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,
67 import ListSetOps ( minusList )
69 import HscTypes ( TyThing(..) )
76 %************************************************************************
78 \subsection{Main wrappers}
80 %************************************************************************
83 tcExpr :: RenamedHsExpr -- Expession to type check
84 -> TcSigmaType -- Expected type (could be a polytpye)
85 -> TcM TcExpr -- Generalised expr with expected type
87 tcExpr expr expected_ty
88 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
89 tc_expr' expr expected_ty
91 tc_expr' expr expected_ty
92 | not (isSigmaTy expected_ty) -- Monomorphic case
93 = tcMonoExpr expr expected_ty
96 = tcGen expected_ty emptyVarSet (
98 ) `thenM` \ (gen_fn, expr') ->
99 returnM (gen_fn <$> expr')
103 %************************************************************************
105 \subsection{The TAUT rules for variables}
107 %************************************************************************
110 tcMonoExpr :: RenamedHsExpr -- Expession to type check
111 -> TcRhoType -- Expected type (could be a type variable)
112 -- Definitely no foralls at the top
116 tcMonoExpr (HsVar name) res_ty
117 = tcId name `thenM` \ (expr', id_ty) ->
118 tcSubExp res_ty id_ty `thenM` \ co_fn ->
119 returnM (co_fn <$> expr')
121 tcMonoExpr (HsIPVar ip) res_ty
122 = -- Implicit parameters must have a *tau-type* not a
123 -- type scheme. We enforce this by creating a fresh
124 -- type variable as its type. (Because res_ty may not
126 newTyVarTy openTypeKind `thenM` \ ip_ty ->
127 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
128 extendLIE inst `thenM_`
129 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
130 returnM (co_fn <$> HsIPVar ip')
134 %************************************************************************
136 \subsection{Expressions type signatures}
138 %************************************************************************
141 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
142 = addErrCtxt (exprSigCtxt in_expr) $
143 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
144 tcExpr expr sig_tc_ty `thenM` \ expr' ->
146 -- Must instantiate the outer for-alls of sig_tc_ty
147 -- else we risk instantiating a ? res_ty to a forall-type
148 -- which breaks the invariant that tcMonoExpr only returns phi-types
149 tcInstCall SignatureOrigin sig_tc_ty `thenM` \ (inst_fn, inst_sig_ty) ->
150 tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
152 returnM (co_fn <$> inst_fn expr')
154 tcMonoExpr (HsType ty) res_ty
155 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
156 -- This is the syntax for type applications that I was planning
157 -- but there are difficulties (e.g. what order for type args)
158 -- so it's not enabled yet.
159 -- Can't eliminate it altogether from the parser, because the
160 -- same parser parses *patterns*.
164 %************************************************************************
166 \subsection{Other expression forms}
168 %************************************************************************
171 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
172 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
173 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
174 returnM (HsPar expr')
175 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
176 returnM (HsSCC lbl expr')
179 tcMonoExpr (NegApp expr neg_name) res_ty
180 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
181 -- ToDo: use tcSyntaxName
183 tcMonoExpr (HsLam match) res_ty
184 = tcMatchLambda match res_ty `thenM` \ match' ->
185 returnM (HsLam match')
187 tcMonoExpr (HsApp e1 e2) res_ty
188 = tcApp e1 [e2] res_ty
191 Note that the operators in sections are expected to be binary, and
192 a type error will occur if they aren't.
195 -- Left sections, equivalent to
202 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
203 = tcExpr_id op `thenM` \ (op', op_ty) ->
204 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
205 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
206 addErrCtxt (exprCtxt in_expr) $
207 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
208 returnM (co_fn <$> SectionL arg1' op')
210 -- Right sections, equivalent to \ x -> x op expr, or
213 tcMonoExpr in_expr@(SectionR op arg2) res_ty
214 = tcExpr_id op `thenM` \ (op', op_ty) ->
215 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
216 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
217 addErrCtxt (exprCtxt in_expr) $
218 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
219 returnM (co_fn <$> SectionR op' arg2')
221 -- equivalent to (op e1) e2:
223 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
224 = tcExpr_id op `thenM` \ (op', op_ty) ->
225 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
226 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
227 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
228 addErrCtxt (exprCtxt in_expr) $
229 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
230 returnM (OpApp arg1' op' fix arg2')
234 tcMonoExpr (HsLet binds expr) res_ty
237 binds -- Bindings to check
238 (tcMonoExpr expr res_ty)
240 combiner is_rec bind expr = HsLet (mkMonoBind bind [] is_rec) expr
242 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
243 = addSrcLoc src_loc $
244 addErrCtxt (caseCtxt in_expr) $
246 -- Typecheck the case alternatives first.
247 -- The case patterns tend to give good type info to use
248 -- when typechecking the scrutinee. For example
251 -- will report that map is applied to too few arguments
253 -- Not only that, but it's better to check the matches on their
254 -- own, so that we get the expected results for scoped type variables.
256 -- (p::a, q::b) -> (q,p)
257 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
258 -- claimed by the pattern signatures. But if we typechecked the
259 -- match with x in scope and x's type as the expected type, we'd be hosed.
261 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
263 addErrCtxt (caseScrutCtxt scrut) (
264 tcMonoExpr scrut scrut_ty
265 ) `thenM` \ scrut' ->
267 returnM (HsCase scrut' matches' src_loc)
269 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
270 = addSrcLoc src_loc $
271 addErrCtxt (predCtxt pred) (
272 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
274 zapToType res_ty `thenM` \ res_ty' ->
275 -- C.f. the call to zapToType in TcMatches.tcMatches
277 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
278 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
279 returnM (HsIf pred' b1' b2' src_loc)
281 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
282 = addSrcLoc src_loc $
283 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
284 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
286 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
287 = unifyListTy res_ty `thenM` \ elt_ty ->
288 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
289 returnM (ExplicitList elt_ty exprs')
292 = addErrCtxt (listCtxt expr) $
293 tcMonoExpr expr elt_ty
295 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
296 = unifyPArrTy res_ty `thenM` \ elt_ty ->
297 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
298 returnM (ExplicitPArr elt_ty exprs')
301 = addErrCtxt (parrCtxt expr) $
302 tcMonoExpr expr elt_ty
304 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
305 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
306 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
307 returnM (ExplicitTuple exprs' boxity)
311 %************************************************************************
315 %************************************************************************
317 The interesting thing about @ccall@ is that it is just a template
318 which we instantiate by filling in details about the types of its
319 argument and result (ie minimal typechecking is performed). So, the
320 basic story is that we allocate a load of type variables (to hold the
321 arg/result types); unify them with the args/result; and store them for
325 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
327 = getDOpts `thenM` \ dflags ->
329 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
330 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
331 text "Either compile with -fvia-C, or, better, rewrite your code",
332 text "to use the foreign function interface. _casm_s are deprecated",
333 text "and support for them may one day disappear."])
336 -- Get the callable and returnable classes.
337 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
338 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
339 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
341 new_arg_dict (arg, arg_ty)
342 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
343 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
344 returnM arg_dicts -- Actually a singleton bag
346 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
350 let tv_idxs | null args = []
351 | otherwise = [1..length args]
353 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
354 tcMonoExprs args arg_tys `thenM` \ args' ->
356 -- The argument types can be unlifted or lifted; the result
357 -- type must, however, be lifted since it's an argument to the IO
359 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
361 io_result_ty = mkTyConApp ioTyCon [result_ty]
363 unifyTauTy res_ty io_result_ty `thenM_`
365 -- Construct the extra insts, which encode the
366 -- constraints on the argument and result types.
367 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
368 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
369 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
370 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
374 %************************************************************************
376 Record construction and update
378 %************************************************************************
381 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
382 = addErrCtxt (recordConCtxt expr) $
383 tcId con_name `thenM` \ (con_expr, con_tau) ->
385 (_, record_ty) = tcSplitFunTys con_tau
386 (tycon, ty_args) = tcSplitTyConApp record_ty
388 ASSERT( isAlgTyCon tycon )
389 unifyTauTy res_ty record_ty `thenM_`
391 -- Check that the record bindings match the constructor
392 -- con_name is syntactically constrained to be a data constructor
393 tcLookupDataCon con_name `thenM` \ data_con ->
395 bad_fields = badFields rbinds data_con
397 if notNull bad_fields then
398 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
399 failM -- Fail now, because tcRecordBinds will crash on a bad field
402 -- Typecheck the record bindings
403 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
405 -- Check for missing fields
406 checkMissingFields data_con rbinds `thenM_`
408 returnM (RecordConOut data_con con_expr rbinds')
410 -- The main complication with RecordUpd is that we need to explicitly
411 -- handle the *non-updated* fields. Consider:
413 -- data T a b = MkT1 { fa :: a, fb :: b }
414 -- | MkT2 { fa :: a, fc :: Int -> Int }
415 -- | MkT3 { fd :: a }
417 -- upd :: T a b -> c -> T a c
418 -- upd t x = t { fb = x}
420 -- The type signature on upd is correct (i.e. the result should not be (T a b))
421 -- because upd should be equivalent to:
423 -- upd t x = case t of
424 -- MkT1 p q -> MkT1 p x
425 -- MkT2 a b -> MkT2 p b
426 -- MkT3 d -> error ...
428 -- So we need to give a completely fresh type to the result record,
429 -- and then constrain it by the fields that are *not* updated ("p" above).
431 -- Note that because MkT3 doesn't contain all the fields being updated,
432 -- its RHS is simply an error, so it doesn't impose any type constraints
434 -- All this is done in STEP 4 below.
436 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
437 = addErrCtxt (recordUpdCtxt expr) $
440 -- Check that the field names are really field names
441 ASSERT( notNull rbinds )
443 field_names = recBindFields rbinds
445 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
447 bad_guys = [ addErrTc (notSelector field_name)
448 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
450 Just (AnId sel_id) -> not (isRecordSelector sel_id)
454 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
457 -- Figure out the tycon and data cons from the first field name
459 -- It's OK to use the non-tc splitters here (for a selector)
460 (Just (AnId sel_id) : _) = maybe_sel_ids
462 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
463 -- when the data type has a context
464 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
465 tycon = tcTyConAppTyCon data_ty
466 data_cons = tyConDataCons tycon
467 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
469 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
472 -- Check that at least one constructor has all the named fields
473 -- i.e. has an empty set of bad fields returned by badFields
474 checkTc (any (null . badFields rbinds) data_cons)
475 (badFieldsUpd rbinds) `thenM_`
478 -- Typecheck the update bindings.
479 -- (Do this after checking for bad fields in case there's a field that
480 -- doesn't match the constructor.)
482 result_record_ty = mkTyConApp tycon result_inst_tys
484 unifyTauTy res_ty result_record_ty `thenM_`
485 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
488 -- Use the un-updated fields to find a vector of booleans saying
489 -- which type arguments must be the same in updatee and result.
491 -- WARNING: this code assumes that all data_cons in a common tycon
492 -- have FieldLabels abstracted over the same tyvars.
494 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
495 con_field_lbls_s = map dataConFieldLabels data_cons
497 -- A constructor is only relevant to this process if
498 -- it contains all the fields that are being updated
499 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
500 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
502 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
503 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
505 mk_inst_ty (tyvar, result_inst_ty)
506 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
507 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
509 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
512 -- Typecheck the expression to be updated
514 record_ty = mkTyConApp tycon inst_tys
516 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
519 -- Figure out the LIE we need. We have to generate some
520 -- dictionaries for the data type context, since we are going to
521 -- do pattern matching over the data cons.
523 -- What dictionaries do we need?
524 -- We just take the context of the type constructor
526 theta' = substTheta inst_env (tyConTheta tycon)
528 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
529 extendLIEs dicts `thenM_`
532 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
536 %************************************************************************
538 Arithmetic sequences e.g. [a,b..]
539 and their parallel-array counterparts e.g. [: a,b.. :]
542 %************************************************************************
545 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
546 = unifyListTy res_ty `thenM` \ elt_ty ->
547 tcMonoExpr expr elt_ty `thenM` \ expr' ->
549 newMethodFromName (ArithSeqOrigin seq)
550 elt_ty enumFromName `thenM` \ enum_from ->
552 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
554 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
555 = addErrCtxt (arithSeqCtxt in_expr) $
556 unifyListTy res_ty `thenM` \ elt_ty ->
557 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
558 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
559 newMethodFromName (ArithSeqOrigin seq)
560 elt_ty enumFromThenName `thenM` \ enum_from_then ->
562 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
565 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
566 = addErrCtxt (arithSeqCtxt in_expr) $
567 unifyListTy res_ty `thenM` \ elt_ty ->
568 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
569 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
570 newMethodFromName (ArithSeqOrigin seq)
571 elt_ty enumFromToName `thenM` \ enum_from_to ->
573 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
575 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
576 = addErrCtxt (arithSeqCtxt in_expr) $
577 unifyListTy res_ty `thenM` \ elt_ty ->
578 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
579 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
580 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
581 newMethodFromName (ArithSeqOrigin seq)
582 elt_ty enumFromThenToName `thenM` \ eft ->
584 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
586 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
587 = addErrCtxt (parrSeqCtxt in_expr) $
588 unifyPArrTy res_ty `thenM` \ elt_ty ->
589 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
590 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
591 newMethodFromName (PArrSeqOrigin seq)
592 elt_ty enumFromToPName `thenM` \ enum_from_to ->
594 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
596 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
597 = addErrCtxt (parrSeqCtxt in_expr) $
598 unifyPArrTy res_ty `thenM` \ elt_ty ->
599 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
600 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
601 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
602 newMethodFromName (PArrSeqOrigin seq)
603 elt_ty enumFromThenToPName `thenM` \ eft ->
605 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
607 tcMonoExpr (PArrSeqIn _) _
608 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
609 -- the parser shouldn't have generated it and the renamer shouldn't have
614 %************************************************************************
618 %************************************************************************
621 #ifdef GHCI /* Only if bootstrapped */
622 -- Rename excludes these cases otherwise
624 tcMonoExpr (HsSplice n expr) res_ty = tcSpliceExpr n expr res_ty
626 tcMonoExpr (HsBracket brack) res_ty
627 = getStage `thenM` \ level ->
628 case bracketOK level of {
629 Nothing -> failWithTc (illegalBracket level) ;
632 -- Typecheck expr to make sure it is valid,
633 -- but throw away the results. We'll type check
634 -- it again when we actually use it.
635 newMutVar [] `thenM` \ pending_splices ->
636 getLIEVar `thenM` \ lie_var ->
638 setStage (Brack next_level pending_splices lie_var) (
639 getLIE (tcBracket brack)
640 ) `thenM` \ (meta_ty, lie) ->
641 tcSimplifyBracket lie `thenM_`
643 unifyTauTy res_ty meta_ty `thenM_`
645 -- Return the original expression, not the type-decorated one
646 readMutVar pending_splices `thenM` \ pendings ->
647 returnM (HsBracketOut brack pendings)
652 %************************************************************************
654 \subsection{Implicit Parameter bindings}
656 %************************************************************************
659 tcMonoExpr (HsWith expr binds is_with) res_ty
660 = getLIE (tcMonoExpr expr res_ty) `thenM` \ (expr', expr_lie) ->
661 mapAndUnzipM tc_ip_bind binds `thenM` \ (avail_ips, binds') ->
663 -- If the binding binds ?x = E, we must now
664 -- discharge any ?x constraints in expr_lie
665 tcSimplifyIPs avail_ips expr_lie `thenM` \ dict_binds ->
667 expr'' = HsLet (mkMonoBind dict_binds [] Recursive) expr'
669 returnM (HsWith expr'' binds' is_with)
671 tc_ip_bind (ip, expr)
672 = newTyVarTy openTypeKind `thenM` \ ty ->
673 getSrcLocM `thenM` \ loc ->
674 newIPDict (IPBind ip) ip ty `thenM` \ (ip', ip_inst) ->
675 tcMonoExpr expr ty `thenM` \ expr' ->
676 returnM (ip_inst, (ip', expr'))
680 %************************************************************************
684 %************************************************************************
687 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
691 %************************************************************************
693 \subsection{@tcApp@ typchecks an application}
695 %************************************************************************
699 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
700 -> TcType -- Expected result type of application
701 -> TcM TcExpr -- Translated fun and args
703 tcApp (HsApp e1 e2) args res_ty
704 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
706 tcApp fun args res_ty
707 = -- First type-check the function
708 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
710 addErrCtxt (wrongArgsCtxt "too many" fun args) (
711 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
712 split_fun_ty fun_ty (length args)
713 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
715 -- Now typecheck the args
717 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
719 -- Unify with expected result after type-checking the args
720 -- so that the info from args percolates to actual_result_ty.
721 -- This is when we might detect a too-few args situation.
722 -- (One can think of cases when the opposite order would give
723 -- a better error message.)
724 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
725 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
727 returnM (co_fn <$> foldl HsApp fun' args')
730 -- If an error happens we try to figure out whether the
731 -- function has been given too many or too few arguments,
733 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
734 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
735 zonkTcType actual_res_ty `thenM` \ act_ty' ->
737 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
738 (env2, act_ty'') = tidyOpenType env1 act_ty'
739 (exp_args, _) = tcSplitFunTys exp_ty''
740 (act_args, _) = tcSplitFunTys act_ty''
742 len_act_args = length act_args
743 len_exp_args = length exp_args
745 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
746 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
747 | otherwise = appCtxt fun args
749 returnM (env2, message)
752 split_fun_ty :: TcType -- The type of the function
753 -> Int -- Number of arguments
754 -> TcM ([TcType], -- Function argument types
755 TcType) -- Function result types
757 split_fun_ty fun_ty 0
758 = returnM ([], fun_ty)
760 split_fun_ty fun_ty n
761 = -- Expect the function to have type A->B
762 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
763 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
764 returnM (arg_ty:arg_tys, final_res_ty)
768 tcArg :: RenamedHsExpr -- The function (for error messages)
769 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
770 -> TcM TcExpr -- Resulting argument and LIE
772 tcArg the_fun (arg, expected_arg_ty, arg_no)
773 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
774 tcExpr arg expected_arg_ty
778 %************************************************************************
780 \subsection{@tcId@ typchecks an identifier occurrence}
782 %************************************************************************
784 tcId instantiates an occurrence of an Id.
785 The instantiate_it loop runs round instantiating the Id.
786 It has to be a loop because we are now prepared to entertain
788 f:: forall a. Eq a => forall b. Baz b => tau
789 We want to instantiate this to
790 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
792 The -fno-method-sharing flag controls what happens so far as the LIE
793 is concerned. The default case is that for an overloaded function we
794 generate a "method" Id, and add the Method Inst to the LIE. So you get
797 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
798 If you specify -fno-method-sharing, the dictionary application
799 isn't shared, so we get
801 f = /\a (d:Num a) (x:a) -> (+) a d x x
802 This gets a bit less sharing, but
803 a) it's better for RULEs involving overloaded functions
804 b) perhaps fewer separated lambdas
807 tcId :: Name -> TcM (TcExpr, TcType)
808 tcId name -- Look up the Id and instantiate its type
809 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
811 -- Check for cross-stage lifting
813 getStage `thenM` \ use_stage ->
815 Brack use_lvl ps_var lie_var
816 | use_lvl > bind_lvl && not (isExternalName name)
817 -> -- E.g. \x -> [| h x |]
818 -- We must behave as if the reference to x was
820 -- We use 'x' itself as the splice proxy, used by
821 -- the desugarer to stitch it all back together
822 -- NB: isExernalName is true of top level things,
823 -- and false of nested bindings
828 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
829 -- If x is polymorphic, its occurrence sites might
830 -- have different instantiations, so we can't use plain
831 -- 'x' as the splice proxy name. I don't know how to
832 -- solve this, and it's probably unimportant, so I'm
833 -- just going to flag an error for now
836 newMethodFromName orig id_ty liftName `thenM` \ lift ->
837 -- Put the 'lift' constraint into the right LIE
839 -- Update the pending splices
840 readMutVar ps_var `thenM` \ ps ->
841 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
843 returnM (HsVar id, id_ty))
847 use_lvl = metaLevel use_stage
849 checkTc (wellStaged bind_lvl use_lvl)
850 (badStageErr id bind_lvl use_lvl) `thenM_`
852 -- This is the bit that handles the no-Template-Haskell case
853 case isDataConWrapId_maybe id of
854 Nothing -> loop (HsVar id) (idType id)
855 Just data_con -> inst_data_con id data_con
858 orig = OccurrenceOf name
860 loop (HsVar fun_id) fun_ty
861 | want_method_inst fun_ty
862 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
863 newMethodWithGivenTy orig fun_id
864 (mkTyVarTys tyvars) theta tau `thenM` \ meth ->
865 loop (HsVar (instToId meth)) tau
869 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
870 loop (inst_fn fun) tau
873 = returnM (fun, fun_ty)
875 want_method_inst fun_ty
876 | opt_NoMethodSharing = False
877 | otherwise = case tcSplitSigmaTy fun_ty of
878 (_,[],_) -> False -- Not overloaded
879 (_,theta,_) -> not (any isLinearPred theta)
880 -- This is a slight hack.
881 -- If f :: (%x :: T) => Int -> Int
882 -- Then if we have two separate calls, (f 3, f 4), we cannot
883 -- make a method constraint that then gets shared, thus:
884 -- let m = f %x in (m 3, m 4)
885 -- because that loses the linearity of the constraint.
886 -- The simplest thing to do is never to construct a method constraint
887 -- in the first place that has a linear implicit parameter in it.
889 -- We treat data constructors differently, because we have to generate
890 -- constraints for their silly theta, which no longer appears in
891 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
892 inst_data_con id data_con
893 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
894 extendLIEs ex_dicts `thenM_`
895 returnM (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) (map instToId ex_dicts),
896 mkFunTys arg_tys result_ty)
899 Typecheck expression which in most cases will be an Id.
900 The expression can return a higher-ranked type, such as
901 (forall a. a->a) -> Int
902 so we must create a HoleTyVarTy to pass in as the expected tyvar.
905 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
906 tcExpr_id (HsVar name) = tcId name
907 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
908 tcMonoExpr expr id_ty `thenM` \ expr' ->
909 readHoleResult id_ty `thenM` \ id_ty' ->
910 returnM (expr', id_ty')
914 %************************************************************************
916 \subsection{Record bindings}
918 %************************************************************************
920 Game plan for record bindings
921 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
922 1. Find the TyCon for the bindings, from the first field label.
924 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
926 For each binding field = value
928 3. Instantiate the field type (from the field label) using the type
931 4 Type check the value using tcArg, passing the field type as
932 the expected argument type.
934 This extends OK when the field types are universally quantified.
939 :: TyCon -- Type constructor for the record
940 -> [TcType] -- Args of this type constructor
941 -> RenamedRecordBinds
944 tcRecordBinds tycon ty_args rbinds
945 = mappM do_bind rbinds
947 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
949 do_bind (field_lbl_name, rhs)
950 = addErrCtxt (fieldCtxt field_lbl_name) $
951 tcLookupId field_lbl_name `thenM` \ sel_id ->
953 field_lbl = recordSelectorFieldLabel sel_id
954 field_ty = substTy tenv (fieldLabelType field_lbl)
956 ASSERT( isRecordSelector sel_id )
957 -- This lookup and assertion will surely succeed, because
958 -- we check that the fields are indeed record selectors
959 -- before calling tcRecordBinds
960 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
961 -- The caller of tcRecordBinds has already checked
962 -- that all the fields come from the same type
964 tcExpr rhs field_ty `thenM` \ rhs' ->
966 returnM (sel_id, rhs')
968 badFields rbinds data_con
969 = filter (not . (`elem` field_names)) (recBindFields rbinds)
971 field_names = map fieldLabelName (dataConFieldLabels data_con)
973 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
974 checkMissingFields data_con rbinds
975 | null field_labels -- Not declared as a record;
976 -- But C{} is still valid if no strict fields
977 = if any isMarkedStrict field_strs then
978 -- Illegal if any arg is strict
979 addErrTc (missingStrictFields data_con [])
983 | otherwise -- A record
984 = checkM (null missing_s_fields)
985 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
987 doptM Opt_WarnMissingFields `thenM` \ warn ->
988 checkM (not (warn && notNull missing_ns_fields))
989 (warnTc True (missingFields data_con missing_ns_fields))
993 = [ fl | (fl, str) <- field_info,
995 not (fieldLabelName fl `elem` field_names_used)
998 = [ fl | (fl, str) <- field_info,
999 not (isMarkedStrict str),
1000 not (fieldLabelName fl `elem` field_names_used)
1003 field_names_used = recBindFields rbinds
1004 field_labels = dataConFieldLabels data_con
1006 field_info = zipEqual "missingFields"
1010 field_strs = dropList ex_theta (dataConStrictMarks data_con)
1011 -- The 'drop' is because dataConStrictMarks
1012 -- includes the existential dictionaries
1013 (_, _, _, ex_theta, _, _) = dataConSig data_con
1016 %************************************************************************
1018 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1020 %************************************************************************
1023 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1025 tcMonoExprs [] [] = returnM []
1026 tcMonoExprs (expr:exprs) (ty:tys)
1027 = tcMonoExpr expr ty `thenM` \ expr' ->
1028 tcMonoExprs exprs tys `thenM` \ exprs' ->
1029 returnM (expr':exprs')
1033 %************************************************************************
1035 \subsection{Literals}
1037 %************************************************************************
1039 Overloaded literals.
1042 tcLit :: HsLit -> TcType -> TcM TcExpr
1043 tcLit (HsLitLit s _) res_ty
1044 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1045 newDicts (LitLitOrigin (unpackFS s))
1046 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1047 extendLIEs dicts `thenM_`
1048 returnM (HsLit (HsLitLit s res_ty))
1051 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1056 %************************************************************************
1058 \subsection{Errors and contexts}
1060 %************************************************************************
1062 Boring and alphabetical:
1065 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1068 badStageErr id bind_lvl use_lvl
1069 = ptext SLIT("Stage error:") <+> quotes (ppr id) <+>
1070 hsep [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
1071 ptext SLIT("but used at stage") <+> ppr use_lvl]
1074 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1077 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1080 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1083 = hang (ptext SLIT("When checking the type signature of the expression:"))
1087 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1089 fieldCtxt field_name
1090 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1092 funAppCtxt fun arg arg_no
1093 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1094 quotes (ppr fun) <> text ", namely"])
1095 4 (quotes (ppr arg))
1098 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1101 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1104 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1106 illegalBracket level
1107 = ptext SLIT("Illegal bracket at level") <+> ppr level
1110 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1112 the_app = foldl HsApp fun args -- Used in error messages
1114 lurkingRank2Err fun fun_ty
1115 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1116 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1117 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1120 = hang (ptext SLIT("No constructor has all these fields:"))
1121 4 (pprQuotedList (recBindFields rbinds))
1123 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1124 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1127 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1129 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1130 missingStrictFields con fields
1133 rest | null fields = empty -- Happens for non-record constructors
1134 -- with strict fields
1135 | otherwise = colon <+> pprWithCommas ppr fields
1137 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1138 ptext SLIT("does not have the required strict field(s)")
1141 missingFields :: DataCon -> [FieldLabel] -> SDoc
1142 missingFields con fields
1143 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1144 <+> pprWithCommas ppr fields
1146 polySpliceErr :: Id -> SDoc
1148 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1150 wrongArgsCtxt too_many_or_few fun args
1151 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1152 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1153 <+> ptext SLIT("arguments in the call"))
1154 4 (parens (ppr the_app))
1156 the_app = foldl HsApp fun args -- Used in error messages