2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcExpr_id, tcMonoExpr ) where
9 #include "HsVersions.h"
11 #ifdef GHCI /* Only if bootstrapped */
12 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
13 import HsSyn ( HsReify(..), ReifyFlavour(..) )
14 import TcType ( isTauTy )
15 import TcEnv ( bracketOK, tcMetaTy, checkWellStaged, metaLevel )
16 import Name ( isExternalName )
17 import qualified DsMeta
20 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..), 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 ( 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
37 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts )
38 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
39 import TcPat ( badFieldCon )
40 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
41 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
42 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
43 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
44 isSigmaTy, mkFunTy, mkFunTys,
45 mkTyConApp, mkClassPred,
46 tyVarsOfTypes, isLinearPred,
47 liftedTypeKind, openTypeKind,
48 tcSplitSigmaTy, tidyOpenType
50 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
51 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector )
52 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks, dataConWrapId )
54 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
55 import Subst ( mkTopTyVarSubst, substTheta, substTy )
56 import VarSet ( emptyVarSet, elemVarSet )
57 import TysWiredIn ( boolTy )
58 import PrelNames ( cCallableClassName, cReturnableClassName,
59 enumFromName, enumFromThenName,
60 enumFromToName, enumFromThenToName,
61 enumFromToPName, enumFromThenToPName,
64 import ListSetOps ( minusList )
66 import HscTypes ( TyThing(..) )
73 %************************************************************************
75 \subsection{Main wrappers}
77 %************************************************************************
80 tcExpr :: RenamedHsExpr -- Expession to type check
81 -> TcSigmaType -- Expected type (could be a polytpye)
82 -> TcM TcExpr -- Generalised expr with expected type
84 tcExpr expr expected_ty
85 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
86 tc_expr' expr expected_ty
88 tc_expr' expr expected_ty
89 | not (isSigmaTy expected_ty) -- Monomorphic case
90 = tcMonoExpr expr expected_ty
93 = tcGen expected_ty emptyVarSet (
95 ) `thenM` \ (gen_fn, expr') ->
96 returnM (gen_fn <$> expr')
100 %************************************************************************
102 \subsection{The TAUT rules for variables}
104 %************************************************************************
107 tcMonoExpr :: RenamedHsExpr -- Expession to type check
108 -> TcRhoType -- Expected type (could be a type variable)
109 -- Definitely no foralls at the top
113 tcMonoExpr (HsVar name) res_ty
114 = tcId name `thenM` \ (expr', id_ty) ->
115 tcSubExp res_ty id_ty `thenM` \ co_fn ->
116 returnM (co_fn <$> expr')
118 tcMonoExpr (HsIPVar ip) res_ty
119 = -- Implicit parameters must have a *tau-type* not a
120 -- type scheme. We enforce this by creating a fresh
121 -- type variable as its type. (Because res_ty may not
123 newTyVarTy openTypeKind `thenM` \ ip_ty ->
124 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
125 extendLIE inst `thenM_`
126 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
127 returnM (co_fn <$> HsIPVar ip')
131 %************************************************************************
133 \subsection{Expressions type signatures}
135 %************************************************************************
138 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
139 = addErrCtxt (exprSigCtxt in_expr) $
140 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
141 tcExpr expr sig_tc_ty `thenM` \ expr' ->
143 -- Must instantiate the outer for-alls of sig_tc_ty
144 -- else we risk instantiating a ? res_ty to a forall-type
145 -- which breaks the invariant that tcMonoExpr only returns phi-types
146 tcInstCall SignatureOrigin sig_tc_ty `thenM` \ (inst_fn, inst_sig_ty) ->
147 tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
149 returnM (co_fn <$> inst_fn expr')
151 tcMonoExpr (HsType ty) res_ty
152 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
153 -- This is the syntax for type applications that I was planning
154 -- but there are difficulties (e.g. what order for type args)
155 -- so it's not enabled yet.
156 -- Can't eliminate it altogether from the parser, because the
157 -- same parser parses *patterns*.
161 %************************************************************************
163 \subsection{Other expression forms}
165 %************************************************************************
168 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
169 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
170 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
171 returnM (HsPar expr')
172 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
173 returnM (HsSCC lbl expr')
175 tcMonoExpr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
176 returnM (HsCoreAnn lbl expr')
177 tcMonoExpr (NegApp expr neg_name) res_ty
178 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
179 -- ToDo: use tcSyntaxName
181 tcMonoExpr (HsLam match) res_ty
182 = tcMatchLambda match res_ty `thenM` \ match' ->
183 returnM (HsLam match')
185 tcMonoExpr (HsApp e1 e2) res_ty
186 = tcApp e1 [e2] res_ty
189 Note that the operators in sections are expected to be binary, and
190 a type error will occur if they aren't.
193 -- Left sections, equivalent to
200 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
201 = tcExpr_id op `thenM` \ (op', op_ty) ->
202 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
203 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
204 addErrCtxt (exprCtxt in_expr) $
205 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
206 returnM (co_fn <$> SectionL arg1' op')
208 -- Right sections, equivalent to \ x -> x op expr, or
211 tcMonoExpr in_expr@(SectionR op arg2) res_ty
212 = tcExpr_id op `thenM` \ (op', op_ty) ->
213 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
214 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
215 addErrCtxt (exprCtxt in_expr) $
216 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
217 returnM (co_fn <$> SectionR op' arg2')
219 -- equivalent to (op e1) e2:
221 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
222 = tcExpr_id op `thenM` \ (op', op_ty) ->
223 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
224 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
225 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
226 addErrCtxt (exprCtxt in_expr) $
227 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
228 returnM (OpApp arg1' op' fix arg2')
232 tcMonoExpr (HsLet binds expr) res_ty
235 binds -- Bindings to check
236 (tcMonoExpr expr res_ty)
238 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
239 = addSrcLoc src_loc $
240 addErrCtxt (caseCtxt in_expr) $
242 -- Typecheck the case alternatives first.
243 -- The case patterns tend to give good type info to use
244 -- when typechecking the scrutinee. For example
247 -- will report that map is applied to too few arguments
249 -- Not only that, but it's better to check the matches on their
250 -- own, so that we get the expected results for scoped type variables.
252 -- (p::a, q::b) -> (q,p)
253 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
254 -- claimed by the pattern signatures. But if we typechecked the
255 -- match with x in scope and x's type as the expected type, we'd be hosed.
257 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
259 addErrCtxt (caseScrutCtxt scrut) (
260 tcMonoExpr scrut scrut_ty
261 ) `thenM` \ scrut' ->
263 returnM (HsCase scrut' matches' src_loc)
265 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
266 = addSrcLoc src_loc $
267 addErrCtxt (predCtxt pred) (
268 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
270 zapToType res_ty `thenM` \ res_ty' ->
271 -- C.f. the call to zapToType in TcMatches.tcMatches
273 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
274 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
275 returnM (HsIf pred' b1' b2' src_loc)
277 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
278 = addSrcLoc src_loc $
279 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
280 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
282 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
283 = unifyListTy res_ty `thenM` \ elt_ty ->
284 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
285 returnM (ExplicitList elt_ty exprs')
288 = addErrCtxt (listCtxt expr) $
289 tcMonoExpr expr elt_ty
291 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
292 = unifyPArrTy res_ty `thenM` \ elt_ty ->
293 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
294 returnM (ExplicitPArr elt_ty exprs')
297 = addErrCtxt (parrCtxt expr) $
298 tcMonoExpr expr elt_ty
300 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
301 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
302 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
303 returnM (ExplicitTuple exprs' boxity)
307 %************************************************************************
311 %************************************************************************
313 The interesting thing about @ccall@ is that it is just a template
314 which we instantiate by filling in details about the types of its
315 argument and result (ie minimal typechecking is performed). So, the
316 basic story is that we allocate a load of type variables (to hold the
317 arg/result types); unify them with the args/result; and store them for
321 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
323 = getDOpts `thenM` \ dflags ->
325 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
326 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
327 text "Either compile with -fvia-C, or, better, rewrite your code",
328 text "to use the foreign function interface. _casm_s are deprecated",
329 text "and support for them may one day disappear."])
332 -- Get the callable and returnable classes.
333 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
334 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
335 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
337 new_arg_dict (arg, arg_ty)
338 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
339 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
340 returnM arg_dicts -- Actually a singleton bag
342 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
346 let tv_idxs | null args = []
347 | otherwise = [1..length args]
349 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
350 tcMonoExprs args arg_tys `thenM` \ args' ->
352 -- The argument types can be unlifted or lifted; the result
353 -- type must, however, be lifted since it's an argument to the IO
355 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
357 io_result_ty = mkTyConApp ioTyCon [result_ty]
359 unifyTauTy res_ty io_result_ty `thenM_`
361 -- Construct the extra insts, which encode the
362 -- constraints on the argument and result types.
363 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
364 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
365 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
366 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
370 %************************************************************************
372 Record construction and update
374 %************************************************************************
377 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
378 = addErrCtxt (recordConCtxt expr) $
379 tcId con_name `thenM` \ (con_expr, con_tau) ->
381 (_, record_ty) = tcSplitFunTys con_tau
382 (tycon, ty_args) = tcSplitTyConApp record_ty
384 ASSERT( isAlgTyCon tycon )
385 unifyTauTy res_ty record_ty `thenM_`
387 -- Check that the record bindings match the constructor
388 -- con_name is syntactically constrained to be a data constructor
389 tcLookupDataCon con_name `thenM` \ data_con ->
391 bad_fields = badFields rbinds data_con
393 if notNull bad_fields then
394 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
395 failM -- Fail now, because tcRecordBinds will crash on a bad field
398 -- Typecheck the record bindings
399 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
401 -- Check for missing fields
402 checkMissingFields data_con rbinds `thenM_`
404 returnM (RecordConOut data_con con_expr rbinds')
406 -- The main complication with RecordUpd is that we need to explicitly
407 -- handle the *non-updated* fields. Consider:
409 -- data T a b = MkT1 { fa :: a, fb :: b }
410 -- | MkT2 { fa :: a, fc :: Int -> Int }
411 -- | MkT3 { fd :: a }
413 -- upd :: T a b -> c -> T a c
414 -- upd t x = t { fb = x}
416 -- The type signature on upd is correct (i.e. the result should not be (T a b))
417 -- because upd should be equivalent to:
419 -- upd t x = case t of
420 -- MkT1 p q -> MkT1 p x
421 -- MkT2 a b -> MkT2 p b
422 -- MkT3 d -> error ...
424 -- So we need to give a completely fresh type to the result record,
425 -- and then constrain it by the fields that are *not* updated ("p" above).
427 -- Note that because MkT3 doesn't contain all the fields being updated,
428 -- its RHS is simply an error, so it doesn't impose any type constraints
430 -- All this is done in STEP 4 below.
432 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
433 = addErrCtxt (recordUpdCtxt expr) $
436 -- Check that the field names are really field names
437 ASSERT( notNull rbinds )
439 field_names = recBindFields rbinds
441 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
443 bad_guys = [ addErrTc (notSelector field_name)
444 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
445 not (is_selector maybe_sel_id)
447 is_selector (Just (AnId sel_id)) = isRecordSelector sel_id -- Excludes class ops
448 is_selector other = False
450 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
453 -- Figure out the tycon and data cons from the first field name
455 -- It's OK to use the non-tc splitters here (for a selector)
456 (Just (AnId sel_id) : _) = maybe_sel_ids
457 field_lbl = recordSelectorFieldLabel sel_id -- We've failed already if
458 tycon = fieldLabelTyCon field_lbl -- it's not a field label
459 data_cons = tyConDataCons tycon
460 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
462 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
465 -- Check that at least one constructor has all the named fields
466 -- i.e. has an empty set of bad fields returned by badFields
467 checkTc (any (null . badFields rbinds) data_cons)
468 (badFieldsUpd rbinds) `thenM_`
471 -- Typecheck the update bindings.
472 -- (Do this after checking for bad fields in case there's a field that
473 -- doesn't match the constructor.)
475 result_record_ty = mkTyConApp tycon result_inst_tys
477 unifyTauTy res_ty result_record_ty `thenM_`
478 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
481 -- Use the un-updated fields to find a vector of booleans saying
482 -- which type arguments must be the same in updatee and result.
484 -- WARNING: this code assumes that all data_cons in a common tycon
485 -- have FieldLabels abstracted over the same tyvars.
487 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
488 con_field_lbls_s = map dataConFieldLabels data_cons
490 -- A constructor is only relevant to this process if
491 -- it contains all the fields that are being updated
492 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
493 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
495 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
496 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
498 mk_inst_ty (tyvar, result_inst_ty)
499 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
500 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
502 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
505 -- Typecheck the expression to be updated
507 record_ty = mkTyConApp tycon inst_tys
509 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
512 -- Figure out the LIE we need. We have to generate some
513 -- dictionaries for the data type context, since we are going to
514 -- do pattern matching over the data cons.
516 -- What dictionaries do we need?
517 -- We just take the context of the type constructor
519 theta' = substTheta inst_env (tyConTheta tycon)
521 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
522 extendLIEs dicts `thenM_`
525 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
529 %************************************************************************
531 Arithmetic sequences e.g. [a,b..]
532 and their parallel-array counterparts e.g. [: a,b.. :]
535 %************************************************************************
538 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
539 = unifyListTy res_ty `thenM` \ elt_ty ->
540 tcMonoExpr expr elt_ty `thenM` \ expr' ->
542 newMethodFromName (ArithSeqOrigin seq)
543 elt_ty enumFromName `thenM` \ enum_from ->
545 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
547 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
548 = addErrCtxt (arithSeqCtxt in_expr) $
549 unifyListTy res_ty `thenM` \ elt_ty ->
550 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
551 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
552 newMethodFromName (ArithSeqOrigin seq)
553 elt_ty enumFromThenName `thenM` \ enum_from_then ->
555 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
558 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
559 = addErrCtxt (arithSeqCtxt in_expr) $
560 unifyListTy res_ty `thenM` \ elt_ty ->
561 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
562 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
563 newMethodFromName (ArithSeqOrigin seq)
564 elt_ty enumFromToName `thenM` \ enum_from_to ->
566 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
568 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
569 = addErrCtxt (arithSeqCtxt in_expr) $
570 unifyListTy res_ty `thenM` \ elt_ty ->
571 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
572 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
573 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
574 newMethodFromName (ArithSeqOrigin seq)
575 elt_ty enumFromThenToName `thenM` \ eft ->
577 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
579 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
580 = addErrCtxt (parrSeqCtxt in_expr) $
581 unifyPArrTy res_ty `thenM` \ elt_ty ->
582 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
583 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
584 newMethodFromName (PArrSeqOrigin seq)
585 elt_ty enumFromToPName `thenM` \ enum_from_to ->
587 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
589 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
590 = addErrCtxt (parrSeqCtxt in_expr) $
591 unifyPArrTy res_ty `thenM` \ elt_ty ->
592 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
593 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
594 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
595 newMethodFromName (PArrSeqOrigin seq)
596 elt_ty enumFromThenToPName `thenM` \ eft ->
598 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
600 tcMonoExpr (PArrSeqIn _) _
601 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
602 -- the parser shouldn't have generated it and the renamer shouldn't have
607 %************************************************************************
611 %************************************************************************
614 #ifdef GHCI /* Only if bootstrapped */
615 -- Rename excludes these cases otherwise
617 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
618 tcMonoExpr (HsBracket brack loc) res_ty = addSrcLoc loc (tcBracket brack res_ty)
620 tcMonoExpr (HsReify (Reify flavour name)) res_ty
621 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
622 tcMetaTy tycon_name `thenM` \ reify_ty ->
623 unifyTauTy res_ty reify_ty `thenM_`
624 returnM (HsReify (ReifyOut flavour name))
626 tycon_name = case flavour of
627 ReifyDecl -> DsMeta.declTyConName
628 ReifyType -> DsMeta.typeTyConName
629 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
634 %************************************************************************
638 %************************************************************************
641 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
645 %************************************************************************
647 \subsection{@tcApp@ typchecks an application}
649 %************************************************************************
653 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
654 -> TcType -- Expected result type of application
655 -> TcM TcExpr -- Translated fun and args
657 tcApp (HsApp e1 e2) args res_ty
658 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
660 tcApp fun args res_ty
661 = -- First type-check the function
662 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
664 addErrCtxt (wrongArgsCtxt "too many" fun args) (
665 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
666 split_fun_ty fun_ty (length args)
667 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
669 -- Now typecheck the args
671 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
673 -- Unify with expected result after type-checking the args
674 -- so that the info from args percolates to actual_result_ty.
675 -- This is when we might detect a too-few args situation.
676 -- (One can think of cases when the opposite order would give
677 -- a better error message.)
678 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
679 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
681 returnM (co_fn <$> foldl HsApp fun' args')
684 -- If an error happens we try to figure out whether the
685 -- function has been given too many or too few arguments,
687 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
688 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
689 zonkTcType actual_res_ty `thenM` \ act_ty' ->
691 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
692 (env2, act_ty'') = tidyOpenType env1 act_ty'
693 (exp_args, _) = tcSplitFunTys exp_ty''
694 (act_args, _) = tcSplitFunTys act_ty''
696 len_act_args = length act_args
697 len_exp_args = length exp_args
699 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
700 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
701 | otherwise = appCtxt fun args
703 returnM (env2, message)
706 split_fun_ty :: TcType -- The type of the function
707 -> Int -- Number of arguments
708 -> TcM ([TcType], -- Function argument types
709 TcType) -- Function result types
711 split_fun_ty fun_ty 0
712 = returnM ([], fun_ty)
714 split_fun_ty fun_ty n
715 = -- Expect the function to have type A->B
716 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
717 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
718 returnM (arg_ty:arg_tys, final_res_ty)
722 tcArg :: RenamedHsExpr -- The function (for error messages)
723 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
724 -> TcM TcExpr -- Resulting argument and LIE
726 tcArg the_fun (arg, expected_arg_ty, arg_no)
727 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
728 tcExpr arg expected_arg_ty
732 %************************************************************************
734 \subsection{@tcId@ typchecks an identifier occurrence}
736 %************************************************************************
738 tcId instantiates an occurrence of an Id.
739 The instantiate_it loop runs round instantiating the Id.
740 It has to be a loop because we are now prepared to entertain
742 f:: forall a. Eq a => forall b. Baz b => tau
743 We want to instantiate this to
744 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
746 The -fno-method-sharing flag controls what happens so far as the LIE
747 is concerned. The default case is that for an overloaded function we
748 generate a "method" Id, and add the Method Inst to the LIE. So you get
751 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
752 If you specify -fno-method-sharing, the dictionary application
753 isn't shared, so we get
755 f = /\a (d:Num a) (x:a) -> (+) a d x x
756 This gets a bit less sharing, but
757 a) it's better for RULEs involving overloaded functions
758 b) perhaps fewer separated lambdas
761 tcId :: Name -> TcM (TcExpr, TcType)
762 tcId name -- Look up the Id and instantiate its type
763 = -- First check whether it's a DataCon
764 -- Reason: we must not forget to chuck in the
765 -- constraints from their "silly context"
766 tcLookupGlobal_maybe name `thenM` \ maybe_thing ->
767 case maybe_thing of {
768 Just (ADataCon data_con) -> inst_data_con data_con ;
771 -- OK, so now look for ordinary Ids
772 tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
775 loop (HsVar id) (idType id) -- Non-TH case
777 #else /* GHCI is on */
778 -- Check for cross-stage lifting
779 getStage `thenM` \ use_stage ->
781 Brack use_lvl ps_var lie_var
782 | use_lvl > bind_lvl && not (isExternalName name)
783 -> -- E.g. \x -> [| h x |]
784 -- We must behave as if the reference to x was
786 -- We use 'x' itself as the splice proxy, used by
787 -- the desugarer to stitch it all back together.
788 -- If 'x' occurs many times we may get many identical
789 -- bindings of the same splice proxy, but that doesn't
790 -- matter, although it's a mite untidy.
792 -- NB: During type-checking, isExernalName is true of
793 -- top level things, and false of nested bindings
794 -- Top-level things don't need lifting.
799 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
800 -- If x is polymorphic, its occurrence sites might
801 -- have different instantiations, so we can't use plain
802 -- 'x' as the splice proxy name. I don't know how to
803 -- solve this, and it's probably unimportant, so I'm
804 -- just going to flag an error for now
807 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
808 -- Put the 'lift' constraint into the right LIE
810 -- Update the pending splices
811 readMutVar ps_var `thenM` \ ps ->
812 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
814 returnM (HsVar id, id_ty))
817 checkWellStaged (quotes (ppr id)) bind_lvl use_stage `thenM_`
818 loop (HsVar id) (idType id)
823 orig = OccurrenceOf name
825 loop (HsVar fun_id) fun_ty
826 | want_method_inst fun_ty
827 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
828 newMethodWithGivenTy orig fun_id
829 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
830 loop (HsVar meth_id) tau
834 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
835 loop (inst_fn fun) tau
838 = returnM (fun, fun_ty)
840 -- Hack Alert (want_method_inst)!
841 -- If f :: (%x :: T) => Int -> Int
842 -- Then if we have two separate calls, (f 3, f 4), we cannot
843 -- make a method constraint that then gets shared, thus:
844 -- let m = f %x in (m 3, m 4)
845 -- because that loses the linearity of the constraint.
846 -- The simplest thing to do is never to construct a method constraint
847 -- in the first place that has a linear implicit parameter in it.
848 want_method_inst fun_ty
849 | opt_NoMethodSharing = False
850 | otherwise = case tcSplitSigmaTy fun_ty of
851 (_,[],_) -> False -- Not overloaded
852 (_,theta,_) -> not (any isLinearPred theta)
855 -- We treat data constructors differently, because we have to generate
856 -- constraints for their silly theta, which no longer appears in
857 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
858 inst_data_con data_con
859 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
860 extendLIEs ex_dicts `thenM_`
861 returnM (mkHsDictApp (mkHsTyApp (HsVar (dataConWrapId data_con)) ty_args)
862 (map instToId ex_dicts),
863 mkFunTys arg_tys result_ty)
866 Typecheck expression which in most cases will be an Id.
867 The expression can return a higher-ranked type, such as
868 (forall a. a->a) -> Int
869 so we must create a HoleTyVarTy to pass in as the expected tyvar.
872 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
873 tcExpr_id (HsVar name) = tcId name
874 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
875 tcMonoExpr expr id_ty `thenM` \ expr' ->
876 readHoleResult id_ty `thenM` \ id_ty' ->
877 returnM (expr', id_ty')
881 %************************************************************************
883 \subsection{Record bindings}
885 %************************************************************************
887 Game plan for record bindings
888 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
889 1. Find the TyCon for the bindings, from the first field label.
891 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
893 For each binding field = value
895 3. Instantiate the field type (from the field label) using the type
898 4 Type check the value using tcArg, passing the field type as
899 the expected argument type.
901 This extends OK when the field types are universally quantified.
906 :: TyCon -- Type constructor for the record
907 -> [TcType] -- Args of this type constructor
908 -> RenamedRecordBinds
911 tcRecordBinds tycon ty_args rbinds
912 = mappM do_bind rbinds
914 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
916 do_bind (field_lbl_name, rhs)
917 = addErrCtxt (fieldCtxt field_lbl_name) $
918 tcLookupId field_lbl_name `thenM` \ sel_id ->
920 field_lbl = recordSelectorFieldLabel sel_id
921 field_ty = substTy tenv (fieldLabelType field_lbl)
923 ASSERT( isRecordSelector sel_id )
924 -- This lookup and assertion will surely succeed, because
925 -- we check that the fields are indeed record selectors
926 -- before calling tcRecordBinds
927 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
928 -- The caller of tcRecordBinds has already checked
929 -- that all the fields come from the same type
931 tcExpr rhs field_ty `thenM` \ rhs' ->
933 returnM (sel_id, rhs')
935 badFields rbinds data_con
936 = filter (not . (`elem` field_names)) (recBindFields rbinds)
938 field_names = map fieldLabelName (dataConFieldLabels data_con)
940 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
941 checkMissingFields data_con rbinds
942 | null field_labels -- Not declared as a record;
943 -- But C{} is still valid if no strict fields
944 = if any isMarkedStrict field_strs then
945 -- Illegal if any arg is strict
946 addErrTc (missingStrictFields data_con [])
950 | otherwise -- A record
951 = checkM (null missing_s_fields)
952 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
954 doptM Opt_WarnMissingFields `thenM` \ warn ->
955 checkM (not (warn && notNull missing_ns_fields))
956 (warnTc True (missingFields data_con missing_ns_fields))
960 = [ fl | (fl, str) <- field_info,
962 not (fieldLabelName fl `elem` field_names_used)
965 = [ fl | (fl, str) <- field_info,
966 not (isMarkedStrict str),
967 not (fieldLabelName fl `elem` field_names_used)
970 field_names_used = recBindFields rbinds
971 field_labels = dataConFieldLabels data_con
973 field_info = zipEqual "missingFields"
977 field_strs = dropList ex_theta (dataConStrictMarks data_con)
978 -- The 'drop' is because dataConStrictMarks
979 -- includes the existential dictionaries
980 (_, _, _, ex_theta, _, _) = dataConSig data_con
983 %************************************************************************
985 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
987 %************************************************************************
990 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
992 tcMonoExprs [] [] = returnM []
993 tcMonoExprs (expr:exprs) (ty:tys)
994 = tcMonoExpr expr ty `thenM` \ expr' ->
995 tcMonoExprs exprs tys `thenM` \ exprs' ->
996 returnM (expr':exprs')
1000 %************************************************************************
1002 \subsection{Literals}
1004 %************************************************************************
1006 Overloaded literals.
1009 tcLit :: HsLit -> TcType -> TcM TcExpr
1010 tcLit (HsLitLit s _) res_ty
1011 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1012 newDicts (LitLitOrigin (unpackFS s))
1013 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1014 extendLIEs dicts `thenM_`
1015 returnM (HsLit (HsLitLit s res_ty))
1018 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1023 %************************************************************************
1025 \subsection{Errors and contexts}
1027 %************************************************************************
1029 Boring and alphabetical:
1032 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1035 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1038 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1041 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1044 = hang (ptext SLIT("When checking the type signature of the expression:"))
1048 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1050 fieldCtxt field_name
1051 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1053 funAppCtxt fun arg arg_no
1054 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1055 quotes (ppr fun) <> text ", namely"])
1056 4 (quotes (ppr arg))
1059 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1062 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1065 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1068 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1070 the_app = foldl HsApp fun args -- Used in error messages
1072 lurkingRank2Err fun fun_ty
1073 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1074 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1075 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1078 = hang (ptext SLIT("No constructor has all these fields:"))
1079 4 (pprQuotedList (recBindFields rbinds))
1081 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1082 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1085 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1087 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1088 missingStrictFields con fields
1091 rest | null fields = empty -- Happens for non-record constructors
1092 -- with strict fields
1093 | otherwise = colon <+> pprWithCommas ppr fields
1095 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1096 ptext SLIT("does not have the required strict field(s)")
1098 missingFields :: DataCon -> [FieldLabel] -> SDoc
1099 missingFields con fields
1100 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1101 <+> pprWithCommas ppr fields
1103 polySpliceErr :: Id -> SDoc
1105 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1107 wrongArgsCtxt too_many_or_few fun args
1108 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1109 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1110 <+> ptext SLIT("arguments in the call"))
1111 4 (parens (ppr the_app))
1113 the_app = foldl HsApp fun args -- Used in error messages