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, tcLookupGlobal,
16 wellStaged, metaLevel )
17 import TcSimplify ( tcSimplifyBracket )
18 import Name ( isExternalName )
19 import qualified DsMeta
22 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..), recBindFields )
23 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
24 import TcHsSyn ( TcExpr, TcRecordBinds, hsLitType, mkHsDictApp, mkHsTyApp, mkHsLet )
26 import TcUnify ( tcSubExp, tcGen, (<$>),
27 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
29 import BasicTypes ( isMarkedStrict )
30 import Inst ( InstOrigin(..),
31 newOverloadedLit, newMethodFromName, newIPDict,
32 newDicts, newMethodWithGivenTy,
33 instToId, tcInstCall, tcInstDataCon
35 import TcBinds ( tcBindsAndThen )
36 import TcEnv ( tcLookupClass, tcLookupGlobal_maybe, tcLookupIdLvl,
37 tcLookupTyCon, tcLookupDataCon, tcLookupId
39 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts )
40 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
41 import TcPat ( badFieldCon )
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, 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 )
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 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
241 = addSrcLoc src_loc $
242 addErrCtxt (caseCtxt in_expr) $
244 -- Typecheck the case alternatives first.
245 -- The case patterns tend to give good type info to use
246 -- when typechecking the scrutinee. For example
249 -- will report that map is applied to too few arguments
251 -- Not only that, but it's better to check the matches on their
252 -- own, so that we get the expected results for scoped type variables.
254 -- (p::a, q::b) -> (q,p)
255 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
256 -- claimed by the pattern signatures. But if we typechecked the
257 -- match with x in scope and x's type as the expected type, we'd be hosed.
259 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
261 addErrCtxt (caseScrutCtxt scrut) (
262 tcMonoExpr scrut scrut_ty
263 ) `thenM` \ scrut' ->
265 returnM (HsCase scrut' matches' src_loc)
267 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
268 = addSrcLoc src_loc $
269 addErrCtxt (predCtxt pred) (
270 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
272 zapToType res_ty `thenM` \ res_ty' ->
273 -- C.f. the call to zapToType in TcMatches.tcMatches
275 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
276 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
277 returnM (HsIf pred' b1' b2' src_loc)
279 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
280 = addSrcLoc src_loc $
281 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
282 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
284 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
285 = unifyListTy res_ty `thenM` \ elt_ty ->
286 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
287 returnM (ExplicitList elt_ty exprs')
290 = addErrCtxt (listCtxt expr) $
291 tcMonoExpr expr elt_ty
293 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
294 = unifyPArrTy res_ty `thenM` \ elt_ty ->
295 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
296 returnM (ExplicitPArr elt_ty exprs')
299 = addErrCtxt (parrCtxt expr) $
300 tcMonoExpr expr elt_ty
302 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
303 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
304 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
305 returnM (ExplicitTuple exprs' boxity)
309 %************************************************************************
313 %************************************************************************
315 The interesting thing about @ccall@ is that it is just a template
316 which we instantiate by filling in details about the types of its
317 argument and result (ie minimal typechecking is performed). So, the
318 basic story is that we allocate a load of type variables (to hold the
319 arg/result types); unify them with the args/result; and store them for
323 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
325 = getDOpts `thenM` \ dflags ->
327 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
328 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
329 text "Either compile with -fvia-C, or, better, rewrite your code",
330 text "to use the foreign function interface. _casm_s are deprecated",
331 text "and support for them may one day disappear."])
334 -- Get the callable and returnable classes.
335 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
336 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
337 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
339 new_arg_dict (arg, arg_ty)
340 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
341 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
342 returnM arg_dicts -- Actually a singleton bag
344 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
348 let tv_idxs | null args = []
349 | otherwise = [1..length args]
351 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
352 tcMonoExprs args arg_tys `thenM` \ args' ->
354 -- The argument types can be unlifted or lifted; the result
355 -- type must, however, be lifted since it's an argument to the IO
357 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
359 io_result_ty = mkTyConApp ioTyCon [result_ty]
361 unifyTauTy res_ty io_result_ty `thenM_`
363 -- Construct the extra insts, which encode the
364 -- constraints on the argument and result types.
365 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
366 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
367 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
368 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
372 %************************************************************************
374 Record construction and update
376 %************************************************************************
379 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
380 = addErrCtxt (recordConCtxt expr) $
381 tcId con_name `thenM` \ (con_expr, con_tau) ->
383 (_, record_ty) = tcSplitFunTys con_tau
384 (tycon, ty_args) = tcSplitTyConApp record_ty
386 ASSERT( isAlgTyCon tycon )
387 unifyTauTy res_ty record_ty `thenM_`
389 -- Check that the record bindings match the constructor
390 -- con_name is syntactically constrained to be a data constructor
391 tcLookupDataCon con_name `thenM` \ data_con ->
393 bad_fields = badFields rbinds data_con
395 if notNull bad_fields then
396 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
397 failM -- Fail now, because tcRecordBinds will crash on a bad field
400 -- Typecheck the record bindings
401 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
403 -- Check for missing fields
404 checkMissingFields data_con rbinds `thenM_`
406 returnM (RecordConOut data_con con_expr rbinds')
408 -- The main complication with RecordUpd is that we need to explicitly
409 -- handle the *non-updated* fields. Consider:
411 -- data T a b = MkT1 { fa :: a, fb :: b }
412 -- | MkT2 { fa :: a, fc :: Int -> Int }
413 -- | MkT3 { fd :: a }
415 -- upd :: T a b -> c -> T a c
416 -- upd t x = t { fb = x}
418 -- The type signature on upd is correct (i.e. the result should not be (T a b))
419 -- because upd should be equivalent to:
421 -- upd t x = case t of
422 -- MkT1 p q -> MkT1 p x
423 -- MkT2 a b -> MkT2 p b
424 -- MkT3 d -> error ...
426 -- So we need to give a completely fresh type to the result record,
427 -- and then constrain it by the fields that are *not* updated ("p" above).
429 -- Note that because MkT3 doesn't contain all the fields being updated,
430 -- its RHS is simply an error, so it doesn't impose any type constraints
432 -- All this is done in STEP 4 below.
434 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
435 = addErrCtxt (recordUpdCtxt expr) $
438 -- Check that the field names are really field names
439 ASSERT( notNull rbinds )
441 field_names = recBindFields rbinds
443 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
445 bad_guys = [ addErrTc (notSelector field_name)
446 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
448 Just (AnId sel_id) -> not (isRecordSelector sel_id)
452 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
455 -- Figure out the tycon and data cons from the first field name
457 -- It's OK to use the non-tc splitters here (for a selector)
458 (Just (AnId sel_id) : _) = maybe_sel_ids
460 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
461 -- when the data type has a context
462 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
463 tycon = tcTyConAppTyCon data_ty
464 data_cons = tyConDataCons tycon
465 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
467 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
470 -- Check that at least one constructor has all the named fields
471 -- i.e. has an empty set of bad fields returned by badFields
472 checkTc (any (null . badFields rbinds) data_cons)
473 (badFieldsUpd rbinds) `thenM_`
476 -- Typecheck the update bindings.
477 -- (Do this after checking for bad fields in case there's a field that
478 -- doesn't match the constructor.)
480 result_record_ty = mkTyConApp tycon result_inst_tys
482 unifyTauTy res_ty result_record_ty `thenM_`
483 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
486 -- Use the un-updated fields to find a vector of booleans saying
487 -- which type arguments must be the same in updatee and result.
489 -- WARNING: this code assumes that all data_cons in a common tycon
490 -- have FieldLabels abstracted over the same tyvars.
492 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
493 con_field_lbls_s = map dataConFieldLabels data_cons
495 -- A constructor is only relevant to this process if
496 -- it contains all the fields that are being updated
497 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
498 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
500 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
501 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
503 mk_inst_ty (tyvar, result_inst_ty)
504 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
505 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
507 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
510 -- Typecheck the expression to be updated
512 record_ty = mkTyConApp tycon inst_tys
514 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
517 -- Figure out the LIE we need. We have to generate some
518 -- dictionaries for the data type context, since we are going to
519 -- do pattern matching over the data cons.
521 -- What dictionaries do we need?
522 -- We just take the context of the type constructor
524 theta' = substTheta inst_env (tyConTheta tycon)
526 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
527 extendLIEs dicts `thenM_`
530 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
534 %************************************************************************
536 Arithmetic sequences e.g. [a,b..]
537 and their parallel-array counterparts e.g. [: a,b.. :]
540 %************************************************************************
543 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
544 = unifyListTy res_ty `thenM` \ elt_ty ->
545 tcMonoExpr expr elt_ty `thenM` \ expr' ->
547 newMethodFromName (ArithSeqOrigin seq)
548 elt_ty enumFromName `thenM` \ enum_from ->
550 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
552 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
553 = addErrCtxt (arithSeqCtxt in_expr) $
554 unifyListTy res_ty `thenM` \ elt_ty ->
555 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
556 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
557 newMethodFromName (ArithSeqOrigin seq)
558 elt_ty enumFromThenName `thenM` \ enum_from_then ->
560 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
563 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
564 = addErrCtxt (arithSeqCtxt in_expr) $
565 unifyListTy res_ty `thenM` \ elt_ty ->
566 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
567 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
568 newMethodFromName (ArithSeqOrigin seq)
569 elt_ty enumFromToName `thenM` \ enum_from_to ->
571 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
573 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
574 = addErrCtxt (arithSeqCtxt in_expr) $
575 unifyListTy res_ty `thenM` \ elt_ty ->
576 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
577 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
578 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
579 newMethodFromName (ArithSeqOrigin seq)
580 elt_ty enumFromThenToName `thenM` \ eft ->
582 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
584 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
585 = addErrCtxt (parrSeqCtxt in_expr) $
586 unifyPArrTy res_ty `thenM` \ elt_ty ->
587 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
588 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
589 newMethodFromName (PArrSeqOrigin seq)
590 elt_ty enumFromToPName `thenM` \ enum_from_to ->
592 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
594 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
595 = addErrCtxt (parrSeqCtxt in_expr) $
596 unifyPArrTy res_ty `thenM` \ elt_ty ->
597 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
598 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
599 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
600 newMethodFromName (PArrSeqOrigin seq)
601 elt_ty enumFromThenToPName `thenM` \ eft ->
603 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
605 tcMonoExpr (PArrSeqIn _) _
606 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
607 -- the parser shouldn't have generated it and the renamer shouldn't have
612 %************************************************************************
616 %************************************************************************
619 #ifdef GHCI /* Only if bootstrapped */
620 -- Rename excludes these cases otherwise
622 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
624 tcMonoExpr (HsBracket brack loc) res_ty
626 getStage `thenM` \ level ->
627 case bracketOK level of {
628 Nothing -> failWithTc (illegalBracket level) ;
631 -- Typecheck expr to make sure it is valid,
632 -- but throw away the results. We'll type check
633 -- it again when we actually use it.
634 newMutVar [] `thenM` \ pending_splices ->
635 getLIEVar `thenM` \ lie_var ->
637 setStage (Brack next_level pending_splices lie_var) (
638 getLIE (tcBracket brack)
639 ) `thenM` \ (meta_ty, lie) ->
640 tcSimplifyBracket lie `thenM_`
642 unifyTauTy res_ty meta_ty `thenM_`
644 -- Return the original expression, not the type-decorated one
645 readMutVar pending_splices `thenM` \ pendings ->
646 returnM (HsBracketOut brack pendings)
649 tcMonoExpr (HsReify (Reify flavour name)) res_ty
650 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
651 tcMetaTy tycon_name `thenM` \ reify_ty ->
652 unifyTauTy res_ty reify_ty `thenM_`
653 returnM (HsReify (ReifyOut flavour name))
655 tycon_name = case flavour of
656 ReifyDecl -> DsMeta.declTyConName
657 ReifyType -> DsMeta.typeTyConName
658 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
663 %************************************************************************
667 %************************************************************************
670 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
674 %************************************************************************
676 \subsection{@tcApp@ typchecks an application}
678 %************************************************************************
682 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
683 -> TcType -- Expected result type of application
684 -> TcM TcExpr -- Translated fun and args
686 tcApp (HsApp e1 e2) args res_ty
687 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
689 tcApp fun args res_ty
690 = -- First type-check the function
691 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
693 addErrCtxt (wrongArgsCtxt "too many" fun args) (
694 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
695 split_fun_ty fun_ty (length args)
696 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
698 -- Now typecheck the args
700 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
702 -- Unify with expected result after type-checking the args
703 -- so that the info from args percolates to actual_result_ty.
704 -- This is when we might detect a too-few args situation.
705 -- (One can think of cases when the opposite order would give
706 -- a better error message.)
707 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
708 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
710 returnM (co_fn <$> foldl HsApp fun' args')
713 -- If an error happens we try to figure out whether the
714 -- function has been given too many or too few arguments,
716 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
717 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
718 zonkTcType actual_res_ty `thenM` \ act_ty' ->
720 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
721 (env2, act_ty'') = tidyOpenType env1 act_ty'
722 (exp_args, _) = tcSplitFunTys exp_ty''
723 (act_args, _) = tcSplitFunTys act_ty''
725 len_act_args = length act_args
726 len_exp_args = length exp_args
728 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
729 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
730 | otherwise = appCtxt fun args
732 returnM (env2, message)
735 split_fun_ty :: TcType -- The type of the function
736 -> Int -- Number of arguments
737 -> TcM ([TcType], -- Function argument types
738 TcType) -- Function result types
740 split_fun_ty fun_ty 0
741 = returnM ([], fun_ty)
743 split_fun_ty fun_ty n
744 = -- Expect the function to have type A->B
745 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
746 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
747 returnM (arg_ty:arg_tys, final_res_ty)
751 tcArg :: RenamedHsExpr -- The function (for error messages)
752 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
753 -> TcM TcExpr -- Resulting argument and LIE
755 tcArg the_fun (arg, expected_arg_ty, arg_no)
756 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
757 tcExpr arg expected_arg_ty
761 %************************************************************************
763 \subsection{@tcId@ typchecks an identifier occurrence}
765 %************************************************************************
767 tcId instantiates an occurrence of an Id.
768 The instantiate_it loop runs round instantiating the Id.
769 It has to be a loop because we are now prepared to entertain
771 f:: forall a. Eq a => forall b. Baz b => tau
772 We want to instantiate this to
773 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
775 The -fno-method-sharing flag controls what happens so far as the LIE
776 is concerned. The default case is that for an overloaded function we
777 generate a "method" Id, and add the Method Inst to the LIE. So you get
780 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
781 If you specify -fno-method-sharing, the dictionary application
782 isn't shared, so we get
784 f = /\a (d:Num a) (x:a) -> (+) a d x x
785 This gets a bit less sharing, but
786 a) it's better for RULEs involving overloaded functions
787 b) perhaps fewer separated lambdas
790 tcId :: Name -> TcM (TcExpr, TcType)
791 tcId name -- Look up the Id and instantiate its type
792 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
794 -- Check for cross-stage lifting
796 getStage `thenM` \ use_stage ->
798 Brack use_lvl ps_var lie_var
799 | use_lvl > bind_lvl && not (isExternalName name)
800 -> -- E.g. \x -> [| h x |]
801 -- We must behave as if the reference to x was
803 -- We use 'x' itself as the splice proxy, used by
804 -- the desugarer to stitch it all back together
805 -- NB: isExernalName is true of top level things,
806 -- and false of nested bindings
811 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
812 -- If x is polymorphic, its occurrence sites might
813 -- have different instantiations, so we can't use plain
814 -- 'x' as the splice proxy name. I don't know how to
815 -- solve this, and it's probably unimportant, so I'm
816 -- just going to flag an error for now
819 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
820 -- Put the 'lift' constraint into the right LIE
822 -- Update the pending splices
823 readMutVar ps_var `thenM` \ ps ->
824 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
826 returnM (HsVar id, id_ty))
830 use_lvl = metaLevel use_stage
832 checkTc (wellStaged bind_lvl use_lvl)
833 (badStageErr id bind_lvl use_lvl) `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 badStageErr id bind_lvl use_lvl
1052 = ptext SLIT("Stage error:") <+> quotes (ppr id) <+>
1053 hsep [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
1054 ptext SLIT("but used at stage") <+> ppr use_lvl]
1057 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1060 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1063 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1066 = hang (ptext SLIT("When checking the type signature of the expression:"))
1070 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1072 fieldCtxt field_name
1073 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1075 funAppCtxt fun arg arg_no
1076 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1077 quotes (ppr fun) <> text ", namely"])
1078 4 (quotes (ppr arg))
1081 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1084 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1087 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1089 illegalBracket level
1090 = ptext SLIT("Illegal bracket at level") <+> ppr level
1093 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1095 the_app = foldl HsApp fun args -- Used in error messages
1097 lurkingRank2Err fun fun_ty
1098 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1099 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1100 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1103 = hang (ptext SLIT("No constructor has all these fields:"))
1104 4 (pprQuotedList (recBindFields rbinds))
1106 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1107 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1110 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1112 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1113 missingStrictFields con fields
1116 rest | null fields = empty -- Happens for non-record constructors
1117 -- with strict fields
1118 | otherwise = colon <+> pprWithCommas ppr fields
1120 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1121 ptext SLIT("does not have the required strict field(s)")
1124 missingFields :: DataCon -> [FieldLabel] -> SDoc
1125 missingFields con fields
1126 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1127 <+> pprWithCommas ppr fields
1129 polySpliceErr :: Id -> SDoc
1131 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1133 wrongArgsCtxt too_many_or_few fun args
1134 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1135 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1136 <+> ptext SLIT("arguments in the call"))
1137 4 (parens (ppr the_app))
1139 the_app = foldl HsApp fun args -- Used in error messages