2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcExpr_id, tcMonoExpr ) where
9 #include "HsVersions.h"
11 #ifdef GHCI /* Only if bootstrapped */
12 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
13 import HsSyn ( HsReify(..), ReifyFlavour(..) )
14 import TcType ( isTauTy )
15 import TcEnv ( bracketOK, tcMetaTy, checkWellStaged, metaLevel )
16 import TcSimplify ( tcSimplifyBracket )
17 import Name ( isExternalName )
18 import qualified DsMeta
21 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..), 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 ( 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
38 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts )
39 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
40 import TcPat ( badFieldCon )
41 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
42 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
43 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
44 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
45 isSigmaTy, mkFunTy, mkFunTys,
46 mkTyConApp, mkClassPred, tcFunArgTy,
47 tyVarsOfTypes, isLinearPred,
48 liftedTypeKind, openTypeKind,
49 tcSplitSigmaTy, tcTyConAppTyCon,
52 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
53 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector, isDataConWrapId_maybe )
54 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks )
56 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
57 import Subst ( mkTopTyVarSubst, substTheta, substTy )
58 import VarSet ( emptyVarSet, elemVarSet )
59 import TysWiredIn ( boolTy )
60 import PrelNames ( cCallableClassName, cReturnableClassName,
61 enumFromName, enumFromThenName,
62 enumFromToName, enumFromThenToName,
63 enumFromToPName, enumFromThenToPName,
66 import ListSetOps ( minusList )
68 import HscTypes ( TyThing(..) )
75 %************************************************************************
77 \subsection{Main wrappers}
79 %************************************************************************
82 tcExpr :: RenamedHsExpr -- Expession to type check
83 -> TcSigmaType -- Expected type (could be a polytpye)
84 -> TcM TcExpr -- Generalised expr with expected type
86 tcExpr expr expected_ty
87 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
88 tc_expr' expr expected_ty
90 tc_expr' expr expected_ty
91 | not (isSigmaTy expected_ty) -- Monomorphic case
92 = tcMonoExpr expr expected_ty
95 = tcGen expected_ty emptyVarSet (
97 ) `thenM` \ (gen_fn, expr') ->
98 returnM (gen_fn <$> expr')
102 %************************************************************************
104 \subsection{The TAUT rules for variables}
106 %************************************************************************
109 tcMonoExpr :: RenamedHsExpr -- Expession to type check
110 -> TcRhoType -- Expected type (could be a type variable)
111 -- Definitely no foralls at the top
115 tcMonoExpr (HsVar name) res_ty
116 = tcId name `thenM` \ (expr', id_ty) ->
117 tcSubExp res_ty id_ty `thenM` \ co_fn ->
118 returnM (co_fn <$> expr')
120 tcMonoExpr (HsIPVar ip) res_ty
121 = -- Implicit parameters must have a *tau-type* not a
122 -- type scheme. We enforce this by creating a fresh
123 -- type variable as its type. (Because res_ty may not
125 newTyVarTy openTypeKind `thenM` \ ip_ty ->
126 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
127 extendLIE inst `thenM_`
128 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
129 returnM (co_fn <$> HsIPVar ip')
133 %************************************************************************
135 \subsection{Expressions type signatures}
137 %************************************************************************
140 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
141 = addErrCtxt (exprSigCtxt in_expr) $
142 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
143 tcExpr expr sig_tc_ty `thenM` \ expr' ->
145 -- Must instantiate the outer for-alls of sig_tc_ty
146 -- else we risk instantiating a ? res_ty to a forall-type
147 -- which breaks the invariant that tcMonoExpr only returns phi-types
148 tcInstCall SignatureOrigin sig_tc_ty `thenM` \ (inst_fn, inst_sig_ty) ->
149 tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
151 returnM (co_fn <$> inst_fn expr')
153 tcMonoExpr (HsType ty) res_ty
154 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
155 -- This is the syntax for type applications that I was planning
156 -- but there are difficulties (e.g. what order for type args)
157 -- so it's not enabled yet.
158 -- Can't eliminate it altogether from the parser, because the
159 -- same parser parses *patterns*.
163 %************************************************************************
165 \subsection{Other expression forms}
167 %************************************************************************
170 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
171 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
172 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
173 returnM (HsPar expr')
174 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
175 returnM (HsSCC lbl expr')
178 tcMonoExpr (NegApp expr neg_name) res_ty
179 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
180 -- ToDo: use tcSyntaxName
182 tcMonoExpr (HsLam match) res_ty
183 = tcMatchLambda match res_ty `thenM` \ match' ->
184 returnM (HsLam match')
186 tcMonoExpr (HsApp e1 e2) res_ty
187 = tcApp e1 [e2] res_ty
190 Note that the operators in sections are expected to be binary, and
191 a type error will occur if they aren't.
194 -- Left sections, equivalent to
201 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
202 = tcExpr_id op `thenM` \ (op', op_ty) ->
203 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
204 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
205 addErrCtxt (exprCtxt in_expr) $
206 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
207 returnM (co_fn <$> SectionL arg1' op')
209 -- Right sections, equivalent to \ x -> x op expr, or
212 tcMonoExpr in_expr@(SectionR op arg2) res_ty
213 = tcExpr_id op `thenM` \ (op', op_ty) ->
214 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
215 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
216 addErrCtxt (exprCtxt in_expr) $
217 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
218 returnM (co_fn <$> SectionR op' arg2')
220 -- equivalent to (op e1) e2:
222 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
223 = tcExpr_id op `thenM` \ (op', op_ty) ->
224 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
225 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
226 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
227 addErrCtxt (exprCtxt in_expr) $
228 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
229 returnM (OpApp arg1' op' fix arg2')
233 tcMonoExpr (HsLet binds expr) res_ty
236 binds -- Bindings to check
237 (tcMonoExpr expr res_ty)
239 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
240 = addSrcLoc src_loc $
241 addErrCtxt (caseCtxt in_expr) $
243 -- Typecheck the case alternatives first.
244 -- The case patterns tend to give good type info to use
245 -- when typechecking the scrutinee. For example
248 -- will report that map is applied to too few arguments
250 -- Not only that, but it's better to check the matches on their
251 -- own, so that we get the expected results for scoped type variables.
253 -- (p::a, q::b) -> (q,p)
254 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
255 -- claimed by the pattern signatures. But if we typechecked the
256 -- match with x in scope and x's type as the expected type, we'd be hosed.
258 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
260 addErrCtxt (caseScrutCtxt scrut) (
261 tcMonoExpr scrut scrut_ty
262 ) `thenM` \ scrut' ->
264 returnM (HsCase scrut' matches' src_loc)
266 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
267 = addSrcLoc src_loc $
268 addErrCtxt (predCtxt pred) (
269 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
271 zapToType res_ty `thenM` \ res_ty' ->
272 -- C.f. the call to zapToType in TcMatches.tcMatches
274 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
275 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
276 returnM (HsIf pred' b1' b2' src_loc)
278 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
279 = addSrcLoc src_loc $
280 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
281 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
283 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
284 = unifyListTy res_ty `thenM` \ elt_ty ->
285 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
286 returnM (ExplicitList elt_ty exprs')
289 = addErrCtxt (listCtxt expr) $
290 tcMonoExpr expr elt_ty
292 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
293 = unifyPArrTy res_ty `thenM` \ elt_ty ->
294 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
295 returnM (ExplicitPArr elt_ty exprs')
298 = addErrCtxt (parrCtxt expr) $
299 tcMonoExpr expr elt_ty
301 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
302 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
303 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
304 returnM (ExplicitTuple exprs' boxity)
308 %************************************************************************
312 %************************************************************************
314 The interesting thing about @ccall@ is that it is just a template
315 which we instantiate by filling in details about the types of its
316 argument and result (ie minimal typechecking is performed). So, the
317 basic story is that we allocate a load of type variables (to hold the
318 arg/result types); unify them with the args/result; and store them for
322 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
324 = getDOpts `thenM` \ dflags ->
326 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
327 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
328 text "Either compile with -fvia-C, or, better, rewrite your code",
329 text "to use the foreign function interface. _casm_s are deprecated",
330 text "and support for them may one day disappear."])
333 -- Get the callable and returnable classes.
334 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
335 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
336 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
338 new_arg_dict (arg, arg_ty)
339 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
340 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
341 returnM arg_dicts -- Actually a singleton bag
343 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
347 let tv_idxs | null args = []
348 | otherwise = [1..length args]
350 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
351 tcMonoExprs args arg_tys `thenM` \ args' ->
353 -- The argument types can be unlifted or lifted; the result
354 -- type must, however, be lifted since it's an argument to the IO
356 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
358 io_result_ty = mkTyConApp ioTyCon [result_ty]
360 unifyTauTy res_ty io_result_ty `thenM_`
362 -- Construct the extra insts, which encode the
363 -- constraints on the argument and result types.
364 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
365 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
366 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
367 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
371 %************************************************************************
373 Record construction and update
375 %************************************************************************
378 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
379 = addErrCtxt (recordConCtxt expr) $
380 tcId con_name `thenM` \ (con_expr, con_tau) ->
382 (_, record_ty) = tcSplitFunTys con_tau
383 (tycon, ty_args) = tcSplitTyConApp record_ty
385 ASSERT( isAlgTyCon tycon )
386 unifyTauTy res_ty record_ty `thenM_`
388 -- Check that the record bindings match the constructor
389 -- con_name is syntactically constrained to be a data constructor
390 tcLookupDataCon con_name `thenM` \ data_con ->
392 bad_fields = badFields rbinds data_con
394 if notNull bad_fields then
395 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
396 failM -- Fail now, because tcRecordBinds will crash on a bad field
399 -- Typecheck the record bindings
400 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
402 -- Check for missing fields
403 checkMissingFields data_con rbinds `thenM_`
405 returnM (RecordConOut data_con con_expr rbinds')
407 -- The main complication with RecordUpd is that we need to explicitly
408 -- handle the *non-updated* fields. Consider:
410 -- data T a b = MkT1 { fa :: a, fb :: b }
411 -- | MkT2 { fa :: a, fc :: Int -> Int }
412 -- | MkT3 { fd :: a }
414 -- upd :: T a b -> c -> T a c
415 -- upd t x = t { fb = x}
417 -- The type signature on upd is correct (i.e. the result should not be (T a b))
418 -- because upd should be equivalent to:
420 -- upd t x = case t of
421 -- MkT1 p q -> MkT1 p x
422 -- MkT2 a b -> MkT2 p b
423 -- MkT3 d -> error ...
425 -- So we need to give a completely fresh type to the result record,
426 -- and then constrain it by the fields that are *not* updated ("p" above).
428 -- Note that because MkT3 doesn't contain all the fields being updated,
429 -- its RHS is simply an error, so it doesn't impose any type constraints
431 -- All this is done in STEP 4 below.
433 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
434 = addErrCtxt (recordUpdCtxt expr) $
437 -- Check that the field names are really field names
438 ASSERT( notNull rbinds )
440 field_names = recBindFields rbinds
442 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
444 bad_guys = [ addErrTc (notSelector field_name)
445 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
447 Just (AnId sel_id) -> not (isRecordSelector sel_id)
451 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
454 -- Figure out the tycon and data cons from the first field name
456 -- It's OK to use the non-tc splitters here (for a selector)
457 (Just (AnId sel_id) : _) = maybe_sel_ids
459 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
460 -- when the data type has a context
461 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
462 tycon = tcTyConAppTyCon data_ty
463 data_cons = tyConDataCons tycon
464 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
466 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
469 -- Check that at least one constructor has all the named fields
470 -- i.e. has an empty set of bad fields returned by badFields
471 checkTc (any (null . badFields rbinds) data_cons)
472 (badFieldsUpd rbinds) `thenM_`
475 -- Typecheck the update bindings.
476 -- (Do this after checking for bad fields in case there's a field that
477 -- doesn't match the constructor.)
479 result_record_ty = mkTyConApp tycon result_inst_tys
481 unifyTauTy res_ty result_record_ty `thenM_`
482 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
485 -- Use the un-updated fields to find a vector of booleans saying
486 -- which type arguments must be the same in updatee and result.
488 -- WARNING: this code assumes that all data_cons in a common tycon
489 -- have FieldLabels abstracted over the same tyvars.
491 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
492 con_field_lbls_s = map dataConFieldLabels data_cons
494 -- A constructor is only relevant to this process if
495 -- it contains all the fields that are being updated
496 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
497 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
499 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
500 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
502 mk_inst_ty (tyvar, result_inst_ty)
503 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
504 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
506 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
509 -- Typecheck the expression to be updated
511 record_ty = mkTyConApp tycon inst_tys
513 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
516 -- Figure out the LIE we need. We have to generate some
517 -- dictionaries for the data type context, since we are going to
518 -- do pattern matching over the data cons.
520 -- What dictionaries do we need?
521 -- We just take the context of the type constructor
523 theta' = substTheta inst_env (tyConTheta tycon)
525 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
526 extendLIEs dicts `thenM_`
529 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
533 %************************************************************************
535 Arithmetic sequences e.g. [a,b..]
536 and their parallel-array counterparts e.g. [: a,b.. :]
539 %************************************************************************
542 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
543 = unifyListTy res_ty `thenM` \ elt_ty ->
544 tcMonoExpr expr elt_ty `thenM` \ expr' ->
546 newMethodFromName (ArithSeqOrigin seq)
547 elt_ty enumFromName `thenM` \ enum_from ->
549 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
551 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
552 = addErrCtxt (arithSeqCtxt in_expr) $
553 unifyListTy res_ty `thenM` \ elt_ty ->
554 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
555 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
556 newMethodFromName (ArithSeqOrigin seq)
557 elt_ty enumFromThenName `thenM` \ enum_from_then ->
559 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
562 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
563 = addErrCtxt (arithSeqCtxt in_expr) $
564 unifyListTy res_ty `thenM` \ elt_ty ->
565 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
566 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
567 newMethodFromName (ArithSeqOrigin seq)
568 elt_ty enumFromToName `thenM` \ enum_from_to ->
570 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
572 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
573 = addErrCtxt (arithSeqCtxt in_expr) $
574 unifyListTy res_ty `thenM` \ elt_ty ->
575 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
576 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
577 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
578 newMethodFromName (ArithSeqOrigin seq)
579 elt_ty enumFromThenToName `thenM` \ eft ->
581 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
583 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
584 = addErrCtxt (parrSeqCtxt in_expr) $
585 unifyPArrTy res_ty `thenM` \ elt_ty ->
586 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
587 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
588 newMethodFromName (PArrSeqOrigin seq)
589 elt_ty enumFromToPName `thenM` \ enum_from_to ->
591 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
593 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
594 = addErrCtxt (parrSeqCtxt in_expr) $
595 unifyPArrTy res_ty `thenM` \ elt_ty ->
596 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
597 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
598 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
599 newMethodFromName (PArrSeqOrigin seq)
600 elt_ty enumFromThenToPName `thenM` \ eft ->
602 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
604 tcMonoExpr (PArrSeqIn _) _
605 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
606 -- the parser shouldn't have generated it and the renamer shouldn't have
611 %************************************************************************
615 %************************************************************************
618 #ifdef GHCI /* Only if bootstrapped */
619 -- Rename excludes these cases otherwise
621 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
623 tcMonoExpr (HsBracket brack loc) res_ty
625 getStage `thenM` \ level ->
626 case bracketOK level of {
627 Nothing -> failWithTc (illegalBracket level) ;
630 -- Typecheck expr to make sure it is valid,
631 -- but throw away the results. We'll type check
632 -- it again when we actually use it.
633 newMutVar [] `thenM` \ pending_splices ->
634 getLIEVar `thenM` \ lie_var ->
636 setStage (Brack next_level pending_splices lie_var) (
637 getLIE (tcBracket brack)
638 ) `thenM` \ (meta_ty, lie) ->
639 tcSimplifyBracket lie `thenM_`
641 unifyTauTy res_ty meta_ty `thenM_`
643 -- Return the original expression, not the type-decorated one
644 readMutVar pending_splices `thenM` \ pendings ->
645 returnM (HsBracketOut brack pendings)
648 tcMonoExpr (HsReify (Reify flavour name)) res_ty
649 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
650 tcMetaTy tycon_name `thenM` \ reify_ty ->
651 unifyTauTy res_ty reify_ty `thenM_`
652 returnM (HsReify (ReifyOut flavour name))
654 tycon_name = case flavour of
655 ReifyDecl -> DsMeta.declTyConName
656 ReifyType -> DsMeta.typeTyConName
657 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
662 %************************************************************************
666 %************************************************************************
669 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
673 %************************************************************************
675 \subsection{@tcApp@ typchecks an application}
677 %************************************************************************
681 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
682 -> TcType -- Expected result type of application
683 -> TcM TcExpr -- Translated fun and args
685 tcApp (HsApp e1 e2) args res_ty
686 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
688 tcApp fun args res_ty
689 = -- First type-check the function
690 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
692 addErrCtxt (wrongArgsCtxt "too many" fun args) (
693 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
694 split_fun_ty fun_ty (length args)
695 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
697 -- Now typecheck the args
699 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
701 -- Unify with expected result after type-checking the args
702 -- so that the info from args percolates to actual_result_ty.
703 -- This is when we might detect a too-few args situation.
704 -- (One can think of cases when the opposite order would give
705 -- a better error message.)
706 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
707 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
709 returnM (co_fn <$> foldl HsApp fun' args')
712 -- If an error happens we try to figure out whether the
713 -- function has been given too many or too few arguments,
715 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
716 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
717 zonkTcType actual_res_ty `thenM` \ act_ty' ->
719 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
720 (env2, act_ty'') = tidyOpenType env1 act_ty'
721 (exp_args, _) = tcSplitFunTys exp_ty''
722 (act_args, _) = tcSplitFunTys act_ty''
724 len_act_args = length act_args
725 len_exp_args = length exp_args
727 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
728 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
729 | otherwise = appCtxt fun args
731 returnM (env2, message)
734 split_fun_ty :: TcType -- The type of the function
735 -> Int -- Number of arguments
736 -> TcM ([TcType], -- Function argument types
737 TcType) -- Function result types
739 split_fun_ty fun_ty 0
740 = returnM ([], fun_ty)
742 split_fun_ty fun_ty n
743 = -- Expect the function to have type A->B
744 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
745 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
746 returnM (arg_ty:arg_tys, final_res_ty)
750 tcArg :: RenamedHsExpr -- The function (for error messages)
751 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
752 -> TcM TcExpr -- Resulting argument and LIE
754 tcArg the_fun (arg, expected_arg_ty, arg_no)
755 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
756 tcExpr arg expected_arg_ty
760 %************************************************************************
762 \subsection{@tcId@ typchecks an identifier occurrence}
764 %************************************************************************
766 tcId instantiates an occurrence of an Id.
767 The instantiate_it loop runs round instantiating the Id.
768 It has to be a loop because we are now prepared to entertain
770 f:: forall a. Eq a => forall b. Baz b => tau
771 We want to instantiate this to
772 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
774 The -fno-method-sharing flag controls what happens so far as the LIE
775 is concerned. The default case is that for an overloaded function we
776 generate a "method" Id, and add the Method Inst to the LIE. So you get
779 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
780 If you specify -fno-method-sharing, the dictionary application
781 isn't shared, so we get
783 f = /\a (d:Num a) (x:a) -> (+) a d x x
784 This gets a bit less sharing, but
785 a) it's better for RULEs involving overloaded functions
786 b) perhaps fewer separated lambdas
789 tcId :: Name -> TcM (TcExpr, TcType)
790 tcId name -- Look up the Id and instantiate its type
791 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
793 -- Check for cross-stage lifting
795 getStage `thenM` \ use_stage ->
797 Brack use_lvl ps_var lie_var
798 | use_lvl > bind_lvl && not (isExternalName name)
799 -> -- E.g. \x -> [| h x |]
800 -- We must behave as if the reference to x was
802 -- We use 'x' itself as the splice proxy, used by
803 -- the desugarer to stitch it all back together.
804 -- If 'x' occurs many times we may get many identical
805 -- bindings of the same splice proxy, but that doesn't
806 -- matter, although it's a mite untidy.
808 -- NB: During type-checking, isExernalName is true of
809 -- top level things, and false of nested bindings
810 -- Top-level things don't need lifting.
815 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
816 -- If x is polymorphic, its occurrence sites might
817 -- have different instantiations, so we can't use plain
818 -- 'x' as the splice proxy name. I don't know how to
819 -- solve this, and it's probably unimportant, so I'm
820 -- just going to flag an error for now
823 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
824 -- Put the 'lift' constraint into the right LIE
826 -- Update the pending splices
827 readMutVar ps_var `thenM` \ ps ->
828 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
830 returnM (HsVar id, id_ty))
833 checkWellStaged (quotes (ppr id)) bind_lvl use_stage `thenM_`
835 -- This is the bit that handles the no-Template-Haskell case
836 case isDataConWrapId_maybe id of
837 Nothing -> loop (HsVar id) (idType id)
838 Just data_con -> inst_data_con id data_con
841 orig = OccurrenceOf name
843 loop (HsVar fun_id) fun_ty
844 | want_method_inst fun_ty
845 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
846 newMethodWithGivenTy orig fun_id
847 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
848 loop (HsVar meth_id) tau
852 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
853 loop (inst_fn fun) tau
856 = returnM (fun, fun_ty)
858 want_method_inst fun_ty
859 | opt_NoMethodSharing = False
860 | otherwise = case tcSplitSigmaTy fun_ty of
861 (_,[],_) -> False -- Not overloaded
862 (_,theta,_) -> not (any isLinearPred theta)
863 -- This is a slight hack.
864 -- If f :: (%x :: T) => Int -> Int
865 -- Then if we have two separate calls, (f 3, f 4), we cannot
866 -- make a method constraint that then gets shared, thus:
867 -- let m = f %x in (m 3, m 4)
868 -- because that loses the linearity of the constraint.
869 -- The simplest thing to do is never to construct a method constraint
870 -- in the first place that has a linear implicit parameter in it.
872 -- We treat data constructors differently, because we have to generate
873 -- constraints for their silly theta, which no longer appears in
874 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
875 inst_data_con id data_con
876 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
877 extendLIEs ex_dicts `thenM_`
878 returnM (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) (map instToId ex_dicts),
879 mkFunTys arg_tys result_ty)
882 Typecheck expression which in most cases will be an Id.
883 The expression can return a higher-ranked type, such as
884 (forall a. a->a) -> Int
885 so we must create a HoleTyVarTy to pass in as the expected tyvar.
888 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
889 tcExpr_id (HsVar name) = tcId name
890 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
891 tcMonoExpr expr id_ty `thenM` \ expr' ->
892 readHoleResult id_ty `thenM` \ id_ty' ->
893 returnM (expr', id_ty')
897 %************************************************************************
899 \subsection{Record bindings}
901 %************************************************************************
903 Game plan for record bindings
904 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
905 1. Find the TyCon for the bindings, from the first field label.
907 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
909 For each binding field = value
911 3. Instantiate the field type (from the field label) using the type
914 4 Type check the value using tcArg, passing the field type as
915 the expected argument type.
917 This extends OK when the field types are universally quantified.
922 :: TyCon -- Type constructor for the record
923 -> [TcType] -- Args of this type constructor
924 -> RenamedRecordBinds
927 tcRecordBinds tycon ty_args rbinds
928 = mappM do_bind rbinds
930 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
932 do_bind (field_lbl_name, rhs)
933 = addErrCtxt (fieldCtxt field_lbl_name) $
934 tcLookupId field_lbl_name `thenM` \ sel_id ->
936 field_lbl = recordSelectorFieldLabel sel_id
937 field_ty = substTy tenv (fieldLabelType field_lbl)
939 ASSERT( isRecordSelector sel_id )
940 -- This lookup and assertion will surely succeed, because
941 -- we check that the fields are indeed record selectors
942 -- before calling tcRecordBinds
943 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
944 -- The caller of tcRecordBinds has already checked
945 -- that all the fields come from the same type
947 tcExpr rhs field_ty `thenM` \ rhs' ->
949 returnM (sel_id, rhs')
951 badFields rbinds data_con
952 = filter (not . (`elem` field_names)) (recBindFields rbinds)
954 field_names = map fieldLabelName (dataConFieldLabels data_con)
956 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
957 checkMissingFields data_con rbinds
958 | null field_labels -- Not declared as a record;
959 -- But C{} is still valid if no strict fields
960 = if any isMarkedStrict field_strs then
961 -- Illegal if any arg is strict
962 addErrTc (missingStrictFields data_con [])
966 | otherwise -- A record
967 = checkM (null missing_s_fields)
968 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
970 doptM Opt_WarnMissingFields `thenM` \ warn ->
971 checkM (not (warn && notNull missing_ns_fields))
972 (warnTc True (missingFields data_con missing_ns_fields))
976 = [ fl | (fl, str) <- field_info,
978 not (fieldLabelName fl `elem` field_names_used)
981 = [ fl | (fl, str) <- field_info,
982 not (isMarkedStrict str),
983 not (fieldLabelName fl `elem` field_names_used)
986 field_names_used = recBindFields rbinds
987 field_labels = dataConFieldLabels data_con
989 field_info = zipEqual "missingFields"
993 field_strs = dropList ex_theta (dataConStrictMarks data_con)
994 -- The 'drop' is because dataConStrictMarks
995 -- includes the existential dictionaries
996 (_, _, _, ex_theta, _, _) = dataConSig data_con
999 %************************************************************************
1001 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1003 %************************************************************************
1006 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1008 tcMonoExprs [] [] = returnM []
1009 tcMonoExprs (expr:exprs) (ty:tys)
1010 = tcMonoExpr expr ty `thenM` \ expr' ->
1011 tcMonoExprs exprs tys `thenM` \ exprs' ->
1012 returnM (expr':exprs')
1016 %************************************************************************
1018 \subsection{Literals}
1020 %************************************************************************
1022 Overloaded literals.
1025 tcLit :: HsLit -> TcType -> TcM TcExpr
1026 tcLit (HsLitLit s _) res_ty
1027 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1028 newDicts (LitLitOrigin (unpackFS s))
1029 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1030 extendLIEs dicts `thenM_`
1031 returnM (HsLit (HsLitLit s res_ty))
1034 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1039 %************************************************************************
1041 \subsection{Errors and contexts}
1043 %************************************************************************
1045 Boring and alphabetical:
1048 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1051 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1054 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1057 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1060 = hang (ptext SLIT("When checking the type signature of the expression:"))
1064 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1066 fieldCtxt field_name
1067 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1069 funAppCtxt fun arg arg_no
1070 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1071 quotes (ppr fun) <> text ", namely"])
1072 4 (quotes (ppr arg))
1075 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1078 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1081 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1083 illegalBracket level
1084 = ptext SLIT("Illegal bracket at level") <+> ppr level
1087 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1089 the_app = foldl HsApp fun args -- Used in error messages
1091 lurkingRank2Err fun fun_ty
1092 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1093 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1094 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1097 = hang (ptext SLIT("No constructor has all these fields:"))
1098 4 (pprQuotedList (recBindFields rbinds))
1100 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1101 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1104 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1106 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1107 missingStrictFields con fields
1110 rest | null fields = empty -- Happens for non-record constructors
1111 -- with strict fields
1112 | otherwise = colon <+> pprWithCommas ppr fields
1114 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1115 ptext SLIT("does not have the required strict field(s)")
1117 missingFields :: DataCon -> [FieldLabel] -> SDoc
1118 missingFields con fields
1119 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1120 <+> pprWithCommas ppr fields
1122 polySpliceErr :: Id -> SDoc
1124 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1126 wrongArgsCtxt too_many_or_few fun args
1127 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1128 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1129 <+> ptext SLIT("arguments in the call"))
1130 4 (parens (ppr the_app))
1132 the_app = foldl HsApp fun args -- Used in error messages