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 TcEnv ( bracketOK )
14 import TcSimplify ( tcSimplifyBracket )
15 import DsMeta ( liftName )
18 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..),
19 mkMonoBind, recBindFields
21 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
22 import TcHsSyn ( TcExpr, TcRecordBinds, hsLitType, mkHsDictApp, mkHsTyApp, mkHsLet )
24 import TcUnify ( tcSubExp, tcGen, (<$>),
25 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
27 import BasicTypes ( RecFlag(..), isMarkedStrict )
28 import Inst ( InstOrigin(..),
29 newOverloadedLit, newMethodFromName, newIPDict,
30 newDicts, newMethodWithGivenTy,
31 instToId, tcInstCall, tcInstDataCon
33 import TcBinds ( tcBindsAndThen )
34 import TcEnv ( tcLookupClass, tcLookupGlobal_maybe, tcLookupIdLvl,
35 tcLookupTyCon, tcLookupDataCon, tcLookupId,
38 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts )
39 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
40 import TcPat ( badFieldCon )
41 import TcSimplify ( tcSimplifyIPs )
42 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
43 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
44 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
45 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
46 isSigmaTy, isTauTy, mkFunTy, mkFunTys,
47 mkTyConApp, mkClassPred, tcFunArgTy,
48 tyVarsOfTypes, isLinearPred,
49 liftedTypeKind, openTypeKind,
50 tcSplitSigmaTy, tcTyConAppTyCon,
53 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
54 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector, isDataConWrapId_maybe )
55 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks )
56 import Name ( Name, isExternalName )
57 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
58 import Subst ( mkTopTyVarSubst, substTheta, substTy )
59 import VarSet ( emptyVarSet, elemVarSet )
60 import TysWiredIn ( boolTy )
61 import PrelNames ( cCallableClassName, cReturnableClassName,
62 enumFromName, enumFromThenName,
63 enumFromToName, enumFromThenToName,
64 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) res_ty = tcSpliceExpr n expr res_ty
627 tcMonoExpr (HsBracket brack) res_ty
628 = getStage `thenM` \ level ->
629 case bracketOK level of {
630 Nothing -> failWithTc (illegalBracket level) ;
633 -- Typecheck expr to make sure it is valid,
634 -- but throw away the results. We'll type check
635 -- it again when we actually use it.
636 newMutVar [] `thenM` \ pending_splices ->
637 getLIEVar `thenM` \ lie_var ->
639 setStage (Brack next_level pending_splices lie_var) (
640 getLIE (tcBracket brack)
641 ) `thenM` \ (meta_ty, lie) ->
642 tcSimplifyBracket lie `thenM_`
644 unifyTauTy res_ty meta_ty `thenM_`
646 -- Return the original expression, not the type-decorated one
647 readMutVar pending_splices `thenM` \ pendings ->
648 returnM (HsBracketOut brack pendings)
653 %************************************************************************
655 \subsection{Implicit Parameter bindings}
657 %************************************************************************
660 tcMonoExpr (HsWith expr binds is_with) res_ty
661 = getLIE (tcMonoExpr expr res_ty) `thenM` \ (expr', expr_lie) ->
662 mapAndUnzipM tc_ip_bind binds `thenM` \ (avail_ips, binds') ->
664 -- If the binding binds ?x = E, we must now
665 -- discharge any ?x constraints in expr_lie
666 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
668 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
670 returnM (HsWith expr'' binds' is_with)
672 tc_ip_bind (ip, expr)
673 = newTyVarTy openTypeKind `thenM` \ ty ->
674 getSrcLocM `thenM` \ loc ->
675 newIPDict (IPBind ip) ip ty `thenM` \ (ip', ip_inst) ->
676 tcMonoExpr expr ty `thenM` \ expr' ->
677 returnM (ip_inst, (ip', expr'))
681 %************************************************************************
685 %************************************************************************
688 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
692 %************************************************************************
694 \subsection{@tcApp@ typchecks an application}
696 %************************************************************************
700 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
701 -> TcType -- Expected result type of application
702 -> TcM TcExpr -- Translated fun and args
704 tcApp (HsApp e1 e2) args res_ty
705 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
707 tcApp fun args res_ty
708 = -- First type-check the function
709 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
711 addErrCtxt (wrongArgsCtxt "too many" fun args) (
712 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
713 split_fun_ty fun_ty (length args)
714 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
716 -- Now typecheck the args
718 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
720 -- Unify with expected result after type-checking the args
721 -- so that the info from args percolates to actual_result_ty.
722 -- This is when we might detect a too-few args situation.
723 -- (One can think of cases when the opposite order would give
724 -- a better error message.)
725 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
726 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
728 returnM (co_fn <$> foldl HsApp fun' args')
731 -- If an error happens we try to figure out whether the
732 -- function has been given too many or too few arguments,
734 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
735 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
736 zonkTcType actual_res_ty `thenM` \ act_ty' ->
738 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
739 (env2, act_ty'') = tidyOpenType env1 act_ty'
740 (exp_args, _) = tcSplitFunTys exp_ty''
741 (act_args, _) = tcSplitFunTys act_ty''
743 len_act_args = length act_args
744 len_exp_args = length exp_args
746 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
747 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
748 | otherwise = appCtxt fun args
750 returnM (env2, message)
753 split_fun_ty :: TcType -- The type of the function
754 -> Int -- Number of arguments
755 -> TcM ([TcType], -- Function argument types
756 TcType) -- Function result types
758 split_fun_ty fun_ty 0
759 = returnM ([], fun_ty)
761 split_fun_ty fun_ty n
762 = -- Expect the function to have type A->B
763 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
764 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
765 returnM (arg_ty:arg_tys, final_res_ty)
769 tcArg :: RenamedHsExpr -- The function (for error messages)
770 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
771 -> TcM TcExpr -- Resulting argument and LIE
773 tcArg the_fun (arg, expected_arg_ty, arg_no)
774 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
775 tcExpr arg expected_arg_ty
779 %************************************************************************
781 \subsection{@tcId@ typchecks an identifier occurrence}
783 %************************************************************************
785 tcId instantiates an occurrence of an Id.
786 The instantiate_it loop runs round instantiating the Id.
787 It has to be a loop because we are now prepared to entertain
789 f:: forall a. Eq a => forall b. Baz b => tau
790 We want to instantiate this to
791 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
793 The -fno-method-sharing flag controls what happens so far as the LIE
794 is concerned. The default case is that for an overloaded function we
795 generate a "method" Id, and add the Method Inst to the LIE. So you get
798 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
799 If you specify -fno-method-sharing, the dictionary application
800 isn't shared, so we get
802 f = /\a (d:Num a) (x:a) -> (+) a d x x
803 This gets a bit less sharing, but
804 a) it's better for RULEs involving overloaded functions
805 b) perhaps fewer separated lambdas
808 tcId :: Name -> TcM (TcExpr, TcType)
809 tcId name -- Look up the Id and instantiate its type
810 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
812 -- Check for cross-stage lifting
814 getStage `thenM` \ use_stage ->
816 Brack use_lvl ps_var lie_var
817 | use_lvl > bind_lvl && not (isExternalName name)
818 -> -- E.g. \x -> [| h x |]
819 -- We must behave as if the reference to x was
821 -- We use 'x' itself as the splice proxy, used by
822 -- the desugarer to stitch it all back together
823 -- NB: isExernalName is true of top level things,
824 -- and false of nested bindings
829 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
830 -- If x is polymorphic, its occurrence sites might
831 -- have different instantiations, so we can't use plain
832 -- 'x' as the splice proxy name. I don't know how to
833 -- solve this, and it's probably unimportant, so I'm
834 -- just going to flag an error for now
837 newMethodFromName orig id_ty liftName `thenM` \ lift ->
838 -- Put the 'lift' constraint into the right LIE
840 -- Update the pending splices
841 readMutVar ps_var `thenM` \ ps ->
842 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
844 returnM (HsVar id, id_ty))
848 use_lvl = metaLevel use_stage
850 checkTc (wellStaged bind_lvl use_lvl)
851 (badStageErr id bind_lvl use_lvl) `thenM_`
853 -- This is the bit that handles the no-Template-Haskell case
854 case isDataConWrapId_maybe id of
855 Nothing -> loop (HsVar id) (idType id)
856 Just data_con -> inst_data_con id data_con
859 orig = OccurrenceOf name
861 loop (HsVar fun_id) fun_ty
862 | want_method_inst fun_ty
863 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
864 newMethodWithGivenTy orig fun_id
865 (mkTyVarTys tyvars) theta tau `thenM` \ meth ->
866 loop (HsVar (instToId meth)) tau
870 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
871 loop (inst_fn fun) tau
874 = returnM (fun, fun_ty)
876 want_method_inst fun_ty
877 | opt_NoMethodSharing = False
878 | otherwise = case tcSplitSigmaTy fun_ty of
879 (_,[],_) -> False -- Not overloaded
880 (_,theta,_) -> not (any isLinearPred theta)
881 -- This is a slight hack.
882 -- If f :: (%x :: T) => Int -> Int
883 -- Then if we have two separate calls, (f 3, f 4), we cannot
884 -- make a method constraint that then gets shared, thus:
885 -- let m = f %x in (m 3, m 4)
886 -- because that loses the linearity of the constraint.
887 -- The simplest thing to do is never to construct a method constraint
888 -- in the first place that has a linear implicit parameter in it.
890 -- We treat data constructors differently, because we have to generate
891 -- constraints for their silly theta, which no longer appears in
892 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
893 inst_data_con id data_con
894 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
895 extendLIEs ex_dicts `thenM_`
896 returnM (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) (map instToId ex_dicts),
897 mkFunTys arg_tys result_ty)
900 Typecheck expression which in most cases will be an Id.
901 The expression can return a higher-ranked type, such as
902 (forall a. a->a) -> Int
903 so we must create a HoleTyVarTy to pass in as the expected tyvar.
906 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
907 tcExpr_id (HsVar name) = tcId name
908 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
909 tcMonoExpr expr id_ty `thenM` \ expr' ->
910 readHoleResult id_ty `thenM` \ id_ty' ->
911 returnM (expr', id_ty')
915 %************************************************************************
917 \subsection{Record bindings}
919 %************************************************************************
921 Game plan for record bindings
922 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
923 1. Find the TyCon for the bindings, from the first field label.
925 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
927 For each binding field = value
929 3. Instantiate the field type (from the field label) using the type
932 4 Type check the value using tcArg, passing the field type as
933 the expected argument type.
935 This extends OK when the field types are universally quantified.
940 :: TyCon -- Type constructor for the record
941 -> [TcType] -- Args of this type constructor
942 -> RenamedRecordBinds
945 tcRecordBinds tycon ty_args rbinds
946 = mappM do_bind rbinds
948 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
950 do_bind (field_lbl_name, rhs)
951 = addErrCtxt (fieldCtxt field_lbl_name) $
952 tcLookupId field_lbl_name `thenM` \ sel_id ->
954 field_lbl = recordSelectorFieldLabel sel_id
955 field_ty = substTy tenv (fieldLabelType field_lbl)
957 ASSERT( isRecordSelector sel_id )
958 -- This lookup and assertion will surely succeed, because
959 -- we check that the fields are indeed record selectors
960 -- before calling tcRecordBinds
961 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
962 -- The caller of tcRecordBinds has already checked
963 -- that all the fields come from the same type
965 tcExpr rhs field_ty `thenM` \ rhs' ->
967 returnM (sel_id, rhs')
969 badFields rbinds data_con
970 = filter (not . (`elem` field_names)) (recBindFields rbinds)
972 field_names = map fieldLabelName (dataConFieldLabels data_con)
974 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
975 checkMissingFields data_con rbinds
976 | null field_labels -- Not declared as a record;
977 -- But C{} is still valid if no strict fields
978 = if any isMarkedStrict field_strs then
979 -- Illegal if any arg is strict
980 addErrTc (missingStrictFields data_con [])
984 | otherwise -- A record
985 = checkM (null missing_s_fields)
986 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
988 doptM Opt_WarnMissingFields `thenM` \ warn ->
989 checkM (not (warn && notNull missing_ns_fields))
990 (warnTc True (missingFields data_con missing_ns_fields))
994 = [ fl | (fl, str) <- field_info,
996 not (fieldLabelName fl `elem` field_names_used)
999 = [ fl | (fl, str) <- field_info,
1000 not (isMarkedStrict str),
1001 not (fieldLabelName fl `elem` field_names_used)
1004 field_names_used = recBindFields rbinds
1005 field_labels = dataConFieldLabels data_con
1007 field_info = zipEqual "missingFields"
1011 field_strs = dropList ex_theta (dataConStrictMarks data_con)
1012 -- The 'drop' is because dataConStrictMarks
1013 -- includes the existential dictionaries
1014 (_, _, _, ex_theta, _, _) = dataConSig data_con
1017 %************************************************************************
1019 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1021 %************************************************************************
1024 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1026 tcMonoExprs [] [] = returnM []
1027 tcMonoExprs (expr:exprs) (ty:tys)
1028 = tcMonoExpr expr ty `thenM` \ expr' ->
1029 tcMonoExprs exprs tys `thenM` \ exprs' ->
1030 returnM (expr':exprs')
1034 %************************************************************************
1036 \subsection{Literals}
1038 %************************************************************************
1040 Overloaded literals.
1043 tcLit :: HsLit -> TcType -> TcM TcExpr
1044 tcLit (HsLitLit s _) res_ty
1045 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1046 newDicts (LitLitOrigin (unpackFS s))
1047 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1048 extendLIEs dicts `thenM_`
1049 returnM (HsLit (HsLitLit s res_ty))
1052 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1057 %************************************************************************
1059 \subsection{Errors and contexts}
1061 %************************************************************************
1063 Boring and alphabetical:
1066 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1069 badStageErr id bind_lvl use_lvl
1070 = ptext SLIT("Stage error:") <+> quotes (ppr id) <+>
1071 hsep [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
1072 ptext SLIT("but used at stage") <+> ppr use_lvl]
1075 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1078 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1081 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1084 = hang (ptext SLIT("When checking the type signature of the expression:"))
1088 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1090 fieldCtxt field_name
1091 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1093 funAppCtxt fun arg arg_no
1094 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1095 quotes (ppr fun) <> text ", namely"])
1096 4 (quotes (ppr arg))
1099 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1102 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1105 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1107 illegalBracket level
1108 = ptext SLIT("Illegal bracket at level") <+> ppr level
1111 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1113 the_app = foldl HsApp fun args -- Used in error messages
1115 lurkingRank2Err fun fun_ty
1116 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1117 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1118 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1121 = hang (ptext SLIT("No constructor has all these fields:"))
1122 4 (pprQuotedList (recBindFields rbinds))
1124 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1125 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1128 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1130 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1131 missingStrictFields con fields
1134 rest | null fields = empty -- Happens for non-record constructors
1135 -- with strict fields
1136 | otherwise = colon <+> pprWithCommas ppr fields
1138 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1139 ptext SLIT("does not have the required strict field(s)")
1142 missingFields :: DataCon -> [FieldLabel] -> SDoc
1143 missingFields con fields
1144 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1145 <+> pprWithCommas ppr fields
1147 polySpliceErr :: Id -> SDoc
1149 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1151 wrongArgsCtxt too_many_or_few fun args
1152 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1153 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1154 <+> ptext SLIT("arguments in the call"))
1155 4 (parens (ppr the_app))
1157 the_app = foldl HsApp fun args -- Used in error messages