
606 tcApp (HsVar fun_name) n_args arg_checker res_ty
607 = tcIdApp fun_name n_args arg_checker res_ty
609 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
610 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
611 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
612 ; arg_tys' <- mapM readFilledBox arg_boxes
613 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
614 ; return (fun', args') }
616 ---------------------------
617 tcIdApp :: Name -- Function
618 -> Arity -- Number of args reqd
619 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
620 -> BoxyRhoType -- Result type
621 -> TcM (HsExpr TcId, results)
623 -- Call (f e1 ... en) :: res_ty
624 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
625 -- (where k <= n; fres has the rest)
626 -- NB: if k < n then the function doesn't have enough args, and
627 -- presumably fres is a type variable that we are going to
628 -- instantiate with a function type
630 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
632 tcIdApp fun_name n_args arg_checker res_ty
633 = do { let orig = OccurrenceOf fun_name
634 ; (fun, fun_ty) <- lookupFun orig fun_name
636 -- Split up the function type
637 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
638 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
640 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
641 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
642 res_qtvs = exactTyVarsOfType fun_res_ty
643 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
644 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
645 k = length fun_arg_tys -- k <= n_args
646 n_missing_args = n_args - k -- Always >= 0
648 -- Match the result type of the function with the
649 -- result type of the context, to get an inital substitution
650 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
651 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
652 res_ty' = mkFunTys extra_arg_tys' res_ty
653 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
655 -- Typecheck the arguments!
656 -- Doing so will fill arg_qtvs and extra_arg_tys'
657 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
659 -- Strip boxes from the qtvs that have been filled in by the arg checking
660 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
662 -- Result subsumption
663 -- This fills in res_qtvs
664 ; let res_subst = zipOpenTvSubst qtvs qtys''
665 fun_res_ty'' = substTy res_subst fun_res_ty
666 res_ty'' = mkFunTys extra_arg_tys'' res_ty
667 ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
669 -- And pack up the results
670 -- By applying the coercion just to the *function* we can make
671 -- tcFun work nicely for OpApp and Sections too
672 ; fun' <- instFun orig fun res_subst tv_theta_prs
673 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
674 ; return (mkHsWrap co_fn' fun', args') }
677 Note [Silly type synonyms in smart-app]
678 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
679 When we call sripBoxyType, all of the boxes should be filled
680 in. But we need to be careful about type synonyms:
684 In the call (f x) we'll typecheck x, expecting it to have type
685 (T box). Usually that would fill in the box, but in this case not;
686 because 'a' is discarded by the silly type synonym T. So we must
687 use exactTyVarsOfType to figure out which type variables are free
688 in the argument type.
691 -- tcId is a specialisation of tcIdApp when there are no arguments
692 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
697 -> BoxyRhoType -- Result type
699 tcId orig fun_name res_ty
700 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
701 ; (fun, fun_ty) <- lookupFun orig fun_name
703 -- Split up the function type
704 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
705 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
706 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
707 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
709 -- Do the subsumption check wrt the result type
710 ; let res_subst = zipTopTvSubst qtvs qtv_tys
711 fun_tau' = substTy res_subst fun_tau
713 ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
715 -- And pack up the results
716 ; fun' <- instFun orig fun res_subst tv_theta_prs
717 ; return (mkHsWrap co_fn fun') }
719 -- Note [Push result type in]
721 -- Unify with expected result before (was: after) type-checking the args
722 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
723 -- This is when we might detect a too-few args situation.
724 -- (One can think of cases when the opposite order would give
725 -- a better error message.)
726 -- [March 2003: I'm experimenting with putting this first. Here's an
727 -- example where it actually makes a real difference
728 -- class C t a b | t a -> b
729 -- instance C Char a Bool
731 -- data P t a = forall b. (C t a b) => MkP b
732 -- data Q t = MkQ (forall a. P t a)
735 -- f1 = MkQ (MkP True)
736 -- f2 = MkQ (MkP True :: forall a. P Char a)
738 -- With the change, f1 will type-check, because the 'Char' info from
739 -- the signature is propagated into MkQ's argument. With the check
740 -- in the other order, the extra signature in f2 is reqd.]
742 ---------------------------
743 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
744 -- Typecheck a syntax operator, checking that it has the specified type
745 -- The operator is always a variable at this stage (i.e. renamer output)
746 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
747 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
749 ---------------------------
750 instFun :: InstOrigin
752 -> TvSubst -- The instantiating substitution
753 -> [([TyVar], ThetaType)] -- Stuff to instantiate
756 instFun orig fun subst []
757 = return fun -- Common short cut
759 instFun orig fun subst tv_theta_prs
760 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
762 -- Make two ad-hoc checks
763 ; doStupidChecks fun ty_theta_prs'
765 -- Now do normal instantiation
766 ; go True fun ty_theta_prs' }
768 subst_pr (tvs, theta)
769 = (substTyVars subst tvs, substTheta subst theta)
771 go _ fun [] = return fun
773 go True (HsVar fun_id) ((tys,theta) : prs)
774 | want_method_inst theta
775 = do { meth_id <- newMethodWithGivenTy orig fun_id tys
776 ; go False (HsVar meth_id) prs }
777 -- Go round with 'False' to prevent further use
778 -- of newMethod: see Note [Multiple instantiation]
780 go _ fun ((tys, theta) : prs)
781 = do { co_fn <- instCall orig tys theta
782 ; go False (HsWrap co_fn fun) prs }
784 -- See Note [No method sharing]
785 want_method_inst theta = not (null theta) -- Overloaded
786 && not opt_NoMethodSharing
789 Note [Multiple instantiation]
790 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
791 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
792 For example, consider
793 f :: forall a. Eq a => forall b. Ord b => a -> b
794 At a call to f, at say [Int, Bool], it's tempting to translate the call to
798 f_m1 :: forall b. Ord b => Int -> b
802 f_m2 = f_m1 Bool dOrdBool
804 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
805 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
807 But it's entirely possible that f_m2 will continue to float out, because it
808 mentions no type variables. Result, f_m1 isn't in scope.
810 Here's a concrete example that does this (test tc200):
813 f :: Eq b => b -> a -> Int
814 baz :: Eq a => Int -> a -> Int
819 Current solution: only do the "method sharing" thing for the first type/dict
820 application, not for the iterated ones. A horribly subtle point.
822 Note [No method sharing]
823 ~~~~~~~~~~~~~~~~~~~~~~~~
824 The -fno-method-sharing flag controls what happens so far as the LIE
825 is concerned. The default case is that for an overloaded function we
826 generate a "method" Id, and add the Method Inst to the LIE. So you get
829 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
830 If you specify -fno-method-sharing, the dictionary application
831 isn't shared, so we get
833 f = /\a (d:Num a) (x:a) -> (+) a d x x
834 This gets a bit less sharing, but
835 a) it's better for RULEs involving overloaded functions
836 b) perhaps fewer separated lambdas
840 tcArgs implements a left-to-right order, which goes beyond what is described in the
841 impredicative type inference paper. In particular, it allows
843 where runST :: (forall s. ST s a) -> a
844 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
845 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
846 before checking foo. The left-to-right order really helps here.
849 tcArgs :: LHsExpr Name -- The function (for error messages)
850 -> [LHsExpr Name] -- Actual args
851 -> ArgChecker [LHsExpr TcId]
853 type ArgChecker results
854 = [TyVar] -> [TcSigmaType] -- Current instantiation
855 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
856 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
858 tcArgs fun args qtvs qtys arg_tys
859 = go 1 qtys args arg_tys
861 go n qtys [] [] = return (qtys, [])
862 go n qtys (arg:args) (arg_ty:arg_tys)
863 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
864 ; qtys' <- mapM refineBox qtys -- Exploit new info
865 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
866 ; return (qtys'', arg':args') }
867 go n qtys args arg_tys = panic "tcArgs"
869 tcArg :: LHsExpr Name -- The function
870 -> Int -- and arg number (for error messages)
872 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
874 -> TcM (LHsExpr TcId) -- Resulting argument
875 tcArg fun arg_no arg qtvs qtys ty
876 = addErrCtxt (funAppCtxt fun arg arg_no) $
877 tcPolyExprNC arg (substTyWith qtvs qtys ty)
883 Nasty check to ensure that tagToEnum# is applied to a type that is an
884 enumeration TyCon. Unification may refine the type later, but this
885 check won't see that, alas. It's crude but it works.
887 Here's are two cases that should fail
889 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
892 g = tagToEnum# 0 -- Int is not an enumeration
896 doStupidChecks :: HsExpr TcId
897 -> [([TcType], ThetaType)]
899 -- Check two tiresome and ad-hoc cases
900 -- (a) the "stupid theta" for a data con; add the constraints
901 -- from the "stupid theta" of a data constructor (sigh)
902 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
904 doStupidChecks (HsVar fun_id) ((tys,_):_)
905 | Just con <- isDataConId_maybe fun_id -- (a)
906 = addDataConStupidTheta con tys
908 | fun_id `hasKey` tagToEnumKey -- (b)
909 = do { tys' <- zonkTcTypes tys
910 ; checkTc (ok tys') (tagToEnumError tys')
914 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
915 Just (tc,_) -> isEnumerationTyCon tc
918 doStupidChecks fun tv_theta_prs
919 = return () -- The common case
923 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
924 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
925 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
927 at_type | null tys = empty -- Probably never happens
928 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
931 %************************************************************************
933 \subsection{@tcId@ typechecks an identifier occurrence}
935 %************************************************************************
938 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
939 lookupFun orig id_name
940 = do { thing <- tcLookup id_name
942 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
944 wrap_id = dataConWrapId con
947 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
948 | otherwise -> return (HsVar id, idType id)
949 -- A global cannot possibly be ill-staged
950 -- nor does it need the 'lifting' treatment
952 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
953 -> do { thLocalId orig id ty lvl
955 Nothing -> return (HsVar id, ty) -- Wobbly, or no free vars
956 Just co -> return (mkHsWrap co (HsVar id), ty) }
958 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
961 #ifndef GHCI /* GHCI and TH is off */
962 --------------------------------------
963 -- thLocalId : Check for cross-stage lifting
964 thLocalId orig id id_ty th_bind_lvl
967 #else /* GHCI and TH is on */
968 thLocalId orig id id_ty th_bind_lvl
969 = do { use_stage <- getStage -- TH case
971 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
972 -> thBrackId orig id ps_var lie_var
973 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
977 --------------------------------------
978 thBrackId orig id ps_var lie_var
979 | isExternalName id_name
980 = -- Top-level identifiers in this module,
981 -- (which have External Names)
982 -- are just like the imported case:
983 -- no need for the 'lifting' treatment
984 -- E.g. this is fine:
987 -- But we do need to put f into the keep-alive
988 -- set, because after desugaring the code will
989 -- only mention f's *name*, not f itself.
990 do { keepAliveTc id_name; return id }
993 = -- Nested identifiers, such as 'x' in
994 -- E.g. \x -> [| h x |]
995 -- We must behave as if the reference to x was
997 -- We use 'x' itself as the splice proxy, used by
998 -- the desugarer to stitch it all back together.
999 -- If 'x' occurs many times we may get many identical
1000 -- bindings of the same splice proxy, but that doesn't
1001 -- matter, although it's a mite untidy.
1002 do { let id_ty = idType id
1003 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1004 -- If x is polymorphic, its occurrence sites might
1005 -- have different instantiations, so we can't use plain
1006 -- 'x' as the splice proxy name. I don't know how to
1007 -- solve this, and it's probably unimportant, so I'm
1008 -- just going to flag an error for now
1010 ; id_ty' <- zapToMonotype id_ty
1011 -- The id_ty might have an OpenTypeKind, but we
1012 -- can't instantiate the Lift class at that kind,
1013 -- so we zap it to a LiftedTypeKind monotype
1014 -- C.f. the call in TcPat.newLitInst
1016 ; setLIEVar lie_var $ do
1017 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
1018 -- Put the 'lift' constraint into the right LIE
1020 -- Update the pending splices
1021 ; ps <- readMutVar ps_var
1022 ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1031 %************************************************************************
1033 \subsection{Record bindings}
1035 %************************************************************************
1037 Game plan for record bindings
1038 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1039 1. Find the TyCon for the bindings, from the first field label.
1041 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1043 For each binding field = value
1045 3. Instantiate the field type (from the field label) using the type
1048 4 Type check the value using tcArg, passing the field type as
1049 the expected argument type.
1051 This extends OK when the field types are universally quantified.
1057 -> [TcType] -- Expected type for each field
1058 -> HsRecordBinds Name
1059 -> TcM (HsRecordBinds TcId)
1061 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1062 = do { mb_binds <- mappM do_bind rbinds
1063 ; return (HsRecFields (catMaybes mb_binds) dd) }
1065 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1066 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1067 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1068 = addErrCtxt (fieldCtxt field_lbl) $
1069 do { rhs' <- tcPolyExprNC rhs field_ty
1070 ; sel_id <- tcLookupField field_lbl
1071 ; ASSERT( isRecordSelector sel_id )
1072 return (Just (fld { hsRecFieldId = L loc sel_id, hsRecFieldArg = rhs' })) }
1074 = do { addErrTc (badFieldCon data_con field_lbl)
1077 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1078 checkMissingFields data_con rbinds
1079 | null field_labels -- Not declared as a record;
1080 -- But C{} is still valid if no strict fields
1081 = if any isMarkedStrict field_strs then
1082 -- Illegal if any arg is strict
1083 addErrTc (missingStrictFields data_con [])
1087 | otherwise -- A record
1088 = checkM (null missing_s_fields)
1089 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1091 doptM Opt_WarnMissingFields `thenM` \ warn ->
1092 checkM (not (warn && notNull missing_ns_fields))
1093 (warnTc True (missingFields data_con missing_ns_fields))
1097 = [ fl | (fl, str) <- field_info,
1099 not (fl `elem` field_names_used)
1102 = [ fl | (fl, str) <- field_info,
1103 not (isMarkedStrict str),
1104 not (fl `elem` field_names_used)
1107 field_names_used = hsRecFields rbinds
1108 field_labels = dataConFieldLabels data_con
1110 field_info = zipEqual "missingFields"
1114 field_strs = dataConStrictMarks data_con
1117 %************************************************************************
1119 \subsection{Errors and contexts}
1121 %************************************************************************
1123 Boring and alphabetical:
1126 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1129 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1131 fieldCtxt field_name
1132 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1134 funAppCtxt fun arg arg_no
1135 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1136 quotes (ppr fun) <> text ", namely"])
1137 4 (quotes (ppr arg))
1140 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1143 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type")
1144 <+> quotes (pprSourceTyCon tycon)
1145 <+> ptext SLIT("is not (yet) supported"),
1146 ptext SLIT("Use pattern-matching instead")]
1148 = hang (ptext SLIT("No constructor has all these fields:"))
1149 4 (pprQuotedList (hsRecFields rbinds))
1151 naughtyRecordSel sel_id
1152 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1153 ptext SLIT("as a function due to escaped type variables") $$
1154 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1157 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1159 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1160 missingStrictFields con fields
1163 rest | null fields = empty -- Happens for non-record constructors
1164 -- with strict fields
1165 | otherwise = colon <+> pprWithCommas ppr fields
1167 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1168 ptext SLIT("does not have the required strict field(s)")
1170 missingFields :: DataCon -> [FieldLabel] -> SDoc
1171 missingFields con fields
1172 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1173 <+> pprWithCommas ppr fields
1175 -- callCtxt fun args = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1178 polySpliceErr :: Id -> SDoc
1180 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)