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 ( RecFlag(..), 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 TcSimplify ( tcSimplifyIPs )
43 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
44 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
45 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
46 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
47 isSigmaTy, mkFunTy, mkFunTys,
48 mkTyConApp, mkClassPred, tcFunArgTy,
49 tyVarsOfTypes, isLinearPred,
50 liftedTypeKind, openTypeKind,
51 tcSplitSigmaTy, tcTyConAppTyCon,
54 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
55 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector, isDataConWrapId_maybe )
56 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks )
58 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
59 import Subst ( mkTopTyVarSubst, substTheta, substTy )
60 import VarSet ( emptyVarSet, elemVarSet )
61 import TysWiredIn ( boolTy )
62 import PrelNames ( cCallableClassName, cReturnableClassName,
63 enumFromName, enumFromThenName,
64 enumFromToName, enumFromThenToName,
65 enumFromToPName, enumFromThenToPName,
68 import ListSetOps ( minusList )
70 import HscTypes ( TyThing(..) )
77 %************************************************************************
79 \subsection{Main wrappers}
81 %************************************************************************
84 tcExpr :: RenamedHsExpr -- Expession to type check
85 -> TcSigmaType -- Expected type (could be a polytpye)
86 -> TcM TcExpr -- Generalised expr with expected type
88 tcExpr expr expected_ty
89 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
90 tc_expr' expr expected_ty
92 tc_expr' expr expected_ty
93 | not (isSigmaTy expected_ty) -- Monomorphic case
94 = tcMonoExpr expr expected_ty
97 = tcGen expected_ty emptyVarSet (
99 ) `thenM` \ (gen_fn, expr') ->
100 returnM (gen_fn <$> expr')
104 %************************************************************************
106 \subsection{The TAUT rules for variables}
108 %************************************************************************
111 tcMonoExpr :: RenamedHsExpr -- Expession to type check
112 -> TcRhoType -- Expected type (could be a type variable)
113 -- Definitely no foralls at the top
117 tcMonoExpr (HsVar name) res_ty
118 = tcId name `thenM` \ (expr', id_ty) ->
119 tcSubExp res_ty id_ty `thenM` \ co_fn ->
120 returnM (co_fn <$> expr')
122 tcMonoExpr (HsIPVar ip) res_ty
123 = -- Implicit parameters must have a *tau-type* not a
124 -- type scheme. We enforce this by creating a fresh
125 -- type variable as its type. (Because res_ty may not
127 newTyVarTy openTypeKind `thenM` \ ip_ty ->
128 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
129 extendLIE inst `thenM_`
130 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
131 returnM (co_fn <$> HsIPVar ip')
135 %************************************************************************
137 \subsection{Expressions type signatures}
139 %************************************************************************
142 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
143 = addErrCtxt (exprSigCtxt in_expr) $
144 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
145 tcExpr expr sig_tc_ty `thenM` \ expr' ->
147 -- Must instantiate the outer for-alls of sig_tc_ty
148 -- else we risk instantiating a ? res_ty to a forall-type
149 -- which breaks the invariant that tcMonoExpr only returns phi-types
150 tcInstCall SignatureOrigin sig_tc_ty `thenM` \ (inst_fn, inst_sig_ty) ->
151 tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
153 returnM (co_fn <$> inst_fn expr')
155 tcMonoExpr (HsType ty) res_ty
156 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
157 -- This is the syntax for type applications that I was planning
158 -- but there are difficulties (e.g. what order for type args)
159 -- so it's not enabled yet.
160 -- Can't eliminate it altogether from the parser, because the
161 -- same parser parses *patterns*.
165 %************************************************************************
167 \subsection{Other expression forms}
169 %************************************************************************
172 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
173 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
174 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
175 returnM (HsPar expr')
176 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
177 returnM (HsSCC lbl expr')
180 tcMonoExpr (NegApp expr neg_name) res_ty
181 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
182 -- ToDo: use tcSyntaxName
184 tcMonoExpr (HsLam match) res_ty
185 = tcMatchLambda match res_ty `thenM` \ match' ->
186 returnM (HsLam match')
188 tcMonoExpr (HsApp e1 e2) res_ty
189 = tcApp e1 [e2] res_ty
192 Note that the operators in sections are expected to be binary, and
193 a type error will occur if they aren't.
196 -- Left sections, equivalent to
203 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
204 = tcExpr_id op `thenM` \ (op', op_ty) ->
205 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
206 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
207 addErrCtxt (exprCtxt in_expr) $
208 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
209 returnM (co_fn <$> SectionL arg1' op')
211 -- Right sections, equivalent to \ x -> x op expr, or
214 tcMonoExpr in_expr@(SectionR op arg2) res_ty
215 = tcExpr_id op `thenM` \ (op', op_ty) ->
216 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
217 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
218 addErrCtxt (exprCtxt in_expr) $
219 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
220 returnM (co_fn <$> SectionR op' arg2')
222 -- equivalent to (op e1) e2:
224 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
225 = tcExpr_id op `thenM` \ (op', op_ty) ->
226 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
227 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
228 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
229 addErrCtxt (exprCtxt in_expr) $
230 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
231 returnM (OpApp arg1' op' fix arg2')
235 tcMonoExpr (HsLet binds expr) res_ty
238 binds -- Bindings to check
239 (tcMonoExpr expr res_ty)
241 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
242 = addSrcLoc src_loc $
243 addErrCtxt (caseCtxt in_expr) $
245 -- Typecheck the case alternatives first.
246 -- The case patterns tend to give good type info to use
247 -- when typechecking the scrutinee. For example
250 -- will report that map is applied to too few arguments
252 -- Not only that, but it's better to check the matches on their
253 -- own, so that we get the expected results for scoped type variables.
255 -- (p::a, q::b) -> (q,p)
256 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
257 -- claimed by the pattern signatures. But if we typechecked the
258 -- match with x in scope and x's type as the expected type, we'd be hosed.
260 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
262 addErrCtxt (caseScrutCtxt scrut) (
263 tcMonoExpr scrut scrut_ty
264 ) `thenM` \ scrut' ->
266 returnM (HsCase scrut' matches' src_loc)
268 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
269 = addSrcLoc src_loc $
270 addErrCtxt (predCtxt pred) (
271 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
273 zapToType res_ty `thenM` \ res_ty' ->
274 -- C.f. the call to zapToType in TcMatches.tcMatches
276 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
277 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
278 returnM (HsIf pred' b1' b2' src_loc)
280 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
281 = addSrcLoc src_loc $
282 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
283 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
285 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
286 = unifyListTy res_ty `thenM` \ elt_ty ->
287 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
288 returnM (ExplicitList elt_ty exprs')
291 = addErrCtxt (listCtxt expr) $
292 tcMonoExpr expr elt_ty
294 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
295 = unifyPArrTy res_ty `thenM` \ elt_ty ->
296 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
297 returnM (ExplicitPArr elt_ty exprs')
300 = addErrCtxt (parrCtxt expr) $
301 tcMonoExpr expr elt_ty
303 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
304 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
305 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
306 returnM (ExplicitTuple exprs' boxity)
310 %************************************************************************
314 %************************************************************************
316 The interesting thing about @ccall@ is that it is just a template
317 which we instantiate by filling in details about the types of its
318 argument and result (ie minimal typechecking is performed). So, the
319 basic story is that we allocate a load of type variables (to hold the
320 arg/result types); unify them with the args/result; and store them for
324 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
326 = getDOpts `thenM` \ dflags ->
328 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
329 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
330 text "Either compile with -fvia-C, or, better, rewrite your code",
331 text "to use the foreign function interface. _casm_s are deprecated",
332 text "and support for them may one day disappear."])
335 -- Get the callable and returnable classes.
336 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
337 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
338 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
340 new_arg_dict (arg, arg_ty)
341 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
342 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
343 returnM arg_dicts -- Actually a singleton bag
345 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
349 let tv_idxs | null args = []
350 | otherwise = [1..length args]
352 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
353 tcMonoExprs args arg_tys `thenM` \ args' ->
355 -- The argument types can be unlifted or lifted; the result
356 -- type must, however, be lifted since it's an argument to the IO
358 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
360 io_result_ty = mkTyConApp ioTyCon [result_ty]
362 unifyTauTy res_ty io_result_ty `thenM_`
364 -- Construct the extra insts, which encode the
365 -- constraints on the argument and result types.
366 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
367 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
368 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
369 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
373 %************************************************************************
375 Record construction and update
377 %************************************************************************
380 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
381 = addErrCtxt (recordConCtxt expr) $
382 tcId con_name `thenM` \ (con_expr, con_tau) ->
384 (_, record_ty) = tcSplitFunTys con_tau
385 (tycon, ty_args) = tcSplitTyConApp record_ty
387 ASSERT( isAlgTyCon tycon )
388 unifyTauTy res_ty record_ty `thenM_`
390 -- Check that the record bindings match the constructor
391 -- con_name is syntactically constrained to be a data constructor
392 tcLookupDataCon con_name `thenM` \ data_con ->
394 bad_fields = badFields rbinds data_con
396 if notNull bad_fields then
397 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
398 failM -- Fail now, because tcRecordBinds will crash on a bad field
401 -- Typecheck the record bindings
402 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
404 -- Check for missing fields
405 checkMissingFields data_con rbinds `thenM_`
407 returnM (RecordConOut data_con con_expr rbinds')
409 -- The main complication with RecordUpd is that we need to explicitly
410 -- handle the *non-updated* fields. Consider:
412 -- data T a b = MkT1 { fa :: a, fb :: b }
413 -- | MkT2 { fa :: a, fc :: Int -> Int }
414 -- | MkT3 { fd :: a }
416 -- upd :: T a b -> c -> T a c
417 -- upd t x = t { fb = x}
419 -- The type signature on upd is correct (i.e. the result should not be (T a b))
420 -- because upd should be equivalent to:
422 -- upd t x = case t of
423 -- MkT1 p q -> MkT1 p x
424 -- MkT2 a b -> MkT2 p b
425 -- MkT3 d -> error ...
427 -- So we need to give a completely fresh type to the result record,
428 -- and then constrain it by the fields that are *not* updated ("p" above).
430 -- Note that because MkT3 doesn't contain all the fields being updated,
431 -- its RHS is simply an error, so it doesn't impose any type constraints
433 -- All this is done in STEP 4 below.
435 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
436 = addErrCtxt (recordUpdCtxt expr) $
439 -- Check that the field names are really field names
440 ASSERT( notNull rbinds )
442 field_names = recBindFields rbinds
444 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
446 bad_guys = [ addErrTc (notSelector field_name)
447 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
449 Just (AnId sel_id) -> not (isRecordSelector sel_id)
453 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
456 -- Figure out the tycon and data cons from the first field name
458 -- It's OK to use the non-tc splitters here (for a selector)
459 (Just (AnId sel_id) : _) = maybe_sel_ids
461 (_, _, tau) = tcSplitSigmaTy (idType sel_id) -- Selectors can be overloaded
462 -- when the data type has a context
463 data_ty = tcFunArgTy tau -- Must succeed since sel_id is a selector
464 tycon = tcTyConAppTyCon data_ty
465 data_cons = tyConDataCons tycon
466 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
468 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
471 -- Check that at least one constructor has all the named fields
472 -- i.e. has an empty set of bad fields returned by badFields
473 checkTc (any (null . badFields rbinds) data_cons)
474 (badFieldsUpd rbinds) `thenM_`
477 -- Typecheck the update bindings.
478 -- (Do this after checking for bad fields in case there's a field that
479 -- doesn't match the constructor.)
481 result_record_ty = mkTyConApp tycon result_inst_tys
483 unifyTauTy res_ty result_record_ty `thenM_`
484 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
487 -- Use the un-updated fields to find a vector of booleans saying
488 -- which type arguments must be the same in updatee and result.
490 -- WARNING: this code assumes that all data_cons in a common tycon
491 -- have FieldLabels abstracted over the same tyvars.
493 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
494 con_field_lbls_s = map dataConFieldLabels data_cons
496 -- A constructor is only relevant to this process if
497 -- it contains all the fields that are being updated
498 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
499 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
501 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
502 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
504 mk_inst_ty (tyvar, result_inst_ty)
505 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
506 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
508 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
511 -- Typecheck the expression to be updated
513 record_ty = mkTyConApp tycon inst_tys
515 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
518 -- Figure out the LIE we need. We have to generate some
519 -- dictionaries for the data type context, since we are going to
520 -- do pattern matching over the data cons.
522 -- What dictionaries do we need?
523 -- We just take the context of the type constructor
525 theta' = substTheta inst_env (tyConTheta tycon)
527 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
528 extendLIEs dicts `thenM_`
531 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
535 %************************************************************************
537 Arithmetic sequences e.g. [a,b..]
538 and their parallel-array counterparts e.g. [: a,b.. :]
541 %************************************************************************
544 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
545 = unifyListTy res_ty `thenM` \ elt_ty ->
546 tcMonoExpr expr elt_ty `thenM` \ expr' ->
548 newMethodFromName (ArithSeqOrigin seq)
549 elt_ty enumFromName `thenM` \ enum_from ->
551 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
553 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
554 = addErrCtxt (arithSeqCtxt in_expr) $
555 unifyListTy res_ty `thenM` \ elt_ty ->
556 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
557 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
558 newMethodFromName (ArithSeqOrigin seq)
559 elt_ty enumFromThenName `thenM` \ enum_from_then ->
561 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
564 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
565 = addErrCtxt (arithSeqCtxt in_expr) $
566 unifyListTy res_ty `thenM` \ elt_ty ->
567 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
568 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
569 newMethodFromName (ArithSeqOrigin seq)
570 elt_ty enumFromToName `thenM` \ enum_from_to ->
572 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
574 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
575 = addErrCtxt (arithSeqCtxt in_expr) $
576 unifyListTy res_ty `thenM` \ elt_ty ->
577 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
578 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
579 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
580 newMethodFromName (ArithSeqOrigin seq)
581 elt_ty enumFromThenToName `thenM` \ eft ->
583 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
585 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
586 = addErrCtxt (parrSeqCtxt in_expr) $
587 unifyPArrTy res_ty `thenM` \ elt_ty ->
588 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
589 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
590 newMethodFromName (PArrSeqOrigin seq)
591 elt_ty enumFromToPName `thenM` \ enum_from_to ->
593 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
595 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
596 = addErrCtxt (parrSeqCtxt in_expr) $
597 unifyPArrTy res_ty `thenM` \ elt_ty ->
598 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
599 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
600 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
601 newMethodFromName (PArrSeqOrigin seq)
602 elt_ty enumFromThenToPName `thenM` \ eft ->
604 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
606 tcMonoExpr (PArrSeqIn _) _
607 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
608 -- the parser shouldn't have generated it and the renamer shouldn't have
613 %************************************************************************
617 %************************************************************************
620 #ifdef GHCI /* Only if bootstrapped */
621 -- Rename excludes these cases otherwise
623 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
625 tcMonoExpr (HsBracket brack loc) 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)
650 tcMonoExpr (HsReify (Reify flavour name)) res_ty
651 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
652 tcMetaTy tycon_name `thenM` \ reify_ty ->
653 unifyTauTy res_ty reify_ty `thenM_`
654 returnM (HsReify (ReifyOut flavour name))
656 tycon_name = case flavour of
657 ReifyDecl -> DsMeta.decTyConName
658 ReifyType -> DsMeta.typTyConName
659 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
664 %************************************************************************
668 %************************************************************************
671 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
675 %************************************************************************
677 \subsection{@tcApp@ typchecks an application}
679 %************************************************************************
683 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
684 -> TcType -- Expected result type of application
685 -> TcM TcExpr -- Translated fun and args
687 tcApp (HsApp e1 e2) args res_ty
688 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
690 tcApp fun args res_ty
691 = -- First type-check the function
692 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
694 addErrCtxt (wrongArgsCtxt "too many" fun args) (
695 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
696 split_fun_ty fun_ty (length args)
697 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
699 -- Now typecheck the args
701 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
703 -- Unify with expected result after type-checking the args
704 -- so that the info from args percolates to actual_result_ty.
705 -- This is when we might detect a too-few args situation.
706 -- (One can think of cases when the opposite order would give
707 -- a better error message.)
708 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
709 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
711 returnM (co_fn <$> foldl HsApp fun' args')
714 -- If an error happens we try to figure out whether the
715 -- function has been given too many or too few arguments,
717 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
718 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
719 zonkTcType actual_res_ty `thenM` \ act_ty' ->
721 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
722 (env2, act_ty'') = tidyOpenType env1 act_ty'
723 (exp_args, _) = tcSplitFunTys exp_ty''
724 (act_args, _) = tcSplitFunTys act_ty''
726 len_act_args = length act_args
727 len_exp_args = length exp_args
729 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
730 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
731 | otherwise = appCtxt fun args
733 returnM (env2, message)
736 split_fun_ty :: TcType -- The type of the function
737 -> Int -- Number of arguments
738 -> TcM ([TcType], -- Function argument types
739 TcType) -- Function result types
741 split_fun_ty fun_ty 0
742 = returnM ([], fun_ty)
744 split_fun_ty fun_ty n
745 = -- Expect the function to have type A->B
746 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
747 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
748 returnM (arg_ty:arg_tys, final_res_ty)
752 tcArg :: RenamedHsExpr -- The function (for error messages)
753 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
754 -> TcM TcExpr -- Resulting argument and LIE
756 tcArg the_fun (arg, expected_arg_ty, arg_no)
757 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
758 tcExpr arg expected_arg_ty
762 %************************************************************************
764 \subsection{@tcId@ typchecks an identifier occurrence}
766 %************************************************************************
768 tcId instantiates an occurrence of an Id.
769 The instantiate_it loop runs round instantiating the Id.
770 It has to be a loop because we are now prepared to entertain
772 f:: forall a. Eq a => forall b. Baz b => tau
773 We want to instantiate this to
774 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
776 The -fno-method-sharing flag controls what happens so far as the LIE
777 is concerned. The default case is that for an overloaded function we
778 generate a "method" Id, and add the Method Inst to the LIE. So you get
781 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
782 If you specify -fno-method-sharing, the dictionary application
783 isn't shared, so we get
785 f = /\a (d:Num a) (x:a) -> (+) a d x x
786 This gets a bit less sharing, but
787 a) it's better for RULEs involving overloaded functions
788 b) perhaps fewer separated lambdas
791 tcId :: Name -> TcM (TcExpr, TcType)
792 tcId name -- Look up the Id and instantiate its type
793 = tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
795 -- Check for cross-stage lifting
797 getStage `thenM` \ use_stage ->
799 Brack use_lvl ps_var lie_var
800 | use_lvl > bind_lvl && not (isExternalName name)
801 -> -- E.g. \x -> [| h x |]
802 -- We must behave as if the reference to x was
804 -- We use 'x' itself as the splice proxy, used by
805 -- the desugarer to stitch it all back together
806 -- NB: isExernalName is true of top level things,
807 -- and false of nested bindings
812 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
813 -- If x is polymorphic, its occurrence sites might
814 -- have different instantiations, so we can't use plain
815 -- 'x' as the splice proxy name. I don't know how to
816 -- solve this, and it's probably unimportant, so I'm
817 -- just going to flag an error for now
820 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
821 -- Put the 'lift' constraint into the right LIE
823 -- Update the pending splices
824 readMutVar ps_var `thenM` \ ps ->
825 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
827 returnM (HsVar id, id_ty))
831 use_lvl = metaLevel use_stage
833 checkTc (wellStaged bind_lvl use_lvl)
834 (badStageErr id bind_lvl use_lvl) `thenM_`
836 -- This is the bit that handles the no-Template-Haskell case
837 case isDataConWrapId_maybe id of
838 Nothing -> loop (HsVar id) (idType id)
839 Just data_con -> inst_data_con id data_con
842 orig = OccurrenceOf name
844 loop (HsVar fun_id) fun_ty
845 | want_method_inst fun_ty
846 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
847 newMethodWithGivenTy orig fun_id
848 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
849 loop (HsVar meth_id) tau
853 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
854 loop (inst_fn fun) tau
857 = returnM (fun, fun_ty)
859 want_method_inst fun_ty
860 | opt_NoMethodSharing = False
861 | otherwise = case tcSplitSigmaTy fun_ty of
862 (_,[],_) -> False -- Not overloaded
863 (_,theta,_) -> not (any isLinearPred theta)
864 -- This is a slight hack.
865 -- If f :: (%x :: T) => Int -> Int
866 -- Then if we have two separate calls, (f 3, f 4), we cannot
867 -- make a method constraint that then gets shared, thus:
868 -- let m = f %x in (m 3, m 4)
869 -- because that loses the linearity of the constraint.
870 -- The simplest thing to do is never to construct a method constraint
871 -- in the first place that has a linear implicit parameter in it.
873 -- We treat data constructors differently, because we have to generate
874 -- constraints for their silly theta, which no longer appears in
875 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
876 inst_data_con id data_con
877 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
878 extendLIEs ex_dicts `thenM_`
879 returnM (mkHsDictApp (mkHsTyApp (HsVar id) ty_args) (map instToId ex_dicts),
880 mkFunTys arg_tys result_ty)
883 Typecheck expression which in most cases will be an Id.
884 The expression can return a higher-ranked type, such as
885 (forall a. a->a) -> Int
886 so we must create a HoleTyVarTy to pass in as the expected tyvar.
889 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
890 tcExpr_id (HsVar name) = tcId name
891 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
892 tcMonoExpr expr id_ty `thenM` \ expr' ->
893 readHoleResult id_ty `thenM` \ id_ty' ->
894 returnM (expr', id_ty')
898 %************************************************************************
900 \subsection{Record bindings}
902 %************************************************************************
904 Game plan for record bindings
905 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
906 1. Find the TyCon for the bindings, from the first field label.
908 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
910 For each binding field = value
912 3. Instantiate the field type (from the field label) using the type
915 4 Type check the value using tcArg, passing the field type as
916 the expected argument type.
918 This extends OK when the field types are universally quantified.
923 :: TyCon -- Type constructor for the record
924 -> [TcType] -- Args of this type constructor
925 -> RenamedRecordBinds
928 tcRecordBinds tycon ty_args rbinds
929 = mappM do_bind rbinds
931 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
933 do_bind (field_lbl_name, rhs)
934 = addErrCtxt (fieldCtxt field_lbl_name) $
935 tcLookupId field_lbl_name `thenM` \ sel_id ->
937 field_lbl = recordSelectorFieldLabel sel_id
938 field_ty = substTy tenv (fieldLabelType field_lbl)
940 ASSERT( isRecordSelector sel_id )
941 -- This lookup and assertion will surely succeed, because
942 -- we check that the fields are indeed record selectors
943 -- before calling tcRecordBinds
944 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
945 -- The caller of tcRecordBinds has already checked
946 -- that all the fields come from the same type
948 tcExpr rhs field_ty `thenM` \ rhs' ->
950 returnM (sel_id, rhs')
952 badFields rbinds data_con
953 = filter (not . (`elem` field_names)) (recBindFields rbinds)
955 field_names = map fieldLabelName (dataConFieldLabels data_con)
957 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
958 checkMissingFields data_con rbinds
959 | null field_labels -- Not declared as a record;
960 -- But C{} is still valid if no strict fields
961 = if any isMarkedStrict field_strs then
962 -- Illegal if any arg is strict
963 addErrTc (missingStrictFields data_con [])
967 | otherwise -- A record
968 = checkM (null missing_s_fields)
969 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
971 doptM Opt_WarnMissingFields `thenM` \ warn ->
972 checkM (not (warn && notNull missing_ns_fields))
973 (warnTc True (missingFields data_con missing_ns_fields))
977 = [ fl | (fl, str) <- field_info,
979 not (fieldLabelName fl `elem` field_names_used)
982 = [ fl | (fl, str) <- field_info,
983 not (isMarkedStrict str),
984 not (fieldLabelName fl `elem` field_names_used)
987 field_names_used = recBindFields rbinds
988 field_labels = dataConFieldLabels data_con
990 field_info = zipEqual "missingFields"
994 field_strs = dropList ex_theta (dataConStrictMarks data_con)
995 -- The 'drop' is because dataConStrictMarks
996 -- includes the existential dictionaries
997 (_, _, _, ex_theta, _, _) = dataConSig data_con
1000 %************************************************************************
1002 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1004 %************************************************************************
1007 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1009 tcMonoExprs [] [] = returnM []
1010 tcMonoExprs (expr:exprs) (ty:tys)
1011 = tcMonoExpr expr ty `thenM` \ expr' ->
1012 tcMonoExprs exprs tys `thenM` \ exprs' ->
1013 returnM (expr':exprs')
1017 %************************************************************************
1019 \subsection{Literals}
1021 %************************************************************************
1023 Overloaded literals.
1026 tcLit :: HsLit -> TcType -> TcM TcExpr
1027 tcLit (HsLitLit s _) res_ty
1028 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1029 newDicts (LitLitOrigin (unpackFS s))
1030 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1031 extendLIEs dicts `thenM_`
1032 returnM (HsLit (HsLitLit s res_ty))
1035 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1040 %************************************************************************
1042 \subsection{Errors and contexts}
1044 %************************************************************************
1046 Boring and alphabetical:
1049 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1052 badStageErr id bind_lvl use_lvl
1053 = ptext SLIT("Stage error:") <+> quotes (ppr id) <+>
1054 hsep [ptext SLIT("is bound at stage") <+> ppr bind_lvl,
1055 ptext SLIT("but used at stage") <+> ppr use_lvl]
1058 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1061 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1064 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1067 = hang (ptext SLIT("When checking the type signature of the expression:"))
1071 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1073 fieldCtxt field_name
1074 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1076 funAppCtxt fun arg arg_no
1077 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1078 quotes (ppr fun) <> text ", namely"])
1079 4 (quotes (ppr arg))
1082 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1085 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1088 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1090 illegalBracket level
1091 = ptext SLIT("Illegal bracket at level") <+> ppr level
1094 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1096 the_app = foldl HsApp fun args -- Used in error messages
1098 lurkingRank2Err fun fun_ty
1099 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1100 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1101 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1104 = hang (ptext SLIT("No constructor has all these fields:"))
1105 4 (pprQuotedList (recBindFields rbinds))
1107 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1108 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1111 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1113 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1114 missingStrictFields con fields
1117 rest | null fields = empty -- Happens for non-record constructors
1118 -- with strict fields
1119 | otherwise = colon <+> pprWithCommas ppr fields
1121 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1122 ptext SLIT("does not have the required strict field(s)")
1125 missingFields :: DataCon -> [FieldLabel] -> SDoc
1126 missingFields con fields
1127 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1128 <+> pprWithCommas ppr fields
1130 polySpliceErr :: Id -> SDoc
1132 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1134 wrongArgsCtxt too_many_or_few fun args
1135 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1136 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1137 <+> ptext SLIT("arguments in the call"))
1138 4 (parens (ppr the_app))
1140 the_app = foldl HsApp fun args -- Used in error messages