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 NegateOrigin 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 { let origin = IPOccOrigin ip
163 -- Implicit parameters must have a *tau-type* not a
164 -- type scheme. We enforce this by creating a fresh
165 -- type variable as its type. (Because res_ty may not
167 ; ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
168 ; co_fn <- tcSubExp origin ip_ty res_ty
169 ; (ip', inst) <- newIPDict origin ip ip_ty
171 ; return (mkHsWrap co_fn (HsIPVar ip')) }
173 tcExpr (HsApp e1 e2) res_ty
176 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
177 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
178 go lfun@(L loc fun) args
179 = do { (fun', args') <- -- addErrCtxt (callCtxt lfun args) $
180 tcApp fun (length args) (tcArgs lfun args) res_ty
181 ; traceTc (text "tcExpr args': " <+> ppr args')
182 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
184 tcExpr (HsLam match) res_ty
185 = do { (co_fn, match') <- tcMatchLambda match res_ty
186 ; return (mkHsWrap co_fn (HsLam match')) }
188 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
189 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
191 -- Remember to extend the lexical type-variable environment
192 ; (gen_fn, expr') <- tcGen sig_tc_ty emptyVarSet (\ skol_tvs res_ty ->
193 tcExtendTyVarEnv2 (hsExplicitTvs sig_ty `zip` mkTyVarTys skol_tvs) $
194 tcPolyExprNC expr res_ty)
196 ; co_fn <- tcSubExp ExprSigOrigin sig_tc_ty res_ty
197 ; return (mkHsWrap co_fn (ExprWithTySigOut (mkLHsWrap gen_fn expr') sig_ty)) }
199 tcExpr (HsType ty) res_ty
200 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
201 -- This is the syntax for type applications that I was planning
202 -- but there are difficulties (e.g. what order for type args)
203 -- so it's not enabled yet.
204 -- Can't eliminate it altogether from the parser, because the
205 -- same parser parses *patterns*.
209 %************************************************************************
211 Infix operators and sections
213 %************************************************************************
216 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
217 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
218 ; return (OpApp arg1' (L loc op') fix arg2') }
220 -- Left sections, equivalent to
227 -- We treat it as similar to the latter, so we don't
228 -- actually require the function to take two arguments
229 -- at all. For example, (x `not`) means (not x);
230 -- you get postfix operators! Not really Haskell 98
231 -- I suppose, but it's less work and kind of useful.
233 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
234 = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
235 ; return (SectionL arg1' (L loc op')) }
237 -- Right sections, equivalent to \ x -> x `op` expr, or
240 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
241 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
242 tcApp op 2 (tc_args arg1_ty') res_ty'
243 ; return (mkHsWrap co_fn (SectionR (L loc op') arg2')) }
245 doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
246 <+> ptext SLIT("takes one argument")
247 tc_args arg1_ty' qtvs qtys [arg1_ty, arg2_ty]
248 = do { boxyUnify arg1_ty' (substTyWith qtvs qtys arg1_ty)
249 ; arg2' <- tcArg lop 2 arg2 qtvs qtys arg2_ty
250 ; qtys' <- mapM refineBox qtys -- c.f. tcArgs
251 ; return (qtys', arg2') }
252 tc_args arg1_ty' _ _ _ = panic "tcExpr SectionR"
256 tcExpr (HsLet binds expr) res_ty
257 = do { (binds', expr') <- tcLocalBinds binds $
258 tcMonoExpr expr res_ty
259 ; return (HsLet binds' expr') }
261 tcExpr (HsCase scrut matches) exp_ty
262 = do { -- We used to typecheck the case alternatives first.
263 -- The case patterns tend to give good type info to use
264 -- when typechecking the scrutinee. For example
267 -- will report that map is applied to too few arguments
269 -- But now, in the GADT world, we need to typecheck the scrutinee
270 -- first, to get type info that may be refined in the case alternatives
271 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
274 ; traceTc (text "HsCase" <+> ppr scrut_ty)
275 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
276 ; return (HsCase scrut' matches') }
278 match_ctxt = MC { mc_what = CaseAlt,
281 tcExpr (HsIf pred b1 b2) res_ty
282 = do { pred' <- addErrCtxt (predCtxt pred) $
283 tcMonoExpr pred boolTy
284 ; b1' <- tcMonoExpr b1 res_ty
285 ; b2' <- tcMonoExpr b2 res_ty
286 ; return (HsIf pred' b1' b2') }
288 tcExpr (HsDo do_or_lc stmts body _) res_ty
289 = tcDoStmts do_or_lc stmts body res_ty
291 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
292 = do { (elt_ty, coi) <- boxySplitListTy res_ty
293 ; exprs' <- mappM (tc_elt elt_ty) exprs
294 ; return $ mkHsWrapCoI coi (ExplicitList elt_ty exprs') }
296 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
298 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
299 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
300 ; exprs' <- mappM (tc_elt elt_ty) exprs
301 ; ifM (null exprs) (zapToMonotype elt_ty)
302 -- If there are no expressions in the comprehension
303 -- we must still fill in the box
304 -- (Not needed for [] and () becuase they happen
305 -- to parse as data constructors.)
306 ; return $ mkHsWrapCoI coi (ExplicitPArr elt_ty exprs') }
308 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
310 -- For tuples, take care to preserve rigidity
311 -- E.g. case (x,y) of ....
312 -- The scrutinee should have a rigid type if x,y do
313 -- The general scheme is the same as in tcIdApp
314 tcExpr (ExplicitTuple exprs boxity) res_ty
315 = do { tvs <- newBoxyTyVars [argTypeKind | e <- exprs]
316 ; let tup_tc = tupleTyCon boxity (length exprs)
317 tup_res_ty = mkTyConApp tup_tc (mkTyVarTys tvs)
318 ; checkWiredInTyCon tup_tc -- Ensure instances are available
319 ; arg_tys <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
320 ; exprs' <- tcPolyExprs exprs arg_tys
321 ; arg_tys' <- mapM refineBox arg_tys
322 ; co_fn <- tcSubExp TupleOrigin (mkTyConApp tup_tc arg_tys') res_ty
323 ; return (mkHsWrap co_fn (ExplicitTuple exprs' boxity)) }
325 tcExpr (HsProc pat cmd) res_ty
326 = do { (pat', cmd', coi) <- tcProc pat cmd res_ty
327 ; return $ mkHsWrapCoI coi (HsProc pat' cmd') }
329 tcExpr e@(HsArrApp _ _ _ _ _) _
330 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
331 ptext SLIT("was found where an expression was expected")])
333 tcExpr e@(HsArrForm _ _ _) _
334 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
335 ptext SLIT("was found where an expression was expected")])
338 %************************************************************************
340 Record construction and update
342 %************************************************************************
345 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
346 = do { data_con <- tcLookupDataCon con_name
348 -- Check for missing fields
349 ; checkMissingFields data_con rbinds
351 ; let arity = dataConSourceArity data_con
352 check_fields qtvs qtys arg_tys
353 = do { let arg_tys' = substTys (zipOpenTvSubst qtvs qtys) arg_tys
354 ; rbinds' <- tcRecordBinds data_con arg_tys' rbinds
355 ; qtys' <- mapM refineBoxToTau qtys
356 ; return (qtys', rbinds') }
357 -- The refineBoxToTau ensures that all the boxes in arg_tys are indeed
358 -- filled, which is the invariant expected by tcIdApp
359 -- How could this not be the case? Consider a record construction
360 -- that does not mention all the fields.
362 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
364 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
366 -- The main complication with RecordUpd is that we need to explicitly
367 -- handle the *non-updated* fields. Consider:
369 -- data T a b = MkT1 { fa :: a, fb :: b }
370 -- | MkT2 { fa :: a, fc :: Int -> Int }
371 -- | MkT3 { fd :: a }
373 -- upd :: T a b -> c -> T a c
374 -- upd t x = t { fb = x}
376 -- The type signature on upd is correct (i.e. the result should not be (T a b))
377 -- because upd should be equivalent to:
379 -- upd t x = case t of
380 -- MkT1 p q -> MkT1 p x
381 -- MkT2 a b -> MkT2 p b
382 -- MkT3 d -> error ...
384 -- So we need to give a completely fresh type to the result record,
385 -- and then constrain it by the fields that are *not* updated ("p" above).
387 -- Note that because MkT3 doesn't contain all the fields being updated,
388 -- its RHS is simply an error, so it doesn't impose any type constraints
390 -- All this is done in STEP 4 below.
394 -- For record update we require that every constructor involved in the
395 -- update (i.e. that has all the specified fields) is "vanilla". I
396 -- don't know how to do the update otherwise.
399 tcExpr expr@(RecordUpd record_expr rbinds _ _ _) res_ty
401 -- Check that the field names are really field names
403 field_names = hsRecFields rbinds
405 ASSERT( notNull field_names )
406 mappM tcLookupField field_names `thenM` \ sel_ids ->
407 -- The renamer has already checked that they
410 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
411 | (fld, sel_id) <- rec_flds rbinds `zip` sel_ids,
412 not (isRecordSelector sel_id), -- Excludes class ops
413 let L loc field_name = hsRecFieldId fld
416 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
419 -- Figure out the tycon and data cons from the first field name
421 -- It's OK to use the non-tc splitters here (for a selector)
423 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
424 data_cons = tyConDataCons tycon -- it's not a field label
425 -- NB: for a data type family, the tycon is the instance tycon
427 relevant_cons = filter is_relevant data_cons
428 is_relevant con = all (`elem` dataConFieldLabels con) field_names
432 -- Check that at least one constructor has all the named fields
433 -- i.e. has an empty set of bad fields returned by badFields
434 checkTc (not (null relevant_cons))
435 (badFieldsUpd rbinds) `thenM_`
437 -- Check that all relevant data cons are vanilla. Doing record updates on
438 -- GADTs and/or existentials is more than my tiny brain can cope with today
439 checkTc (all isVanillaDataCon relevant_cons)
440 (nonVanillaUpd tycon) `thenM_`
443 -- Use the un-updated fields to find a vector of booleans saying
444 -- which type arguments must be the same in updatee and result.
446 -- WARNING: this code assumes that all data_cons in a common tycon
447 -- have FieldLabels abstracted over the same tyvars.
449 -- A constructor is only relevant to this process if
450 -- it contains *all* the fields that are being updated
451 con1 = ASSERT( not (null relevant_cons) ) head relevant_cons -- A representative constructor
452 (con1_tyvars, theta, con1_arg_tys, con1_res_ty) = dataConSig con1
453 con1_flds = dataConFieldLabels con1
454 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
455 , not (fld `elem` field_names) ]
457 is_common_tv tv = tv `elemVarSet` common_tyvars
459 mk_inst_ty tv result_inst_ty
460 | is_common_tv tv = returnM result_inst_ty -- Same as result type
461 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
463 ASSERT( null theta ) -- Vanilla datacon
464 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, result_inst_env) ->
465 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ scrut_inst_tys ->
467 -- STEP 3: Typecheck the update bindings.
468 -- Do this after checking for bad fields in case
469 -- there's a field that doesn't match the constructor.
471 result_ty = substTy result_inst_env con1_res_ty
472 con1_arg_tys' = map (substTy result_inst_env) con1_arg_tys
473 origin = RecordUpdOrigin
475 tcSubExp origin result_ty res_ty `thenM` \ co_fn ->
476 tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
478 -- STEP 5: Typecheck the expression to be updated
480 scrut_inst_env = zipTopTvSubst con1_tyvars scrut_inst_tys
481 scrut_ty = substTy scrut_inst_env con1_res_ty
482 -- This is one place where the isVanilla check is important
483 -- So that inst_tys matches the con1_tyvars
485 tcMonoExpr record_expr scrut_ty `thenM` \ record_expr' ->
487 -- STEP 6: Figure out the LIE we need.
488 -- We have to generate some dictionaries for the data type context,
489 -- since we are going to do pattern matching over the data cons.
491 -- What dictionaries do we need? The dataConStupidTheta tells us.
493 theta' = substTheta scrut_inst_env (dataConStupidTheta con1)
495 instStupidTheta origin theta' `thenM_`
497 -- Step 7: make a cast for the scrutinee, in the case that it's from a type family
498 let scrut_co | Just co_con <- tyConFamilyCoercion_maybe tycon
499 = WpCo $ mkTyConApp co_con scrut_inst_tys
504 returnM (mkHsWrap co_fn (RecordUpd (mkLHsWrap scrut_co record_expr') rbinds'
505 relevant_cons scrut_inst_tys result_inst_tys))
509 %************************************************************************
511 Arithmetic sequences e.g. [a,b..]
512 and their parallel-array counterparts e.g. [: a,b.. :]
515 %************************************************************************
518 tcExpr (ArithSeq _ seq@(From expr)) res_ty
519 = do { (elt_ty, coi) <- boxySplitListTy res_ty
520 ; expr' <- tcPolyExpr expr elt_ty
521 ; enum_from <- newMethodFromName (ArithSeqOrigin seq)
523 ; return $ mkHsWrapCoI coi (ArithSeq (HsVar enum_from) (From expr')) }
525 tcExpr in_expr@(ArithSeq _ seq@(FromThen expr1 expr2)) res_ty
526 = do { (elt_ty, coi) <- boxySplitListTy res_ty
527 ; expr1' <- tcPolyExpr expr1 elt_ty
528 ; expr2' <- tcPolyExpr expr2 elt_ty
529 ; enum_from_then <- newMethodFromName (ArithSeqOrigin seq)
530 elt_ty enumFromThenName
531 ; return $ mkHsWrapCoI coi
532 (ArithSeq (HsVar enum_from_then) (FromThen expr1' expr2')) }
534 tcExpr in_expr@(ArithSeq _ seq@(FromTo expr1 expr2)) res_ty
535 = do { (elt_ty, coi) <- boxySplitListTy res_ty
536 ; expr1' <- tcPolyExpr expr1 elt_ty
537 ; expr2' <- tcPolyExpr expr2 elt_ty
538 ; enum_from_to <- newMethodFromName (ArithSeqOrigin seq)
539 elt_ty enumFromToName
540 ; return $ mkHsWrapCoI coi
541 (ArithSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
543 tcExpr in_expr@(ArithSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
544 = do { (elt_ty, coi) <- boxySplitListTy res_ty
545 ; expr1' <- tcPolyExpr expr1 elt_ty
546 ; expr2' <- tcPolyExpr expr2 elt_ty
547 ; expr3' <- tcPolyExpr expr3 elt_ty
548 ; eft <- newMethodFromName (ArithSeqOrigin seq)
549 elt_ty enumFromThenToName
550 ; return $ mkHsWrapCoI coi
551 (ArithSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
553 tcExpr in_expr@(PArrSeq _ seq@(FromTo expr1 expr2)) res_ty
554 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
555 ; expr1' <- tcPolyExpr expr1 elt_ty
556 ; expr2' <- tcPolyExpr expr2 elt_ty
557 ; enum_from_to <- newMethodFromName (PArrSeqOrigin seq)
558 elt_ty enumFromToPName
559 ; return $ mkHsWrapCoI coi
560 (PArrSeq (HsVar enum_from_to) (FromTo expr1' expr2')) }
562 tcExpr in_expr@(PArrSeq _ seq@(FromThenTo expr1 expr2 expr3)) res_ty
563 = do { (elt_ty, coi) <- boxySplitPArrTy res_ty
564 ; expr1' <- tcPolyExpr expr1 elt_ty
565 ; expr2' <- tcPolyExpr expr2 elt_ty
566 ; expr3' <- tcPolyExpr expr3 elt_ty
567 ; eft <- newMethodFromName (PArrSeqOrigin seq)
568 elt_ty enumFromThenToPName
569 ; return $ mkHsWrapCoI coi
570 (PArrSeq (HsVar eft) (FromThenTo expr1' expr2' expr3')) }
572 tcExpr (PArrSeq _ _) _
573 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
574 -- the parser shouldn't have generated it and the renamer shouldn't have
579 %************************************************************************
583 %************************************************************************
586 #ifdef GHCI /* Only if bootstrapped */
587 -- Rename excludes these cases otherwise
588 tcExpr (HsSpliceE splice) res_ty = tcSpliceExpr splice res_ty
589 tcExpr (HsBracket brack) res_ty = do { e <- tcBracket brack res_ty
591 tcExpr e@(HsQuasiQuoteE _) res_ty =
592 pprPanic "Should never see HsQuasiQuoteE in type checker" (ppr e)
597 %************************************************************************
601 %************************************************************************
604 tcExpr other _ = pprPanic "tcMonoExpr" (ppr other)
608 %************************************************************************
612 %************************************************************************
615 ---------------------------
616 tcApp :: HsExpr Name -- Function
617 -> Arity -- Number of args reqd
618 -> ArgChecker results
619 -> BoxyRhoType -- Result type
620 -> TcM (HsExpr TcId, results)
622 -- (tcFun fun n_args arg_checker res_ty)
623 -- The argument type checker, arg_checker, will be passed exactly n_args types
625 tcApp (HsVar fun_name) n_args arg_checker res_ty
626 = tcIdApp fun_name n_args arg_checker res_ty
628 tcApp fun n_args arg_checker res_ty -- The vanilla case (rula APP)
629 = do { arg_boxes <- newBoxyTyVars (replicate n_args argTypeKind)
630 ; fun' <- tcExpr fun (mkFunTys (mkTyVarTys arg_boxes) res_ty)
631 ; arg_tys' <- mapM readFilledBox arg_boxes
632 ; (_, args') <- arg_checker [] [] arg_tys' -- Yuk
633 ; return (fun', args') }
635 ---------------------------
636 tcIdApp :: Name -- Function
637 -> Arity -- Number of args reqd
638 -> ArgChecker results -- The arg-checker guarantees to fill all boxes in the arg types
639 -> BoxyRhoType -- Result type
640 -> TcM (HsExpr TcId, results)
642 -- Call (f e1 ... en) :: res_ty
643 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
644 -- (where k <= n; fres has the rest)
645 -- NB: if k < n then the function doesn't have enough args, and
646 -- presumably fres is a type variable that we are going to
647 -- instantiate with a function type
649 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
651 tcIdApp fun_name n_args arg_checker res_ty
652 = do { let orig = OccurrenceOf fun_name
653 ; (fun, fun_ty) <- lookupFun orig fun_name
655 -- Split up the function type
656 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy fun_ty
657 (fun_arg_tys, fun_res_ty) = tcSplitFunTysN rho n_args
659 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
660 arg_qtvs = exactTyVarsOfTypes fun_arg_tys
661 res_qtvs = exactTyVarsOfType fun_res_ty
662 -- NB: exactTyVarsOfType. See Note [Silly type synonyms in smart-app]
663 tau_qtvs = arg_qtvs `unionVarSet` res_qtvs
664 k = length fun_arg_tys -- k <= n_args
665 n_missing_args = n_args - k -- Always >= 0
667 -- Match the result type of the function with the
668 -- result type of the context, to get an inital substitution
669 ; extra_arg_boxes <- newBoxyTyVars (replicate n_missing_args argTypeKind)
670 ; let extra_arg_tys' = mkTyVarTys extra_arg_boxes
671 res_ty' = mkFunTys extra_arg_tys' res_ty
672 ; qtys' <- preSubType qtvs tau_qtvs fun_res_ty res_ty'
674 -- Typecheck the arguments!
675 -- Doing so will fill arg_qtvs and extra_arg_tys'
676 ; (qtys'', args') <- arg_checker qtvs qtys' (fun_arg_tys ++ extra_arg_tys')
678 -- Strip boxes from the qtvs that have been filled in by the arg checking
679 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
681 -- Result subsumption
682 -- This fills in res_qtvs
683 ; let res_subst = zipOpenTvSubst qtvs qtys''
684 fun_res_ty'' = substTy res_subst fun_res_ty
685 res_ty'' = mkFunTys extra_arg_tys'' res_ty
686 ; co_fn <- tcSubExp orig fun_res_ty'' res_ty''
688 -- And pack up the results
689 -- By applying the coercion just to the *function* we can make
690 -- tcFun work nicely for OpApp and Sections too
691 ; fun' <- instFun orig fun res_subst tv_theta_prs
692 ; co_fn' <- wrapFunResCoercion (substTys res_subst fun_arg_tys) co_fn
693 ; traceTc (text "tcIdApp: " <+> ppr (mkHsWrap co_fn' fun') <+> ppr tv_theta_prs <+> ppr co_fn' <+> ppr fun')
694 ; return (mkHsWrap co_fn' fun', args') }
697 Note [Silly type synonyms in smart-app]
698 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
699 When we call sripBoxyType, all of the boxes should be filled
700 in. But we need to be careful about type synonyms:
704 In the call (f x) we'll typecheck x, expecting it to have type
705 (T box). Usually that would fill in the box, but in this case not;
706 because 'a' is discarded by the silly type synonym T. So we must
707 use exactTyVarsOfType to figure out which type variables are free
708 in the argument type.
711 -- tcId is a specialisation of tcIdApp when there are no arguments
712 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
717 -> BoxyRhoType -- Result type
719 tcId orig fun_name res_ty
720 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
721 ; (fun, fun_ty) <- lookupFun orig fun_name
723 -- Split up the function type
724 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy fun_ty
725 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
726 tau_qtvs = exactTyVarsOfType fun_tau -- Mentioned in the tau part
727 ; qtv_tys <- preSubType qtvs tau_qtvs fun_tau res_ty
729 -- Do the subsumption check wrt the result type
730 ; let res_subst = zipTopTvSubst qtvs qtv_tys
731 fun_tau' = substTy res_subst fun_tau
733 ; co_fn <- tcSubExp orig fun_tau' res_ty
735 -- And pack up the results
736 ; fun' <- instFun orig fun res_subst tv_theta_prs
737 ; traceTc (text "tcId yields" <+> ppr (mkHsWrap co_fn fun'))
738 ; return (mkHsWrap co_fn fun') }
740 -- Note [Push result type in]
742 -- Unify with expected result before (was: after) type-checking the args
743 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
744 -- This is when we might detect a too-few args situation.
745 -- (One can think of cases when the opposite order would give
746 -- a better error message.)
747 -- [March 2003: I'm experimenting with putting this first. Here's an
748 -- example where it actually makes a real difference
749 -- class C t a b | t a -> b
750 -- instance C Char a Bool
752 -- data P t a = forall b. (C t a b) => MkP b
753 -- data Q t = MkQ (forall a. P t a)
756 -- f1 = MkQ (MkP True)
757 -- f2 = MkQ (MkP True :: forall a. P Char a)
759 -- With the change, f1 will type-check, because the 'Char' info from
760 -- the signature is propagated into MkQ's argument. With the check
761 -- in the other order, the extra signature in f2 is reqd.]
763 ---------------------------
764 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
765 -- Typecheck a syntax operator, checking that it has the specified type
766 -- The operator is always a variable at this stage (i.e. renamer output)
767 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
768 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
770 ---------------------------
771 instFun :: InstOrigin
773 -> TvSubst -- The instantiating substitution
774 -> [([TyVar], ThetaType)] -- Stuff to instantiate
777 instFun orig fun subst []
778 = return fun -- Common short cut
780 instFun orig fun subst tv_theta_prs
781 = do { let ty_theta_prs' = map subst_pr tv_theta_prs
782 ; traceTc (text "instFun" <+> ppr ty_theta_prs')
783 -- Make two ad-hoc checks
784 ; doStupidChecks fun ty_theta_prs'
786 -- Now do normal instantiation
787 ; result <- go True fun ty_theta_prs'
788 ; traceTc (text "instFun result" <+> ppr result)
792 subst_pr (tvs, theta)
793 = (substTyVars subst tvs, substTheta subst theta)
795 go _ fun [] = do {traceTc (text "go _ fun [] returns" <+> ppr fun) ; return fun }
797 go True (HsVar fun_id) ((tys,theta) : prs)
798 | want_method_inst theta
799 = do { traceTc (text "go (HsVar fun_id) ((tys,theta) : prs) | want_method_inst theta")
800 ; meth_id <- newMethodWithGivenTy orig fun_id tys
801 ; go False (HsVar meth_id) prs }
802 -- Go round with 'False' to prevent further use
803 -- of newMethod: see Note [Multiple instantiation]
805 go _ fun ((tys, theta) : prs)
806 = do { co_fn <- instCall orig tys theta
807 ; traceTc (text "go yields co_fn" <+> ppr co_fn)
808 ; go False (HsWrap co_fn fun) prs }
810 -- See Note [No method sharing]
811 want_method_inst theta = not (null theta) -- Overloaded
812 && not opt_NoMethodSharing
815 Note [Multiple instantiation]
816 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
817 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
818 For example, consider
819 f :: forall a. Eq a => forall b. Ord b => a -> b
820 At a call to f, at say [Int, Bool], it's tempting to translate the call to
824 f_m1 :: forall b. Ord b => Int -> b
828 f_m2 = f_m1 Bool dOrdBool
830 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
831 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
833 But it's entirely possible that f_m2 will continue to float out, because it
834 mentions no type variables. Result, f_m1 isn't in scope.
836 Here's a concrete example that does this (test tc200):
839 f :: Eq b => b -> a -> Int
840 baz :: Eq a => Int -> a -> Int
845 Current solution: only do the "method sharing" thing for the first type/dict
846 application, not for the iterated ones. A horribly subtle point.
848 Note [No method sharing]
849 ~~~~~~~~~~~~~~~~~~~~~~~~
850 The -fno-method-sharing flag controls what happens so far as the LIE
851 is concerned. The default case is that for an overloaded function we
852 generate a "method" Id, and add the Method Inst to the LIE. So you get
855 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
856 If you specify -fno-method-sharing, the dictionary application
857 isn't shared, so we get
859 f = /\a (d:Num a) (x:a) -> (+) a d x x
860 This gets a bit less sharing, but
861 a) it's better for RULEs involving overloaded functions
862 b) perhaps fewer separated lambdas
866 tcArgs implements a left-to-right order, which goes beyond what is described in the
867 impredicative type inference paper. In particular, it allows
869 where runST :: (forall s. ST s a) -> a
870 When typechecking the application of ($)::(a->b) -> a -> b, we first check that
871 runST has type (a->b), thereby filling in a=forall s. ST s a. Then we un-box this type
872 before checking foo. The left-to-right order really helps here.
875 tcArgs :: LHsExpr Name -- The function (for error messages)
876 -> [LHsExpr Name] -- Actual args
877 -> ArgChecker [LHsExpr TcId]
879 type ArgChecker results
880 = [TyVar] -> [TcSigmaType] -- Current instantiation
881 -> [TcSigmaType] -- Expected arg types (**before** applying the instantiation)
882 -> TcM ([TcSigmaType], results) -- Resulting instaniation and args
884 tcArgs fun args qtvs qtys arg_tys
885 = go 1 qtys args arg_tys
887 go n qtys [] [] = return (qtys, [])
888 go n qtys (arg:args) (arg_ty:arg_tys)
889 = do { arg' <- tcArg fun n arg qtvs qtys arg_ty
890 ; qtys' <- mapM refineBox qtys -- Exploit new info
891 ; (qtys'', args') <- go (n+1) qtys' args arg_tys
892 ; return (qtys'', arg':args') }
893 go n qtys args arg_tys = panic "tcArgs"
895 tcArg :: LHsExpr Name -- The function
896 -> Int -- and arg number (for error messages)
898 -> [TyVar] -> [TcSigmaType] -- Instantiate the arg type like this
900 -> TcM (LHsExpr TcId) -- Resulting argument
901 tcArg fun arg_no arg qtvs qtys ty
902 = addErrCtxt (funAppCtxt fun arg arg_no) $
903 tcPolyExprNC arg (substTyWith qtvs qtys ty)
909 Nasty check to ensure that tagToEnum# is applied to a type that is an
910 enumeration TyCon. Unification may refine the type later, but this
911 check won't see that, alas. It's crude but it works.
913 Here's are two cases that should fail
915 f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable
918 g = tagToEnum# 0 -- Int is not an enumeration
922 doStupidChecks :: HsExpr TcId
923 -> [([TcType], ThetaType)]
925 -- Check two tiresome and ad-hoc cases
926 -- (a) the "stupid theta" for a data con; add the constraints
927 -- from the "stupid theta" of a data constructor (sigh)
928 -- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
930 doStupidChecks (HsVar fun_id) ((tys,_):_)
931 | Just con <- isDataConId_maybe fun_id -- (a)
932 = addDataConStupidTheta con tys
934 | fun_id `hasKey` tagToEnumKey -- (b)
935 = do { tys' <- zonkTcTypes tys
936 ; checkTc (ok tys') (tagToEnumError tys')
940 ok (ty:tys) = case tcSplitTyConApp_maybe ty of
941 Just (tc,_) -> isEnumerationTyCon tc
944 doStupidChecks fun tv_theta_prs
945 = return () -- The common case
949 = hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
950 2 (vcat [ptext SLIT("Specify the type by giving a type signature"),
951 ptext SLIT("e.g. (tagToEnum# x) :: Bool")])
953 at_type | null tys = empty -- Probably never happens
954 | otherwise = ptext SLIT("at type") <+> ppr (head tys)
957 %************************************************************************
959 \subsection{@tcId@ typechecks an identifier occurrence}
961 %************************************************************************
964 lookupFun :: InstOrigin -> Name -> TcM (HsExpr TcId, TcType)
965 lookupFun orig id_name
966 = do { thing <- tcLookup id_name
968 AGlobal (ADataCon con) -> return (HsVar wrap_id, idType wrap_id)
970 wrap_id = dataConWrapId con
973 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
974 | otherwise -> return (HsVar id, idType id)
975 -- A global cannot possibly be ill-staged
976 -- nor does it need the 'lifting' treatment
978 ATcId { tct_id = id, tct_type = ty, tct_co = mb_co, tct_level = lvl }
979 -> do { thLocalId orig id ty lvl
981 Unrefineable -> return (HsVar id, ty)
982 Rigid co -> return (mkHsWrap co (HsVar id), ty)
983 Wobbly -> traceTc (text "lookupFun" <+> ppr id) >> return (HsVar id, ty) -- Wobbly, or no free vars
984 WobblyInvisible -> failWithTc (ppr id_name <+> ptext SLIT(" not in scope because it has a wobbly type (solution: add a type annotation)"))
987 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
990 #ifndef GHCI /* GHCI and TH is off */
991 --------------------------------------
992 -- thLocalId : Check for cross-stage lifting
993 thLocalId orig id id_ty th_bind_lvl
996 #else /* GHCI and TH is on */
997 thLocalId orig id id_ty th_bind_lvl
998 = do { use_stage <- getStage -- TH case
1000 Brack use_lvl ps_var lie_var | use_lvl > th_bind_lvl
1001 -> thBrackId orig id ps_var lie_var
1002 other -> do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
1006 --------------------------------------
1007 thBrackId orig id ps_var lie_var
1009 = -- Top-level identifiers in this module,
1010 -- (which have External Names)
1011 -- are just like the imported case:
1012 -- no need for the 'lifting' treatment
1013 -- E.g. this is fine:
1016 -- But we do need to put f into the keep-alive
1017 -- set, because after desugaring the code will
1018 -- only mention f's *name*, not f itself.
1019 do { keepAliveTc id; return id }
1022 = -- Nested identifiers, such as 'x' in
1023 -- E.g. \x -> [| h x |]
1024 -- We must behave as if the reference to x was
1026 -- We use 'x' itself as the splice proxy, used by
1027 -- the desugarer to stitch it all back together.
1028 -- If 'x' occurs many times we may get many identical
1029 -- bindings of the same splice proxy, but that doesn't
1030 -- matter, although it's a mite untidy.
1031 do { let id_ty = idType id
1032 ; checkTc (isTauTy id_ty) (polySpliceErr id)
1033 -- If x is polymorphic, its occurrence sites might
1034 -- have different instantiations, so we can't use plain
1035 -- 'x' as the splice proxy name. I don't know how to
1036 -- solve this, and it's probably unimportant, so I'm
1037 -- just going to flag an error for now
1039 ; id_ty' <- zapToMonotype id_ty
1040 -- The id_ty might have an OpenTypeKind, but we
1041 -- can't instantiate the Lift class at that kind,
1042 -- so we zap it to a LiftedTypeKind monotype
1043 -- C.f. the call in TcPat.newLitInst
1045 ; setLIEVar lie_var $ do
1046 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
1047 -- Put the 'lift' constraint into the right LIE
1049 -- Update the pending splices
1050 ; ps <- readMutVar ps_var
1051 ; writeMutVar ps_var ((idName id, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
1058 %************************************************************************
1060 \subsection{Record bindings}
1062 %************************************************************************
1064 Game plan for record bindings
1065 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1066 1. Find the TyCon for the bindings, from the first field label.
1068 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1070 For each binding field = value
1072 3. Instantiate the field type (from the field label) using the type
1075 4 Type check the value using tcArg, passing the field type as
1076 the expected argument type.
1078 This extends OK when the field types are universally quantified.
1084 -> [TcType] -- Expected type for each field
1085 -> HsRecordBinds Name
1086 -> TcM (HsRecordBinds TcId)
1088 tcRecordBinds data_con arg_tys (HsRecFields rbinds dd)
1089 = do { mb_binds <- mappM do_bind rbinds
1090 ; return (HsRecFields (catMaybes mb_binds) dd) }
1092 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1093 do_bind fld@(HsRecField { hsRecFieldId = L loc field_lbl, hsRecFieldArg = rhs })
1094 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1095 = addErrCtxt (fieldCtxt field_lbl) $
1096 do { rhs' <- tcPolyExprNC rhs field_ty
1097 ; sel_id <- tcLookupField field_lbl
1098 ; ASSERT( isRecordSelector sel_id )
1099 return (Just (fld { hsRecFieldId = L loc sel_id, hsRecFieldArg = rhs' })) }
1101 = do { addErrTc (badFieldCon data_con field_lbl)
1104 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1105 checkMissingFields data_con rbinds
1106 | null field_labels -- Not declared as a record;
1107 -- But C{} is still valid if no strict fields
1108 = if any isMarkedStrict field_strs then
1109 -- Illegal if any arg is strict
1110 addErrTc (missingStrictFields data_con [])
1114 | otherwise -- A record
1115 = checkM (null missing_s_fields)
1116 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1118 doptM Opt_WarnMissingFields `thenM` \ warn ->
1119 checkM (not (warn && notNull missing_ns_fields))
1120 (warnTc True (missingFields data_con missing_ns_fields))
1124 = [ fl | (fl, str) <- field_info,
1126 not (fl `elem` field_names_used)
1129 = [ fl | (fl, str) <- field_info,
1130 not (isMarkedStrict str),
1131 not (fl `elem` field_names_used)
1134 field_names_used = hsRecFields rbinds
1135 field_labels = dataConFieldLabels data_con
1137 field_info = zipEqual "missingFields"
1141 field_strs = dataConStrictMarks data_con
1144 %************************************************************************
1146 \subsection{Errors and contexts}
1148 %************************************************************************
1150 Boring and alphabetical:
1153 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1156 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1158 fieldCtxt field_name
1159 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1161 funAppCtxt fun arg arg_no
1162 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1163 quotes (ppr fun) <> text ", namely"])
1164 4 (quotes (ppr arg))
1167 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1170 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type")
1171 <+> quotes (pprSourceTyCon tycon)
1172 <+> ptext SLIT("is not (yet) supported"),
1173 ptext SLIT("Use pattern-matching instead")]
1175 = hang (ptext SLIT("No constructor has all these fields:"))
1176 4 (pprQuotedList (hsRecFields rbinds))
1178 naughtyRecordSel sel_id
1179 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1180 ptext SLIT("as a function due to escaped type variables") $$
1181 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1184 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1186 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1187 missingStrictFields con fields
1190 rest | null fields = empty -- Happens for non-record constructors
1191 -- with strict fields
1192 | otherwise = colon <+> pprWithCommas ppr fields
1194 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1195 ptext SLIT("does not have the required strict field(s)")
1197 missingFields :: DataCon -> [FieldLabel] -> SDoc
1198 missingFields con fields
1199 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1200 <+> pprWithCommas ppr fields
1202 -- callCtxt fun args = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1205 polySpliceErr :: Id -> SDoc
1207 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)