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 ( cCallableClassName, cReturnableClassName,
58 enumFromName, enumFromThenName,
59 enumFromToName, enumFromThenToName,
60 enumFromToPName, enumFromThenToPName,
63 import ListSetOps ( minusList )
65 import HscTypes ( TyThing(..) )
72 %************************************************************************
74 \subsection{Main wrappers}
76 %************************************************************************
79 -- tcCheckSigma does type *checking*; it's passed the expected type of the result
80 tcCheckSigma :: RenamedHsExpr -- Expession to type check
81 -> TcSigmaType -- Expected type (could be a polytpye)
82 -> TcM TcExpr -- Generalised expr with expected type
84 tcCheckSigma expr expected_ty
85 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
86 tc_expr' expr expected_ty
88 tc_expr' expr sigma_ty
90 = tcGen sigma_ty emptyVarSet (
91 \ rho_ty -> tcCheckRho expr rho_ty
92 ) `thenM` \ (gen_fn, expr') ->
93 returnM (gen_fn <$> expr')
95 tc_expr' expr rho_ty -- Monomorphic case
96 = tcCheckRho expr rho_ty
99 Typecheck expression which in most cases will be an Id.
100 The expression can return a higher-ranked type, such as
101 (forall a. a->a) -> Int
102 so we must create a hole to pass in as the expected tyvar.
105 tcCheckRho :: RenamedHsExpr -> TcRhoType -> TcM TcExpr
106 tcCheckRho expr rho_ty = tcMonoExpr expr (Check rho_ty)
108 tcInferRho :: RenamedHsExpr -> TcM (TcExpr, TcRhoType)
109 tcInferRho (HsVar name) = tcId name
110 tcInferRho expr = newHole `thenM` \ hole ->
111 tcMonoExpr expr (Infer hole) `thenM` \ expr' ->
112 readMutVar hole `thenM` \ rho_ty ->
113 returnM (expr', rho_ty)
118 %************************************************************************
120 \subsection{The TAUT rules for variables}
122 %************************************************************************
125 tcMonoExpr :: RenamedHsExpr -- Expession to type check
126 -> Expected TcRhoType -- Expected type (could be a type variable)
127 -- Definitely no foralls at the top
131 tcMonoExpr (HsVar name) res_ty
132 = tcId name `thenM` \ (expr', id_ty) ->
133 tcSubExp res_ty id_ty `thenM` \ co_fn ->
134 returnM (co_fn <$> expr')
136 tcMonoExpr (HsIPVar ip) res_ty
137 = -- Implicit parameters must have a *tau-type* not a
138 -- type scheme. We enforce this by creating a fresh
139 -- type variable as its type. (Because res_ty may not
141 newTyVarTy openTypeKind `thenM` \ ip_ty ->
142 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
143 extendLIE inst `thenM_`
144 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
145 returnM (co_fn <$> HsIPVar ip')
149 %************************************************************************
151 \subsection{Expressions type signatures}
153 %************************************************************************
156 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
157 = addErrCtxt (exprSigCtxt in_expr) $
158 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
159 tcThingWithSig sig_tc_ty (tcCheckRho expr) res_ty `thenM` \ (co_fn, expr') ->
160 returnM (co_fn <$> expr')
162 tcMonoExpr (HsType ty) res_ty
163 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
164 -- This is the syntax for type applications that I was planning
165 -- but there are difficulties (e.g. what order for type args)
166 -- so it's not enabled yet.
167 -- Can't eliminate it altogether from the parser, because the
168 -- same parser parses *patterns*.
172 %************************************************************************
174 \subsection{Other expression forms}
176 %************************************************************************
179 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
180 tcMonoExpr (HsOverLit lit) res_ty = zapExpectedType res_ty `thenM` \ res_ty' ->
181 newOverloadedLit (LiteralOrigin lit) lit res_ty'
182 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
183 returnM (HsPar expr')
184 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
185 returnM (HsSCC lbl expr')
187 tcMonoExpr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
188 returnM (HsCoreAnn lbl expr')
189 tcMonoExpr (NegApp expr neg_name) res_ty
190 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
191 -- ToDo: use tcSyntaxName
193 tcMonoExpr (HsLam match) res_ty
194 = tcMatchLambda match res_ty `thenM` \ match' ->
195 returnM (HsLam match')
197 tcMonoExpr (HsApp e1 e2) res_ty
198 = tcApp e1 [e2] res_ty
201 Note that the operators in sections are expected to be binary, and
202 a type error will occur if they aren't.
205 -- Left sections, equivalent to
212 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
213 = tcInferRho op `thenM` \ (op', op_ty) ->
214 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
215 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
216 addErrCtxt (exprCtxt in_expr) $
217 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
218 returnM (co_fn <$> SectionL arg1' op')
220 -- Right sections, equivalent to \ x -> x op expr, or
223 tcMonoExpr in_expr@(SectionR op arg2) res_ty
224 = tcInferRho op `thenM` \ (op', op_ty) ->
225 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
226 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
227 addErrCtxt (exprCtxt in_expr) $
228 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
229 returnM (co_fn <$> SectionR op' arg2')
231 -- equivalent to (op e1) e2:
233 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
234 = tcInferRho op `thenM` \ (op', op_ty) ->
235 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
236 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
237 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
238 addErrCtxt (exprCtxt in_expr) $
239 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
240 returnM (OpApp arg1' op' fix arg2')
244 tcMonoExpr (HsLet binds expr) res_ty
247 binds -- Bindings to check
248 (tcMonoExpr expr res_ty)
250 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
251 = addSrcLoc src_loc $
252 addErrCtxt (caseCtxt in_expr) $
254 -- Typecheck the case alternatives first.
255 -- The case patterns tend to give good type info to use
256 -- when typechecking the scrutinee. For example
259 -- will report that map is applied to too few arguments
261 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
263 addErrCtxt (caseScrutCtxt scrut) (
264 tcCheckRho scrut scrut_ty
265 ) `thenM` \ scrut' ->
267 returnM (HsCase scrut' matches' src_loc)
269 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
270 = addSrcLoc src_loc $
271 addErrCtxt (predCtxt pred) (
272 tcCheckRho pred boolTy ) `thenM` \ pred' ->
274 zapExpectedType res_ty `thenM` \ res_ty' ->
275 -- C.f. the call to zapToType in TcMatches.tcMatches
277 tcCheckRho b1 res_ty' `thenM` \ b1' ->
278 tcCheckRho b2 res_ty' `thenM` \ b2' ->
279 returnM (HsIf pred' b1' b2' src_loc)
281 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
282 = addSrcLoc src_loc $
283 zapExpectedType res_ty `thenM` \ res_ty' ->
284 -- All comprehensions yield a monotype
285 tcDoStmts do_or_lc stmts method_names res_ty' `thenM` \ (stmts', methods') ->
286 returnM (HsDo do_or_lc stmts' methods' res_ty' src_loc)
288 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
289 = zapToListTy res_ty `thenM` \ elt_ty ->
290 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
291 returnM (ExplicitList elt_ty exprs')
294 = addErrCtxt (listCtxt expr) $
295 tcCheckRho expr elt_ty
297 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
298 = zapToPArrTy res_ty `thenM` \ elt_ty ->
299 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
300 returnM (ExplicitPArr elt_ty exprs')
303 = addErrCtxt (parrCtxt expr) $
304 tcCheckRho expr elt_ty
306 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
307 = zapToTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
308 tcCheckRhos exprs arg_tys `thenM` \ exprs' ->
309 returnM (ExplicitTuple exprs' boxity)
311 tcMonoExpr (HsProc pat cmd loc) res_ty
313 tcProc pat cmd res_ty `thenM` \ (pat', cmd') ->
314 returnM (HsProc pat' cmd' loc)
318 %************************************************************************
322 %************************************************************************
324 The interesting thing about @ccall@ is that it is just a template
325 which we instantiate by filling in details about the types of its
326 argument and result (ie minimal typechecking is performed). So, the
327 basic story is that we allocate a load of type variables (to hold the
328 arg/result types); unify them with the args/result; and store them for
332 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
334 = getDOpts `thenM` \ dflags ->
336 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
337 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
338 text "Either compile with -fvia-C, or, better, rewrite your code",
339 text "to use the foreign function interface. _casm_s are deprecated",
340 text "and support for them may one day disappear."])
343 -- Get the callable and returnable classes.
344 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
345 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
346 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
348 new_arg_dict (arg, arg_ty)
349 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
350 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
351 returnM arg_dicts -- Actually a singleton bag
353 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
357 let tv_idxs | null args = []
358 | otherwise = [1..length args]
360 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
361 tcCheckRhos args arg_tys `thenM` \ args' ->
363 -- The argument types can be unlifted or lifted; the result
364 -- type must, however, be lifted since it's an argument to the IO
366 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
368 io_result_ty = mkTyConApp ioTyCon [result_ty]
370 zapExpectedTo res_ty io_result_ty `thenM_`
372 -- Construct the extra insts, which encode the
373 -- constraints on the argument and result types.
374 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
375 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
376 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
377 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
381 %************************************************************************
383 Record construction and update
385 %************************************************************************
388 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
389 = addErrCtxt (recordConCtxt expr) $
390 tcId con_name `thenM` \ (con_expr, con_tau) ->
392 (_, record_ty) = tcSplitFunTys con_tau
393 (tycon, ty_args) = tcSplitTyConApp record_ty
395 ASSERT( isAlgTyCon tycon )
396 zapExpectedTo res_ty record_ty `thenM_`
398 -- Check that the record bindings match the constructor
399 -- con_name is syntactically constrained to be a data constructor
400 tcLookupDataCon con_name `thenM` \ data_con ->
402 bad_fields = badFields rbinds data_con
404 if notNull bad_fields then
405 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
406 failM -- Fail now, because tcRecordBinds will crash on a bad field
409 -- Typecheck the record bindings
410 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
412 -- Check for missing fields
413 checkMissingFields data_con rbinds `thenM_`
415 returnM (RecordConOut data_con con_expr rbinds')
417 -- The main complication with RecordUpd is that we need to explicitly
418 -- handle the *non-updated* fields. Consider:
420 -- data T a b = MkT1 { fa :: a, fb :: b }
421 -- | MkT2 { fa :: a, fc :: Int -> Int }
422 -- | MkT3 { fd :: a }
424 -- upd :: T a b -> c -> T a c
425 -- upd t x = t { fb = x}
427 -- The type signature on upd is correct (i.e. the result should not be (T a b))
428 -- because upd should be equivalent to:
430 -- upd t x = case t of
431 -- MkT1 p q -> MkT1 p x
432 -- MkT2 a b -> MkT2 p b
433 -- MkT3 d -> error ...
435 -- So we need to give a completely fresh type to the result record,
436 -- and then constrain it by the fields that are *not* updated ("p" above).
438 -- Note that because MkT3 doesn't contain all the fields being updated,
439 -- its RHS is simply an error, so it doesn't impose any type constraints
441 -- All this is done in STEP 4 below.
443 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
444 = addErrCtxt (recordUpdCtxt expr) $
447 -- Check that the field names are really field names
448 ASSERT( notNull rbinds )
450 field_names = recBindFields rbinds
452 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
454 bad_guys = [ addErrTc (notSelector field_name)
455 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
456 not (is_selector maybe_sel_id)
458 is_selector (Just (AnId sel_id)) = isRecordSelector sel_id -- Excludes class ops
459 is_selector other = False
461 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
464 -- Figure out the tycon and data cons from the first field name
466 -- It's OK to use the non-tc splitters here (for a selector)
467 (Just (AnId sel_id) : _) = maybe_sel_ids
468 field_lbl = recordSelectorFieldLabel sel_id -- We've failed already if
469 tycon = fieldLabelTyCon field_lbl -- it's not a field label
470 data_cons = tyConDataCons tycon
471 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
473 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
476 -- Check that at least one constructor has all the named fields
477 -- i.e. has an empty set of bad fields returned by badFields
478 checkTc (any (null . badFields rbinds) data_cons)
479 (badFieldsUpd rbinds) `thenM_`
482 -- Typecheck the update bindings.
483 -- (Do this after checking for bad fields in case there's a field that
484 -- doesn't match the constructor.)
486 result_record_ty = mkTyConApp tycon result_inst_tys
488 zapExpectedTo res_ty result_record_ty `thenM_`
489 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
492 -- Use the un-updated fields to find a vector of booleans saying
493 -- which type arguments must be the same in updatee and result.
495 -- WARNING: this code assumes that all data_cons in a common tycon
496 -- have FieldLabels abstracted over the same tyvars.
498 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
499 con_field_lbls_s = map dataConFieldLabels data_cons
501 -- A constructor is only relevant to this process if
502 -- it contains all the fields that are being updated
503 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
504 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
506 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
507 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
509 mk_inst_ty (tyvar, result_inst_ty)
510 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
511 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
513 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
516 -- Typecheck the expression to be updated
518 record_ty = mkTyConApp tycon inst_tys
520 tcCheckRho record_expr record_ty `thenM` \ record_expr' ->
523 -- Figure out the LIE we need. We have to generate some
524 -- dictionaries for the data type context, since we are going to
525 -- do pattern matching over the data cons.
527 -- What dictionaries do we need?
528 -- We just take the context of the type constructor
530 theta' = substTheta inst_env (tyConTheta tycon)
532 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
533 extendLIEs dicts `thenM_`
536 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
540 %************************************************************************
542 Arithmetic sequences e.g. [a,b..]
543 and their parallel-array counterparts e.g. [: a,b.. :]
546 %************************************************************************
549 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
550 = zapToListTy res_ty `thenM` \ elt_ty ->
551 tcCheckRho expr elt_ty `thenM` \ expr' ->
553 newMethodFromName (ArithSeqOrigin seq)
554 elt_ty enumFromName `thenM` \ enum_from ->
556 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
558 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
559 = addErrCtxt (arithSeqCtxt in_expr) $
560 zapToListTy res_ty `thenM` \ elt_ty ->
561 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
562 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
563 newMethodFromName (ArithSeqOrigin seq)
564 elt_ty enumFromThenName `thenM` \ enum_from_then ->
566 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
569 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
570 = addErrCtxt (arithSeqCtxt in_expr) $
571 zapToListTy res_ty `thenM` \ elt_ty ->
572 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
573 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
574 newMethodFromName (ArithSeqOrigin seq)
575 elt_ty enumFromToName `thenM` \ enum_from_to ->
577 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
579 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
580 = addErrCtxt (arithSeqCtxt in_expr) $
581 zapToListTy res_ty `thenM` \ elt_ty ->
582 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
583 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
584 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
585 newMethodFromName (ArithSeqOrigin seq)
586 elt_ty enumFromThenToName `thenM` \ eft ->
588 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
590 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
591 = addErrCtxt (parrSeqCtxt in_expr) $
592 zapToPArrTy res_ty `thenM` \ elt_ty ->
593 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
594 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
595 newMethodFromName (PArrSeqOrigin seq)
596 elt_ty enumFromToPName `thenM` \ enum_from_to ->
598 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
600 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
601 = addErrCtxt (parrSeqCtxt in_expr) $
602 zapToPArrTy res_ty `thenM` \ elt_ty ->
603 tcCheckRho expr1 elt_ty `thenM` \ expr1' ->
604 tcCheckRho expr2 elt_ty `thenM` \ expr2' ->
605 tcCheckRho expr3 elt_ty `thenM` \ expr3' ->
606 newMethodFromName (PArrSeqOrigin seq)
607 elt_ty enumFromThenToPName `thenM` \ eft ->
609 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
611 tcMonoExpr (PArrSeqIn _) _
612 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
613 -- the parser shouldn't have generated it and the renamer shouldn't have
618 %************************************************************************
622 %************************************************************************
625 #ifdef GHCI /* Only if bootstrapped */
626 -- Rename excludes these cases otherwise
628 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
629 tcMonoExpr (HsBracket brack loc) res_ty = addSrcLoc loc (tcBracket brack res_ty)
631 tcMonoExpr (HsReify (Reify flavour name)) res_ty
632 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
633 tcMetaTy tycon_name `thenM` \ reify_ty ->
634 zapExpectedTo res_ty reify_ty `thenM_`
635 returnM (HsReify (ReifyOut flavour name))
637 tycon_name = case flavour of
638 ReifyDecl -> DsMeta.decQTyConName
639 ReifyType -> DsMeta.typeQTyConName
640 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
645 %************************************************************************
649 %************************************************************************
652 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
656 %************************************************************************
658 \subsection{@tcApp@ typchecks an application}
660 %************************************************************************
664 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
665 -> Expected TcRhoType -- Expected result type of application
666 -> TcM TcExpr -- Translated fun and args
668 tcApp (HsApp e1 e2) args res_ty
669 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
671 tcApp fun args res_ty
672 = -- First type-check the function
673 tcInferRho fun `thenM` \ (fun', fun_ty) ->
675 addErrCtxt (wrongArgsCtxt "too many" fun args) (
676 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
677 split_fun_ty fun_ty (length args)
678 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
680 -- Unify with expected result before (was: after) type-checking the args
681 -- so that the info from res_ty (was: args) percolates to args (was actual_result_ty).
682 -- This is when we might detect a too-few args situation.
683 -- (One can think of cases when the opposite order would give
684 -- a better error message.)
685 -- [March 2003: I'm experimenting with putting this first. Here's an
686 -- example where it actually makes a real difference
687 -- class C t a b | t a -> b
688 -- instance C Char a Bool
690 -- data P t a = forall b. (C t a b) => MkP b
691 -- data Q t = MkQ (forall a. P t a)
694 -- f1 = MkQ (MkP True)
695 -- f2 = MkQ (MkP True :: forall a. P Char a)
697 -- With the change, f1 will type-check, because the 'Char' info from
698 -- the signature is propagated into MkQ's argument. With the check
699 -- in the other order, the extra signature in f2 is reqd.]
701 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
702 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
704 -- Now typecheck the args
706 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
708 returnM (co_fn <$> foldl HsApp fun' args')
711 -- If an error happens we try to figure out whether the
712 -- function has been given too many or too few arguments,
714 -- The ~(Check...) is because in the Infer case the tcSubExp
715 -- definitely won't fail, so we can be certain we're in the Check branch
716 checkArgsCtxt fun args ~(Check expected_res_ty) actual_res_ty tidy_env
717 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
718 zonkTcType actual_res_ty `thenM` \ act_ty' ->
720 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
721 (env2, act_ty'') = tidyOpenType env1 act_ty'
722 (exp_args, _) = tcSplitFunTys exp_ty''
723 (act_args, _) = tcSplitFunTys act_ty''
725 len_act_args = length act_args
726 len_exp_args = length exp_args
728 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
729 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
730 | otherwise = appCtxt fun args
732 returnM (env2, message)
735 split_fun_ty :: TcRhoType -- The type of the function
736 -> Int -- Number of arguments
737 -> TcM ([TcType], -- Function argument types
738 TcType) -- Function result types
740 split_fun_ty fun_ty 0
741 = returnM ([], fun_ty)
743 split_fun_ty fun_ty n
744 = -- Expect the function to have type A->B
745 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
746 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
747 returnM (arg_ty:arg_tys, final_res_ty)
751 tcArg :: RenamedHsExpr -- The function (for error messages)
752 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
753 -> TcM TcExpr -- Resulting argument and LIE
755 tcArg the_fun (arg, expected_arg_ty, arg_no)
756 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
757 tcCheckSigma arg expected_arg_ty
761 %************************************************************************
763 \subsection{@tcId@ typchecks an identifier occurrence}
765 %************************************************************************
767 tcId instantiates an occurrence of an Id.
768 The instantiate_it loop runs round instantiating the Id.
769 It has to be a loop because we are now prepared to entertain
771 f:: forall a. Eq a => forall b. Baz b => tau
772 We want to instantiate this to
773 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
775 The -fno-method-sharing flag controls what happens so far as the LIE
776 is concerned. The default case is that for an overloaded function we
777 generate a "method" Id, and add the Method Inst to the LIE. So you get
780 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
781 If you specify -fno-method-sharing, the dictionary application
782 isn't shared, so we get
784 f = /\a (d:Num a) (x:a) -> (+) a d x x
785 This gets a bit less sharing, but
786 a) it's better for RULEs involving overloaded functions
787 b) perhaps fewer separated lambdas
790 tcId :: Name -> TcM (TcExpr, TcRhoType)
791 tcId name -- Look up the Id and instantiate its type
792 = -- First check whether it's a DataCon
793 -- Reason: we must not forget to chuck in the
794 -- constraints from their "silly context"
795 tcLookup name `thenM` \ maybe_thing ->
796 case maybe_thing of {
797 AGlobal (ADataCon data_con) -> inst_data_con data_con
798 ; AGlobal (AnId id) -> loop (HsVar id) (idType id)
799 -- A global cannot possibly be ill-staged
800 -- nor does it need the 'lifting' treatment
802 ; ATcId id th_level proc_level -> tc_local_id id th_level proc_level
803 ; other -> pprPanic "tcId" (ppr name)
808 tc_local_id id th_bind_lvl proc_lvl -- Non-TH case
809 = checkProcLevel id proc_lvl `thenM_`
810 loop (HsVar id) (idType id)
812 #else /* GHCI and TH is on */
813 tc_local_id id th_bind_lvl proc_lvl -- TH case
814 = checkProcLevel id proc_lvl `thenM_`
816 -- Check for cross-stage lifting
817 getStage `thenM` \ use_stage ->
819 Brack use_lvl ps_var lie_var
820 | use_lvl > th_bind_lvl
821 -> -- E.g. \x -> [| h x |]
822 -- We must behave as if the reference to x was
825 -- We use 'x' itself as the splice proxy, used by
826 -- the desugarer to stitch it all back together.
827 -- If 'x' occurs many times we may get many identical
828 -- bindings of the same splice proxy, but that doesn't
829 -- matter, although it's a mite untidy.
833 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
834 -- If x is polymorphic, its occurrence sites might
835 -- have different instantiations, so we can't use plain
836 -- 'x' as the splice proxy name. I don't know how to
837 -- solve this, and it's probably unimportant, so I'm
838 -- just going to flag an error for now
841 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
842 -- Put the 'lift' constraint into the right LIE
844 -- Update the pending splices
845 readMutVar ps_var `thenM` \ ps ->
846 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
848 returnM (HsVar id, id_ty))
851 checkWellStaged (quotes (ppr id)) th_bind_lvl use_stage `thenM_`
852 loop (HsVar id) (idType id)
855 loop (HsVar fun_id) fun_ty
856 | want_method_inst fun_ty
857 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
858 newMethodWithGivenTy orig fun_id
859 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
860 loop (HsVar meth_id) tau
864 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
865 loop (inst_fn <$> fun) tau
868 = returnM (fun, fun_ty)
870 -- Hack Alert (want_method_inst)!
871 -- If f :: (%x :: T) => Int -> Int
872 -- Then if we have two separate calls, (f 3, f 4), we cannot
873 -- make a method constraint that then gets shared, thus:
874 -- let m = f %x in (m 3, m 4)
875 -- because that loses the linearity of the constraint.
876 -- The simplest thing to do is never to construct a method constraint
877 -- in the first place that has a linear implicit parameter in it.
878 want_method_inst fun_ty
879 | opt_NoMethodSharing = False
880 | otherwise = case tcSplitSigmaTy fun_ty of
881 (_,[],_) -> False -- Not overloaded
882 (_,theta,_) -> not (any isLinearPred theta)
885 -- We treat data constructors differently, because we have to generate
886 -- constraints for their silly theta, which no longer appears in
887 -- the type of dataConWrapId (see note on "stupid context" in DataCon.lhs
888 -- It's dual to TcPat.tcConstructor
889 inst_data_con data_con
890 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
891 extendLIEs ex_dicts `thenM_`
892 returnM (mkHsDictApp (mkHsTyApp (HsVar (dataConWrapId data_con)) ty_args)
893 (map instToId ex_dicts),
894 mkFunTys arg_tys result_ty)
896 orig = OccurrenceOf name
899 %************************************************************************
901 \subsection{Record bindings}
903 %************************************************************************
905 Game plan for record bindings
906 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
907 1. Find the TyCon for the bindings, from the first field label.
909 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
911 For each binding field = value
913 3. Instantiate the field type (from the field label) using the type
916 4 Type check the value using tcArg, passing the field type as
917 the expected argument type.
919 This extends OK when the field types are universally quantified.
924 :: TyCon -- Type constructor for the record
925 -> [TcType] -- Args of this type constructor
926 -> RenamedRecordBinds
929 tcRecordBinds tycon ty_args rbinds
930 = mappM do_bind rbinds
932 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
934 do_bind (field_lbl_name, rhs)
935 = addErrCtxt (fieldCtxt field_lbl_name) $
936 tcLookupId field_lbl_name `thenM` \ sel_id ->
938 field_lbl = recordSelectorFieldLabel sel_id
939 field_ty = substTy tenv (fieldLabelType field_lbl)
941 ASSERT( isRecordSelector sel_id )
942 -- This lookup and assertion will surely succeed, because
943 -- we check that the fields are indeed record selectors
944 -- before calling tcRecordBinds
945 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
946 -- The caller of tcRecordBinds has already checked
947 -- that all the fields come from the same type
949 tcCheckSigma rhs field_ty `thenM` \ rhs' ->
951 returnM (sel_id, rhs')
953 badFields rbinds data_con
954 = filter (not . (`elem` field_names)) (recBindFields rbinds)
956 field_names = map fieldLabelName (dataConFieldLabels data_con)
958 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
959 checkMissingFields data_con rbinds
960 | null field_labels -- Not declared as a record;
961 -- But C{} is still valid if no strict fields
962 = if any isMarkedStrict field_strs then
963 -- Illegal if any arg is strict
964 addErrTc (missingStrictFields data_con [])
968 | otherwise -- A record
969 = checkM (null missing_s_fields)
970 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
972 doptM Opt_WarnMissingFields `thenM` \ warn ->
973 checkM (not (warn && notNull missing_ns_fields))
974 (warnTc True (missingFields data_con missing_ns_fields))
978 = [ fl | (fl, str) <- field_info,
980 not (fieldLabelName fl `elem` field_names_used)
983 = [ fl | (fl, str) <- field_info,
984 not (isMarkedStrict str),
985 not (fieldLabelName fl `elem` field_names_used)
988 field_names_used = recBindFields rbinds
989 field_labels = dataConFieldLabels data_con
991 field_info = zipEqual "missingFields"
995 field_strs = dropList ex_theta (dataConStrictMarks data_con)
996 -- The 'drop' is because dataConStrictMarks
997 -- includes the existential dictionaries
998 (_, _, _, ex_theta, _, _) = dataConSig data_con
1001 %************************************************************************
1003 \subsection{@tcCheckRhos@ typechecks a {\em list} of expressions}
1005 %************************************************************************
1008 tcCheckRhos :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1010 tcCheckRhos [] [] = returnM []
1011 tcCheckRhos (expr:exprs) (ty:tys)
1012 = tcCheckRho expr ty `thenM` \ expr' ->
1013 tcCheckRhos exprs tys `thenM` \ exprs' ->
1014 returnM (expr':exprs')
1018 %************************************************************************
1020 \subsection{Literals}
1022 %************************************************************************
1024 Overloaded literals.
1027 tcLit :: HsLit -> Expected TcRhoType -> TcM TcExpr
1028 tcLit (HsLitLit s _) res_ty
1029 = zapExpectedType res_ty `thenM` \ res_ty' ->
1030 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1031 newDicts (LitLitOrigin (unpackFS s))
1032 [mkClassPred cCallableClass [res_ty']] `thenM` \ dicts ->
1033 extendLIEs dicts `thenM_`
1034 returnM (HsLit (HsLitLit s res_ty'))
1037 = zapExpectedTo res_ty (hsLitType lit) `thenM_`
1042 %************************************************************************
1044 \subsection{Errors and contexts}
1046 %************************************************************************
1048 Boring and alphabetical:
1051 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1054 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1057 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1060 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1063 = hang (ptext SLIT("When checking the type signature of the expression:"))
1067 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1069 fieldCtxt field_name
1070 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1072 funAppCtxt fun arg arg_no
1073 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1074 quotes (ppr fun) <> text ", namely"])
1075 4 (quotes (ppr arg))
1078 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1081 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1084 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1087 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1089 the_app = foldl HsApp fun args -- Used in error messages
1091 lurkingRank2Err fun fun_ty
1092 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1093 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1094 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1097 = hang (ptext SLIT("No constructor has all these fields:"))
1098 4 (pprQuotedList (recBindFields rbinds))
1100 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1101 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1104 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1106 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1107 missingStrictFields con fields
1110 rest | null fields = empty -- Happens for non-record constructors
1111 -- with strict fields
1112 | otherwise = colon <+> pprWithCommas ppr fields
1114 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1115 ptext SLIT("does not have the required strict field(s)")
1117 missingFields :: DataCon -> [FieldLabel] -> SDoc
1118 missingFields con fields
1119 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1120 <+> pprWithCommas ppr fields
1122 polySpliceErr :: Id -> SDoc
1124 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1126 wrongArgsCtxt too_many_or_few fun args
1127 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1128 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1129 <+> ptext SLIT("arguments in the call"))
1130 4 (parens (ppr the_app))
1132 the_app = foldl HsApp fun args -- Used in error messages