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 TcType ( isTauTy )
15 import TcEnv ( bracketOK, tcMetaTy, tcLookupGlobal,
16 wellStaged, metaLevel )
17 import TcSimplify ( tcSimplifyBracket )
18 import Name ( isExternalName )
19 import qualified DsMeta
22 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
23 mkMonoBind, recBindFields
25 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
26 import TcHsSyn ( TcExpr, TcRecordBinds, hsLitType, mkHsDictApp, mkHsTyApp, mkHsLet )
28 import TcUnify ( tcSubExp, tcGen, (<$>),
29 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
31 import BasicTypes ( RecFlag(..), isMarkedStrict )
32 import Inst ( InstOrigin(..),
33 newOverloadedLit, newMethodFromName, newIPDict,
34 newDicts, newMethodWithGivenTy,
35 instToId, tcInstCall, tcInstDataCon
37 import TcBinds ( tcBindsAndThen )
38 import TcEnv ( tcLookupClass, tcLookupGlobal_maybe, tcLookupIdLvl,
39 tcLookupTyCon, tcLookupDataCon, tcLookupId
41 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts )
42 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
43 import TcPat ( badFieldCon )
44 import TcSimplify ( tcSimplifyIPs )
45 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
46 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
47 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
48 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
49 isSigmaTy, mkFunTy, mkFunTys,
50 mkTyConApp, mkClassPred, tcFunArgTy,
51 tyVarsOfTypes, isLinearPred,
52 liftedTypeKind, openTypeKind,
53 tcSplitSigmaTy, tcTyConAppTyCon,
56 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
57 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector, isDataConWrapId_maybe )
58 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks )
60 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
61 import Subst ( mkTopTyVarSubst, substTheta, substTy )
62 import VarSet ( emptyVarSet, elemVarSet )
63 import TysWiredIn ( boolTy )
64 import PrelNames ( cCallableClassName, cReturnableClassName,
65 enumFromName, enumFromThenName,
66 enumFromToName, enumFromThenToName,
67 enumFromToPName, enumFromThenToPName,
70 import ListSetOps ( minusList )
72 import HscTypes ( TyThing(..) )
79 %************************************************************************
81 \subsection{Main wrappers}
83 %************************************************************************
86 tcExpr :: RenamedHsExpr -- Expession to type check
87 -> TcSigmaType -- Expected type (could be a polytpye)
88 -> TcM TcExpr -- Generalised expr with expected type
90 tcExpr expr expected_ty
91 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
92 tc_expr' expr expected_ty
94 tc_expr' expr expected_ty
95 | not (isSigmaTy expected_ty) -- Monomorphic case
96 = tcMonoExpr expr expected_ty
99 = tcGen expected_ty emptyVarSet (
101 ) `thenM` \ (gen_fn, expr') ->
102 returnM (gen_fn <$> expr')
106 %************************************************************************
108 \subsection{The TAUT rules for variables}
110 %************************************************************************
113 tcMonoExpr :: RenamedHsExpr -- Expession to type check
114 -> TcRhoType -- Expected type (could be a type variable)
115 -- Definitely no foralls at the top
119 tcMonoExpr (HsVar name) res_ty
120 = tcId name `thenM` \ (expr', id_ty) ->
121 tcSubExp res_ty id_ty `thenM` \ co_fn ->
122 returnM (co_fn <$> expr')
124 tcMonoExpr (HsIPVar ip) res_ty
125 = -- Implicit parameters must have a *tau-type* not a
126 -- type scheme. We enforce this by creating a fresh
127 -- type variable as its type. (Because res_ty may not
129 newTyVarTy openTypeKind `thenM` \ ip_ty ->
130 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
131 extendLIE inst `thenM_`
132 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
133 returnM (co_fn <$> HsIPVar ip')
137 %************************************************************************
139 \subsection{Expressions type signatures}
141 %************************************************************************
144 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
145 = addErrCtxt (exprSigCtxt in_expr) $
146 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
147 tcExpr expr sig_tc_ty `thenM` \ expr' ->
149 -- Must instantiate the outer for-alls of sig_tc_ty
150 -- else we risk instantiating a ? res_ty to a forall-type
151 -- which breaks the invariant that tcMonoExpr only returns phi-types
152 tcInstCall SignatureOrigin sig_tc_ty `thenM` \ (inst_fn, inst_sig_ty) ->
153 tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
155 returnM (co_fn <$> inst_fn expr')
157 tcMonoExpr (HsType ty) res_ty
158 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
159 -- This is the syntax for type applications that I was planning
160 -- but there are difficulties (e.g. what order for type args)
161 -- so it's not enabled yet.
162 -- Can't eliminate it altogether from the parser, because the
163 -- same parser parses *patterns*.
167 %************************************************************************
169 \subsection{Other expression forms}
171 %************************************************************************
174 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
175 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
176 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
177 returnM (HsPar expr')
178 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
179 returnM (HsSCC lbl expr')
182 tcMonoExpr (NegApp expr neg_name) res_ty
183 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
184 -- ToDo: use tcSyntaxName
186 tcMonoExpr (HsLam match) res_ty
187 = tcMatchLambda match res_ty `thenM` \ match' ->
188 returnM (HsLam match')
190 tcMonoExpr (HsApp e1 e2) res_ty
191 = tcApp e1 [e2] res_ty
194 Note that the operators in sections are expected to be binary, and
195 a type error will occur if they aren't.
198 -- Left sections, equivalent to
205 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
206 = tcExpr_id op `thenM` \ (op', op_ty) ->
207 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
208 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
209 addErrCtxt (exprCtxt in_expr) $
210 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
211 returnM (co_fn <$> SectionL arg1' op')
213 -- Right sections, equivalent to \ x -> x op expr, or
216 tcMonoExpr in_expr@(SectionR op arg2) res_ty
217 = tcExpr_id op `thenM` \ (op', op_ty) ->
218 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
219 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
220 addErrCtxt (exprCtxt in_expr) $
221 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
222 returnM (co_fn <$> SectionR op' arg2')
224 -- equivalent to (op e1) e2:
226 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
227 = tcExpr_id op `thenM` \ (op', op_ty) ->
228 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
229 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
230 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
231 addErrCtxt (exprCtxt in_expr) $
232 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
233 returnM (OpApp arg1' op' fix arg2')
237 tcMonoExpr (HsLet binds expr) res_ty
240 binds -- Bindings to check
241 (tcMonoExpr expr res_ty)
243 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
245 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
246 = addSrcLoc src_loc $
247 addErrCtxt (caseCtxt in_expr) $
249 -- Typecheck the case alternatives first.
250 -- The case patterns tend to give good type info to use
251 -- when typechecking the scrutinee. For example
254 -- will report that map is applied to too few arguments
256 -- Not only that, but it's better to check the matches on their
257 -- own, so that we get the expected results for scoped type variables.
259 -- (p::a, q::b) -> (q,p)
260 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
261 -- claimed by the pattern signatures. But if we typechecked the
262 -- match with x in scope and x's type as the expected type, we'd be hosed.
264 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
266 addErrCtxt (caseScrutCtxt scrut) (
267 tcMonoExpr scrut scrut_ty
268 ) `thenM` \ scrut' ->
270 returnM (HsCase scrut' matches' src_loc)
272 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
273 = addSrcLoc src_loc $
274 addErrCtxt (predCtxt pred) (
275 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
277 zapToType res_ty `thenM` \ res_ty' ->
278 -- C.f. the call to zapToType in TcMatches.tcMatches
280 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
281 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
282 returnM (HsIf pred' b1' b2' src_loc)
284 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
285 = addSrcLoc src_loc $
286 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
287 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
289 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
290 = unifyListTy res_ty `thenM` \ elt_ty ->
291 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
292 returnM (ExplicitList elt_ty exprs')
295 = addErrCtxt (listCtxt expr) $
296 tcMonoExpr expr elt_ty
298 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
299 = unifyPArrTy res_ty `thenM` \ elt_ty ->
300 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
301 returnM (ExplicitPArr elt_ty exprs')
304 = addErrCtxt (parrCtxt expr) $
305 tcMonoExpr expr elt_ty
307 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
308 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
309 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
310 returnM (ExplicitTuple exprs' boxity)
314 %************************************************************************
318 %************************************************************************
320 The interesting thing about @ccall@ is that it is just a template
321 which we instantiate by filling in details about the types of its
322 argument and result (ie minimal typechecking is performed). So, the
323 basic story is that we allocate a load of type variables (to hold the
324 arg/result types); unify them with the args/result; and store them for
328 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
330 = getDOpts `thenM` \ dflags ->
332 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
333 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
334 text "Either compile with -fvia-C, or, better, rewrite your code",
335 text "to use the foreign function interface. _casm_s are deprecated",
336 text "and support for them may one day disappear."])
339 -- Get the callable and returnable classes.
340 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
341 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
342 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
344 new_arg_dict (arg, arg_ty)
345 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
346 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
347 returnM arg_dicts -- Actually a singleton bag
349 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
353 let tv_idxs | null args = []
354 | otherwise = [1..length args]
356 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
357 tcMonoExprs args arg_tys `thenM` \ args' ->
359 -- The argument types can be unlifted or lifted; the result
360 -- type must, however, be lifted since it's an argument to the IO
362 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
364 io_result_ty = mkTyConApp ioTyCon [result_ty]
366 unifyTauTy res_ty io_result_ty `thenM_`
368 -- Construct the extra insts, which encode the
369 -- constraints on the argument and result types.
370 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
371 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
372 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
373 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
377 %************************************************************************
379 Record construction and update
381 %************************************************************************
384 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
385 = addErrCtxt (recordConCtxt expr) $
386 tcId con_name `thenM` \ (con_expr, con_tau) ->
388 (_, record_ty) = tcSplitFunTys con_tau
389 (tycon, ty_args) = tcSplitTyConApp record_ty
391 ASSERT( isAlgTyCon tycon )
392 unifyTauTy res_ty record_ty `thenM_`
394 -- Check that the record bindings match the constructor
395 -- con_name is syntactically constrained to be a data constructor
396 tcLookupDataCon con_name `thenM` \ data_con ->
398 bad_fields = badFields rbinds data_con
400 if notNull bad_fields then
401 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
402 failM -- Fail now, because tcRecordBinds will crash on a bad field
405 -- Typecheck the record bindings
406 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
408 -- Check for missing fields
409 checkMissingFields data_con rbinds `thenM_`
411 returnM (RecordConOut data_con con_expr rbinds')
413 -- The main complication with RecordUpd is that we need to explicitly
414 -- handle the *non-updated* fields. Consider:
416 -- data T a b = MkT1 { fa :: a, fb :: b }
417 -- | MkT2 { fa :: a, fc :: Int -> Int }
418 -- | MkT3 { fd :: a }
420 -- upd :: T a b -> c -> T a c
421 -- upd t x = t { fb = x}
423 -- The type signature on upd is correct (i.e. the result should not be (T a b))
424 -- because upd should be equivalent to:
426 -- upd t x = case t of
427 -- MkT1 p q -> MkT1 p x
428 -- MkT2 a b -> MkT2 p b
429 -- MkT3 d -> error ...
431 -- So we need to give a completely fresh type to the result record,
432 -- and then constrain it by the fields that are *not* updated ("p" above).
434 -- Note that because MkT3 doesn't contain all the fields being updated,
435 -- its RHS is simply an error, so it doesn't impose any type constraints
437 -- All this is done in STEP 4 below.
439 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
440 = addErrCtxt (recordUpdCtxt expr) $
443 -- Check that the field names are really field names
444 ASSERT( notNull rbinds )
446 field_names = recBindFields rbinds
448 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
450 bad_guys = [ addErrTc (notSelector field_name)
451 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
453 Just (AnId sel_id) -> not (isRecordSelector sel_id)
457 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
460 -- Figure out the tycon and data cons from the first field name
462 -- It's OK to use the non-tc splitters here (for a selector)
463 (Just (AnId sel_id) : _) = maybe_sel_ids
465 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
466 -- when the data type has a context
467 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
468 tycon = tcTyConAppTyCon data_ty
469 data_cons = tyConDataCons tycon
470 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
472 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
475 -- Check that at least one constructor has all the named fields
476 -- i.e. has an empty set of bad fields returned by badFields
477 checkTc (any (null . badFields rbinds) data_cons)
478 (badFieldsUpd rbinds) `thenM_`
481 -- Typecheck the update bindings.
482 -- (Do this after checking for bad fields in case there's a field that
483 -- doesn't match the constructor.)
485 result_record_ty = mkTyConApp tycon result_inst_tys
487 unifyTauTy res_ty result_record_ty `thenM_`
488 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
491 -- Use the un-updated fields to find a vector of booleans saying
492 -- which type arguments must be the same in updatee and result.
494 -- WARNING: this code assumes that all data_cons in a common tycon
495 -- have FieldLabels abstracted over the same tyvars.
497 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
498 con_field_lbls_s = map dataConFieldLabels data_cons
500 -- A constructor is only relevant to this process if
501 -- it contains all the fields that are being updated
502 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
503 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
505 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
506 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
508 mk_inst_ty (tyvar, result_inst_ty)
509 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
510 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
512 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
515 -- Typecheck the expression to be updated
517 record_ty = mkTyConApp tycon inst_tys
519 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
522 -- Figure out the LIE we need. We have to generate some
523 -- dictionaries for the data type context, since we are going to
524 -- do pattern matching over the data cons.
526 -- What dictionaries do we need?
527 -- We just take the context of the type constructor
529 theta' = substTheta inst_env (tyConTheta tycon)
531 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
532 extendLIEs dicts `thenM_`
535 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
539 %************************************************************************
541 Arithmetic sequences e.g. [a,b..]
542 and their parallel-array counterparts e.g. [: a,b.. :]
545 %************************************************************************
548 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
549 = unifyListTy res_ty `thenM` \ elt_ty ->
550 tcMonoExpr expr elt_ty `thenM` \ expr' ->
552 newMethodFromName (ArithSeqOrigin seq)
553 elt_ty enumFromName `thenM` \ enum_from ->
555 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
557 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
558 = addErrCtxt (arithSeqCtxt in_expr) $
559 unifyListTy res_ty `thenM` \ elt_ty ->
560 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
561 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
562 newMethodFromName (ArithSeqOrigin seq)
563 elt_ty enumFromThenName `thenM` \ enum_from_then ->
565 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
568 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
569 = addErrCtxt (arithSeqCtxt in_expr) $
570 unifyListTy res_ty `thenM` \ elt_ty ->
571 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
572 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
573 newMethodFromName (ArithSeqOrigin seq)
574 elt_ty enumFromToName `thenM` \ enum_from_to ->
576 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
578 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
579 = addErrCtxt (arithSeqCtxt in_expr) $
580 unifyListTy res_ty `thenM` \ elt_ty ->
581 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
582 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
583 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
584 newMethodFromName (ArithSeqOrigin seq)
585 elt_ty enumFromThenToName `thenM` \ eft ->
587 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
589 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
590 = addErrCtxt (parrSeqCtxt in_expr) $
591 unifyPArrTy res_ty `thenM` \ elt_ty ->
592 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
593 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
594 newMethodFromName (PArrSeqOrigin seq)
595 elt_ty enumFromToPName `thenM` \ enum_from_to ->
597 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
599 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
600 = addErrCtxt (parrSeqCtxt in_expr) $
601 unifyPArrTy res_ty `thenM` \ elt_ty ->
602 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
603 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
604 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
605 newMethodFromName (PArrSeqOrigin seq)
606 elt_ty enumFromThenToPName `thenM` \ eft ->
608 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
610 tcMonoExpr (PArrSeqIn _) _
611 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
612 -- the parser shouldn't have generated it and the renamer shouldn't have
617 %************************************************************************
621 %************************************************************************
624 #ifdef GHCI /* Only if bootstrapped */
625 -- Rename excludes these cases otherwise
627 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
629 tcMonoExpr (HsBracket brack loc) res_ty
631 getStage `thenM` \ level ->
632 case bracketOK level of {
633 Nothing -> failWithTc (illegalBracket level) ;
636 -- Typecheck expr to make sure it is valid,
637 -- but throw away the results. We'll type check
638 -- it again when we actually use it.
639 newMutVar [] `thenM` \ pending_splices ->
640 getLIEVar `thenM` \ lie_var ->
642 setStage (Brack next_level pending_splices lie_var) (
643 getLIE (tcBracket brack)
644 ) `thenM` \ (meta_ty, lie) ->
645 tcSimplifyBracket lie `thenM_`
647 unifyTauTy res_ty meta_ty `thenM_`
649 -- Return the original expression, not the type-decorated one
650 readMutVar pending_splices `thenM` \ pendings ->
651 returnM (HsBracketOut brack pendings)
654 tcMonoExpr (HsReify (Reify flavour name)) res_ty
655 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
656 tcMetaTy tycon_name `thenM` \ reify_ty ->
657 unifyTauTy res_ty reify_ty `thenM_`
658 returnM (HsReify (ReifyOut flavour name))
660 tycon_name = case flavour of
661 ReifyDecl -> DsMeta.decTyConName
662 ReifyType -> DsMeta.typTyConName
663 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
667 %************************************************************************
669 \subsection{Implicit Parameter bindings}
671 %************************************************************************
674 tcMonoExpr (HsWith expr binds is_with) res_ty
675 = getLIE (tcMonoExpr expr res_ty) `thenM` \ (expr', expr_lie) ->
676 mapAndUnzipM tc_ip_bind binds `thenM` \ (avail_ips, binds') ->
678 -- If the binding binds ?x = E, we must now
679 -- discharge any ?x constraints in expr_lie
680 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
682 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
684 returnM (HsWith expr'' binds' is_with)
686 tc_ip_bind (ip, expr)
687 = newTyVarTy openTypeKind `thenM` \ ty ->
688 getSrcLocM `thenM` \ loc ->
689 newIPDict (IPBind ip) ip ty `thenM` \ (ip', ip_inst) ->
690 tcMonoExpr expr ty `thenM` \ expr' ->
691 returnM (ip_inst, (ip', expr'))
695 %************************************************************************
699 %************************************************************************
702 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
706 %************************************************************************
708 \subsection{@tcApp@ typchecks an application}
710 %************************************************************************
714 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
715 -> TcType -- Expected result type of application
716 -> TcM TcExpr -- Translated fun and args
718 tcApp (HsApp e1 e2) args res_ty
719 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
721 tcApp fun args res_ty
722 = -- First type-check the function
723 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
725 addErrCtxt (wrongArgsCtxt "too many" fun args) (
726 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
727 split_fun_ty fun_ty (length args)
728 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
730 -- Now typecheck the args
732 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
734 -- Unify with expected result after type-checking the args
735 -- so that the info from args percolates to actual_result_ty.
736 -- This is when we might detect a too-few args situation.
737 -- (One can think of cases when the opposite order would give
738 -- a better error message.)
739 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
740 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
742 returnM (co_fn <$> foldl HsApp fun' args')
745 -- If an error happens we try to figure out whether the
746 -- function has been given too many or too few arguments,
748 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
749 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
750 zonkTcType actual_res_ty `thenM` \ act_ty' ->
752 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
753 (env2, act_ty'') = tidyOpenType env1 act_ty'
754 (exp_args, _) = tcSplitFunTys exp_ty''
755 (act_args, _) = tcSplitFunTys act_ty''
757 len_act_args = length act_args
758 len_exp_args = length exp_args
760 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
761 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
762 | otherwise = appCtxt fun args
764 returnM (env2, message)
767 split_fun_ty :: TcType -- The type of the function
768 -> Int -- Number of arguments
769 -> TcM ([TcType], -- Function argument types
770 TcType) -- Function result types
772 split_fun_ty fun_ty 0
773 = returnM ([], fun_ty)
775 split_fun_ty fun_ty n
776 = -- Expect the function to have type A->B
777 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
778 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
779 returnM (arg_ty:arg_tys, final_res_ty)
783 tcArg :: RenamedHsExpr -- The function (for error messages)
784 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
785 -> TcM TcExpr -- Resulting argument and LIE
787 tcArg the_fun (arg, expected_arg_ty, arg_no)
788 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
789 tcExpr arg expected_arg_ty
793 %************************************************************************
795 \subsection{@tcId@ typchecks an identifier occurrence}
797 %************************************************************************
799 tcId instantiates an occurrence of an Id.
800 The instantiate_it loop runs round instantiating the Id.
801 It has to be a loop because we are now prepared to entertain
803 f:: forall a. Eq a => forall b. Baz b => tau
804 We want to instantiate this to
805 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
807 The -fno-method-sharing flag controls what happens so far as the LIE
808 is concerned. The default case is that for an overloaded function we
809 generate a "method" Id, and add the Method Inst to the LIE. So you get
812 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
813 If you specify -fno-method-sharing, the dictionary application
814 isn't shared, so we get
816 f = /\a (d:Num a) (x:a) -> (+) a d x x
817 This gets a bit less sharing, but
818 a) it's better for RULEs involving overloaded functions
819 b) perhaps fewer separated lambdas
822 tcId :: Name -> TcM (TcExpr, TcType)
823 tcId name -- Look up the Id and instantiate its type
824 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
826 -- Check for cross-stage lifting
828 getStage `thenM` \ use_stage ->
830 Brack use_lvl ps_var lie_var
831 | use_lvl > bind_lvl && not (isExternalName name)
832 -> -- E.g. \x -> [| h x |]
833 -- We must behave as if the reference to x was
835 -- We use 'x' itself as the splice proxy, used by
836 -- the desugarer to stitch it all back together
837 -- NB: isExernalName is true of top level things,
838 -- and false of nested bindings
843 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
844 -- If x is polymorphic, its occurrence sites might
845 -- have different instantiations, so we can't use plain
846 -- 'x' as the splice proxy name. I don't know how to
847 -- solve this, and it's probably unimportant, so I'm
848 -- just going to flag an error for now
851 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
852 -- Put the 'lift' constraint into the right LIE
854 -- Update the pending splices
855 readMutVar ps_var `thenM` \ ps ->
856 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
858 returnM (HsVar id, id_ty))
862 use_lvl = metaLevel use_stage
864 checkTc (wellStaged bind_lvl use_lvl)
865 (badStageErr id bind_lvl use_lvl) `thenM_`
867 -- This is the bit that handles the no-Template-Haskell case
868 case isDataConWrapId_maybe id of
869 Nothing -> loop (HsVar id) (idType id)
870 Just data_con -> inst_data_con id data_con
873 orig = OccurrenceOf name
875 loop (HsVar fun_id) fun_ty
876 | want_method_inst fun_ty
877 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
878 newMethodWithGivenTy orig fun_id
879 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
880 loop (HsVar meth_id) tau
884 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
885 loop (inst_fn fun) tau
888 = returnM (fun, fun_ty)
890 want_method_inst fun_ty
891 | opt_NoMethodSharing = False
892 | otherwise = case tcSplitSigmaTy fun_ty of
893 (_,[],_) -> False -- Not overloaded
894 (_,theta,_) -> not (any isLinearPred theta)
895 -- This is a slight hack.
896 -- If f :: (%x :: T) => Int -> Int
897 -- Then if we have two separate calls, (f 3, f 4), we cannot
898 -- make a method constraint that then gets shared, thus:
899 -- let m = f %x in (m 3, m 4)
900 -- because that loses the linearity of the constraint.
901 -- The simplest thing to do is never to construct a method constraint
902 -- in the first place that has a linear implicit parameter in it.
904 -- We treat data constructors differently, because we have to generate
905 -- constraints for their silly theta, which no longer appears in
906 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
907 inst_data_con id data_con
908 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
909 extendLIEs ex_dicts `thenM_`
910 returnM (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) (map instToId ex_dicts),
911 mkFunTys arg_tys result_ty)
914 Typecheck expression which in most cases will be an Id.
915 The expression can return a higher-ranked type, such as
916 (forall a. a->a) -> Int
917 so we must create a HoleTyVarTy to pass in as the expected tyvar.
920 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
921 tcExpr_id (HsVar name) = tcId name
922 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
923 tcMonoExpr expr id_ty `thenM` \ expr' ->
924 readHoleResult id_ty `thenM` \ id_ty' ->
925 returnM (expr', id_ty')
929 %************************************************************************
931 \subsection{Record bindings}
933 %************************************************************************
935 Game plan for record bindings
936 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
937 1. Find the TyCon for the bindings, from the first field label.
939 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
941 For each binding field = value
943 3. Instantiate the field type (from the field label) using the type
946 4 Type check the value using tcArg, passing the field type as
947 the expected argument type.
949 This extends OK when the field types are universally quantified.
954 :: TyCon -- Type constructor for the record
955 -> [TcType] -- Args of this type constructor
956 -> RenamedRecordBinds
959 tcRecordBinds tycon ty_args rbinds
960 = mappM do_bind rbinds
962 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
964 do_bind (field_lbl_name, rhs)
965 = addErrCtxt (fieldCtxt field_lbl_name) $
966 tcLookupId field_lbl_name `thenM` \ sel_id ->
968 field_lbl = recordSelectorFieldLabel sel_id
969 field_ty = substTy tenv (fieldLabelType field_lbl)
971 ASSERT( isRecordSelector sel_id )
972 -- This lookup and assertion will surely succeed, because
973 -- we check that the fields are indeed record selectors
974 -- before calling tcRecordBinds
975 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
976 -- The caller of tcRecordBinds has already checked
977 -- that all the fields come from the same type
979 tcExpr rhs field_ty `thenM` \ rhs' ->
981 returnM (sel_id, rhs')
983 badFields rbinds data_con
984 = filter (not . (`elem` field_names)) (recBindFields rbinds)
986 field_names = map fieldLabelName (dataConFieldLabels data_con)
988 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
989 checkMissingFields data_con rbinds
990 | null field_labels -- Not declared as a record;
991 -- But C{} is still valid if no strict fields
992 = if any isMarkedStrict field_strs then
993 -- Illegal if any arg is strict
994 addErrTc (missingStrictFields data_con [])
998 | otherwise -- A record
999 = checkM (null missing_s_fields)
1000 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1002 doptM Opt_WarnMissingFields `thenM` \ warn ->
1003 checkM (not (warn && notNull missing_ns_fields))
1004 (warnTc True (missingFields data_con missing_ns_fields))
1008 = [ fl | (fl, str) <- field_info,
1010 not (fieldLabelName fl `elem` field_names_used)
1013 = [ fl | (fl, str) <- field_info,
1014 not (isMarkedStrict str),
1015 not (fieldLabelName fl `elem` field_names_used)
1018 field_names_used = recBindFields rbinds
1019 field_labels = dataConFieldLabels data_con
1021 field_info = zipEqual "missingFields"
1025 field_strs = dropList ex_theta (dataConStrictMarks data_con)
1026 -- The 'drop' is because dataConStrictMarks
1027 -- includes the existential dictionaries
1028 (_, _, _, ex_theta, _, _) = dataConSig data_con
1031 %************************************************************************
1033 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1035 %************************************************************************
1038 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1040 tcMonoExprs [] [] = returnM []
1041 tcMonoExprs (expr:exprs) (ty:tys)
1042 = tcMonoExpr expr ty `thenM` \ expr' ->
1043 tcMonoExprs exprs tys `thenM` \ exprs' ->
1044 returnM (expr':exprs')
1048 %************************************************************************
1050 \subsection{Literals}
1052 %************************************************************************
1054 Overloaded literals.
1057 tcLit :: HsLit -> TcType -> TcM TcExpr
1058 tcLit (HsLitLit s _) res_ty
1059 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1060 newDicts (LitLitOrigin (unpackFS s))
1061 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1062 extendLIEs dicts `thenM_`
1063 returnM (HsLit (HsLitLit s res_ty))
1066 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1071 %************************************************************************
1073 \subsection{Errors and contexts}
1075 %************************************************************************
1077 Boring and alphabetical:
1080 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1083 badStageErr id bind_lvl use_lvl
1084 = ptext SLIT("Stage error:") <+> quotes (ppr id) <+>
1085 hsep [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
1086 ptext SLIT("but used at stage") <+> ppr use_lvl]
1089 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1092 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1095 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1098 = hang (ptext SLIT("When checking the type signature of the expression:"))
1102 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1104 fieldCtxt field_name
1105 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1107 funAppCtxt fun arg arg_no
1108 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1109 quotes (ppr fun) <> text ", namely"])
1110 4 (quotes (ppr arg))
1113 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1116 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1119 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1121 illegalBracket level
1122 = ptext SLIT("Illegal bracket at level") <+> ppr level
1125 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1127 the_app = foldl HsApp fun args -- Used in error messages
1129 lurkingRank2Err fun fun_ty
1130 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1131 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1132 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1135 = hang (ptext SLIT("No constructor has all these fields:"))
1136 4 (pprQuotedList (recBindFields rbinds))
1138 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1139 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1142 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1144 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1145 missingStrictFields con fields
1148 rest | null fields = empty -- Happens for non-record constructors
1149 -- with strict fields
1150 | otherwise = colon <+> pprWithCommas ppr fields
1152 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1153 ptext SLIT("does not have the required strict field(s)")
1156 missingFields :: DataCon -> [FieldLabel] -> SDoc
1157 missingFields con fields
1158 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1159 <+> pprWithCommas ppr fields
1161 polySpliceErr :: Id -> SDoc
1163 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1165 wrongArgsCtxt too_many_or_few fun args
1166 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1167 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1168 <+> ptext SLIT("arguments in the call"))
1169 4 (parens (ppr the_app))
1171 the_app = foldl HsApp fun args -- Used in error messages