2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcExpr_id, 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 TcEnv ( bracketOK, tcMetaTy, tcLookupGlobal,
15 wellStaged, metaLevel )
16 import TcSimplify ( tcSimplifyBracket )
17 import Name ( isExternalName )
18 import qualified DsMeta
21 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
22 mkMonoBind, recBindFields
24 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
25 import TcHsSyn ( TcExpr, TcRecordBinds, hsLitType, mkHsDictApp, mkHsTyApp, mkHsLet )
27 import TcUnify ( tcSubExp, tcGen, (<$>),
28 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
30 import BasicTypes ( RecFlag(..), isMarkedStrict )
31 import Inst ( InstOrigin(..),
32 newOverloadedLit, newMethodFromName, newIPDict,
33 newDicts, newMethodWithGivenTy,
34 instToId, tcInstCall, tcInstDataCon
36 import TcBinds ( tcBindsAndThen )
37 import TcEnv ( tcLookupClass, tcLookupGlobal_maybe, tcLookupIdLvl,
38 tcLookupTyCon, tcLookupDataCon, tcLookupId
40 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts )
41 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
42 import TcPat ( badFieldCon )
43 import TcSimplify ( tcSimplifyIPs )
44 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
45 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
46 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
47 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
48 isSigmaTy, mkFunTy, mkFunTys,
49 mkTyConApp, mkClassPred, tcFunArgTy,
50 tyVarsOfTypes, isLinearPred,
51 liftedTypeKind, openTypeKind,
52 tcSplitSigmaTy, tcTyConAppTyCon,
55 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
56 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector, isDataConWrapId_maybe )
57 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks )
59 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
60 import Subst ( mkTopTyVarSubst, substTheta, substTy )
61 import VarSet ( emptyVarSet, elemVarSet )
62 import TysWiredIn ( boolTy )
63 import PrelNames ( cCallableClassName, cReturnableClassName,
64 enumFromName, enumFromThenName,
65 enumFromToName, enumFromThenToName,
66 enumFromToPName, enumFromThenToPName,
69 import ListSetOps ( minusList )
71 import HscTypes ( TyThing(..) )
78 %************************************************************************
80 \subsection{Main wrappers}
82 %************************************************************************
85 tcExpr :: RenamedHsExpr -- Expession to type check
86 -> TcSigmaType -- Expected type (could be a polytpye)
87 -> TcM TcExpr -- Generalised expr with expected type
89 tcExpr expr expected_ty
90 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
91 tc_expr' expr expected_ty
93 tc_expr' expr expected_ty
94 | not (isSigmaTy expected_ty) -- Monomorphic case
95 = tcMonoExpr expr expected_ty
98 = tcGen expected_ty emptyVarSet (
100 ) `thenM` \ (gen_fn, expr') ->
101 returnM (gen_fn <$> expr')
105 %************************************************************************
107 \subsection{The TAUT rules for variables}
109 %************************************************************************
112 tcMonoExpr :: RenamedHsExpr -- Expession to type check
113 -> TcRhoType -- Expected type (could be a type variable)
114 -- Definitely no foralls at the top
118 tcMonoExpr (HsVar name) res_ty
119 = tcId name `thenM` \ (expr', id_ty) ->
120 tcSubExp res_ty id_ty `thenM` \ co_fn ->
121 returnM (co_fn <$> expr')
123 tcMonoExpr (HsIPVar ip) res_ty
124 = -- Implicit parameters must have a *tau-type* not a
125 -- type scheme. We enforce this by creating a fresh
126 -- type variable as its type. (Because res_ty may not
128 newTyVarTy openTypeKind `thenM` \ ip_ty ->
129 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
130 extendLIE inst `thenM_`
131 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
132 returnM (co_fn <$> HsIPVar ip')
136 %************************************************************************
138 \subsection{Expressions type signatures}
140 %************************************************************************
143 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
144 = addErrCtxt (exprSigCtxt in_expr) $
145 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
146 tcExpr expr sig_tc_ty `thenM` \ expr' ->
148 -- Must instantiate the outer for-alls of sig_tc_ty
149 -- else we risk instantiating a ? res_ty to a forall-type
150 -- which breaks the invariant that tcMonoExpr only returns phi-types
151 tcInstCall SignatureOrigin sig_tc_ty `thenM` \ (inst_fn, inst_sig_ty) ->
152 tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
154 returnM (co_fn <$> inst_fn expr')
156 tcMonoExpr (HsType ty) res_ty
157 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
158 -- This is the syntax for type applications that I was planning
159 -- but there are difficulties (e.g. what order for type args)
160 -- so it's not enabled yet.
161 -- Can't eliminate it altogether from the parser, because the
162 -- same parser parses *patterns*.
166 %************************************************************************
168 \subsection{Other expression forms}
170 %************************************************************************
173 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
174 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
175 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
176 returnM (HsPar expr')
177 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
178 returnM (HsSCC lbl expr')
181 tcMonoExpr (NegApp expr neg_name) res_ty
182 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
183 -- ToDo: use tcSyntaxName
185 tcMonoExpr (HsLam match) res_ty
186 = tcMatchLambda match res_ty `thenM` \ match' ->
187 returnM (HsLam match')
189 tcMonoExpr (HsApp e1 e2) res_ty
190 = tcApp e1 [e2] res_ty
193 Note that the operators in sections are expected to be binary, and
194 a type error will occur if they aren't.
197 -- Left sections, equivalent to
204 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
205 = tcExpr_id op `thenM` \ (op', op_ty) ->
206 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
207 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
208 addErrCtxt (exprCtxt in_expr) $
209 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
210 returnM (co_fn <$> SectionL arg1' op')
212 -- Right sections, equivalent to \ x -> x op expr, or
215 tcMonoExpr in_expr@(SectionR op arg2) res_ty
216 = tcExpr_id op `thenM` \ (op', op_ty) ->
217 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
218 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
219 addErrCtxt (exprCtxt in_expr) $
220 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
221 returnM (co_fn <$> SectionR op' arg2')
223 -- equivalent to (op e1) e2:
225 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
226 = tcExpr_id op `thenM` \ (op', op_ty) ->
227 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
228 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
229 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
230 addErrCtxt (exprCtxt in_expr) $
231 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
232 returnM (OpApp arg1' op' fix arg2')
236 tcMonoExpr (HsLet binds expr) res_ty
239 binds -- Bindings to check
240 (tcMonoExpr expr res_ty)
242 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
244 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
245 = addSrcLoc src_loc $
246 addErrCtxt (caseCtxt in_expr) $
248 -- Typecheck the case alternatives first.
249 -- The case patterns tend to give good type info to use
250 -- when typechecking the scrutinee. For example
253 -- will report that map is applied to too few arguments
255 -- Not only that, but it's better to check the matches on their
256 -- own, so that we get the expected results for scoped type variables.
258 -- (p::a, q::b) -> (q,p)
259 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
260 -- claimed by the pattern signatures. But if we typechecked the
261 -- match with x in scope and x's type as the expected type, we'd be hosed.
263 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
265 addErrCtxt (caseScrutCtxt scrut) (
266 tcMonoExpr scrut scrut_ty
267 ) `thenM` \ scrut' ->
269 returnM (HsCase scrut' matches' src_loc)
271 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
272 = addSrcLoc src_loc $
273 addErrCtxt (predCtxt pred) (
274 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
276 zapToType res_ty `thenM` \ res_ty' ->
277 -- C.f. the call to zapToType in TcMatches.tcMatches
279 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
280 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
281 returnM (HsIf pred' b1' b2' src_loc)
283 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
284 = addSrcLoc src_loc $
285 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
286 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
288 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
289 = unifyListTy 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 tcMonoExpr expr elt_ty
297 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
298 = unifyPArrTy 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 tcMonoExpr expr elt_ty
306 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
307 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
308 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
309 returnM (ExplicitTuple exprs' boxity)
313 %************************************************************************
317 %************************************************************************
319 The interesting thing about @ccall@ is that it is just a template
320 which we instantiate by filling in details about the types of its
321 argument and result (ie minimal typechecking is performed). So, the
322 basic story is that we allocate a load of type variables (to hold the
323 arg/result types); unify them with the args/result; and store them for
327 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
329 = getDOpts `thenM` \ dflags ->
331 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
332 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
333 text "Either compile with -fvia-C, or, better, rewrite your code",
334 text "to use the foreign function interface. _casm_s are deprecated",
335 text "and support for them may one day disappear."])
338 -- Get the callable and returnable classes.
339 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
340 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
341 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
343 new_arg_dict (arg, arg_ty)
344 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
345 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
346 returnM arg_dicts -- Actually a singleton bag
348 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
352 let tv_idxs | null args = []
353 | otherwise = [1..length args]
355 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
356 tcMonoExprs args arg_tys `thenM` \ args' ->
358 -- The argument types can be unlifted or lifted; the result
359 -- type must, however, be lifted since it's an argument to the IO
361 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
363 io_result_ty = mkTyConApp ioTyCon [result_ty]
365 unifyTauTy res_ty io_result_ty `thenM_`
367 -- Construct the extra insts, which encode the
368 -- constraints on the argument and result types.
369 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
370 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
371 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
372 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
376 %************************************************************************
378 Record construction and update
380 %************************************************************************
383 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
384 = addErrCtxt (recordConCtxt expr) $
385 tcId con_name `thenM` \ (con_expr, con_tau) ->
387 (_, record_ty) = tcSplitFunTys con_tau
388 (tycon, ty_args) = tcSplitTyConApp record_ty
390 ASSERT( isAlgTyCon tycon )
391 unifyTauTy res_ty record_ty `thenM_`
393 -- Check that the record bindings match the constructor
394 -- con_name is syntactically constrained to be a data constructor
395 tcLookupDataCon con_name `thenM` \ data_con ->
397 bad_fields = badFields rbinds data_con
399 if notNull bad_fields then
400 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
401 failM -- Fail now, because tcRecordBinds will crash on a bad field
404 -- Typecheck the record bindings
405 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
407 -- Check for missing fields
408 checkMissingFields data_con rbinds `thenM_`
410 returnM (RecordConOut data_con con_expr rbinds')
412 -- The main complication with RecordUpd is that we need to explicitly
413 -- handle the *non-updated* fields. Consider:
415 -- data T a b = MkT1 { fa :: a, fb :: b }
416 -- | MkT2 { fa :: a, fc :: Int -> Int }
417 -- | MkT3 { fd :: a }
419 -- upd :: T a b -> c -> T a c
420 -- upd t x = t { fb = x}
422 -- The type signature on upd is correct (i.e. the result should not be (T a b))
423 -- because upd should be equivalent to:
425 -- upd t x = case t of
426 -- MkT1 p q -> MkT1 p x
427 -- MkT2 a b -> MkT2 p b
428 -- MkT3 d -> error ...
430 -- So we need to give a completely fresh type to the result record,
431 -- and then constrain it by the fields that are *not* updated ("p" above).
433 -- Note that because MkT3 doesn't contain all the fields being updated,
434 -- its RHS is simply an error, so it doesn't impose any type constraints
436 -- All this is done in STEP 4 below.
438 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
439 = addErrCtxt (recordUpdCtxt expr) $
442 -- Check that the field names are really field names
443 ASSERT( notNull rbinds )
445 field_names = recBindFields rbinds
447 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
449 bad_guys = [ addErrTc (notSelector field_name)
450 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
452 Just (AnId sel_id) -> not (isRecordSelector sel_id)
456 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
459 -- Figure out the tycon and data cons from the first field name
461 -- It's OK to use the non-tc splitters here (for a selector)
462 (Just (AnId sel_id) : _) = maybe_sel_ids
464 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
465 -- when the data type has a context
466 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
467 tycon = tcTyConAppTyCon data_ty
468 data_cons = tyConDataCons tycon
469 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
471 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
474 -- Check that at least one constructor has all the named fields
475 -- i.e. has an empty set of bad fields returned by badFields
476 checkTc (any (null . badFields rbinds) data_cons)
477 (badFieldsUpd rbinds) `thenM_`
480 -- Typecheck the update bindings.
481 -- (Do this after checking for bad fields in case there's a field that
482 -- doesn't match the constructor.)
484 result_record_ty = mkTyConApp tycon result_inst_tys
486 unifyTauTy res_ty result_record_ty `thenM_`
487 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
490 -- Use the un-updated fields to find a vector of booleans saying
491 -- which type arguments must be the same in updatee and result.
493 -- WARNING: this code assumes that all data_cons in a common tycon
494 -- have FieldLabels abstracted over the same tyvars.
496 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
497 con_field_lbls_s = map dataConFieldLabels data_cons
499 -- A constructor is only relevant to this process if
500 -- it contains all the fields that are being updated
501 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
502 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
504 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
505 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
507 mk_inst_ty (tyvar, result_inst_ty)
508 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
509 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
511 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
514 -- Typecheck the expression to be updated
516 record_ty = mkTyConApp tycon inst_tys
518 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
521 -- Figure out the LIE we need. We have to generate some
522 -- dictionaries for the data type context, since we are going to
523 -- do pattern matching over the data cons.
525 -- What dictionaries do we need?
526 -- We just take the context of the type constructor
528 theta' = substTheta inst_env (tyConTheta tycon)
530 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
531 extendLIEs dicts `thenM_`
534 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
538 %************************************************************************
540 Arithmetic sequences e.g. [a,b..]
541 and their parallel-array counterparts e.g. [: a,b.. :]
544 %************************************************************************
547 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
548 = unifyListTy res_ty `thenM` \ elt_ty ->
549 tcMonoExpr expr elt_ty `thenM` \ expr' ->
551 newMethodFromName (ArithSeqOrigin seq)
552 elt_ty enumFromName `thenM` \ enum_from ->
554 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
556 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
557 = addErrCtxt (arithSeqCtxt in_expr) $
558 unifyListTy res_ty `thenM` \ elt_ty ->
559 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
560 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
561 newMethodFromName (ArithSeqOrigin seq)
562 elt_ty enumFromThenName `thenM` \ enum_from_then ->
564 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
567 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
568 = addErrCtxt (arithSeqCtxt in_expr) $
569 unifyListTy res_ty `thenM` \ elt_ty ->
570 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
571 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
572 newMethodFromName (ArithSeqOrigin seq)
573 elt_ty enumFromToName `thenM` \ enum_from_to ->
575 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
577 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
578 = addErrCtxt (arithSeqCtxt in_expr) $
579 unifyListTy res_ty `thenM` \ elt_ty ->
580 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
581 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
582 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
583 newMethodFromName (ArithSeqOrigin seq)
584 elt_ty enumFromThenToName `thenM` \ eft ->
586 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
588 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
589 = addErrCtxt (parrSeqCtxt in_expr) $
590 unifyPArrTy res_ty `thenM` \ elt_ty ->
591 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
592 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
593 newMethodFromName (PArrSeqOrigin seq)
594 elt_ty enumFromToPName `thenM` \ enum_from_to ->
596 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
598 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
599 = addErrCtxt (parrSeqCtxt in_expr) $
600 unifyPArrTy res_ty `thenM` \ elt_ty ->
601 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
602 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
603 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
604 newMethodFromName (PArrSeqOrigin seq)
605 elt_ty enumFromThenToPName `thenM` \ eft ->
607 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
609 tcMonoExpr (PArrSeqIn _) _
610 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
611 -- the parser shouldn't have generated it and the renamer shouldn't have
616 %************************************************************************
620 %************************************************************************
623 #ifdef GHCI /* Only if bootstrapped */
624 -- Rename excludes these cases otherwise
626 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
628 tcMonoExpr (HsBracket brack loc) res_ty
630 getStage `thenM` \ level ->
631 case bracketOK level of {
632 Nothing -> failWithTc (illegalBracket level) ;
635 -- Typecheck expr to make sure it is valid,
636 -- but throw away the results. We'll type check
637 -- it again when we actually use it.
638 newMutVar [] `thenM` \ pending_splices ->
639 getLIEVar `thenM` \ lie_var ->
641 setStage (Brack next_level pending_splices lie_var) (
642 getLIE (tcBracket brack)
643 ) `thenM` \ (meta_ty, lie) ->
644 tcSimplifyBracket lie `thenM_`
646 unifyTauTy res_ty meta_ty `thenM_`
648 -- Return the original expression, not the type-decorated one
649 readMutVar pending_splices `thenM` \ pendings ->
650 returnM (HsBracketOut brack pendings)
653 tcMonoExpr (HsReify (Reify flavour name)) res_ty
654 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
655 tcMetaTy tycon_name `thenM` \ reify_ty ->
656 unifyTauTy res_ty reify_ty `thenM_`
657 returnM (HsReify (ReifyOut flavour name))
659 tycon_name = case flavour of
660 ReifyDecl -> DsMeta.decTyConName
661 ReifyType -> DsMeta.typTyConName
662 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
666 %************************************************************************
668 \subsection{Implicit Parameter bindings}
670 %************************************************************************
673 tcMonoExpr (HsWith expr binds is_with) res_ty
674 = getLIE (tcMonoExpr expr res_ty) `thenM` \ (expr', expr_lie) ->
675 mapAndUnzipM tc_ip_bind binds `thenM` \ (avail_ips, binds') ->
677 -- If the binding binds ?x = E, we must now
678 -- discharge any ?x constraints in expr_lie
679 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
681 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
683 returnM (HsWith expr'' binds' is_with)
685 tc_ip_bind (ip, expr)
686 = newTyVarTy openTypeKind `thenM` \ ty ->
687 getSrcLocM `thenM` \ loc ->
688 newIPDict (IPBind ip) ip ty `thenM` \ (ip', ip_inst) ->
689 tcMonoExpr expr ty `thenM` \ expr' ->
690 returnM (ip_inst, (ip', expr'))
694 %************************************************************************
698 %************************************************************************
701 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
705 %************************************************************************
707 \subsection{@tcApp@ typchecks an application}
709 %************************************************************************
713 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
714 -> TcType -- Expected result type of application
715 -> TcM TcExpr -- Translated fun and args
717 tcApp (HsApp e1 e2) args res_ty
718 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
720 tcApp fun args res_ty
721 = -- First type-check the function
722 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
724 addErrCtxt (wrongArgsCtxt "too many" fun args) (
725 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
726 split_fun_ty fun_ty (length args)
727 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
729 -- Now typecheck the args
731 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
733 -- Unify with expected result after type-checking the args
734 -- so that the info from args percolates to actual_result_ty.
735 -- This is when we might detect a too-few args situation.
736 -- (One can think of cases when the opposite order would give
737 -- a better error message.)
738 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
739 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
741 returnM (co_fn <$> foldl HsApp fun' args')
744 -- If an error happens we try to figure out whether the
745 -- function has been given too many or too few arguments,
747 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
748 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
749 zonkTcType actual_res_ty `thenM` \ act_ty' ->
751 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
752 (env2, act_ty'') = tidyOpenType env1 act_ty'
753 (exp_args, _) = tcSplitFunTys exp_ty''
754 (act_args, _) = tcSplitFunTys act_ty''
756 len_act_args = length act_args
757 len_exp_args = length exp_args
759 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
760 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
761 | otherwise = appCtxt fun args
763 returnM (env2, message)
766 split_fun_ty :: TcType -- The type of the function
767 -> Int -- Number of arguments
768 -> TcM ([TcType], -- Function argument types
769 TcType) -- Function result types
771 split_fun_ty fun_ty 0
772 = returnM ([], fun_ty)
774 split_fun_ty fun_ty n
775 = -- Expect the function to have type A->B
776 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
777 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
778 returnM (arg_ty:arg_tys, final_res_ty)
782 tcArg :: RenamedHsExpr -- The function (for error messages)
783 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
784 -> TcM TcExpr -- Resulting argument and LIE
786 tcArg the_fun (arg, expected_arg_ty, arg_no)
787 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
788 tcExpr arg expected_arg_ty
792 %************************************************************************
794 \subsection{@tcId@ typchecks an identifier occurrence}
796 %************************************************************************
798 tcId instantiates an occurrence of an Id.
799 The instantiate_it loop runs round instantiating the Id.
800 It has to be a loop because we are now prepared to entertain
802 f:: forall a. Eq a => forall b. Baz b => tau
803 We want to instantiate this to
804 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
806 The -fno-method-sharing flag controls what happens so far as the LIE
807 is concerned. The default case is that for an overloaded function we
808 generate a "method" Id, and add the Method Inst to the LIE. So you get
811 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
812 If you specify -fno-method-sharing, the dictionary application
813 isn't shared, so we get
815 f = /\a (d:Num a) (x:a) -> (+) a d x x
816 This gets a bit less sharing, but
817 a) it's better for RULEs involving overloaded functions
818 b) perhaps fewer separated lambdas
821 tcId :: Name -> TcM (TcExpr, TcType)
822 tcId name -- Look up the Id and instantiate its type
823 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
825 -- Check for cross-stage lifting
827 getStage `thenM` \ use_stage ->
829 Brack use_lvl ps_var lie_var
830 | use_lvl > bind_lvl && not (isExternalName name)
831 -> -- E.g. \x -> [| h x |]
832 -- We must behave as if the reference to x was
834 -- We use 'x' itself as the splice proxy, used by
835 -- the desugarer to stitch it all back together
836 -- NB: isExernalName is true of top level things,
837 -- and false of nested bindings
842 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
843 -- If x is polymorphic, its occurrence sites might
844 -- have different instantiations, so we can't use plain
845 -- 'x' as the splice proxy name. I don't know how to
846 -- solve this, and it's probably unimportant, so I'm
847 -- just going to flag an error for now
850 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
851 -- Put the 'lift' constraint into the right LIE
853 -- Update the pending splices
854 readMutVar ps_var `thenM` \ ps ->
855 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
857 returnM (HsVar id, id_ty))
861 use_lvl = metaLevel use_stage
863 checkTc (wellStaged bind_lvl use_lvl)
864 (badStageErr id bind_lvl use_lvl) `thenM_`
866 -- This is the bit that handles the no-Template-Haskell case
867 case isDataConWrapId_maybe id of
868 Nothing -> loop (HsVar id) (idType id)
869 Just data_con -> inst_data_con id data_con
872 orig = OccurrenceOf name
874 loop (HsVar fun_id) fun_ty
875 | want_method_inst fun_ty
876 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
877 newMethodWithGivenTy orig fun_id
878 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
879 loop (HsVar meth_id) tau
883 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
884 loop (inst_fn fun) tau
887 = returnM (fun, fun_ty)
889 want_method_inst fun_ty
890 | opt_NoMethodSharing = False
891 | otherwise = case tcSplitSigmaTy fun_ty of
892 (_,[],_) -> False -- Not overloaded
893 (_,theta,_) -> not (any isLinearPred theta)
894 -- This is a slight hack.
895 -- If f :: (%x :: T) => Int -> Int
896 -- Then if we have two separate calls, (f 3, f 4), we cannot
897 -- make a method constraint that then gets shared, thus:
898 -- let m = f %x in (m 3, m 4)
899 -- because that loses the linearity of the constraint.
900 -- The simplest thing to do is never to construct a method constraint
901 -- in the first place that has a linear implicit parameter in it.
903 -- We treat data constructors differently, because we have to generate
904 -- constraints for their silly theta, which no longer appears in
905 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
906 inst_data_con id data_con
907 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
908 extendLIEs ex_dicts `thenM_`
909 returnM (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) (map instToId ex_dicts),
910 mkFunTys arg_tys result_ty)
913 Typecheck expression which in most cases will be an Id.
914 The expression can return a higher-ranked type, such as
915 (forall a. a->a) -> Int
916 so we must create a HoleTyVarTy to pass in as the expected tyvar.
919 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
920 tcExpr_id (HsVar name) = tcId name
921 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
922 tcMonoExpr expr id_ty `thenM` \ expr' ->
923 readHoleResult id_ty `thenM` \ id_ty' ->
924 returnM (expr', id_ty')
928 %************************************************************************
930 \subsection{Record bindings}
932 %************************************************************************
934 Game plan for record bindings
935 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
936 1. Find the TyCon for the bindings, from the first field label.
938 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
940 For each binding field = value
942 3. Instantiate the field type (from the field label) using the type
945 4 Type check the value using tcArg, passing the field type as
946 the expected argument type.
948 This extends OK when the field types are universally quantified.
953 :: TyCon -- Type constructor for the record
954 -> [TcType] -- Args of this type constructor
955 -> RenamedRecordBinds
958 tcRecordBinds tycon ty_args rbinds
959 = mappM do_bind rbinds
961 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
963 do_bind (field_lbl_name, rhs)
964 = addErrCtxt (fieldCtxt field_lbl_name) $
965 tcLookupId field_lbl_name `thenM` \ sel_id ->
967 field_lbl = recordSelectorFieldLabel sel_id
968 field_ty = substTy tenv (fieldLabelType field_lbl)
970 ASSERT( isRecordSelector sel_id )
971 -- This lookup and assertion will surely succeed, because
972 -- we check that the fields are indeed record selectors
973 -- before calling tcRecordBinds
974 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
975 -- The caller of tcRecordBinds has already checked
976 -- that all the fields come from the same type
978 tcExpr rhs field_ty `thenM` \ rhs' ->
980 returnM (sel_id, rhs')
982 badFields rbinds data_con
983 = filter (not . (`elem` field_names)) (recBindFields rbinds)
985 field_names = map fieldLabelName (dataConFieldLabels data_con)
987 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
988 checkMissingFields data_con rbinds
989 | null field_labels -- Not declared as a record;
990 -- But C{} is still valid if no strict fields
991 = if any isMarkedStrict field_strs then
992 -- Illegal if any arg is strict
993 addErrTc (missingStrictFields data_con [])
997 | otherwise -- A record
998 = checkM (null missing_s_fields)
999 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1001 doptM Opt_WarnMissingFields `thenM` \ warn ->
1002 checkM (not (warn && notNull missing_ns_fields))
1003 (warnTc True (missingFields data_con missing_ns_fields))
1007 = [ fl | (fl, str) <- field_info,
1009 not (fieldLabelName fl `elem` field_names_used)
1012 = [ fl | (fl, str) <- field_info,
1013 not (isMarkedStrict str),
1014 not (fieldLabelName fl `elem` field_names_used)
1017 field_names_used = recBindFields rbinds
1018 field_labels = dataConFieldLabels data_con
1020 field_info = zipEqual "missingFields"
1024 field_strs = dropList ex_theta (dataConStrictMarks data_con)
1025 -- The 'drop' is because dataConStrictMarks
1026 -- includes the existential dictionaries
1027 (_, _, _, ex_theta, _, _) = dataConSig data_con
1030 %************************************************************************
1032 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1034 %************************************************************************
1037 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1039 tcMonoExprs [] [] = returnM []
1040 tcMonoExprs (expr:exprs) (ty:tys)
1041 = tcMonoExpr expr ty `thenM` \ expr' ->
1042 tcMonoExprs exprs tys `thenM` \ exprs' ->
1043 returnM (expr':exprs')
1047 %************************************************************************
1049 \subsection{Literals}
1051 %************************************************************************
1053 Overloaded literals.
1056 tcLit :: HsLit -> TcType -> TcM TcExpr
1057 tcLit (HsLitLit s _) res_ty
1058 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1059 newDicts (LitLitOrigin (unpackFS s))
1060 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1061 extendLIEs dicts `thenM_`
1062 returnM (HsLit (HsLitLit s res_ty))
1065 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1070 %************************************************************************
1072 \subsection{Errors and contexts}
1074 %************************************************************************
1076 Boring and alphabetical:
1079 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1082 badStageErr id bind_lvl use_lvl
1083 = ptext SLIT("Stage error:") <+> quotes (ppr id) <+>
1084 hsep [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
1085 ptext SLIT("but used at stage") <+> ppr use_lvl]
1088 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1091 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1094 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1097 = hang (ptext SLIT("When checking the type signature of the expression:"))
1101 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1103 fieldCtxt field_name
1104 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1106 funAppCtxt fun arg arg_no
1107 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1108 quotes (ppr fun) <> text ", namely"])
1109 4 (quotes (ppr arg))
1112 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1115 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1118 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1120 illegalBracket level
1121 = ptext SLIT("Illegal bracket at level") <+> ppr level
1124 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1126 the_app = foldl HsApp fun args -- Used in error messages
1128 lurkingRank2Err fun fun_ty
1129 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1130 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1131 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1134 = hang (ptext SLIT("No constructor has all these fields:"))
1135 4 (pprQuotedList (recBindFields rbinds))
1137 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1138 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1141 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1143 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1144 missingStrictFields con fields
1147 rest | null fields = empty -- Happens for non-record constructors
1148 -- with strict fields
1149 | otherwise = colon <+> pprWithCommas ppr fields
1151 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1152 ptext SLIT("does not have the required strict field(s)")
1155 missingFields :: DataCon -> [FieldLabel] -> SDoc
1156 missingFields con fields
1157 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1158 <+> pprWithCommas ppr fields
1160 polySpliceErr :: Id -> SDoc
1162 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1164 wrongArgsCtxt too_many_or_few fun args
1165 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1166 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1167 <+> ptext SLIT("arguments in the call"))
1168 4 (parens (ppr the_app))
1170 the_app = foldl HsApp fun args -- Used in error messages