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(..) )
14 import TcType ( isTauTy )
15 import TcEnv ( bracketOK, tcMetaTy, checkWellStaged )
16 import Name ( isExternalName )
17 import qualified DsMeta
20 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..), recBindFields )
21 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
22 import TcHsSyn ( TcExpr, TcRecordBinds, hsLitType, mkHsDictApp, mkHsTyApp, mkHsLet, (<$>) )
24 import TcUnify ( Expected(..), newHole, zapExpectedType, zapExpectedTo, tcSubExp, tcGen,
25 unifyFunTy, zapToListTy, zapToPArrTy, zapToTupleTy )
26 import BasicTypes ( isMarkedStrict )
27 import Inst ( InstOrigin(..),
28 newOverloadedLit, newMethodFromName, newIPDict,
29 newDicts, newMethodWithGivenTy,
30 instToId, tcInstCall, tcInstDataCon
32 import TcBinds ( tcBindsAndThen )
33 import TcEnv ( tcLookupClass, tcLookupGlobal_maybe, tcLookup,
34 tcLookupTyCon, tcLookupDataCon, tcLookupId, checkProcLevel
36 import TcArrows ( tcProc )
37 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts, tcThingWithSig )
38 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
39 import TcPat ( badFieldCon )
40 import TcMType ( tcInstTyVars, tcInstType, newTyVarTy, newTyVarTys, zonkTcType )
41 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
42 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
43 isSigmaTy, mkFunTy, mkFunTys,
44 mkTyConApp, mkClassPred,
45 tyVarsOfTypes, isLinearPred,
46 liftedTypeKind, openTypeKind,
47 tcSplitSigmaTy, tidyOpenType
49 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
50 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector )
51 import DataCon ( DataCon, dataConFieldLabels, dataConSig, 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,
62 import ListSetOps ( minusList )
64 import HscTypes ( TyThing(..) )
71 %************************************************************************
73 \subsection{Main wrappers}
75 %************************************************************************
78 -- tcCheckSigma does type *checking*; it's passed the expected type of the result
79 tcCheckSigma :: RenamedHsExpr -- Expession to type check
80 -> TcSigmaType -- Expected type (could be a polytpye)
81 -> TcM TcExpr -- Generalised expr with expected type
83 tcCheckSigma expr expected_ty
84 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
85 tc_expr' expr expected_ty
87 tc_expr' expr sigma_ty
89 = tcGen sigma_ty emptyVarSet (
90 \ rho_ty -> tcCheckRho expr rho_ty
91 ) `thenM` \ (gen_fn, expr') ->
92 returnM (gen_fn <$> expr')
94 tc_expr' expr rho_ty -- Monomorphic case
95 = tcCheckRho expr rho_ty
98 Typecheck expression which in most cases will be an Id.
99 The expression can return a higher-ranked type, such as
100 (forall a. a->a) -> Int
101 so we must create a hole to pass in as the expected tyvar.
104 tcCheckRho :: RenamedHsExpr -> TcRhoType -> TcM TcExpr
105 tcCheckRho expr rho_ty = tcMonoExpr expr (Check rho_ty)
107 tcInferRho :: RenamedHsExpr -> TcM (TcExpr, TcRhoType)
108 tcInferRho (HsVar name) = tcId name
109 tcInferRho expr = newHole `thenM` \ hole ->
110 tcMonoExpr expr (Infer hole) `thenM` \ expr' ->
111 readMutVar hole `thenM` \ rho_ty ->
112 returnM (expr', rho_ty)
117 %************************************************************************
119 \subsection{The TAUT rules for variables}
121 %************************************************************************
124 tcMonoExpr :: RenamedHsExpr -- Expession to type check
125 -> Expected TcRhoType -- Expected type (could be a type variable)
126 -- Definitely no foralls at the top
130 tcMonoExpr (HsVar name) res_ty
131 = tcId name `thenM` \ (expr', id_ty) ->
132 tcSubExp res_ty id_ty `thenM` \ co_fn ->
133 returnM (co_fn <$> expr')
135 tcMonoExpr (HsIPVar ip) res_ty
136 = -- Implicit parameters must have a *tau-type* not a
137 -- type scheme. We enforce this by creating a fresh
138 -- type variable as its type. (Because res_ty may not
140 newTyVarTy openTypeKind `thenM` \ ip_ty ->
141 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
142 extendLIE inst `thenM_`
143 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
144 returnM (co_fn <$> HsIPVar ip')
148 %************************************************************************
150 \subsection{Expressions type signatures}
152 %************************************************************************
155 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
156 = addErrCtxt (exprSigCtxt in_expr) $
157 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
158 tcThingWithSig sig_tc_ty (tcCheckRho expr) res_ty `thenM` \ (co_fn, expr') ->
159 returnM (co_fn <$> expr')
161 tcMonoExpr (HsType ty) res_ty
162 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
163 -- This is the syntax for type applications that I was planning
164 -- but there are difficulties (e.g. what order for type args)
165 -- so it's not enabled yet.
166 -- Can't eliminate it altogether from the parser, because the
167 -- same parser parses *patterns*.
171 %************************************************************************
173 \subsection{Other expression forms}
175 %************************************************************************
178 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
179 tcMonoExpr (HsOverLit lit) res_ty = zapExpectedType res_ty `thenM` \ res_ty' ->
180 newOverloadedLit (LiteralOrigin lit) lit res_ty'
181 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
182 returnM (HsPar expr')
183 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
184 returnM (HsSCC lbl expr')
186 tcMonoExpr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
187 returnM (HsCoreAnn lbl expr')
188 tcMonoExpr (NegApp expr neg_name) res_ty
189 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
190 -- ToDo: use tcSyntaxName
192 tcMonoExpr (HsLam match) res_ty
193 = tcMatchLambda match res_ty `thenM` \ match' ->
194 returnM (HsLam match')
196 tcMonoExpr (HsApp e1 e2) res_ty
197 = tcApp e1 [e2] res_ty
200 Note that the operators in sections are expected to be binary, and
201 a type error will occur if they aren't.
204 -- Left sections, equivalent to
211 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
212 = tcInferRho op `thenM` \ (op', op_ty) ->
213 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
214 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
215 addErrCtxt (exprCtxt in_expr) $
216 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
217 returnM (co_fn <$> SectionL arg1' op')
219 -- Right sections, equivalent to \ x -> x op expr, or
222 tcMonoExpr in_expr@(SectionR op arg2) res_ty
223 = tcInferRho op `thenM` \ (op', op_ty) ->
224 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
225 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
226 addErrCtxt (exprCtxt in_expr) $
227 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
228 returnM (co_fn <$> SectionR op' arg2')
230 -- equivalent to (op e1) e2:
232 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
233 = tcInferRho op `thenM` \ (op', op_ty) ->
234 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
235 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
236 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
237 addErrCtxt (exprCtxt in_expr) $
238 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
239 returnM (OpApp arg1' op' fix arg2')
243 tcMonoExpr (HsLet binds expr) res_ty
246 binds -- Bindings to check
247 (tcMonoExpr expr res_ty)
249 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
250 = addSrcLoc src_loc $
251 addErrCtxt (caseCtxt in_expr) $
253 -- Typecheck the case alternatives first.
254 -- The case patterns tend to give good type info to use
255 -- when typechecking the scrutinee. For example
258 -- will report that map is applied to too few arguments
260 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
262 addErrCtxt (caseScrutCtxt scrut) (
263 tcCheckRho scrut scrut_ty
264 ) `thenM` \ scrut' ->
266 returnM (HsCase scrut' matches' src_loc)
268 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
269 = addSrcLoc src_loc $
270 addErrCtxt (predCtxt pred) (
271 tcCheckRho pred boolTy ) `thenM` \ pred' ->
273 zapExpectedType res_ty `thenM` \ res_ty' ->
274 -- C.f. the call to zapToType in TcMatches.tcMatches
276 tcCheckRho b1 res_ty' `thenM` \ b1' ->
277 tcCheckRho b2 res_ty' `thenM` \ b2' ->
278 returnM (HsIf pred' b1' b2' src_loc)
280 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
281 = addSrcLoc src_loc $
282 zapExpectedType res_ty `thenM` \ res_ty' ->
283 -- All comprehensions yield a monotype
284 tcDoStmts do_or_lc stmts method_names res_ty' `thenM` \ (stmts', methods') ->
285 returnM (HsDo do_or_lc stmts' methods' res_ty' src_loc)
287 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
288 = zapToListTy res_ty `thenM` \ elt_ty ->
289 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
290 returnM (ExplicitList elt_ty exprs')
293 = addErrCtxt (listCtxt expr) $
294 tcCheckRho expr elt_ty
296 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
297 = zapToPArrTy res_ty `thenM` \ elt_ty ->
298 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
299 returnM (ExplicitPArr elt_ty exprs')
302 = addErrCtxt (parrCtxt expr) $
303 tcCheckRho expr elt_ty
305 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
306 = zapToTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
307 tcCheckRhos exprs arg_tys `thenM` \ exprs' ->
308 returnM (ExplicitTuple exprs' boxity)
310 tcMonoExpr (HsProc pat cmd loc) res_ty
312 tcProc pat cmd res_ty `thenM` \ (pat', cmd') ->
313 returnM (HsProc pat' cmd' loc)
316 %************************************************************************
318 Record construction and update
320 %************************************************************************
323 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
324 = addErrCtxt (recordConCtxt expr) $
325 tcId con_name `thenM` \ (con_expr, con_tau) ->
327 (_, record_ty) = tcSplitFunTys con_tau
328 (tycon, ty_args) = tcSplitTyConApp record_ty
330 ASSERT( isAlgTyCon tycon )
331 zapExpectedTo res_ty record_ty `thenM_`
333 -- Check that the record bindings match the constructor
334 -- con_name is syntactically constrained to be a data constructor
335 tcLookupDataCon con_name `thenM` \ data_con ->
337 bad_fields = badFields rbinds data_con
339 if notNull bad_fields then
340 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
341 failM -- Fail now, because tcRecordBinds will crash on a bad field
344 -- Typecheck the record bindings
345 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
347 -- Check for missing fields
348 checkMissingFields data_con rbinds `thenM_`
350 returnM (RecordConOut data_con con_expr rbinds')
352 -- The main complication with RecordUpd is that we need to explicitly
353 -- handle the *non-updated* fields. Consider:
355 -- data T a b = MkT1 { fa :: a, fb :: b }
356 -- | MkT2 { fa :: a, fc :: Int -> Int }
357 -- | MkT3 { fd :: a }
359 -- upd :: T a b -> c -> T a c
360 -- upd t x = t { fb = x}
362 -- The type signature on upd is correct (i.e. the result should not be (T a b))
363 -- because upd should be equivalent to:
365 -- upd t x = case t of
366 -- MkT1 p q -> MkT1 p x
367 -- MkT2 a b -> MkT2 p b
368 -- MkT3 d -> error ...
370 -- So we need to give a completely fresh type to the result record,
371 -- and then constrain it by the fields that are *not* updated ("p" above).
373 -- Note that because MkT3 doesn't contain all the fields being updated,
374 -- its RHS is simply an error, so it doesn't impose any type constraints
376 -- All this is done in STEP 4 below.
378 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
379 = addErrCtxt (recordUpdCtxt expr) $
382 -- Check that the field names are really field names
383 ASSERT( notNull rbinds )
385 field_names = recBindFields rbinds
387 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
389 bad_guys = [ addErrTc (notSelector field_name)
390 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
391 not (is_selector maybe_sel_id)
393 is_selector (Just (AnId sel_id)) = isRecordSelector sel_id -- Excludes class ops
394 is_selector other = False
396 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
399 -- Figure out the tycon and data cons from the first field name
401 -- It's OK to use the non-tc splitters here (for a selector)
402 (Just (AnId sel_id) : _) = maybe_sel_ids
403 field_lbl = recordSelectorFieldLabel sel_id -- We've failed already if
404 tycon = fieldLabelTyCon field_lbl -- it's not a field label
405 data_cons = tyConDataCons tycon
406 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
408 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
411 -- Check that at least one constructor has all the named fields
412 -- i.e. has an empty set of bad fields returned by badFields
413 checkTc (any (null . badFields rbinds) data_cons)
414 (badFieldsUpd rbinds) `thenM_`
417 -- Typecheck the update bindings.
418 -- (Do this after checking for bad fields in case there's a field that
419 -- doesn't match the constructor.)
421 result_record_ty = mkTyConApp tycon result_inst_tys
423 zapExpectedTo res_ty result_record_ty `thenM_`
424 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
427 -- Use the un-updated fields to find a vector of booleans saying
428 -- which type arguments must be the same in updatee and result.
430 -- WARNING: this code assumes that all data_cons in a common tycon
431 -- have FieldLabels abstracted over the same tyvars.
433 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
434 con_field_lbls_s = map dataConFieldLabels data_cons
436 -- A constructor is only relevant to this process if
437 -- it contains all the fields that are being updated
438 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
439 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
441 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
442 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
444 mk_inst_ty (tyvar, result_inst_ty)
445 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
446 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
448 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
451 -- Typecheck the expression to be updated
453 record_ty = mkTyConApp tycon inst_tys
455 tcCheckRho record_expr record_ty `thenM` \ record_expr' ->
458 -- Figure out the LIE we need. We have to generate some
459 -- dictionaries for the data type context, since we are going to
460 -- do pattern matching over the data cons.
462 -- What dictionaries do we need?
463 -- We just take the context of the type constructor
465 theta' = substTheta inst_env (tyConTheta tycon)
467 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
468 extendLIEs dicts `thenM_`
471 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
475 %************************************************************************
477 Arithmetic sequences e.g. [a,b..]
478 and their parallel-array counterparts e.g. [: a,b.. :]
481 %************************************************************************
484 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
485 = zapToListTy res_ty `thenM` \ elt_ty ->
486 tcCheckRho expr elt_ty `thenM` \ expr' ->
488 newMethodFromName (ArithSeqOrigin seq)
489 elt_ty enumFromName `thenM` \ enum_from ->
491 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
493 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
494 = addErrCtxt (arithSeqCtxt in_expr) $
495 zapToListTy res_ty `thenM` \ elt_ty ->
496 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
497 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
498 newMethodFromName (ArithSeqOrigin seq)
499 elt_ty enumFromThenName `thenM` \ enum_from_then ->
501 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
504 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
505 = addErrCtxt (arithSeqCtxt in_expr) $
506 zapToListTy res_ty `thenM` \ elt_ty ->
507 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
508 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
509 newMethodFromName (ArithSeqOrigin seq)
510 elt_ty enumFromToName `thenM` \ enum_from_to ->
512 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
514 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
515 = addErrCtxt (arithSeqCtxt in_expr) $
516 zapToListTy res_ty `thenM` \ elt_ty ->
517 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
518 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
519 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
520 newMethodFromName (ArithSeqOrigin seq)
521 elt_ty enumFromThenToName `thenM` \ eft ->
523 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
525 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
526 = addErrCtxt (parrSeqCtxt in_expr) $
527 zapToPArrTy res_ty `thenM` \ elt_ty ->
528 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
529 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
530 newMethodFromName (PArrSeqOrigin seq)
531 elt_ty enumFromToPName `thenM` \ enum_from_to ->
533 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
535 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
536 = addErrCtxt (parrSeqCtxt in_expr) $
537 zapToPArrTy res_ty `thenM` \ elt_ty ->
538 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
539 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
540 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
541 newMethodFromName (PArrSeqOrigin seq)
542 elt_ty enumFromThenToPName `thenM` \ eft ->
544 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
546 tcMonoExpr (PArrSeqIn _) _
547 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
548 -- the parser shouldn't have generated it and the renamer shouldn't have
553 %************************************************************************
557 %************************************************************************
560 #ifdef GHCI /* Only if bootstrapped */
561 -- Rename excludes these cases otherwise
563 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
564 tcMonoExpr (HsBracket brack loc) res_ty = addSrcLoc loc (tcBracket brack res_ty)
566 tcMonoExpr (HsReify (Reify flavour name)) res_ty
567 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
568 tcMetaTy tycon_name `thenM` \ reify_ty ->
569 zapExpectedTo res_ty reify_ty `thenM_`
570 returnM (HsReify (ReifyOut flavour name))
572 tycon_name = case flavour of
573 ReifyDecl -> DsMeta.decQTyConName
574 ReifyType -> DsMeta.typeQTyConName
575 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
580 %************************************************************************
584 %************************************************************************
587 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
591 %************************************************************************
593 \subsection{@tcApp@ typchecks an application}
595 %************************************************************************
599 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
600 -> Expected TcRhoType -- Expected result type of application
601 -> TcM TcExpr -- Translated fun and args
603 tcApp (HsApp e1 e2) args res_ty
604 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
606 tcApp fun args res_ty
607 = -- First type-check the function
608 tcInferRho fun `thenM` \ (fun', fun_ty) ->
610 addErrCtxt (wrongArgsCtxt "too many" fun args) (
611 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
612 split_fun_ty fun_ty (length args)
613 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
615 -- Unify with expected result before (was: after) type-checking the args
616 -- so that the info from res_ty (was: args) percolates to args (was actual_result_ty).
617 -- This is when we might detect a too-few args situation.
618 -- (One can think of cases when the opposite order would give
619 -- a better error message.)
620 -- [March 2003: I'm experimenting with putting this first. Here's an
621 -- example where it actually makes a real difference
622 -- class C t a b | t a -> b
623 -- instance C Char a Bool
625 -- data P t a = forall b. (C t a b) => MkP b
626 -- data Q t = MkQ (forall a. P t a)
629 -- f1 = MkQ (MkP True)
630 -- f2 = MkQ (MkP True :: forall a. P Char a)
632 -- With the change, f1 will type-check, because the 'Char' info from
633 -- the signature is propagated into MkQ's argument. With the check
634 -- in the other order, the extra signature in f2 is reqd.]
636 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
637 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
639 -- Now typecheck the args
641 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
643 returnM (co_fn <$> foldl HsApp fun' args')
646 -- If an error happens we try to figure out whether the
647 -- function has been given too many or too few arguments,
649 -- The ~(Check...) is because in the Infer case the tcSubExp
650 -- definitely won't fail, so we can be certain we're in the Check branch
651 checkArgsCtxt fun args ~(Check expected_res_ty) actual_res_ty tidy_env
652 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
653 zonkTcType actual_res_ty `thenM` \ act_ty' ->
655 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
656 (env2, act_ty'') = tidyOpenType env1 act_ty'
657 (exp_args, _) = tcSplitFunTys exp_ty''
658 (act_args, _) = tcSplitFunTys act_ty''
660 len_act_args = length act_args
661 len_exp_args = length exp_args
663 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
664 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
665 | otherwise = appCtxt fun args
667 returnM (env2, message)
670 split_fun_ty :: TcRhoType -- The type of the function
671 -> Int -- Number of arguments
672 -> TcM ([TcType], -- Function argument types
673 TcType) -- Function result types
675 split_fun_ty fun_ty 0
676 = returnM ([], fun_ty)
678 split_fun_ty fun_ty n
679 = -- Expect the function to have type A->B
680 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
681 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
682 returnM (arg_ty:arg_tys, final_res_ty)
686 tcArg :: RenamedHsExpr -- The function (for error messages)
687 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
688 -> TcM TcExpr -- Resulting argument and LIE
690 tcArg the_fun (arg, expected_arg_ty, arg_no)
691 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
692 tcCheckSigma arg expected_arg_ty
696 %************************************************************************
698 \subsection{@tcId@ typchecks an identifier occurrence}
700 %************************************************************************
702 tcId instantiates an occurrence of an Id.
703 The instantiate_it loop runs round instantiating the Id.
704 It has to be a loop because we are now prepared to entertain
706 f:: forall a. Eq a => forall b. Baz b => tau
707 We want to instantiate this to
708 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
710 The -fno-method-sharing flag controls what happens so far as the LIE
711 is concerned. The default case is that for an overloaded function we
712 generate a "method" Id, and add the Method Inst to the LIE. So you get
715 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
716 If you specify -fno-method-sharing, the dictionary application
717 isn't shared, so we get
719 f = /\a (d:Num a) (x:a) -> (+) a d x x
720 This gets a bit less sharing, but
721 a) it's better for RULEs involving overloaded functions
722 b) perhaps fewer separated lambdas
725 tcId :: Name -> TcM (TcExpr, TcRhoType)
726 tcId name -- Look up the Id and instantiate its type
727 = -- First check whether it's a DataCon
728 -- Reason: we must not forget to chuck in the
729 -- constraints from their "silly context"
730 tcLookup name `thenM` \ maybe_thing ->
731 case maybe_thing of {
732 AGlobal (ADataCon data_con) -> inst_data_con data_con
733 ; AGlobal (AnId id) -> loop (HsVar id) (idType id)
734 -- A global cannot possibly be ill-staged
735 -- nor does it need the 'lifting' treatment
737 ; ATcId id th_level proc_level -> tc_local_id id th_level proc_level
738 ; other -> pprPanic "tcId" (ppr name)
743 tc_local_id id th_bind_lvl proc_lvl -- Non-TH case
744 = checkProcLevel id proc_lvl `thenM_`
745 loop (HsVar id) (idType id)
747 #else /* GHCI and TH is on */
748 tc_local_id id th_bind_lvl proc_lvl -- TH case
749 = checkProcLevel id proc_lvl `thenM_`
751 -- Check for cross-stage lifting
752 getStage `thenM` \ use_stage ->
754 Brack use_lvl ps_var lie_var
755 | use_lvl > th_bind_lvl
756 -> -- E.g. \x -> [| h x |]
757 -- We must behave as if the reference to x was
760 -- We use 'x' itself as the splice proxy, used by
761 -- the desugarer to stitch it all back together.
762 -- If 'x' occurs many times we may get many identical
763 -- bindings of the same splice proxy, but that doesn't
764 -- matter, although it's a mite untidy.
768 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
769 -- If x is polymorphic, its occurrence sites might
770 -- have different instantiations, so we can't use plain
771 -- 'x' as the splice proxy name. I don't know how to
772 -- solve this, and it's probably unimportant, so I'm
773 -- just going to flag an error for now
776 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
777 -- Put the 'lift' constraint into the right LIE
779 -- Update the pending splices
780 readMutVar ps_var `thenM` \ ps ->
781 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
783 returnM (HsVar id, id_ty))
786 checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage `thenM_`
787 loop (HsVar id) (idType id)
790 loop (HsVar fun_id) fun_ty
791 | want_method_inst fun_ty
792 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
793 newMethodWithGivenTy orig fun_id
794 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
795 loop (HsVar meth_id) tau
799 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
800 loop (inst_fn <$> fun) tau
803 = returnM (fun, fun_ty)
805 -- Hack Alert (want_method_inst)!
806 -- If f :: (%x :: T) => Int -> Int
807 -- Then if we have two separate calls, (f 3, f 4), we cannot
808 -- make a method constraint that then gets shared, thus:
809 -- let m = f %x in (m 3, m 4)
810 -- because that loses the linearity of the constraint.
811 -- The simplest thing to do is never to construct a method constraint
812 -- in the first place that has a linear implicit parameter in it.
813 want_method_inst fun_ty
814 | opt_NoMethodSharing = False
815 | otherwise = case tcSplitSigmaTy fun_ty of
816 (_,[],_) -> False -- Not overloaded
817 (_,theta,_) -> not (any isLinearPred theta)
820 -- We treat data constructors differently, because we have to generate
821 -- constraints for their silly theta, which no longer appears in
822 -- the type of dataConWrapId (see note on "stupid context" in DataCon.lhs
823 -- It's dual to TcPat.tcConstructor
824 inst_data_con data_con
825 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
826 extendLIEs ex_dicts `thenM_`
827 returnM (mkHsDictApp (mkHsTyApp (HsVar (dataConWrapId data_con)) ty_args)
828 (map instToId ex_dicts),
829 mkFunTys arg_tys result_ty)
831 orig = OccurrenceOf name
834 %************************************************************************
836 \subsection{Record bindings}
838 %************************************************************************
840 Game plan for record bindings
841 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
842 1. Find the TyCon for the bindings, from the first field label.
844 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
846 For each binding field = value
848 3. Instantiate the field type (from the field label) using the type
851 4 Type check the value using tcArg, passing the field type as
852 the expected argument type.
854 This extends OK when the field types are universally quantified.
859 :: TyCon -- Type constructor for the record
860 -> [TcType] -- Args of this type constructor
861 -> RenamedRecordBinds
864 tcRecordBinds tycon ty_args rbinds
865 = mappM do_bind rbinds
867 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
869 do_bind (field_lbl_name, rhs)
870 = addErrCtxt (fieldCtxt field_lbl_name) $
871 tcLookupId field_lbl_name `thenM` \ sel_id ->
873 field_lbl = recordSelectorFieldLabel sel_id
874 field_ty = substTy tenv (fieldLabelType field_lbl)
876 ASSERT( isRecordSelector sel_id )
877 -- This lookup and assertion will surely succeed, because
878 -- we check that the fields are indeed record selectors
879 -- before calling tcRecordBinds
880 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
881 -- The caller of tcRecordBinds has already checked
882 -- that all the fields come from the same type
884 tcCheckSigma rhs field_ty `thenM` \ rhs' ->
886 returnM (sel_id, rhs')
888 badFields rbinds data_con
889 = filter (not . (`elem` field_names)) (recBindFields rbinds)
891 field_names = map fieldLabelName (dataConFieldLabels data_con)
893 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
894 checkMissingFields data_con rbinds
895 | null field_labels -- Not declared as a record;
896 -- But C{} is still valid if no strict fields
897 = if any isMarkedStrict field_strs then
898 -- Illegal if any arg is strict
899 addErrTc (missingStrictFields data_con [])
903 | otherwise -- A record
904 = checkM (null missing_s_fields)
905 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
907 doptM Opt_WarnMissingFields `thenM` \ warn ->
908 checkM (not (warn && notNull missing_ns_fields))
909 (warnTc True (missingFields data_con missing_ns_fields))
913 = [ fl | (fl, str) <- field_info,
915 not (fieldLabelName fl `elem` field_names_used)
918 = [ fl | (fl, str) <- field_info,
919 not (isMarkedStrict str),
920 not (fieldLabelName fl `elem` field_names_used)
923 field_names_used = recBindFields rbinds
924 field_labels = dataConFieldLabels data_con
926 field_info = zipEqual "missingFields"
930 field_strs = dropList ex_theta (dataConStrictMarks data_con)
931 -- The 'drop' is because dataConStrictMarks
932 -- includes the existential dictionaries
933 (_, _, _, ex_theta, _, _) = dataConSig data_con
936 %************************************************************************
938 \subsection{@tcCheckRhos@ typechecks a {\em list} of expressions}
940 %************************************************************************
943 tcCheckRhos :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
945 tcCheckRhos [] [] = returnM []
946 tcCheckRhos (expr:exprs) (ty:tys)
947 = tcCheckRho expr ty `thenM` \ expr' ->
948 tcCheckRhos exprs tys `thenM` \ exprs' ->
949 returnM (expr':exprs')
953 %************************************************************************
955 \subsection{Literals}
957 %************************************************************************
962 tcLit :: HsLit -> Expected TcRhoType -> TcM TcExpr
964 = zapExpectedTo res_ty (hsLitType lit) `thenM_`
969 %************************************************************************
971 \subsection{Errors and contexts}
973 %************************************************************************
975 Boring and alphabetical:
978 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
981 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
984 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
987 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
990 = hang (ptext SLIT("When checking the type signature of the expression:"))
994 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
997 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
999 funAppCtxt fun arg arg_no
1000 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1001 quotes (ppr fun) <> text ", namely"])
1002 4 (quotes (ppr arg))
1005 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1008 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1011 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1014 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1016 the_app = foldl HsApp fun args -- Used in error messages
1018 lurkingRank2Err fun fun_ty
1019 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1020 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1021 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1024 = hang (ptext SLIT("No constructor has all these fields:"))
1025 4 (pprQuotedList (recBindFields rbinds))
1027 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1028 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1031 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1033 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1034 missingStrictFields con fields
1037 rest | null fields = empty -- Happens for non-record constructors
1038 -- with strict fields
1039 | otherwise = colon <+> pprWithCommas ppr fields
1041 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1042 ptext SLIT("does not have the required strict field(s)")
1044 missingFields :: DataCon -> [FieldLabel] -> SDoc
1045 missingFields con fields
1046 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1047 <+> pprWithCommas ppr fields
1049 polySpliceErr :: Id -> SDoc
1051 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1053 wrongArgsCtxt too_many_or_few fun args
1054 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1055 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1056 <+> ptext SLIT("arguments in the call"))
1057 4 (parens (ppr the_app))
1059 the_app = foldl HsApp fun args -- Used in error messages