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 tcLookupGlobal name `thenM` \ thing ->
655 -- For now, we can only reify top-level things
656 -- The complication for non-top-level things is just that
657 -- they might be a TcId, and need zonking etc.
659 tcMetaTy tycon_name `thenM` \ reify_ty ->
660 unifyTauTy res_ty reify_ty `thenM_`
662 returnM (HsReify (ReifyOut flavour thing))
664 tycon_name = case flavour of
665 ReifyDecl -> DsMeta.decTyConName
666 ReifyType -> DsMeta.typTyConName
667 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
671 %************************************************************************
673 \subsection{Implicit Parameter bindings}
675 %************************************************************************
678 tcMonoExpr (HsWith expr binds is_with) res_ty
679 = getLIE (tcMonoExpr expr res_ty) `thenM` \ (expr', expr_lie) ->
680 mapAndUnzipM tc_ip_bind binds `thenM` \ (avail_ips, binds') ->
682 -- If the binding binds ?x = E, we must now
683 -- discharge any ?x constraints in expr_lie
684 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
686 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
688 returnM (HsWith expr'' binds' is_with)
690 tc_ip_bind (ip, expr)
691 = newTyVarTy openTypeKind `thenM` \ ty ->
692 getSrcLocM `thenM` \ loc ->
693 newIPDict (IPBind ip) ip ty `thenM` \ (ip', ip_inst) ->
694 tcMonoExpr expr ty `thenM` \ expr' ->
695 returnM (ip_inst, (ip', expr'))
699 %************************************************************************
703 %************************************************************************
706 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
710 %************************************************************************
712 \subsection{@tcApp@ typchecks an application}
714 %************************************************************************
718 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
719 -> TcType -- Expected result type of application
720 -> TcM TcExpr -- Translated fun and args
722 tcApp (HsApp e1 e2) args res_ty
723 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
725 tcApp fun args res_ty
726 = -- First type-check the function
727 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
729 addErrCtxt (wrongArgsCtxt "too many" fun args) (
730 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
731 split_fun_ty fun_ty (length args)
732 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
734 -- Now typecheck the args
736 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
738 -- Unify with expected result after type-checking the args
739 -- so that the info from args percolates to actual_result_ty.
740 -- This is when we might detect a too-few args situation.
741 -- (One can think of cases when the opposite order would give
742 -- a better error message.)
743 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
744 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
746 returnM (co_fn <$> foldl HsApp fun' args')
749 -- If an error happens we try to figure out whether the
750 -- function has been given too many or too few arguments,
752 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
753 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
754 zonkTcType actual_res_ty `thenM` \ act_ty' ->
756 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
757 (env2, act_ty'') = tidyOpenType env1 act_ty'
758 (exp_args, _) = tcSplitFunTys exp_ty''
759 (act_args, _) = tcSplitFunTys act_ty''
761 len_act_args = length act_args
762 len_exp_args = length exp_args
764 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
765 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
766 | otherwise = appCtxt fun args
768 returnM (env2, message)
771 split_fun_ty :: TcType -- The type of the function
772 -> Int -- Number of arguments
773 -> TcM ([TcType], -- Function argument types
774 TcType) -- Function result types
776 split_fun_ty fun_ty 0
777 = returnM ([], fun_ty)
779 split_fun_ty fun_ty n
780 = -- Expect the function to have type A->B
781 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
782 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
783 returnM (arg_ty:arg_tys, final_res_ty)
787 tcArg :: RenamedHsExpr -- The function (for error messages)
788 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
789 -> TcM TcExpr -- Resulting argument and LIE
791 tcArg the_fun (arg, expected_arg_ty, arg_no)
792 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
793 tcExpr arg expected_arg_ty
797 %************************************************************************
799 \subsection{@tcId@ typchecks an identifier occurrence}
801 %************************************************************************
803 tcId instantiates an occurrence of an Id.
804 The instantiate_it loop runs round instantiating the Id.
805 It has to be a loop because we are now prepared to entertain
807 f:: forall a. Eq a => forall b. Baz b => tau
808 We want to instantiate this to
809 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
811 The -fno-method-sharing flag controls what happens so far as the LIE
812 is concerned. The default case is that for an overloaded function we
813 generate a "method" Id, and add the Method Inst to the LIE. So you get
816 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
817 If you specify -fno-method-sharing, the dictionary application
818 isn't shared, so we get
820 f = /\a (d:Num a) (x:a) -> (+) a d x x
821 This gets a bit less sharing, but
822 a) it's better for RULEs involving overloaded functions
823 b) perhaps fewer separated lambdas
826 tcId :: Name -> TcM (TcExpr, TcType)
827 tcId name -- Look up the Id and instantiate its type
828 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
830 -- Check for cross-stage lifting
832 getStage `thenM` \ use_stage ->
834 Brack use_lvl ps_var lie_var
835 | use_lvl > bind_lvl && not (isExternalName name)
836 -> -- E.g. \x -> [| h x |]
837 -- We must behave as if the reference to x was
839 -- We use 'x' itself as the splice proxy, used by
840 -- the desugarer to stitch it all back together
841 -- NB: isExernalName is true of top level things,
842 -- and false of nested bindings
847 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
848 -- If x is polymorphic, its occurrence sites might
849 -- have different instantiations, so we can't use plain
850 -- 'x' as the splice proxy name. I don't know how to
851 -- solve this, and it's probably unimportant, so I'm
852 -- just going to flag an error for now
855 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
856 -- Put the 'lift' constraint into the right LIE
858 -- Update the pending splices
859 readMutVar ps_var `thenM` \ ps ->
860 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
862 returnM (HsVar id, id_ty))
866 use_lvl = metaLevel use_stage
868 checkTc (wellStaged bind_lvl use_lvl)
869 (badStageErr id bind_lvl use_lvl) `thenM_`
871 -- This is the bit that handles the no-Template-Haskell case
872 case isDataConWrapId_maybe id of
873 Nothing -> loop (HsVar id) (idType id)
874 Just data_con -> inst_data_con id data_con
877 orig = OccurrenceOf name
879 loop (HsVar fun_id) fun_ty
880 | want_method_inst fun_ty
881 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
882 newMethodWithGivenTy orig fun_id
883 (mkTyVarTys tyvars) theta tau `thenM` \ meth ->
884 loop (HsVar (instToId meth)) tau
888 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
889 loop (inst_fn fun) tau
892 = returnM (fun, fun_ty)
894 want_method_inst fun_ty
895 | opt_NoMethodSharing = False
896 | otherwise = case tcSplitSigmaTy fun_ty of
897 (_,[],_) -> False -- Not overloaded
898 (_,theta,_) -> not (any isLinearPred theta)
899 -- This is a slight hack.
900 -- If f :: (%x :: T) => Int -> Int
901 -- Then if we have two separate calls, (f 3, f 4), we cannot
902 -- make a method constraint that then gets shared, thus:
903 -- let m = f %x in (m 3, m 4)
904 -- because that loses the linearity of the constraint.
905 -- The simplest thing to do is never to construct a method constraint
906 -- in the first place that has a linear implicit parameter in it.
908 -- We treat data constructors differently, because we have to generate
909 -- constraints for their silly theta, which no longer appears in
910 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
911 inst_data_con id data_con
912 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
913 extendLIEs ex_dicts `thenM_`
914 returnM (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) (map instToId ex_dicts),
915 mkFunTys arg_tys result_ty)
918 Typecheck expression which in most cases will be an Id.
919 The expression can return a higher-ranked type, such as
920 (forall a. a->a) -> Int
921 so we must create a HoleTyVarTy to pass in as the expected tyvar.
924 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
925 tcExpr_id (HsVar name) = tcId name
926 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
927 tcMonoExpr expr id_ty `thenM` \ expr' ->
928 readHoleResult id_ty `thenM` \ id_ty' ->
929 returnM (expr', id_ty')
933 %************************************************************************
935 \subsection{Record bindings}
937 %************************************************************************
939 Game plan for record bindings
940 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
941 1. Find the TyCon for the bindings, from the first field label.
943 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
945 For each binding field = value
947 3. Instantiate the field type (from the field label) using the type
950 4 Type check the value using tcArg, passing the field type as
951 the expected argument type.
953 This extends OK when the field types are universally quantified.
958 :: TyCon -- Type constructor for the record
959 -> [TcType] -- Args of this type constructor
960 -> RenamedRecordBinds
963 tcRecordBinds tycon ty_args rbinds
964 = mappM do_bind rbinds
966 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
968 do_bind (field_lbl_name, rhs)
969 = addErrCtxt (fieldCtxt field_lbl_name) $
970 tcLookupId field_lbl_name `thenM` \ sel_id ->
972 field_lbl = recordSelectorFieldLabel sel_id
973 field_ty = substTy tenv (fieldLabelType field_lbl)
975 ASSERT( isRecordSelector sel_id )
976 -- This lookup and assertion will surely succeed, because
977 -- we check that the fields are indeed record selectors
978 -- before calling tcRecordBinds
979 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
980 -- The caller of tcRecordBinds has already checked
981 -- that all the fields come from the same type
983 tcExpr rhs field_ty `thenM` \ rhs' ->
985 returnM (sel_id, rhs')
987 badFields rbinds data_con
988 = filter (not . (`elem` field_names)) (recBindFields rbinds)
990 field_names = map fieldLabelName (dataConFieldLabels data_con)
992 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
993 checkMissingFields data_con rbinds
994 | null field_labels -- Not declared as a record;
995 -- But C{} is still valid if no strict fields
996 = if any isMarkedStrict field_strs then
997 -- Illegal if any arg is strict
998 addErrTc (missingStrictFields data_con [])
1002 | otherwise -- A record
1003 = checkM (null missing_s_fields)
1004 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
1006 doptM Opt_WarnMissingFields `thenM` \ warn ->
1007 checkM (not (warn && notNull missing_ns_fields))
1008 (warnTc True (missingFields data_con missing_ns_fields))
1012 = [ fl | (fl, str) <- field_info,
1014 not (fieldLabelName fl `elem` field_names_used)
1017 = [ fl | (fl, str) <- field_info,
1018 not (isMarkedStrict str),
1019 not (fieldLabelName fl `elem` field_names_used)
1022 field_names_used = recBindFields rbinds
1023 field_labels = dataConFieldLabels data_con
1025 field_info = zipEqual "missingFields"
1029 field_strs = dropList ex_theta (dataConStrictMarks data_con)
1030 -- The 'drop' is because dataConStrictMarks
1031 -- includes the existential dictionaries
1032 (_, _, _, ex_theta, _, _) = dataConSig data_con
1035 %************************************************************************
1037 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1039 %************************************************************************
1042 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1044 tcMonoExprs [] [] = returnM []
1045 tcMonoExprs (expr:exprs) (ty:tys)
1046 = tcMonoExpr expr ty `thenM` \ expr' ->
1047 tcMonoExprs exprs tys `thenM` \ exprs' ->
1048 returnM (expr':exprs')
1052 %************************************************************************
1054 \subsection{Literals}
1056 %************************************************************************
1058 Overloaded literals.
1061 tcLit :: HsLit -> TcType -> TcM TcExpr
1062 tcLit (HsLitLit s _) res_ty
1063 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1064 newDicts (LitLitOrigin (unpackFS s))
1065 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1066 extendLIEs dicts `thenM_`
1067 returnM (HsLit (HsLitLit s res_ty))
1070 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1075 %************************************************************************
1077 \subsection{Errors and contexts}
1079 %************************************************************************
1081 Boring and alphabetical:
1084 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1087 badStageErr id bind_lvl use_lvl
1088 = ptext SLIT("Stage error:") <+> quotes (ppr id) <+>
1089 hsep [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
1090 ptext SLIT("but used at stage") <+> ppr use_lvl]
1093 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1096 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1099 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1102 = hang (ptext SLIT("When checking the type signature of the expression:"))
1106 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1108 fieldCtxt field_name
1109 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1111 funAppCtxt fun arg arg_no
1112 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1113 quotes (ppr fun) <> text ", namely"])
1114 4 (quotes (ppr arg))
1117 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1120 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1123 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1125 illegalBracket level
1126 = ptext SLIT("Illegal bracket at level") <+> ppr level
1129 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1131 the_app = foldl HsApp fun args -- Used in error messages
1133 lurkingRank2Err fun fun_ty
1134 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1135 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1136 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1139 = hang (ptext SLIT("No constructor has all these fields:"))
1140 4 (pprQuotedList (recBindFields rbinds))
1142 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1143 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1146 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1148 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1149 missingStrictFields con fields
1152 rest | null fields = empty -- Happens for non-record constructors
1153 -- with strict fields
1154 | otherwise = colon <+> pprWithCommas ppr fields
1156 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1157 ptext SLIT("does not have the required strict field(s)")
1160 missingFields :: DataCon -> [FieldLabel] -> SDoc
1161 missingFields con fields
1162 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1163 <+> pprWithCommas ppr fields
1165 polySpliceErr :: Id -> SDoc
1167 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1169 wrongArgsCtxt too_many_or_few fun args
1170 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1171 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1172 <+> ptext SLIT("arguments in the call"))
1173 4 (parens (ppr the_app))
1175 the_app = foldl HsApp fun args -- Used in error messages