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 )
15 import TcSimplify ( tcSimplifyBracket )
16 import qualified DsMeta
19 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
20 mkMonoBind, recBindFields
22 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
23 import TcHsSyn ( TcExpr, TcRecordBinds, hsLitType, mkHsDictApp, mkHsTyApp, mkHsLet )
25 import TcUnify ( tcSubExp, tcGen, (<$>),
26 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
28 import BasicTypes ( RecFlag(..), isMarkedStrict )
29 import Inst ( InstOrigin(..),
30 newOverloadedLit, newMethodFromName, newIPDict,
31 newDicts, newMethodWithGivenTy,
32 instToId, tcInstCall, tcInstDataCon
34 import TcBinds ( tcBindsAndThen )
35 import TcEnv ( tcLookupClass, tcLookupGlobal_maybe, tcLookupIdLvl,
36 tcLookupTyCon, tcLookupDataCon, tcLookupId, tcLookupGlobal,
39 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts )
40 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
41 import TcPat ( badFieldCon )
42 import TcSimplify ( tcSimplifyIPs )
43 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
44 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
45 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
46 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
47 isSigmaTy, isTauTy, mkFunTy, mkFunTys,
48 mkTyConApp, mkClassPred, tcFunArgTy,
49 tyVarsOfTypes, isLinearPred,
50 liftedTypeKind, openTypeKind,
51 tcSplitSigmaTy, tcTyConAppTyCon,
54 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
55 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector, isDataConWrapId_maybe )
56 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks )
57 import Name ( Name, isExternalName )
58 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
59 import Subst ( mkTopTyVarSubst, substTheta, substTy )
60 import VarSet ( emptyVarSet, elemVarSet )
61 import TysWiredIn ( boolTy )
62 import PrelNames ( cCallableClassName, cReturnableClassName,
63 enumFromName, enumFromThenName,
64 enumFromToName, enumFromThenToName,
65 enumFromToPName, enumFromThenToPName,
68 import ListSetOps ( minusList )
70 import HscTypes ( TyThing(..) )
77 %************************************************************************
79 \subsection{Main wrappers}
81 %************************************************************************
84 tcExpr :: RenamedHsExpr -- Expession to type check
85 -> TcSigmaType -- Expected type (could be a polytpye)
86 -> TcM TcExpr -- Generalised expr with expected type
88 tcExpr expr expected_ty
89 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
90 tc_expr' expr expected_ty
92 tc_expr' expr expected_ty
93 | not (isSigmaTy expected_ty) -- Monomorphic case
94 = tcMonoExpr expr expected_ty
97 = tcGen expected_ty emptyVarSet (
99 ) `thenM` \ (gen_fn, expr') ->
100 returnM (gen_fn <$> expr')
104 %************************************************************************
106 \subsection{The TAUT rules for variables}
108 %************************************************************************
111 tcMonoExpr :: RenamedHsExpr -- Expession to type check
112 -> TcRhoType -- Expected type (could be a type variable)
113 -- Definitely no foralls at the top
117 tcMonoExpr (HsVar name) res_ty
118 = tcId name `thenM` \ (expr', id_ty) ->
119 tcSubExp res_ty id_ty `thenM` \ co_fn ->
120 returnM (co_fn <$> expr')
122 tcMonoExpr (HsIPVar ip) res_ty
123 = -- Implicit parameters must have a *tau-type* not a
124 -- type scheme. We enforce this by creating a fresh
125 -- type variable as its type. (Because res_ty may not
127 newTyVarTy openTypeKind `thenM` \ ip_ty ->
128 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
129 extendLIE inst `thenM_`
130 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
131 returnM (co_fn <$> HsIPVar ip')
135 %************************************************************************
137 \subsection{Expressions type signatures}
139 %************************************************************************
142 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
143 = addErrCtxt (exprSigCtxt in_expr) $
144 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
145 tcExpr expr sig_tc_ty `thenM` \ expr' ->
147 -- Must instantiate the outer for-alls of sig_tc_ty
148 -- else we risk instantiating a ? res_ty to a forall-type
149 -- which breaks the invariant that tcMonoExpr only returns phi-types
150 tcInstCall SignatureOrigin sig_tc_ty `thenM` \ (inst_fn, inst_sig_ty) ->
151 tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
153 returnM (co_fn <$> inst_fn expr')
155 tcMonoExpr (HsType ty) res_ty
156 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
157 -- This is the syntax for type applications that I was planning
158 -- but there are difficulties (e.g. what order for type args)
159 -- so it's not enabled yet.
160 -- Can't eliminate it altogether from the parser, because the
161 -- same parser parses *patterns*.
165 %************************************************************************
167 \subsection{Other expression forms}
169 %************************************************************************
172 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
173 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
174 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
175 returnM (HsPar expr')
176 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
177 returnM (HsSCC lbl expr')
180 tcMonoExpr (NegApp expr neg_name) res_ty
181 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
182 -- ToDo: use tcSyntaxName
184 tcMonoExpr (HsLam match) res_ty
185 = tcMatchLambda match res_ty `thenM` \ match' ->
186 returnM (HsLam match')
188 tcMonoExpr (HsApp e1 e2) res_ty
189 = tcApp e1 [e2] res_ty
192 Note that the operators in sections are expected to be binary, and
193 a type error will occur if they aren't.
196 -- Left sections, equivalent to
203 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
204 = tcExpr_id op `thenM` \ (op', op_ty) ->
205 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
206 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
207 addErrCtxt (exprCtxt in_expr) $
208 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
209 returnM (co_fn <$> SectionL arg1' op')
211 -- Right sections, equivalent to \ x -> x op expr, or
214 tcMonoExpr in_expr@(SectionR op arg2) res_ty
215 = tcExpr_id op `thenM` \ (op', op_ty) ->
216 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
217 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
218 addErrCtxt (exprCtxt in_expr) $
219 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
220 returnM (co_fn <$> SectionR op' arg2')
222 -- equivalent to (op e1) e2:
224 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
225 = tcExpr_id op `thenM` \ (op', op_ty) ->
226 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
227 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
228 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
229 addErrCtxt (exprCtxt in_expr) $
230 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
231 returnM (OpApp arg1' op' fix arg2')
235 tcMonoExpr (HsLet binds expr) res_ty
238 binds -- Bindings to check
239 (tcMonoExpr expr res_ty)
241 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
243 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
244 = addSrcLoc src_loc $
245 addErrCtxt (caseCtxt in_expr) $
247 -- Typecheck the case alternatives first.
248 -- The case patterns tend to give good type info to use
249 -- when typechecking the scrutinee. For example
252 -- will report that map is applied to too few arguments
254 -- Not only that, but it's better to check the matches on their
255 -- own, so that we get the expected results for scoped type variables.
257 -- (p::a, q::b) -> (q,p)
258 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
259 -- claimed by the pattern signatures. But if we typechecked the
260 -- match with x in scope and x's type as the expected type, we'd be hosed.
262 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
264 addErrCtxt (caseScrutCtxt scrut) (
265 tcMonoExpr scrut scrut_ty
266 ) `thenM` \ scrut' ->
268 returnM (HsCase scrut' matches' src_loc)
270 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
271 = addSrcLoc src_loc $
272 addErrCtxt (predCtxt pred) (
273 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
275 zapToType res_ty `thenM` \ res_ty' ->
276 -- C.f. the call to zapToType in TcMatches.tcMatches
278 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
279 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
280 returnM (HsIf pred' b1' b2' src_loc)
282 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
283 = addSrcLoc src_loc $
284 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
285 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
287 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
288 = unifyListTy res_ty `thenM` \ elt_ty ->
289 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
290 returnM (ExplicitList elt_ty exprs')
293 = addErrCtxt (listCtxt expr) $
294 tcMonoExpr expr elt_ty
296 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
297 = unifyPArrTy res_ty `thenM` \ elt_ty ->
298 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
299 returnM (ExplicitPArr elt_ty exprs')
302 = addErrCtxt (parrCtxt expr) $
303 tcMonoExpr expr elt_ty
305 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
306 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
307 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
308 returnM (ExplicitTuple exprs' boxity)
312 %************************************************************************
316 %************************************************************************
318 The interesting thing about @ccall@ is that it is just a template
319 which we instantiate by filling in details about the types of its
320 argument and result (ie minimal typechecking is performed). So, the
321 basic story is that we allocate a load of type variables (to hold the
322 arg/result types); unify them with the args/result; and store them for
326 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
328 = getDOpts `thenM` \ dflags ->
330 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
331 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
332 text "Either compile with -fvia-C, or, better, rewrite your code",
333 text "to use the foreign function interface. _casm_s are deprecated",
334 text "and support for them may one day disappear."])
337 -- Get the callable and returnable classes.
338 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
339 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
340 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
342 new_arg_dict (arg, arg_ty)
343 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
344 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
345 returnM arg_dicts -- Actually a singleton bag
347 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
351 let tv_idxs | null args = []
352 | otherwise = [1..length args]
354 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
355 tcMonoExprs args arg_tys `thenM` \ args' ->
357 -- The argument types can be unlifted or lifted; the result
358 -- type must, however, be lifted since it's an argument to the IO
360 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
362 io_result_ty = mkTyConApp ioTyCon [result_ty]
364 unifyTauTy res_ty io_result_ty `thenM_`
366 -- Construct the extra insts, which encode the
367 -- constraints on the argument and result types.
368 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
369 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
370 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
371 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
375 %************************************************************************
377 Record construction and update
379 %************************************************************************
382 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
383 = addErrCtxt (recordConCtxt expr) $
384 tcId con_name `thenM` \ (con_expr, con_tau) ->
386 (_, record_ty) = tcSplitFunTys con_tau
387 (tycon, ty_args) = tcSplitTyConApp record_ty
389 ASSERT( isAlgTyCon tycon )
390 unifyTauTy res_ty record_ty `thenM_`
392 -- Check that the record bindings match the constructor
393 -- con_name is syntactically constrained to be a data constructor
394 tcLookupDataCon con_name `thenM` \ data_con ->
396 bad_fields = badFields rbinds data_con
398 if notNull bad_fields then
399 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
400 failM -- Fail now, because tcRecordBinds will crash on a bad field
403 -- Typecheck the record bindings
404 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
406 -- Check for missing fields
407 checkMissingFields data_con rbinds `thenM_`
409 returnM (RecordConOut data_con con_expr rbinds')
411 -- The main complication with RecordUpd is that we need to explicitly
412 -- handle the *non-updated* fields. Consider:
414 -- data T a b = MkT1 { fa :: a, fb :: b }
415 -- | MkT2 { fa :: a, fc :: Int -> Int }
416 -- | MkT3 { fd :: a }
418 -- upd :: T a b -> c -> T a c
419 -- upd t x = t { fb = x}
421 -- The type signature on upd is correct (i.e. the result should not be (T a b))
422 -- because upd should be equivalent to:
424 -- upd t x = case t of
425 -- MkT1 p q -> MkT1 p x
426 -- MkT2 a b -> MkT2 p b
427 -- MkT3 d -> error ...
429 -- So we need to give a completely fresh type to the result record,
430 -- and then constrain it by the fields that are *not* updated ("p" above).
432 -- Note that because MkT3 doesn't contain all the fields being updated,
433 -- its RHS is simply an error, so it doesn't impose any type constraints
435 -- All this is done in STEP 4 below.
437 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
438 = addErrCtxt (recordUpdCtxt expr) $
441 -- Check that the field names are really field names
442 ASSERT( notNull rbinds )
444 field_names = recBindFields rbinds
446 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
448 bad_guys = [ addErrTc (notSelector field_name)
449 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
451 Just (AnId sel_id) -> not (isRecordSelector sel_id)
455 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
458 -- Figure out the tycon and data cons from the first field name
460 -- It's OK to use the non-tc splitters here (for a selector)
461 (Just (AnId sel_id) : _) = maybe_sel_ids
463 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
464 -- when the data type has a context
465 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
466 tycon = tcTyConAppTyCon data_ty
467 data_cons = tyConDataCons tycon
468 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
470 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
473 -- Check that at least one constructor has all the named fields
474 -- i.e. has an empty set of bad fields returned by badFields
475 checkTc (any (null . badFields rbinds) data_cons)
476 (badFieldsUpd rbinds) `thenM_`
479 -- Typecheck the update bindings.
480 -- (Do this after checking for bad fields in case there's a field that
481 -- doesn't match the constructor.)
483 result_record_ty = mkTyConApp tycon result_inst_tys
485 unifyTauTy res_ty result_record_ty `thenM_`
486 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
489 -- Use the un-updated fields to find a vector of booleans saying
490 -- which type arguments must be the same in updatee and result.
492 -- WARNING: this code assumes that all data_cons in a common tycon
493 -- have FieldLabels abstracted over the same tyvars.
495 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
496 con_field_lbls_s = map dataConFieldLabels data_cons
498 -- A constructor is only relevant to this process if
499 -- it contains all the fields that are being updated
500 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
501 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
503 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
504 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
506 mk_inst_ty (tyvar, result_inst_ty)
507 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
508 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
510 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
513 -- Typecheck the expression to be updated
515 record_ty = mkTyConApp tycon inst_tys
517 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
520 -- Figure out the LIE we need. We have to generate some
521 -- dictionaries for the data type context, since we are going to
522 -- do pattern matching over the data cons.
524 -- What dictionaries do we need?
525 -- We just take the context of the type constructor
527 theta' = substTheta inst_env (tyConTheta tycon)
529 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
530 extendLIEs dicts `thenM_`
533 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
537 %************************************************************************
539 Arithmetic sequences e.g. [a,b..]
540 and their parallel-array counterparts e.g. [: a,b.. :]
543 %************************************************************************
546 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
547 = unifyListTy res_ty `thenM` \ elt_ty ->
548 tcMonoExpr expr elt_ty `thenM` \ expr' ->
550 newMethodFromName (ArithSeqOrigin seq)
551 elt_ty enumFromName `thenM` \ enum_from ->
553 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
555 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
556 = addErrCtxt (arithSeqCtxt in_expr) $
557 unifyListTy res_ty `thenM` \ elt_ty ->
558 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
559 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
560 newMethodFromName (ArithSeqOrigin seq)
561 elt_ty enumFromThenName `thenM` \ enum_from_then ->
563 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
566 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
567 = addErrCtxt (arithSeqCtxt in_expr) $
568 unifyListTy res_ty `thenM` \ elt_ty ->
569 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
570 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
571 newMethodFromName (ArithSeqOrigin seq)
572 elt_ty enumFromToName `thenM` \ enum_from_to ->
574 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
576 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
577 = addErrCtxt (arithSeqCtxt in_expr) $
578 unifyListTy res_ty `thenM` \ elt_ty ->
579 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
580 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
581 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
582 newMethodFromName (ArithSeqOrigin seq)
583 elt_ty enumFromThenToName `thenM` \ eft ->
585 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
587 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
588 = addErrCtxt (parrSeqCtxt in_expr) $
589 unifyPArrTy res_ty `thenM` \ elt_ty ->
590 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
591 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
592 newMethodFromName (PArrSeqOrigin seq)
593 elt_ty enumFromToPName `thenM` \ enum_from_to ->
595 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
597 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
598 = addErrCtxt (parrSeqCtxt in_expr) $
599 unifyPArrTy res_ty `thenM` \ elt_ty ->
600 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
601 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
602 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
603 newMethodFromName (PArrSeqOrigin seq)
604 elt_ty enumFromThenToPName `thenM` \ eft ->
606 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
608 tcMonoExpr (PArrSeqIn _) _
609 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
610 -- the parser shouldn't have generated it and the renamer shouldn't have
615 %************************************************************************
619 %************************************************************************
622 #ifdef GHCI /* Only if bootstrapped */
623 -- Rename excludes these cases otherwise
625 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
627 tcMonoExpr (HsBracket brack loc) res_ty
629 getStage `thenM` \ level ->
630 case bracketOK level of {
631 Nothing -> failWithTc (illegalBracket level) ;
634 -- Typecheck expr to make sure it is valid,
635 -- but throw away the results. We'll type check
636 -- it again when we actually use it.
637 newMutVar [] `thenM` \ pending_splices ->
638 getLIEVar `thenM` \ lie_var ->
640 setStage (Brack next_level pending_splices lie_var) (
641 getLIE (tcBracket brack)
642 ) `thenM` \ (meta_ty, lie) ->
643 tcSimplifyBracket lie `thenM_`
645 unifyTauTy res_ty meta_ty `thenM_`
647 -- Return the original expression, not the type-decorated one
648 readMutVar pending_splices `thenM` \ pendings ->
649 returnM (HsBracketOut brack pendings)
652 tcMonoExpr (HsReify (Reify flavour name)) res_ty
653 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
654 tcMetaTy tycon_name `thenM` \ reify_ty ->
655 unifyTauTy res_ty reify_ty `thenM_`
656 returnM (HsReify (ReifyOut flavour name))
658 tycon_name = case flavour of
659 ReifyDecl -> DsMeta.decTyConName
660 ReifyType -> DsMeta.typTyConName
661 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
665 %************************************************************************
667 \subsection{Implicit Parameter bindings}
669 %************************************************************************
672 tcMonoExpr (HsWith expr binds is_with) res_ty
673 = getLIE (tcMonoExpr expr res_ty) `thenM` \ (expr', expr_lie) ->
674 mapAndUnzipM tc_ip_bind binds `thenM` \ (avail_ips, binds') ->
676 -- If the binding binds ?x = E, we must now
677 -- discharge any ?x constraints in expr_lie
678 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
680 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
682 returnM (HsWith expr'' binds' is_with)
684 tc_ip_bind (ip, expr)
685 = newTyVarTy openTypeKind `thenM` \ ty ->
686 getSrcLocM `thenM` \ loc ->
687 newIPDict (IPBind ip) ip ty `thenM` \ (ip', ip_inst) ->
688 tcMonoExpr expr ty `thenM` \ expr' ->
689 returnM (ip_inst, (ip', expr'))
693 %************************************************************************
697 %************************************************************************
700 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
704 %************************************************************************
706 \subsection{@tcApp@ typchecks an application}
708 %************************************************************************
712 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
713 -> TcType -- Expected result type of application
714 -> TcM TcExpr -- Translated fun and args
716 tcApp (HsApp e1 e2) args res_ty
717 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
719 tcApp fun args res_ty
720 = -- First type-check the function
721 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
723 addErrCtxt (wrongArgsCtxt "too many" fun args) (
724 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
725 split_fun_ty fun_ty (length args)
726 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
728 -- Now typecheck the args
730 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
732 -- Unify with expected result after type-checking the args
733 -- so that the info from args percolates to actual_result_ty.
734 -- This is when we might detect a too-few args situation.
735 -- (One can think of cases when the opposite order would give
736 -- a better error message.)
737 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
738 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
740 returnM (co_fn <$> foldl HsApp fun' args')
743 -- If an error happens we try to figure out whether the
744 -- function has been given too many or too few arguments,
746 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
747 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
748 zonkTcType actual_res_ty `thenM` \ act_ty' ->
750 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
751 (env2, act_ty'') = tidyOpenType env1 act_ty'
752 (exp_args, _) = tcSplitFunTys exp_ty''
753 (act_args, _) = tcSplitFunTys act_ty''
755 len_act_args = length act_args
756 len_exp_args = length exp_args
758 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
759 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
760 | otherwise = appCtxt fun args
762 returnM (env2, message)
765 split_fun_ty :: TcType -- The type of the function
766 -> Int -- Number of arguments
767 -> TcM ([TcType], -- Function argument types
768 TcType) -- Function result types
770 split_fun_ty fun_ty 0
771 = returnM ([], fun_ty)
773 split_fun_ty fun_ty n
774 = -- Expect the function to have type A->B
775 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
776 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
777 returnM (arg_ty:arg_tys, final_res_ty)
781 tcArg :: RenamedHsExpr -- The function (for error messages)
782 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
783 -> TcM TcExpr -- Resulting argument and LIE
785 tcArg the_fun (arg, expected_arg_ty, arg_no)
786 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
787 tcExpr arg expected_arg_ty
791 %************************************************************************
793 \subsection{@tcId@ typchecks an identifier occurrence}
795 %************************************************************************
797 tcId instantiates an occurrence of an Id.
798 The instantiate_it loop runs round instantiating the Id.
799 It has to be a loop because we are now prepared to entertain
801 f:: forall a. Eq a => forall b. Baz b => tau
802 We want to instantiate this to
803 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
805 The -fno-method-sharing flag controls what happens so far as the LIE
806 is concerned. The default case is that for an overloaded function we
807 generate a "method" Id, and add the Method Inst to the LIE. So you get
810 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
811 If you specify -fno-method-sharing, the dictionary application
812 isn't shared, so we get
814 f = /\a (d:Num a) (x:a) -> (+) a d x x
815 This gets a bit less sharing, but
816 a) it's better for RULEs involving overloaded functions
817 b) perhaps fewer separated lambdas
820 tcId :: Name -> TcM (TcExpr, TcType)
821 tcId name -- Look up the Id and instantiate its type
822 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
824 -- Check for cross-stage lifting
826 getStage `thenM` \ use_stage ->
828 Brack use_lvl ps_var lie_var
829 | use_lvl > bind_lvl && not (isExternalName name)
830 -> -- E.g. \x -> [| h x |]
831 -- We must behave as if the reference to x was
833 -- We use 'x' itself as the splice proxy, used by
834 -- the desugarer to stitch it all back together
835 -- NB: isExernalName is true of top level things,
836 -- and false of nested bindings
841 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
842 -- If x is polymorphic, its occurrence sites might
843 -- have different instantiations, so we can't use plain
844 -- 'x' as the splice proxy name. I don't know how to
845 -- solve this, and it's probably unimportant, so I'm
846 -- just going to flag an error for now
849 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
850 -- Put the 'lift' constraint into the right LIE
852 -- Update the pending splices
853 readMutVar ps_var `thenM` \ ps ->
854 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
856 returnM (HsVar id, id_ty))
860 use_lvl = metaLevel use_stage
862 checkTc (wellStaged bind_lvl use_lvl)
863 (badStageErr id bind_lvl use_lvl) `thenM_`
865 -- This is the bit that handles the no-Template-Haskell case
866 case isDataConWrapId_maybe id of
867 Nothing -> loop (HsVar id) (idType id)
868 Just data_con -> inst_data_con id data_con
871 orig = OccurrenceOf name
873 loop (HsVar fun_id) fun_ty
874 | want_method_inst fun_ty
875 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
876 newMethodWithGivenTy orig fun_id
877 (mkTyVarTys tyvars) theta tau `thenM` \ meth ->
878 loop (HsVar (instToId meth)) tau
882 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
883 loop (inst_fn fun) tau
886 = returnM (fun, fun_ty)
888 want_method_inst fun_ty
889 | opt_NoMethodSharing = False
890 | otherwise = case tcSplitSigmaTy fun_ty of
891 (_,[],_) -> False -- Not overloaded
892 (_,theta,_) -> not (any isLinearPred theta)
893 -- This is a slight hack.
894 -- If f :: (%x :: T) => Int -> Int
895 -- Then if we have two separate calls, (f 3, f 4), we cannot
896 -- make a method constraint that then gets shared, thus:
897 -- let m = f %x in (m 3, m 4)
898 -- because that loses the linearity of the constraint.
899 -- The simplest thing to do is never to construct a method constraint
900 -- in the first place that has a linear implicit parameter in it.
902 -- We treat data constructors differently, because we have to generate
903 -- constraints for their silly theta, which no longer appears in
904 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
905 inst_data_con id data_con
906 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
907 extendLIEs ex_dicts `thenM_`
908 returnM (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) (map instToId ex_dicts),
909 mkFunTys arg_tys result_ty)
912 Typecheck expression which in most cases will be an Id.
913 The expression can return a higher-ranked type, such as
914 (forall a. a->a) -> Int
915 so we must create a HoleTyVarTy to pass in as the expected tyvar.
918 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
919 tcExpr_id (HsVar name) = tcId name
920 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
921 tcMonoExpr expr id_ty `thenM` \ expr' ->
922 readHoleResult id_ty `thenM` \ id_ty' ->
923 returnM (expr', id_ty')
927 %************************************************************************
929 \subsection{Record bindings}
931 %************************************************************************
933 Game plan for record bindings
934 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
935 1. Find the TyCon for the bindings, from the first field label.
937 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
939 For each binding field = value
941 3. Instantiate the field type (from the field label) using the type
944 4 Type check the value using tcArg, passing the field type as
945 the expected argument type.
947 This extends OK when the field types are universally quantified.
952 :: TyCon -- Type constructor for the record
953 -> [TcType] -- Args of this type constructor
954 -> RenamedRecordBinds
957 tcRecordBinds tycon ty_args rbinds
958 = mappM do_bind rbinds
960 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
962 do_bind (field_lbl_name, rhs)
963 = addErrCtxt (fieldCtxt field_lbl_name) $
964 tcLookupId field_lbl_name `thenM` \ sel_id ->
966 field_lbl = recordSelectorFieldLabel sel_id
967 field_ty = substTy tenv (fieldLabelType field_lbl)
969 ASSERT( isRecordSelector sel_id )
970 -- This lookup and assertion will surely succeed, because
971 -- we check that the fields are indeed record selectors
972 -- before calling tcRecordBinds
973 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
974 -- The caller of tcRecordBinds has already checked
975 -- that all the fields come from the same type
977 tcExpr rhs field_ty `thenM` \ rhs' ->
979 returnM (sel_id, rhs')
981 badFields rbinds data_con
982 = filter (not . (`elem` field_names)) (recBindFields rbinds)
984 field_names = map fieldLabelName (dataConFieldLabels data_con)
986 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
987 checkMissingFields data_con rbinds
988 | null field_labels -- Not declared as a record;
989 -- But C{} is still valid if no strict fields
990 = if any isMarkedStrict field_strs then
991 -- Illegal if any arg is strict
992 addErrTc (missingStrictFields data_con [])
996 | otherwise -- A record
997 = checkM (null missing_s_fields)
998 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1000 doptM Opt_WarnMissingFields `thenM` \ warn ->
1001 checkM (not (warn && notNull missing_ns_fields))
1002 (warnTc True (missingFields data_con missing_ns_fields))
1006 = [ fl | (fl, str) <- field_info,
1008 not (fieldLabelName fl `elem` field_names_used)
1011 = [ fl | (fl, str) <- field_info,
1012 not (isMarkedStrict str),
1013 not (fieldLabelName fl `elem` field_names_used)
1016 field_names_used = recBindFields rbinds
1017 field_labels = dataConFieldLabels data_con
1019 field_info = zipEqual "missingFields"
1023 field_strs = dropList ex_theta (dataConStrictMarks data_con)
1024 -- The 'drop' is because dataConStrictMarks
1025 -- includes the existential dictionaries
1026 (_, _, _, ex_theta, _, _) = dataConSig data_con
1029 %************************************************************************
1031 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1033 %************************************************************************
1036 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1038 tcMonoExprs [] [] = returnM []
1039 tcMonoExprs (expr:exprs) (ty:tys)
1040 = tcMonoExpr expr ty `thenM` \ expr' ->
1041 tcMonoExprs exprs tys `thenM` \ exprs' ->
1042 returnM (expr':exprs')
1046 %************************************************************************
1048 \subsection{Literals}
1050 %************************************************************************
1052 Overloaded literals.
1055 tcLit :: HsLit -> TcType -> TcM TcExpr
1056 tcLit (HsLitLit s _) res_ty
1057 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1058 newDicts (LitLitOrigin (unpackFS s))
1059 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1060 extendLIEs dicts `thenM_`
1061 returnM (HsLit (HsLitLit s res_ty))
1064 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1069 %************************************************************************
1071 \subsection{Errors and contexts}
1073 %************************************************************************
1075 Boring and alphabetical:
1078 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1081 badStageErr id bind_lvl use_lvl
1082 = ptext SLIT("Stage error:") <+> quotes (ppr id) <+>
1083 hsep [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
1084 ptext SLIT("but used at stage") <+> ppr use_lvl]
1087 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1090 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1093 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1096 = hang (ptext SLIT("When checking the type signature of the expression:"))
1100 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1102 fieldCtxt field_name
1103 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1105 funAppCtxt fun arg arg_no
1106 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1107 quotes (ppr fun) <> text ", namely"])
1108 4 (quotes (ppr arg))
1111 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1114 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1117 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1119 illegalBracket level
1120 = ptext SLIT("Illegal bracket at level") <+> ppr level
1123 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1125 the_app = foldl HsApp fun args -- Used in error messages
1127 lurkingRank2Err fun fun_ty
1128 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1129 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1130 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1133 = hang (ptext SLIT("No constructor has all these fields:"))
1134 4 (pprQuotedList (recBindFields rbinds))
1136 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1137 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1140 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1142 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1143 missingStrictFields con fields
1146 rest | null fields = empty -- Happens for non-record constructors
1147 -- with strict fields
1148 | otherwise = colon <+> pprWithCommas ppr fields
1150 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1151 ptext SLIT("does not have the required strict field(s)")
1154 missingFields :: DataCon -> [FieldLabel] -> SDoc
1155 missingFields con fields
1156 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1157 <+> pprWithCommas ppr fields
1159 polySpliceErr :: Id -> SDoc
1161 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1163 wrongArgsCtxt too_many_or_few fun args
1164 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1165 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1166 <+> ptext SLIT("arguments in the call"))
1167 4 (parens (ppr the_app))
1169 the_app = foldl HsApp fun args -- Used in error messages