2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcCheckSigma, tcCheckRho, tcInferRho, tcMonoExpr ) where
9 #include "HsVersions.h"
11 #ifdef GHCI /* Only if bootstrapped */
12 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
13 import HsSyn ( HsReify(..), ReifyFlavour(..) )
15 import TcType ( isTauTy )
16 import TcEnv ( tcMetaTy, checkWellStaged )
17 import qualified DsMeta
20 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..), recBindFields,
22 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
23 import TcHsSyn ( TcExpr, TcRecordBinds, hsLitType, mkHsDictApp, mkHsTyApp, (<$>) )
25 import TcUnify ( Expected(..), newHole, zapExpectedType, zapExpectedTo, tcSubExp, tcGen,
26 unifyFunTy, zapToListTy, zapToPArrTy, zapToTupleTy )
27 import BasicTypes ( isMarkedStrict )
28 import Inst ( InstOrigin(..),
29 newOverloadedLit, newMethodFromName, newIPDict,
30 newDicts, newMethodWithGivenTy,
31 instToId, tcInstCall, tcInstDataCon
33 import TcBinds ( tcBindsAndThen )
34 import TcEnv ( tcLookup, tcLookupGlobalId,
35 tcLookupDataCon, tcLookupId, checkProcLevel
37 import TcArrows ( tcProc )
38 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts, tcThingWithSig, TcMatchCtxt(..) )
39 import TcHsType ( tcHsSigType, UserTypeCtxt(..) )
40 import TcPat ( badFieldCon )
41 import TcMType ( tcInstTyVars, tcInstType, newTyVarTy, zonkTcType )
42 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
43 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
44 isSigmaTy, mkFunTy, mkFunTys,
45 mkTyConApp, tyVarsOfTypes, isLinearPred,
46 liftedTypeKind, openTypeKind,
47 tcSplitSigmaTy, tidyOpenType
49 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
50 import Id ( idType, recordSelectorFieldLabel, isRecordSelector )
51 import DataCon ( DataCon, dataConFieldLabels, dataConStrictMarks, dataConWrapId )
53 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
54 import Subst ( mkTopTyVarSubst, substTheta, substTy )
55 import VarSet ( emptyVarSet, elemVarSet )
56 import TysWiredIn ( boolTy )
57 import PrelNames ( enumFromName, enumFromThenName,
58 enumFromToName, enumFromThenToName,
59 enumFromToPName, enumFromThenToPName
61 import ListSetOps ( minusList )
63 import HscTypes ( TyThing(..) )
70 %************************************************************************
72 \subsection{Main wrappers}
74 %************************************************************************
77 -- tcCheckSigma does type *checking*; it's passed the expected type of the result
78 tcCheckSigma :: RenamedHsExpr -- Expession to type check
79 -> TcSigmaType -- Expected type (could be a polytpye)
80 -> TcM TcExpr -- Generalised expr with expected type
82 tcCheckSigma expr expected_ty
83 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
84 tc_expr' expr expected_ty
86 tc_expr' expr sigma_ty
88 = tcGen sigma_ty emptyVarSet (
89 \ rho_ty -> tcCheckRho expr rho_ty
90 ) `thenM` \ (gen_fn, expr') ->
91 returnM (gen_fn <$> expr')
93 tc_expr' expr rho_ty -- Monomorphic case
94 = tcCheckRho expr rho_ty
97 Typecheck expression which in most cases will be an Id.
98 The expression can return a higher-ranked type, such as
99 (forall a. a->a) -> Int
100 so we must create a hole to pass in as the expected tyvar.
103 tcCheckRho :: RenamedHsExpr -> TcRhoType -> TcM TcExpr
104 tcCheckRho expr rho_ty = tcMonoExpr expr (Check rho_ty)
106 tcInferRho :: RenamedHsExpr -> TcM (TcExpr, TcRhoType)
107 tcInferRho (HsVar name) = tcId name
108 tcInferRho expr = newHole `thenM` \ hole ->
109 tcMonoExpr expr (Infer hole) `thenM` \ expr' ->
110 readMutVar hole `thenM` \ rho_ty ->
111 returnM (expr', rho_ty)
116 %************************************************************************
118 \subsection{The TAUT rules for variables}
120 %************************************************************************
123 tcMonoExpr :: RenamedHsExpr -- Expession to type check
124 -> Expected TcRhoType -- Expected type (could be a type variable)
125 -- Definitely no foralls at the top
129 tcMonoExpr (HsVar name) res_ty
130 = tcId name `thenM` \ (expr', id_ty) ->
131 tcSubExp res_ty id_ty `thenM` \ co_fn ->
132 returnM (co_fn <$> expr')
134 tcMonoExpr (HsIPVar ip) res_ty
135 = -- Implicit parameters must have a *tau-type* not a
136 -- type scheme. We enforce this by creating a fresh
137 -- type variable as its type. (Because res_ty may not
139 newTyVarTy openTypeKind `thenM` \ ip_ty ->
140 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
141 extendLIE inst `thenM_`
142 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
143 returnM (co_fn <$> HsIPVar ip')
147 %************************************************************************
149 \subsection{Expressions type signatures}
151 %************************************************************************
154 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
155 = addErrCtxt (exprSigCtxt in_expr) $
156 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
157 tcThingWithSig sig_tc_ty (tcCheckRho expr) res_ty `thenM` \ (co_fn, expr') ->
158 returnM (co_fn <$> expr')
160 tcMonoExpr (HsType ty) res_ty
161 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
162 -- This is the syntax for type applications that I was planning
163 -- but there are difficulties (e.g. what order for type args)
164 -- so it's not enabled yet.
165 -- Can't eliminate it altogether from the parser, because the
166 -- same parser parses *patterns*.
170 %************************************************************************
172 \subsection{Other expression forms}
174 %************************************************************************
177 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
178 tcMonoExpr (HsOverLit lit) res_ty = zapExpectedType res_ty `thenM` \ res_ty' ->
179 newOverloadedLit (LiteralOrigin lit) lit res_ty'
180 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
181 returnM (HsPar expr')
182 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
183 returnM (HsSCC lbl expr')
185 tcMonoExpr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
186 returnM (HsCoreAnn lbl expr')
187 tcMonoExpr (NegApp expr neg_name) res_ty
188 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
189 -- ToDo: use tcSyntaxName
191 tcMonoExpr (HsLam match) res_ty
192 = tcMatchLambda match res_ty `thenM` \ match' ->
193 returnM (HsLam match')
195 tcMonoExpr (HsApp e1 e2) res_ty
196 = tcApp e1 [e2] res_ty
199 Note that the operators in sections are expected to be binary, and
200 a type error will occur if they aren't.
203 -- Left sections, equivalent to
210 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
211 = tcInferRho op `thenM` \ (op', op_ty) ->
212 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
213 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
214 addErrCtxt (exprCtxt in_expr) $
215 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
216 returnM (co_fn <$> SectionL arg1' op')
218 -- Right sections, equivalent to \ x -> x op expr, or
221 tcMonoExpr in_expr@(SectionR op arg2) res_ty
222 = tcInferRho op `thenM` \ (op', op_ty) ->
223 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
224 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
225 addErrCtxt (exprCtxt in_expr) $
226 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
227 returnM (co_fn <$> SectionR op' arg2')
229 -- equivalent to (op e1) e2:
231 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
232 = tcInferRho op `thenM` \ (op', op_ty) ->
233 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
234 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
235 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
236 addErrCtxt (exprCtxt in_expr) $
237 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
238 returnM (OpApp arg1' op' fix arg2')
242 tcMonoExpr (HsLet binds expr) res_ty
245 binds -- Bindings to check
246 (tcMonoExpr expr res_ty)
248 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
249 = addSrcLoc src_loc $
250 addErrCtxt (caseCtxt in_expr) $
252 -- Typecheck the case alternatives first.
253 -- The case patterns tend to give good type info to use
254 -- when typechecking the scrutinee. For example
257 -- will report that map is applied to too few arguments
259 tcMatchesCase match_ctxt matches res_ty `thenM` \ (scrut_ty, matches') ->
261 addErrCtxt (caseScrutCtxt scrut) (
262 tcCheckRho scrut scrut_ty
263 ) `thenM` \ scrut' ->
265 returnM (HsCase scrut' matches' src_loc)
267 match_ctxt = MC { mc_what = CaseAlt,
268 mc_body = tcMonoExpr }
270 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
271 = addSrcLoc src_loc $
272 addErrCtxt (predCtxt pred) (
273 tcCheckRho pred boolTy ) `thenM` \ pred' ->
275 zapExpectedType res_ty `thenM` \ res_ty' ->
276 -- C.f. the call to zapToType in TcMatches.tcMatches
278 tcCheckRho b1 res_ty' `thenM` \ b1' ->
279 tcCheckRho b2 res_ty' `thenM` \ b2' ->
280 returnM (HsIf pred' b1' b2' src_loc)
282 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
283 = addSrcLoc src_loc $
284 zapExpectedType res_ty `thenM` \ res_ty' ->
285 -- All comprehensions yield a monotype
286 tcDoStmts do_or_lc stmts method_names res_ty' `thenM` \ (stmts', methods') ->
287 returnM (HsDo do_or_lc stmts' methods' res_ty' src_loc)
289 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
290 = zapToListTy res_ty `thenM` \ elt_ty ->
291 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
292 returnM (ExplicitList elt_ty exprs')
295 = addErrCtxt (listCtxt expr) $
296 tcCheckRho expr elt_ty
298 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
299 = zapToPArrTy res_ty `thenM` \ elt_ty ->
300 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
301 returnM (ExplicitPArr elt_ty exprs')
304 = addErrCtxt (parrCtxt expr) $
305 tcCheckRho expr elt_ty
307 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
308 = zapToTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
309 tcCheckRhos exprs arg_tys `thenM` \ exprs' ->
310 returnM (ExplicitTuple exprs' boxity)
312 tcMonoExpr (HsProc pat cmd loc) res_ty
314 tcProc pat cmd res_ty `thenM` \ (pat', cmd') ->
315 returnM (HsProc pat' cmd' loc)
318 %************************************************************************
320 Record construction and update
322 %************************************************************************
325 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
326 = addErrCtxt (recordConCtxt expr) $
327 tcId con_name `thenM` \ (con_expr, con_tau) ->
329 (_, record_ty) = tcSplitFunTys con_tau
330 (tycon, ty_args) = tcSplitTyConApp record_ty
332 ASSERT( isAlgTyCon tycon )
333 zapExpectedTo res_ty record_ty `thenM_`
335 -- Check that the record bindings match the constructor
336 -- con_name is syntactically constrained to be a data constructor
337 tcLookupDataCon con_name `thenM` \ data_con ->
339 bad_fields = badFields rbinds data_con
341 if notNull bad_fields then
342 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
343 failM -- Fail now, because tcRecordBinds will crash on a bad field
346 -- Typecheck the record bindings
347 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
349 -- Check for missing fields
350 checkMissingFields data_con rbinds `thenM_`
352 returnM (RecordConOut 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.
380 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
381 = addErrCtxt (recordUpdCtxt expr) $
384 -- Check that the field names are really field names
385 ASSERT( notNull rbinds )
387 field_names = recBindFields rbinds
389 mappM tcLookupGlobalId field_names `thenM` \ sel_ids ->
390 -- The renamer has already checked that they
393 bad_guys = [ addErrTc (notSelector field_name)
394 | (field_name, sel_id) <- field_names `zip` sel_ids,
395 not (isRecordSelector sel_id) -- Excludes class ops
398 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
401 -- Figure out the tycon and data cons from the first field name
403 -- It's OK to use the non-tc splitters here (for a selector)
405 field_lbl = recordSelectorFieldLabel sel_id -- We've failed already if
406 tycon = fieldLabelTyCon field_lbl -- it's not a field label
407 data_cons = tyConDataCons tycon
408 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
410 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
413 -- Check that at least one constructor has all the named fields
414 -- i.e. has an empty set of bad fields returned by badFields
415 checkTc (any (null . badFields rbinds) data_cons)
416 (badFieldsUpd rbinds) `thenM_`
419 -- Typecheck the update bindings.
420 -- (Do this after checking for bad fields in case there's a field that
421 -- doesn't match the constructor.)
423 result_record_ty = mkTyConApp tycon result_inst_tys
425 zapExpectedTo res_ty result_record_ty `thenM_`
426 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
429 -- Use the un-updated fields to find a vector of booleans saying
430 -- which type arguments must be the same in updatee and result.
432 -- WARNING: this code assumes that all data_cons in a common tycon
433 -- have FieldLabels abstracted over the same tyvars.
435 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
436 con_field_lbls_s = map dataConFieldLabels data_cons
438 -- A constructor is only relevant to this process if
439 -- it contains all the fields that are being updated
440 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
441 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
443 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
444 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
446 mk_inst_ty (tyvar, result_inst_ty)
447 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
448 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
450 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
453 -- Typecheck the expression to be updated
455 record_ty = mkTyConApp tycon inst_tys
457 tcCheckRho record_expr record_ty `thenM` \ record_expr' ->
460 -- Figure out the LIE we need. We have to generate some
461 -- dictionaries for the data type context, since we are going to
462 -- do pattern matching over the data cons.
464 -- What dictionaries do we need?
465 -- We just take the context of the type constructor
467 theta' = substTheta inst_env (tyConTheta tycon)
469 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
470 extendLIEs dicts `thenM_`
473 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
477 %************************************************************************
479 Arithmetic sequences e.g. [a,b..]
480 and their parallel-array counterparts e.g. [: a,b.. :]
483 %************************************************************************
486 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
487 = zapToListTy res_ty `thenM` \ elt_ty ->
488 tcCheckRho expr elt_ty `thenM` \ expr' ->
490 newMethodFromName (ArithSeqOrigin seq)
491 elt_ty enumFromName `thenM` \ enum_from ->
493 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
495 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
496 = addErrCtxt (arithSeqCtxt in_expr) $
497 zapToListTy res_ty `thenM` \ elt_ty ->
498 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
499 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
500 newMethodFromName (ArithSeqOrigin seq)
501 elt_ty enumFromThenName `thenM` \ enum_from_then ->
503 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
506 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
507 = addErrCtxt (arithSeqCtxt in_expr) $
508 zapToListTy res_ty `thenM` \ elt_ty ->
509 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
510 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
511 newMethodFromName (ArithSeqOrigin seq)
512 elt_ty enumFromToName `thenM` \ enum_from_to ->
514 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
516 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
517 = addErrCtxt (arithSeqCtxt in_expr) $
518 zapToListTy res_ty `thenM` \ elt_ty ->
519 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
520 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
521 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
522 newMethodFromName (ArithSeqOrigin seq)
523 elt_ty enumFromThenToName `thenM` \ eft ->
525 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
527 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
528 = addErrCtxt (parrSeqCtxt in_expr) $
529 zapToPArrTy res_ty `thenM` \ elt_ty ->
530 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
531 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
532 newMethodFromName (PArrSeqOrigin seq)
533 elt_ty enumFromToPName `thenM` \ enum_from_to ->
535 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
537 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
538 = addErrCtxt (parrSeqCtxt in_expr) $
539 zapToPArrTy res_ty `thenM` \ elt_ty ->
540 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
541 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
542 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
543 newMethodFromName (PArrSeqOrigin seq)
544 elt_ty enumFromThenToPName `thenM` \ eft ->
546 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
548 tcMonoExpr (PArrSeqIn _) _
549 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
550 -- the parser shouldn't have generated it and the renamer shouldn't have
555 %************************************************************************
559 %************************************************************************
562 #ifdef GHCI /* Only if bootstrapped */
563 -- Rename excludes these cases otherwise
565 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
566 tcMonoExpr (HsBracket brack loc) res_ty = addSrcLoc loc (tcBracket brack res_ty)
568 tcMonoExpr (HsReify (Reify flavour name)) res_ty
569 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
570 tcMetaTy tycon_name `thenM` \ reify_ty ->
571 zapExpectedTo res_ty reify_ty `thenM_`
572 returnM (HsReify (ReifyOut flavour name))
574 tycon_name = case flavour of
575 ReifyDecl -> DsMeta.decQTyConName
576 ReifyType -> DsMeta.typeQTyConName
577 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
582 %************************************************************************
586 %************************************************************************
589 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
593 %************************************************************************
595 \subsection{@tcApp@ typchecks an application}
597 %************************************************************************
601 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
602 -> Expected TcRhoType -- Expected result type of application
603 -> TcM TcExpr -- Translated fun and args
605 tcApp (HsApp e1 e2) args res_ty
606 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
608 tcApp fun args res_ty
609 = -- First type-check the function
610 tcInferRho fun `thenM` \ (fun', fun_ty) ->
612 addErrCtxt (wrongArgsCtxt "too many" fun args) (
613 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
614 split_fun_ty fun_ty (length args)
615 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
617 -- Unify with expected result before (was: after) type-checking the args
618 -- so that the info from res_ty (was: args) percolates to args (was actual_result_ty).
619 -- This is when we might detect a too-few args situation.
620 -- (One can think of cases when the opposite order would give
621 -- a better error message.)
622 -- [March 2003: I'm experimenting with putting this first. Here's an
623 -- example where it actually makes a real difference
624 -- class C t a b | t a -> b
625 -- instance C Char a Bool
627 -- data P t a = forall b. (C t a b) => MkP b
628 -- data Q t = MkQ (forall a. P t a)
631 -- f1 = MkQ (MkP True)
632 -- f2 = MkQ (MkP True :: forall a. P Char a)
634 -- With the change, f1 will type-check, because the 'Char' info from
635 -- the signature is propagated into MkQ's argument. With the check
636 -- in the other order, the extra signature in f2 is reqd.]
638 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
639 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
641 -- Now typecheck the args
643 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
645 returnM (co_fn <$> foldl HsApp fun' args')
648 -- If an error happens we try to figure out whether the
649 -- function has been given too many or too few arguments,
651 -- The ~(Check...) is because in the Infer case the tcSubExp
652 -- definitely won't fail, so we can be certain we're in the Check branch
653 checkArgsCtxt fun args ~(Check expected_res_ty) actual_res_ty tidy_env
654 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
655 zonkTcType actual_res_ty `thenM` \ act_ty' ->
657 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
658 (env2, act_ty'') = tidyOpenType env1 act_ty'
659 (exp_args, _) = tcSplitFunTys exp_ty''
660 (act_args, _) = tcSplitFunTys act_ty''
662 len_act_args = length act_args
663 len_exp_args = length exp_args
665 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
666 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
667 | otherwise = appCtxt fun args
669 returnM (env2, message)
672 split_fun_ty :: TcRhoType -- The type of the function
673 -> Int -- Number of arguments
674 -> TcM ([TcType], -- Function argument types
675 TcType) -- Function result types
677 split_fun_ty fun_ty 0
678 = returnM ([], fun_ty)
680 split_fun_ty fun_ty n
681 = -- Expect the function to have type A->B
682 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
683 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
684 returnM (arg_ty:arg_tys, final_res_ty)
688 tcArg :: RenamedHsExpr -- The function (for error messages)
689 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
690 -> TcM TcExpr -- Resulting argument and LIE
692 tcArg the_fun (arg, expected_arg_ty, arg_no)
693 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
694 tcCheckSigma arg expected_arg_ty
698 %************************************************************************
700 \subsection{@tcId@ typchecks an identifier occurrence}
702 %************************************************************************
704 tcId instantiates an occurrence of an Id.
705 The instantiate_it loop runs round instantiating the Id.
706 It has to be a loop because we are now prepared to entertain
708 f:: forall a. Eq a => forall b. Baz b => tau
709 We want to instantiate this to
710 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
712 The -fno-method-sharing flag controls what happens so far as the LIE
713 is concerned. The default case is that for an overloaded function we
714 generate a "method" Id, and add the Method Inst to the LIE. So you get
717 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
718 If you specify -fno-method-sharing, the dictionary application
719 isn't shared, so we get
721 f = /\a (d:Num a) (x:a) -> (+) a d x x
722 This gets a bit less sharing, but
723 a) it's better for RULEs involving overloaded functions
724 b) perhaps fewer separated lambdas
727 tcId :: Name -> TcM (TcExpr, TcRhoType)
728 tcId name -- Look up the Id and instantiate its type
729 = -- First check whether it's a DataCon
730 -- Reason: we must not forget to chuck in the
731 -- constraints from their "silly context"
732 tcLookup name `thenM` \ thing ->
734 AGlobal (ADataCon data_con) -> inst_data_con data_con
735 ; AGlobal (AnId id) -> loop (HsVar id) (idType id)
736 -- A global cannot possibly be ill-staged
737 -- nor does it need the 'lifting' treatment
739 ; ATcId id th_level proc_level -> tc_local_id id th_level proc_level
740 ; other -> pprPanic "tcId" (ppr name $$ ppr thing)
745 tc_local_id id th_bind_lvl proc_lvl -- Non-TH case
746 = checkProcLevel id proc_lvl `thenM_`
747 loop (HsVar id) (idType id)
749 #else /* GHCI and TH is on */
750 tc_local_id id th_bind_lvl proc_lvl -- TH case
751 = checkProcLevel id proc_lvl `thenM_`
753 -- Check for cross-stage lifting
754 getStage `thenM` \ use_stage ->
756 Brack use_lvl ps_var lie_var
757 | use_lvl > th_bind_lvl
758 -> -- E.g. \x -> [| h x |]
759 -- We must behave as if the reference to x was
762 -- We use 'x' itself as the splice proxy, used by
763 -- the desugarer to stitch it all back together.
764 -- If 'x' occurs many times we may get many identical
765 -- bindings of the same splice proxy, but that doesn't
766 -- matter, although it's a mite untidy.
770 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
771 -- If x is polymorphic, its occurrence sites might
772 -- have different instantiations, so we can't use plain
773 -- 'x' as the splice proxy name. I don't know how to
774 -- solve this, and it's probably unimportant, so I'm
775 -- just going to flag an error for now
778 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
779 -- Put the 'lift' constraint into the right LIE
781 -- Update the pending splices
782 readMutVar ps_var `thenM` \ ps ->
783 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
785 returnM (HsVar id, id_ty))
788 checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage `thenM_`
789 loop (HsVar id) (idType id)
792 loop (HsVar fun_id) fun_ty
793 | want_method_inst fun_ty
794 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
795 newMethodWithGivenTy orig fun_id
796 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
797 loop (HsVar meth_id) tau
801 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
802 loop (inst_fn <$> fun) tau
805 = returnM (fun, fun_ty)
807 -- Hack Alert (want_method_inst)!
808 -- If f :: (%x :: T) => Int -> Int
809 -- Then if we have two separate calls, (f 3, f 4), we cannot
810 -- make a method constraint that then gets shared, thus:
811 -- let m = f %x in (m 3, m 4)
812 -- because that loses the linearity of the constraint.
813 -- The simplest thing to do is never to construct a method constraint
814 -- in the first place that has a linear implicit parameter in it.
815 want_method_inst fun_ty
816 | opt_NoMethodSharing = False
817 | otherwise = case tcSplitSigmaTy fun_ty of
818 (_,[],_) -> False -- Not overloaded
819 (_,theta,_) -> not (any isLinearPred theta)
822 -- We treat data constructors differently, because we have to generate
823 -- constraints for their silly theta, which no longer appears in
824 -- the type of dataConWrapId (see note on "stupid context" in DataCon.lhs
825 -- It's dual to TcPat.tcConstructor
826 inst_data_con data_con
827 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
828 extendLIEs ex_dicts `thenM_`
829 returnM (mkHsDictApp (mkHsTyApp (HsVar (dataConWrapId data_con)) ty_args)
830 (map instToId ex_dicts),
831 mkFunTys arg_tys result_ty)
833 orig = OccurrenceOf name
836 %************************************************************************
838 \subsection{Record bindings}
840 %************************************************************************
842 Game plan for record bindings
843 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
844 1. Find the TyCon for the bindings, from the first field label.
846 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
848 For each binding field = value
850 3. Instantiate the field type (from the field label) using the type
853 4 Type check the value using tcArg, passing the field type as
854 the expected argument type.
856 This extends OK when the field types are universally quantified.
861 :: TyCon -- Type constructor for the record
862 -> [TcType] -- Args of this type constructor
863 -> RenamedRecordBinds
866 tcRecordBinds tycon ty_args rbinds
867 = mappM do_bind rbinds
869 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
871 do_bind (field_lbl_name, rhs)
872 = addErrCtxt (fieldCtxt field_lbl_name) $
873 tcLookupId field_lbl_name `thenM` \ sel_id ->
875 field_lbl = recordSelectorFieldLabel sel_id
876 field_ty = substTy tenv (fieldLabelType field_lbl)
878 ASSERT( isRecordSelector sel_id )
879 -- This lookup and assertion will surely succeed, because
880 -- we check that the fields are indeed record selectors
881 -- before calling tcRecordBinds
882 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
883 -- The caller of tcRecordBinds has already checked
884 -- that all the fields come from the same type
886 tcCheckSigma rhs field_ty `thenM` \ rhs' ->
888 returnM (sel_id, rhs')
890 badFields rbinds data_con
891 = filter (not . (`elem` field_names)) (recBindFields rbinds)
893 field_names = map fieldLabelName (dataConFieldLabels data_con)
895 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
896 checkMissingFields data_con rbinds
897 | null field_labels -- Not declared as a record;
898 -- But C{} is still valid if no strict fields
899 = if any isMarkedStrict field_strs then
900 -- Illegal if any arg is strict
901 addErrTc (missingStrictFields data_con [])
905 | otherwise -- A record
906 = checkM (null missing_s_fields)
907 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
909 doptM Opt_WarnMissingFields `thenM` \ warn ->
910 checkM (not (warn && notNull missing_ns_fields))
911 (warnTc True (missingFields data_con missing_ns_fields))
915 = [ fl | (fl, str) <- field_info,
917 not (fieldLabelName fl `elem` field_names_used)
920 = [ fl | (fl, str) <- field_info,
921 not (isMarkedStrict str),
922 not (fieldLabelName fl `elem` field_names_used)
925 field_names_used = recBindFields rbinds
926 field_labels = dataConFieldLabels data_con
928 field_info = zipEqual "missingFields"
932 field_strs = dataConStrictMarks data_con
935 %************************************************************************
937 \subsection{@tcCheckRhos@ typechecks a {\em list} of expressions}
939 %************************************************************************
942 tcCheckRhos :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
944 tcCheckRhos [] [] = returnM []
945 tcCheckRhos (expr:exprs) (ty:tys)
946 = tcCheckRho expr ty `thenM` \ expr' ->
947 tcCheckRhos exprs tys `thenM` \ exprs' ->
948 returnM (expr':exprs')
952 %************************************************************************
954 \subsection{Literals}
956 %************************************************************************
961 tcLit :: HsLit -> Expected TcRhoType -> TcM TcExpr
963 = zapExpectedTo res_ty (hsLitType lit) `thenM_`
968 %************************************************************************
970 \subsection{Errors and contexts}
972 %************************************************************************
974 Boring and alphabetical:
977 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
980 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
983 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
986 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
989 = hang (ptext SLIT("In the type signature of the expression:"))
993 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
996 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
998 funAppCtxt fun arg arg_no
999 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1000 quotes (ppr fun) <> text ", namely"])
1001 4 (quotes (ppr arg))
1004 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1007 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1010 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1013 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1015 the_app = foldl HsApp fun args -- Used in error messages
1018 = hang (ptext SLIT("No constructor has all these fields:"))
1019 4 (pprQuotedList (recBindFields rbinds))
1021 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1022 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1025 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1027 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1028 missingStrictFields con fields
1031 rest | null fields = empty -- Happens for non-record constructors
1032 -- with strict fields
1033 | otherwise = colon <+> pprWithCommas ppr fields
1035 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1036 ptext SLIT("does not have the required strict field(s)")
1038 missingFields :: DataCon -> [FieldLabel] -> SDoc
1039 missingFields con fields
1040 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1041 <+> pprWithCommas ppr fields
1043 wrongArgsCtxt too_many_or_few fun args
1044 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1045 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1046 <+> ptext SLIT("arguments in the call"))
1047 4 (parens (ppr the_app))
1049 the_app = foldl HsApp fun args -- Used in error messages
1052 polySpliceErr :: Id -> SDoc
1054 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)