2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcPolyExpr, tcPolyExprNC,
8 tcMonoExpr, tcInferRho, tcSyntaxOp ) where
10 #include "HsVersions.h"
12 #ifdef GHCI /* Only if bootstrapped */
13 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
14 import HsSyn ( nlHsVar )
16 import Name ( isExternalName )
17 import TcType ( isTauTy )
18 import TcEnv ( checkWellStaged )
19 import HsSyn ( nlHsApp )
20 import qualified DsMeta
23 import HsSyn ( HsExpr(..), LHsExpr, ArithSeqInfo(..), recBindFields,
24 HsMatchContext(..), HsRecordBinds,
25 mkHsCoerce, mkHsApp, mkHsDictApp, mkHsTyApp )
26 import TcHsSyn ( hsLitType )
28 import TcUnify ( tcInfer, tcSubExp, tcFunResTy, tcGen, boxyUnify, subFunTys, zapToMonotype, stripBoxyType,
29 boxySplitListTy, boxySplitTyConApp, wrapFunResCoercion, boxySubMatchType,
31 import BasicTypes ( Arity, isMarkedStrict )
32 import Inst ( newMethodFromName, newIPDict, instToId,
33 newDicts, newMethodWithGivenTy, tcInstStupidTheta )
34 import TcBinds ( tcLocalBinds )
35 import TcEnv ( tcLookup, tcLookupId,
36 tcLookupDataCon, tcLookupGlobalId
38 import TcArrows ( tcProc )
39 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts, TcMatchCtxt(..) )
40 import TcHsType ( tcHsSigType, UserTypeCtxt(..) )
41 import TcPat ( tcOverloadedLit, badFieldCon )
42 import TcMType ( tcInstTyVars, newFlexiTyVarTy, newBoxyTyVars, readFilledBox,
43 tcInstBoxyTyVar, tcInstTyVar )
44 import TcType ( TcType, TcSigmaType, TcRhoType,
45 BoxySigmaType, BoxyRhoType, ThetaType,
46 mkTyVarTys, mkFunTys, tcMultiSplitSigmaTy, tcSplitFunTysN,
47 isSigmaTy, mkFunTy, mkTyConApp, isLinearPred,
48 exactTyVarsOfType, exactTyVarsOfTypes, mkTyVarTy,
49 zipTopTvSubst, zipOpenTvSubst, substTys, substTyVar, lookupTyVar
51 import Kind ( argTypeKind )
53 import Id ( idType, idName, recordSelectorFieldLabel, isRecordSelector,
54 isNaughtyRecordSelector, isDataConId_maybe )
55 import DataCon ( DataCon, dataConFieldLabels, dataConStrictMarks, dataConSourceArity,
56 dataConWrapId, isVanillaDataCon, dataConTyVars, dataConOrigArgTys )
58 import TyCon ( FieldLabel, tyConStupidTheta, tyConDataCons )
59 import Type ( substTheta, substTy )
60 import Var ( TyVar, tyVarKind )
61 import VarSet ( emptyVarSet, elemVarSet, unionVarSet )
62 import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
63 import PrelNames ( enumFromName, enumFromThenName,
64 enumFromToName, enumFromThenToName,
65 enumFromToPName, enumFromThenToPName, negateName
68 import StaticFlags ( opt_NoMethodSharing )
69 import HscTypes ( TyThing(..) )
70 import SrcLoc ( Located(..), unLoc, noLoc, getLoc )
72 import ListSetOps ( assocMaybe )
73 import Maybes ( catMaybes )
78 import TyCon ( tyConArity )
82 %************************************************************************
84 \subsection{Main wrappers}
86 %************************************************************************
89 tcPolyExpr, tcPolyExprNC
90 :: LHsExpr Name -- Expession to type check
91 -> BoxySigmaType -- Expected type (could be a polytpye)
92 -> TcM (LHsExpr TcId) -- Generalised expr with expected type
94 -- tcPolyExpr is a convenient place (frequent but not too frequent) place
95 -- to add context information.
96 -- The NC version does not do so, usually because the caller wants
99 tcPolyExpr expr res_ty
100 = addErrCtxt (exprCtxt (unLoc expr)) $
101 tcPolyExprNC expr res_ty
103 tcPolyExprNC expr res_ty
105 = do { (gen_fn, expr') <- tcGen res_ty emptyVarSet (tcPolyExprNC expr)
106 -- Note the recursive call to tcPolyExpr, because the
107 -- type may have multiple layers of for-alls
108 ; return (L (getLoc expr') (mkHsCoerce gen_fn (unLoc expr'))) }
111 = tcMonoExpr expr res_ty
114 tcPolyExprs :: [LHsExpr Name] -> [TcType] -> TcM [LHsExpr TcId]
115 tcPolyExprs [] [] = returnM []
116 tcPolyExprs (expr:exprs) (ty:tys)
117 = do { expr' <- tcPolyExpr expr ty
118 ; exprs' <- tcPolyExprs exprs tys
119 ; returnM (expr':exprs') }
120 tcPolyExprs exprs tys = pprPanic "tcPolyExprs" (ppr exprs $$ ppr tys)
123 tcMonoExpr :: LHsExpr Name -- Expression to type check
124 -> BoxyRhoType -- Expected type (could be a type variable)
125 -- Definitely no foralls at the top
126 -- Can contain boxes, which will be filled in
127 -> TcM (LHsExpr TcId)
129 tcMonoExpr (L loc expr) res_ty
130 = ASSERT( not (isSigmaTy res_ty) )
132 do { expr' <- tcExpr expr res_ty
133 ; return (L loc expr') }
136 tcInferRho :: LHsExpr Name -> TcM (LHsExpr TcId, TcRhoType)
137 tcInferRho expr = tcInfer (tcMonoExpr expr)
142 %************************************************************************
144 tcExpr: the main expression typechecker
146 %************************************************************************
149 tcExpr :: HsExpr Name -> BoxyRhoType -> TcM (HsExpr TcId)
150 tcExpr (HsVar name) res_ty = tcId (OccurrenceOf name) name res_ty
152 tcExpr (HsLit lit) res_ty = do { boxyUnify (hsLitType lit) res_ty
153 ; return (HsLit lit) }
155 tcExpr (HsPar expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
156 ; return (HsPar expr') }
158 tcExpr (HsSCC lbl expr) res_ty = do { expr' <- tcMonoExpr expr res_ty
159 ; returnM (HsSCC lbl expr') }
161 tcExpr (HsCoreAnn lbl expr) res_ty -- hdaume: core annotation
162 = do { expr' <- tcMonoExpr expr res_ty
163 ; return (HsCoreAnn lbl expr') }
165 tcExpr (HsOverLit lit) res_ty
166 = do { lit' <- tcOverloadedLit (LiteralOrigin lit) lit res_ty
167 ; return (HsOverLit lit') }
169 tcExpr (NegApp expr neg_expr) res_ty
170 = do { neg_expr' <- tcSyntaxOp (OccurrenceOf negateName) neg_expr
171 (mkFunTy res_ty res_ty)
172 ; expr' <- tcMonoExpr expr res_ty
173 ; return (NegApp expr' neg_expr') }
175 tcExpr (HsIPVar ip) res_ty
176 = do { -- Implicit parameters must have a *tau-type* not a
177 -- type scheme. We enforce this by creating a fresh
178 -- type variable as its type. (Because res_ty may not
180 ip_ty <- newFlexiTyVarTy argTypeKind -- argTypeKind: it can't be an unboxed tuple
181 ; co_fn <- tcSubExp ip_ty res_ty
182 ; (ip', inst) <- newIPDict (IPOccOrigin ip) ip ip_ty
184 ; return (mkHsCoerce co_fn (HsIPVar ip')) }
186 tcExpr (HsApp e1 e2) res_ty
189 go :: LHsExpr Name -> [LHsExpr Name] -> TcM (HsExpr TcId)
190 go (L _ (HsApp e1 e2)) args = go e1 (e2:args)
191 go lfun@(L loc fun) args
192 = do { (fun', args') <- addErrCtxt (callCtxt lfun args) $
193 tcApp fun (length args) (tcArgs lfun args) res_ty
194 ; return (unLoc (foldl mkHsApp (L loc fun') args')) }
196 tcExpr (HsLam match) res_ty
197 = do { (co_fn, match') <- tcMatchLambda match res_ty
198 ; return (mkHsCoerce co_fn (HsLam match')) }
200 tcExpr in_expr@(ExprWithTySig expr sig_ty) res_ty
201 = do { sig_tc_ty <- tcHsSigType ExprSigCtxt sig_ty
202 ; expr' <- tcPolyExpr expr sig_tc_ty
203 ; co_fn <- tcSubExp sig_tc_ty res_ty
204 ; return (mkHsCoerce co_fn (ExprWithTySigOut expr' sig_ty)) }
206 tcExpr (HsType ty) res_ty
207 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
208 -- This is the syntax for type applications that I was planning
209 -- but there are difficulties (e.g. what order for type args)
210 -- so it's not enabled yet.
211 -- Can't eliminate it altogether from the parser, because the
212 -- same parser parses *patterns*.
216 %************************************************************************
218 Infix operators and sections
220 %************************************************************************
223 tcExpr in_expr@(OpApp arg1 lop@(L loc op) fix arg2) res_ty
224 = do { (op', [arg1', arg2']) <- tcApp op 2 (tcArgs lop [arg1,arg2]) res_ty
225 ; return (OpApp arg1' (L loc op') fix arg2') }
227 -- Left sections, equivalent to
234 -- We treat it as similar to the latter, so we don't
235 -- actually require the function to take two arguments
236 -- at all. For example, (x `not`) means (not x);
237 -- you get postfix operators! Not really Haskell 98
238 -- I suppose, but it's less work and kind of useful.
240 tcExpr in_expr@(SectionL arg1 lop@(L loc op)) res_ty
241 = do { (op', [arg1']) <- tcApp op 1 (tcArgs lop [arg1]) res_ty
242 ; return (SectionL arg1' (L loc op')) }
244 -- Right sections, equivalent to \ x -> x `op` expr, or
247 tcExpr in_expr@(SectionR lop@(L loc op) arg2) res_ty
248 = do { (co_fn, (op', arg2')) <- subFunTys doc 1 res_ty $ \ [arg1_ty'] res_ty' ->
249 tcApp op 2 (tc_args arg1_ty') res_ty'
250 ; return (mkHsCoerce co_fn (SectionR (L loc op') arg2')) }
252 doc = ptext SLIT("The section") <+> quotes (ppr in_expr)
253 <+> ptext SLIT("takes one argument")
254 tc_args arg1_ty' [arg1_ty, arg2_ty]
255 = do { boxyUnify arg1_ty' arg1_ty
256 ; tcArg lop (arg2, arg2_ty, 2) }
260 tcExpr (HsLet binds expr) res_ty
261 = do { (binds', expr') <- tcLocalBinds binds $
262 tcMonoExpr expr res_ty
263 ; return (HsLet binds' expr') }
265 tcExpr (HsCase scrut matches) exp_ty
266 = do { -- We used to typecheck the case alternatives first.
267 -- The case patterns tend to give good type info to use
268 -- when typechecking the scrutinee. For example
271 -- will report that map is applied to too few arguments
273 -- But now, in the GADT world, we need to typecheck the scrutinee
274 -- first, to get type info that may be refined in the case alternatives
275 (scrut', scrut_ty) <- addErrCtxt (caseScrutCtxt scrut)
278 ; traceTc (text "HsCase" <+> ppr scrut_ty)
279 ; matches' <- tcMatchesCase match_ctxt scrut_ty matches exp_ty
280 ; return (HsCase scrut' matches') }
282 match_ctxt = MC { mc_what = CaseAlt,
283 mc_body = tcPolyExpr }
285 tcExpr (HsIf pred b1 b2) res_ty
286 = do { pred' <- addErrCtxt (predCtxt pred) $
287 tcMonoExpr pred boolTy
288 ; b1' <- tcMonoExpr b1 res_ty
289 ; b2' <- tcMonoExpr b2 res_ty
290 ; return (HsIf pred' b1' b2') }
292 tcExpr (HsDo do_or_lc stmts body _) res_ty
293 = tcDoStmts do_or_lc stmts body res_ty
295 tcExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
296 = do { elt_ty <- boxySplitListTy res_ty
297 ; exprs' <- mappM (tc_elt elt_ty) exprs
298 ; return (ExplicitList elt_ty exprs') }
300 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
302 tcExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
303 = do { [elt_ty] <- boxySplitTyConApp parrTyCon res_ty
304 ; exprs' <- mappM (tc_elt elt_ty) exprs
305 ; ifM (null exprs) (zapToMonotype elt_ty)
306 -- If there are no expressions in the comprehension
307 -- we must still fill in the box
308 -- (Not needed for [] and () becuase they happen
309 -- to parse as data constructors.)
310 ; return (ExplicitPArr elt_ty exprs') }
312 tc_elt elt_ty expr = tcPolyExpr expr elt_ty
314 tcExpr (ExplicitTuple exprs boxity) res_ty
315 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length exprs)) res_ty
316 ; exprs' <- tcPolyExprs exprs arg_tys
317 ; return (ExplicitTuple exprs' boxity) }
319 tcExpr (HsProc pat cmd) res_ty
320 = do { (pat', cmd') <- tcProc pat cmd res_ty
321 ; return (HsProc pat' cmd') }
323 tcExpr e@(HsArrApp _ _ _ _ _) _
324 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
325 ptext SLIT("was found where an expression was expected")])
327 tcExpr e@(HsArrForm _ _ _) _
328 = failWithTc (vcat [ptext SLIT("The arrow command"), nest 2 (ppr e),
329 ptext SLIT("was found where an expression was expected")])
332 %************************************************************************
334 Record construction and update
336 %************************************************************************
339 tcExpr expr@(RecordCon (L loc con_name) _ rbinds) res_ty
340 = do { data_con <- tcLookupDataCon con_name
342 -- Check for missing fields
343 ; checkMissingFields data_con rbinds
345 ; let arity = dataConSourceArity data_con
347 = do { rbinds' <- tcRecordBinds data_con arg_tys rbinds
350 -- The unBox ensures that all the boxes in arg_tys are indeed
351 -- filled, which is the invariant expected by tcIdApp
353 ; (con_expr, rbinds') <- tcIdApp con_name arity check_fields res_ty
355 ; returnM (RecordCon (L loc (dataConWrapId data_con)) con_expr rbinds') }
357 -- The main complication with RecordUpd is that we need to explicitly
358 -- handle the *non-updated* fields. Consider:
360 -- data T a b = MkT1 { fa :: a, fb :: b }
361 -- | MkT2 { fa :: a, fc :: Int -> Int }
362 -- | MkT3 { fd :: a }
364 -- upd :: T a b -> c -> T a c
365 -- upd t x = t { fb = x}
367 -- The type signature on upd is correct (i.e. the result should not be (T a b))
368 -- because upd should be equivalent to:
370 -- upd t x = case t of
371 -- MkT1 p q -> MkT1 p x
372 -- MkT2 a b -> MkT2 p b
373 -- MkT3 d -> error ...
375 -- So we need to give a completely fresh type to the result record,
376 -- and then constrain it by the fields that are *not* updated ("p" above).
378 -- Note that because MkT3 doesn't contain all the fields being updated,
379 -- its RHS is simply an error, so it doesn't impose any type constraints
381 -- All this is done in STEP 4 below.
385 -- For record update we require that every constructor involved in the
386 -- update (i.e. that has all the specified fields) is "vanilla". I
387 -- don't know how to do the update otherwise.
390 tcExpr expr@(RecordUpd record_expr rbinds _ _) res_ty
392 -- Check that the field names are really field names
393 ASSERT( notNull rbinds )
395 field_names = map fst rbinds
397 mappM (tcLookupGlobalId.unLoc) field_names `thenM` \ sel_ids ->
398 -- The renamer has already checked that they
401 bad_guys = [ setSrcSpan loc $ addErrTc (notSelector field_name)
402 | (L loc field_name, sel_id) <- field_names `zip` sel_ids,
403 not (isRecordSelector sel_id) -- Excludes class ops
406 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
409 -- Figure out the tycon and data cons from the first field name
411 -- It's OK to use the non-tc splitters here (for a selector)
412 upd_field_lbls = recBindFields rbinds
414 (tycon, _) = recordSelectorFieldLabel sel_id -- We've failed already if
415 data_cons = tyConDataCons tycon -- it's not a field label
416 relevant_cons = filter is_relevant data_cons
417 is_relevant con = all (`elem` dataConFieldLabels con) upd_field_lbls
421 -- Check that at least one constructor has all the named fields
422 -- i.e. has an empty set of bad fields returned by badFields
423 checkTc (not (null relevant_cons))
424 (badFieldsUpd rbinds) `thenM_`
426 -- Check that all relevant data cons are vanilla. Doing record updates on
427 -- GADTs and/or existentials is more than my tiny brain can cope with today
428 checkTc (all isVanillaDataCon relevant_cons)
429 (nonVanillaUpd tycon) `thenM_`
432 -- Use the un-updated fields to find a vector of booleans saying
433 -- which type arguments must be the same in updatee and result.
435 -- WARNING: this code assumes that all data_cons in a common tycon
436 -- have FieldLabels abstracted over the same tyvars.
438 -- A constructor is only relevant to this process if
439 -- it contains *all* the fields that are being updated
440 con1 = head relevant_cons -- A representative constructor
441 con1_tyvars = dataConTyVars con1
442 con1_flds = dataConFieldLabels con1
443 con1_arg_tys = dataConOrigArgTys con1
444 common_tyvars = exactTyVarsOfTypes [ty | (fld,ty) <- con1_flds `zip` con1_arg_tys
445 , not (fld `elem` upd_field_lbls) ]
447 is_common_tv tv = tv `elemVarSet` common_tyvars
449 mk_inst_ty tv result_inst_ty
450 | is_common_tv tv = returnM result_inst_ty -- Same as result type
451 | otherwise = newFlexiTyVarTy (tyVarKind tv) -- Fresh type, of correct kind
453 tcInstTyVars con1_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
454 zipWithM mk_inst_ty con1_tyvars result_inst_tys `thenM` \ inst_tys ->
457 -- Typecheck the update bindings.
458 -- (Do this after checking for bad fields in case there's a field that
459 -- doesn't match the constructor.)
461 result_record_ty = mkTyConApp tycon result_inst_tys
462 con1_arg_tys' = map (substTy inst_env) con1_arg_tys
464 tcSubExp result_record_ty res_ty `thenM` \ co_fn ->
465 tcRecordBinds con1 con1_arg_tys' rbinds `thenM` \ rbinds' ->
468 -- Typecheck the expression to be updated
470 record_ty = ASSERT( length inst_tys == tyConArity tycon )
471 mkTyConApp tycon inst_tys
472 -- This is one place where the isVanilla check is important
473 -- So that inst_tys matches the tycon
475 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
478 -- Figure out the LIE we need. We have to generate some
479 -- dictionaries for the data type context, since we are going to
480 -- do pattern matching over the data cons.
482 -- What dictionaries do we need?
483 -- We just take the context of the first data constructor
484 -- This isn't right, but I just can't bear to union up all the relevant ones
486 theta' = substTheta inst_env (tyConStupidTheta tycon)
488 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
489 extendLIEs dicts `thenM_`
492 returnM (mkHsCoerce co_fn (RecordUpd record_expr' rbinds' record_ty result_record_ty))
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 -> ([BoxySigmaType] -> TcM arg_results) -- Argument type-checker
600 -> BoxyRhoType -- Result type
601 -> TcM (HsExpr TcId, arg_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'
614 ; return (fun', args') }
616 ---------------------------
617 tcIdApp :: Name -- Function
618 -> Arity -- Number of args reqd
619 -> ([BoxySigmaType] -> TcM arg_results) -- Argument type-checker
620 -- The arg-checker guarantees to fill all boxes in the arg types
621 -> BoxyRhoType -- Result type
622 -> TcM (HsExpr TcId, arg_results)
624 -- Call (f e1 ... en) :: res_ty
625 -- Type f :: forall a b c. theta => fa_1 -> ... -> fa_k -> fres
626 -- (where k <= n; fres has the rest)
627 -- NB: if k < n then the function doesn't have enough args, and
628 -- presumably fres is a type variable that we are going to
629 -- instantiate with a function type
631 -- Then fres <= bx_(k+1) -> ... -> bx_n -> res_ty
633 tcIdApp fun_name n_args arg_checker res_ty
634 = do { fun_id <- lookupFun (OccurrenceOf fun_name) fun_name
636 -- Split up the function type
637 ; let (tv_theta_prs, rho) = tcMultiSplitSigmaTy (idType fun_id)
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 subst = boxySubMatchType arg_qtvs fun_res_ty res_ty'
654 -- Only bind arg_qtvs, since only they will be
655 -- *definitely* be filled in by arg_checker
656 -- E.g. error :: forall a. String -> a
657 -- (error "foo") :: bx5
658 -- Don't make subst [a |-> bx5]
659 -- because then the result subsumption becomes
661 -- and the unifer doesn't expect the
662 -- same box on both sides
663 inst_qtv tv | Just boxy_ty <- lookupTyVar subst tv = return boxy_ty
664 | tv `elemVarSet` tau_qtvs = do { tv' <- tcInstBoxyTyVar tv
665 ; return (mkTyVarTy tv') }
666 | otherwise = do { tv' <- tcInstTyVar tv
667 ; return (mkTyVarTy tv') }
668 -- The 'otherwise' case handles type variables that are
669 -- mentioned only in the constraints, not in argument or
670 -- result types. We'll make them tau-types
672 ; qtys' <- mapM inst_qtv qtvs
673 ; let arg_subst = zipOpenTvSubst qtvs qtys'
674 fun_arg_tys' = substTys arg_subst fun_arg_tys
676 -- Typecheck the arguments!
677 -- Doing so will fill arg_qtvs and extra_arg_tys'
678 ; args' <- arg_checker (fun_arg_tys' ++ extra_arg_tys')
680 ; let strip qtv qty' | qtv `elemVarSet` arg_qtvs = stripBoxyType qty'
681 | otherwise = return qty'
682 ; qtys'' <- zipWithM strip qtvs qtys'
683 ; extra_arg_tys'' <- mapM readFilledBox extra_arg_boxes
685 -- Result subsumption
686 ; let res_subst = zipOpenTvSubst qtvs qtys''
687 fun_res_ty'' = substTy res_subst fun_res_ty
688 res_ty'' = mkFunTys extra_arg_tys'' res_ty
689 ; co_fn <- tcFunResTy fun_name fun_res_ty'' res_ty''
691 -- And pack up the results
692 -- By applying the coercion just to the *function* we can make
693 -- tcFun work nicely for OpApp and Sections too
694 ; fun' <- instFun fun_id qtvs qtys'' tv_theta_prs
695 ; co_fn' <- wrapFunResCoercion fun_arg_tys' co_fn
696 ; return (mkHsCoerce co_fn' fun', args') }
699 Note [Silly type synonyms in smart-app]
700 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
701 When we call sripBoxyType, all of the boxes should be filled
702 in. But we need to be careful about type synonyms:
706 In the call (f x) we'll typecheck x, expecting it to have type
707 (T box). Usually that would fill in the box, but in this case not;
708 because 'a' is discarded by the silly type synonym T. So we must
709 use exactTyVarsOfType to figure out which type variables are free
710 in the argument type.
713 -- tcId is a specialisation of tcIdApp when there are no arguments
714 -- tcId f ty = do { (res, _) <- tcIdApp f [] (\[] -> return ()) ty
719 -> BoxyRhoType -- Result type
721 tcId orig fun_name res_ty
722 = do { traceTc (text "tcId" <+> ppr fun_name <+> ppr res_ty)
723 ; fun_id <- lookupFun orig fun_name
725 -- Split up the function type
726 ; let (tv_theta_prs, fun_tau) = tcMultiSplitSigmaTy (idType fun_id)
727 qtvs = concatMap fst tv_theta_prs -- Quantified tyvars
728 tau_qtvs = exactTyVarsOfType fun_tau -- Mentiond in the tau part
729 inst_qtv tv | tv `elemVarSet` tau_qtvs = do { tv' <- tcInstBoxyTyVar tv
730 ; return (mkTyVarTy tv') }
731 | otherwise = do { tv' <- tcInstTyVar tv
732 ; return (mkTyVarTy tv') }
734 -- Do the subsumption check wrt the result type
735 ; qtv_tys <- mapM inst_qtv qtvs
736 ; let res_subst = zipTopTvSubst qtvs qtv_tys
737 fun_tau' = substTy res_subst fun_tau
739 ; co_fn <- tcFunResTy fun_name fun_tau' res_ty
741 -- And pack up the results
742 ; fun' <- instFun fun_id qtvs qtv_tys tv_theta_prs
743 ; return (mkHsCoerce co_fn fun') }
745 -- Note [Push result type in]
747 -- Unify with expected result before (was: after) type-checking the args
748 -- so that the info from res_ty (was: args) percolates to args (was actual_res_ty).
749 -- This is when we might detect a too-few args situation.
750 -- (One can think of cases when the opposite order would give
751 -- a better error message.)
752 -- [March 2003: I'm experimenting with putting this first. Here's an
753 -- example where it actually makes a real difference
754 -- class C t a b | t a -> b
755 -- instance C Char a Bool
757 -- data P t a = forall b. (C t a b) => MkP b
758 -- data Q t = MkQ (forall a. P t a)
761 -- f1 = MkQ (MkP True)
762 -- f2 = MkQ (MkP True :: forall a. P Char a)
764 -- With the change, f1 will type-check, because the 'Char' info from
765 -- the signature is propagated into MkQ's argument. With the check
766 -- in the other order, the extra signature in f2 is reqd.]
768 ---------------------------
769 tcSyntaxOp :: InstOrigin -> HsExpr Name -> TcType -> TcM (HsExpr TcId)
770 -- Typecheck a syntax operator, checking that it has the specified type
771 -- The operator is always a variable at this stage (i.e. renamer output)
772 tcSyntaxOp orig (HsVar op) ty = tcId orig op ty
773 tcSyntaxOp orig other ty = pprPanic "tcSyntaxOp" (ppr other)
775 ---------------------------
777 -> [TyVar] -> [TcType] -- Quantified type variables and
778 -- their instantiating types
779 -> [([TyVar], ThetaType)] -- Stuff to instantiate
781 instFun fun_id qtvs qtv_tys []
782 = return (HsVar fun_id) -- Common short cut
784 instFun fun_id qtvs qtv_tys tv_theta_prs
785 = do { let subst = zipOpenTvSubst qtvs qtv_tys
786 ty_theta_prs' = map subst_pr tv_theta_prs
787 subst_pr (tvs, theta) = (map (substTyVar subst) tvs,
788 substTheta subst theta)
790 -- The ty_theta_prs' is always non-empty
791 ((tys1',theta1') : further_prs') = ty_theta_prs'
793 -- First, chuck in the constraints from
794 -- the "stupid theta" of a data constructor (sigh)
795 ; case isDataConId_maybe fun_id of
796 Just con -> tcInstStupidTheta con tys1'
799 ; if want_method_inst theta1'
800 then do { meth_id <- newMethodWithGivenTy orig fun_id tys1'
801 -- See Note [Multiple instantiation]
802 ; go (HsVar meth_id) further_prs' }
803 else go (HsVar fun_id) ty_theta_prs'
806 orig = OccurrenceOf (idName fun_id)
808 go fun [] = return fun
810 go fun ((tys, theta) : prs)
811 = do { dicts <- newDicts orig theta
813 ; let the_app = unLoc $ mkHsDictApp (mkHsTyApp (noLoc fun) tys)
817 -- Hack Alert (want_method_inst)!
818 -- See Note [No method sharing]
819 -- If f :: (%x :: T) => Int -> Int
820 -- Then if we have two separate calls, (f 3, f 4), we cannot
821 -- make a method constraint that then gets shared, thus:
822 -- let m = f %x in (m 3, m 4)
823 -- because that loses the linearity of the constraint.
824 -- The simplest thing to do is never to construct a method constraint
825 -- in the first place that has a linear implicit parameter in it.
826 want_method_inst theta = not (null theta) -- Overloaded
827 && not (any isLinearPred theta) -- Not linear
828 && not opt_NoMethodSharing
829 -- See Note [No method sharing] below
832 Note [Multiple instantiation]
833 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
834 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
835 For example, consider
836 f :: forall a. Eq a => forall b. Ord b => a -> b
837 At a call to f, at say [Int, Bool], it's tempting to translate the call to
841 f_m1 :: forall b. Ord b => Int -> b
845 f_m2 = f_m1 Bool dOrdBool
847 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
848 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
850 But it's entirely possible that f_m2 will continue to float out, because it
851 mentions no type variables. Result, f_m1 isn't in scope.
853 Here's a concrete example that does this (test tc200):
856 f :: Eq b => b -> a -> Int
857 baz :: Eq a => Int -> a -> Int
862 Current solution: only do the "method sharing" thing for the first type/dict
863 application, not for the iterated ones. A horribly subtle point.
865 Note [No method sharing]
866 ~~~~~~~~~~~~~~~~~~~~~~~~
867 The -fno-method-sharing flag controls what happens so far as the LIE
868 is concerned. The default case is that for an overloaded function we
869 generate a "method" Id, and add the Method Inst to the LIE. So you get
872 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
873 If you specify -fno-method-sharing, the dictionary application
874 isn't shared, so we get
876 f = /\a (d:Num a) (x:a) -> (+) a d x x
877 This gets a bit less sharing, but
878 a) it's better for RULEs involving overloaded functions
879 b) perhaps fewer separated lambdas
882 tcArgs :: LHsExpr Name -- The function (for error messages)
883 -> [LHsExpr Name] -> [TcSigmaType] -- Actual arguments and expected arg types
884 -> TcM [LHsExpr TcId] -- Resulting args
886 tcArgs fun args expected_arg_tys
887 = mapM (tcArg fun) (zip3 args expected_arg_tys [1..])
889 tcArg :: LHsExpr Name -- The function (for error messages)
890 -> (LHsExpr Name, BoxySigmaType, Int) -- Actual argument and expected arg type
891 -> TcM (LHsExpr TcId) -- Resulting argument
892 tcArg fun (arg, ty, arg_no) = addErrCtxt (funAppCtxt fun arg arg_no) $
897 %************************************************************************
899 \subsection{@tcId@ typchecks an identifier occurrence}
901 %************************************************************************
904 lookupFun :: InstOrigin -> Name -> TcM TcId
905 lookupFun orig id_name
906 = do { thing <- tcLookup id_name
908 AGlobal (ADataCon con) -> return (dataConWrapId con)
911 | isNaughtyRecordSelector id -> failWithTc (naughtyRecordSel id)
912 | otherwise -> return id
913 -- A global cannot possibly be ill-staged
914 -- nor does it need the 'lifting' treatment
917 ATcId id th_level _ -> return id -- Non-TH case
919 ATcId id th_level _ -> do { use_stage <- getStage -- TH case
920 ; thLocalId orig id_name id th_level use_stage }
923 other -> failWithTc (ppr other <+> ptext SLIT("used where a value identifer was expected"))
926 #ifdef GHCI /* GHCI and TH is on */
927 --------------------------------------
928 -- thLocalId : Check for cross-stage lifting
929 thLocalId orig id_name id th_bind_lvl (Brack use_lvl ps_var lie_var)
930 | use_lvl > th_bind_lvl
931 = thBrackId orig id_name id ps_var lie_var
932 thLocalId orig id_name id th_bind_lvl use_stage
933 = do { checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage
936 --------------------------------------
937 thBrackId orig id_name id ps_var lie_var
938 | isExternalName id_name
939 = -- Top-level identifiers in this module,
940 -- (which have External Names)
941 -- are just like the imported case:
942 -- no need for the 'lifting' treatment
943 -- E.g. this is fine:
946 -- But we do need to put f into the keep-alive
947 -- set, because after desugaring the code will
948 -- only mention f's *name*, not f itself.
949 do { keepAliveTc id_name; return id }
952 = -- Nested identifiers, such as 'x' in
953 -- E.g. \x -> [| h x |]
954 -- We must behave as if the reference to x was
956 -- We use 'x' itself as the splice proxy, used by
957 -- the desugarer to stitch it all back together.
958 -- If 'x' occurs many times we may get many identical
959 -- bindings of the same splice proxy, but that doesn't
960 -- matter, although it's a mite untidy.
961 do { let id_ty = idType id
962 ; checkTc (isTauTy id_ty) (polySpliceErr id)
963 -- If x is polymorphic, its occurrence sites might
964 -- have different instantiations, so we can't use plain
965 -- 'x' as the splice proxy name. I don't know how to
966 -- solve this, and it's probably unimportant, so I'm
967 -- just going to flag an error for now
969 ; id_ty' <- zapToMonotype id_ty
970 -- The id_ty might have an OpenTypeKind, but we
971 -- can't instantiate the Lift class at that kind,
972 -- so we zap it to a LiftedTypeKind monotype
973 -- C.f. the call in TcPat.newLitInst
975 ; setLIEVar lie_var $ do
976 { lift <- newMethodFromName orig id_ty' DsMeta.liftName
977 -- Put the 'lift' constraint into the right LIE
979 -- Update the pending splices
980 ; ps <- readMutVar ps_var
981 ; writeMutVar ps_var ((id_name, nlHsApp (nlHsVar lift) (nlHsVar id)) : ps)
987 Note [Multiple instantiation]
988 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
989 We are careful never to make a MethodInst that has, as its meth_id, another MethodInst.
990 For example, consider
991 f :: forall a. Eq a => forall b. Ord b => a -> b
992 At a call to f, at say [Int, Bool], it's tempting to translate the call to
996 f_m1 :: forall b. Ord b => Int -> b
1000 f_m2 = f_m1 Bool dOrdBool
1002 But notice that f_m2 has f_m1 as its meth_id. Now the danger is that if we do
1003 a tcSimplCheck with a Given f_mx :: f Int dEqInt, we may make a binding
1005 But it's entirely possible that f_m2 will continue to float out, because it
1006 mentions no type variables. Result, f_m1 isn't in scope.
1008 Here's a concrete example that does this (test tc200):
1011 f :: Eq b => b -> a -> Int
1012 baz :: Eq a => Int -> a -> Int
1014 instance C Int where
1017 Current solution: only do the "method sharing" thing for the first type/dict
1018 application, not for the iterated ones. A horribly subtle point.
1021 %************************************************************************
1023 \subsection{Record bindings}
1025 %************************************************************************
1027 Game plan for record bindings
1028 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1029 1. Find the TyCon for the bindings, from the first field label.
1031 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
1033 For each binding field = value
1035 3. Instantiate the field type (from the field label) using the type
1038 4 Type check the value using tcArg, passing the field type as
1039 the expected argument type.
1041 This extends OK when the field types are universally quantified.
1047 -> [TcType] -- Expected type for each field
1048 -> HsRecordBinds Name
1049 -> TcM (HsRecordBinds TcId)
1051 tcRecordBinds data_con arg_tys rbinds
1052 = do { mb_binds <- mappM do_bind rbinds
1053 ; return (catMaybes mb_binds) }
1055 flds_w_tys = zipEqual "tcRecordBinds" (dataConFieldLabels data_con) arg_tys
1056 do_bind (L loc field_lbl, rhs)
1057 | Just field_ty <- assocMaybe flds_w_tys field_lbl
1058 = addErrCtxt (fieldCtxt field_lbl) $
1059 do { rhs' <- tcPolyExprNC rhs field_ty
1060 ; sel_id <- tcLookupId field_lbl
1061 ; ASSERT( isRecordSelector sel_id )
1062 return (Just (L loc sel_id, rhs')) }
1064 = do { addErrTc (badFieldCon data_con field_lbl)
1067 checkMissingFields :: DataCon -> HsRecordBinds Name -> TcM ()
1068 checkMissingFields data_con rbinds
1069 | null field_labels -- Not declared as a record;
1070 -- But C{} is still valid if no strict fields
1071 = if any isMarkedStrict field_strs then
1072 -- Illegal if any arg is strict
1073 addErrTc (missingStrictFields data_con [])
1077 | otherwise -- A record
1078 = checkM (null missing_s_fields)
1079 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1081 doptM Opt_WarnMissingFields `thenM` \ warn ->
1082 checkM (not (warn && notNull missing_ns_fields))
1083 (warnTc True (missingFields data_con missing_ns_fields))
1087 = [ fl | (fl, str) <- field_info,
1089 not (fl `elem` field_names_used)
1092 = [ fl | (fl, str) <- field_info,
1093 not (isMarkedStrict str),
1094 not (fl `elem` field_names_used)
1097 field_names_used = recBindFields rbinds
1098 field_labels = dataConFieldLabels data_con
1100 field_info = zipEqual "missingFields"
1104 field_strs = dataConStrictMarks data_con
1107 %************************************************************************
1109 \subsection{Errors and contexts}
1111 %************************************************************************
1113 Boring and alphabetical:
1116 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1119 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1121 fieldCtxt field_name
1122 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1124 funAppCtxt fun arg arg_no
1125 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1126 quotes (ppr fun) <> text ", namely"])
1127 4 (quotes (ppr arg))
1130 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1133 = vcat [ptext SLIT("Record update for the non-Haskell-98 data type") <+> quotes (ppr tycon)
1134 <+> ptext SLIT("is not (yet) supported"),
1135 ptext SLIT("Use pattern-matching instead")]
1137 = hang (ptext SLIT("No constructor has all these fields:"))
1138 4 (pprQuotedList (recBindFields rbinds))
1140 naughtyRecordSel sel_id
1141 = ptext SLIT("Cannot use record selector") <+> quotes (ppr sel_id) <+>
1142 ptext SLIT("as a function due to escaped type variables") $$
1143 ptext SLIT("Probably fix: use pattern-matching syntax instead")
1146 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1148 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1149 missingStrictFields con fields
1152 rest | null fields = empty -- Happens for non-record constructors
1153 -- with strict fields
1154 | otherwise = colon <+> pprWithCommas ppr fields
1156 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1157 ptext SLIT("does not have the required strict field(s)")
1159 missingFields :: DataCon -> [FieldLabel] -> SDoc
1160 missingFields con fields
1161 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1162 <+> pprWithCommas ppr fields
1165 = ptext SLIT("In the call") <+> parens (ppr (foldl mkHsApp fun args))
1168 polySpliceErr :: Id -> SDoc
1170 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)