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, unifyTupleTy )
26 import BasicTypes ( isMarkedStrict )
27 import Inst ( InstOrigin(..),
28 newOverloadedLit, newMethodFromName, newIPDict,
29 newDicts, newMethodWithGivenTy,
30 instToId, tcInstCall, tcInstDataCon
32 import TcBinds ( tcBindsAndThen )
33 import TcEnv ( tcLookupClass, tcLookupGlobal_maybe, tcLookupIdLvl,
34 tcLookupTyCon, tcLookupDataCon, tcLookupId
36 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts, tcThingWithSig )
37 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
38 import TcPat ( badFieldCon )
39 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
40 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
41 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
42 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
43 isSigmaTy, mkFunTy, mkFunTys,
44 mkTyConApp, mkClassPred,
45 tyVarsOfTypes, isLinearPred,
46 liftedTypeKind, openTypeKind,
47 tcSplitSigmaTy, tidyOpenType
49 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
50 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector )
51 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks, dataConWrapId )
53 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons )
54 import Subst ( mkTopTyVarSubst, substTheta, substTy )
55 import VarSet ( emptyVarSet, elemVarSet )
56 import TysWiredIn ( boolTy )
57 import PrelNames ( cCallableClassName, cReturnableClassName,
58 enumFromName, enumFromThenName,
59 enumFromToName, enumFromThenToName,
60 enumFromToPName, enumFromThenToPName,
63 import ListSetOps ( minusList )
65 import HscTypes ( TyThing(..) )
72 %************************************************************************
74 \subsection{Main wrappers}
76 %************************************************************************
79 tcExpr :: RenamedHsExpr -- Expession to type check
80 -> TcSigmaType -- Expected type (could be a polytpye)
81 -> TcM TcExpr -- Generalised expr with expected type
83 tcExpr expr expected_ty
84 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
85 tc_expr' expr expected_ty
87 tc_expr' expr expected_ty
88 | not (isSigmaTy expected_ty) -- Monomorphic case
89 = tcMonoExpr expr expected_ty
92 = tcGen expected_ty emptyVarSet (
94 ) `thenM` \ (gen_fn, expr') ->
95 returnM (gen_fn <$> expr')
99 %************************************************************************
101 \subsection{The TAUT rules for variables}
103 %************************************************************************
106 tcMonoExpr :: RenamedHsExpr -- Expession to type check
107 -> TcRhoType -- Expected type (could be a type variable)
108 -- Definitely no foralls at the top
112 tcMonoExpr (HsVar name) res_ty
113 = tcId name `thenM` \ (expr', id_ty) ->
114 tcSubExp res_ty id_ty `thenM` \ co_fn ->
115 returnM (co_fn <$> expr')
117 tcMonoExpr (HsIPVar ip) res_ty
118 = -- Implicit parameters must have a *tau-type* not a
119 -- type scheme. We enforce this by creating a fresh
120 -- type variable as its type. (Because res_ty may not
122 newTyVarTy openTypeKind `thenM` \ ip_ty ->
123 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
124 extendLIE inst `thenM_`
125 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
126 returnM (co_fn <$> HsIPVar ip')
130 %************************************************************************
132 \subsection{Expressions type signatures}
134 %************************************************************************
137 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
138 = addErrCtxt (exprSigCtxt in_expr) $
139 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
140 tcThingWithSig sig_tc_ty (tcMonoExpr expr) res_ty `thenM` \ (co_fn, expr') ->
141 returnM (co_fn <$> expr')
143 tcMonoExpr (HsType ty) res_ty
144 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
145 -- This is the syntax for type applications that I was planning
146 -- but there are difficulties (e.g. what order for type args)
147 -- so it's not enabled yet.
148 -- Can't eliminate it altogether from the parser, because the
149 -- same parser parses *patterns*.
153 %************************************************************************
155 \subsection{Other expression forms}
157 %************************************************************************
160 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
161 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
162 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
163 returnM (HsPar expr')
164 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
165 returnM (HsSCC lbl expr')
167 tcMonoExpr (HsCoreAnn lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' -> -- hdaume: core annotation
168 returnM (HsCoreAnn lbl expr')
169 tcMonoExpr (NegApp expr neg_name) res_ty
170 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
171 -- ToDo: use tcSyntaxName
173 tcMonoExpr (HsLam match) res_ty
174 = tcMatchLambda match res_ty `thenM` \ match' ->
175 returnM (HsLam match')
177 tcMonoExpr (HsApp e1 e2) res_ty
178 = tcApp e1 [e2] res_ty
181 Note that the operators in sections are expected to be binary, and
182 a type error will occur if they aren't.
185 -- Left sections, equivalent to
192 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
193 = tcExpr_id op `thenM` \ (op', op_ty) ->
194 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
195 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
196 addErrCtxt (exprCtxt in_expr) $
197 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
198 returnM (co_fn <$> SectionL arg1' op')
200 -- Right sections, equivalent to \ x -> x op expr, or
203 tcMonoExpr in_expr@(SectionR op arg2) 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 (arg2, arg2_ty, 2) `thenM` \ arg2' ->
207 addErrCtxt (exprCtxt in_expr) $
208 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
209 returnM (co_fn <$> SectionR op' arg2')
211 -- equivalent to (op e1) e2:
213 tcMonoExpr in_expr@(OpApp arg1 op fix 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 (arg1, arg1_ty, 1) `thenM` \ arg1' ->
217 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
218 addErrCtxt (exprCtxt in_expr) $
219 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
220 returnM (OpApp arg1' op' fix arg2')
224 tcMonoExpr (HsLet binds expr) res_ty
227 binds -- Bindings to check
228 (tcMonoExpr expr res_ty)
230 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
231 = addSrcLoc src_loc $
232 addErrCtxt (caseCtxt in_expr) $
234 -- Typecheck the case alternatives first.
235 -- The case patterns tend to give good type info to use
236 -- when typechecking the scrutinee. For example
239 -- will report that map is applied to too few arguments
241 -- Not only that, but it's better to check the matches on their
242 -- own, so that we get the expected results for scoped type variables.
244 -- (p::a, q::b) -> (q,p)
245 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
246 -- claimed by the pattern signatures. But if we typechecked the
247 -- match with x in scope and x's type as the expected type, we'd be hosed.
249 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
251 addErrCtxt (caseScrutCtxt scrut) (
252 tcMonoExpr scrut scrut_ty
253 ) `thenM` \ scrut' ->
255 returnM (HsCase scrut' matches' src_loc)
257 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
258 = addSrcLoc src_loc $
259 addErrCtxt (predCtxt pred) (
260 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
262 zapToType res_ty `thenM` \ res_ty' ->
263 -- C.f. the call to zapToType in TcMatches.tcMatches
265 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
266 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
267 returnM (HsIf pred' b1' b2' src_loc)
269 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
270 = addSrcLoc src_loc $
271 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
272 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
274 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
275 = unifyListTy res_ty `thenM` \ elt_ty ->
276 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
277 returnM (ExplicitList elt_ty exprs')
280 = addErrCtxt (listCtxt expr) $
281 tcMonoExpr expr elt_ty
283 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
284 = unifyPArrTy res_ty `thenM` \ elt_ty ->
285 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
286 returnM (ExplicitPArr elt_ty exprs')
289 = addErrCtxt (parrCtxt expr) $
290 tcMonoExpr expr elt_ty
292 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
293 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
294 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
295 returnM (ExplicitTuple exprs' boxity)
299 %************************************************************************
303 %************************************************************************
305 The interesting thing about @ccall@ is that it is just a template
306 which we instantiate by filling in details about the types of its
307 argument and result (ie minimal typechecking is performed). So, the
308 basic story is that we allocate a load of type variables (to hold the
309 arg/result types); unify them with the args/result; and store them for
313 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
315 = getDOpts `thenM` \ dflags ->
317 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
318 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
319 text "Either compile with -fvia-C, or, better, rewrite your code",
320 text "to use the foreign function interface. _casm_s are deprecated",
321 text "and support for them may one day disappear."])
324 -- Get the callable and returnable classes.
325 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
326 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
327 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
329 new_arg_dict (arg, arg_ty)
330 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
331 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
332 returnM arg_dicts -- Actually a singleton bag
334 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
338 let tv_idxs | null args = []
339 | otherwise = [1..length args]
341 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
342 tcMonoExprs args arg_tys `thenM` \ args' ->
344 -- The argument types can be unlifted or lifted; the result
345 -- type must, however, be lifted since it's an argument to the IO
347 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
349 io_result_ty = mkTyConApp ioTyCon [result_ty]
351 unifyTauTy res_ty io_result_ty `thenM_`
353 -- Construct the extra insts, which encode the
354 -- constraints on the argument and result types.
355 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
356 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
357 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
358 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
362 %************************************************************************
364 Record construction and update
366 %************************************************************************
369 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
370 = addErrCtxt (recordConCtxt expr) $
371 tcId con_name `thenM` \ (con_expr, con_tau) ->
373 (_, record_ty) = tcSplitFunTys con_tau
374 (tycon, ty_args) = tcSplitTyConApp record_ty
376 ASSERT( isAlgTyCon tycon )
377 unifyTauTy res_ty record_ty `thenM_`
379 -- Check that the record bindings match the constructor
380 -- con_name is syntactically constrained to be a data constructor
381 tcLookupDataCon con_name `thenM` \ data_con ->
383 bad_fields = badFields rbinds data_con
385 if notNull bad_fields then
386 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
387 failM -- Fail now, because tcRecordBinds will crash on a bad field
390 -- Typecheck the record bindings
391 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
393 -- Check for missing fields
394 checkMissingFields data_con rbinds `thenM_`
396 returnM (RecordConOut data_con con_expr rbinds')
398 -- The main complication with RecordUpd is that we need to explicitly
399 -- handle the *non-updated* fields. Consider:
401 -- data T a b = MkT1 { fa :: a, fb :: b }
402 -- | MkT2 { fa :: a, fc :: Int -> Int }
403 -- | MkT3 { fd :: a }
405 -- upd :: T a b -> c -> T a c
406 -- upd t x = t { fb = x}
408 -- The type signature on upd is correct (i.e. the result should not be (T a b))
409 -- because upd should be equivalent to:
411 -- upd t x = case t of
412 -- MkT1 p q -> MkT1 p x
413 -- MkT2 a b -> MkT2 p b
414 -- MkT3 d -> error ...
416 -- So we need to give a completely fresh type to the result record,
417 -- and then constrain it by the fields that are *not* updated ("p" above).
419 -- Note that because MkT3 doesn't contain all the fields being updated,
420 -- its RHS is simply an error, so it doesn't impose any type constraints
422 -- All this is done in STEP 4 below.
424 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
425 = addErrCtxt (recordUpdCtxt expr) $
428 -- Check that the field names are really field names
429 ASSERT( notNull rbinds )
431 field_names = recBindFields rbinds
433 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
435 bad_guys = [ addErrTc (notSelector field_name)
436 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
437 not (is_selector maybe_sel_id)
439 is_selector (Just (AnId sel_id)) = isRecordSelector sel_id -- Excludes class ops
440 is_selector other = False
442 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
445 -- Figure out the tycon and data cons from the first field name
447 -- It's OK to use the non-tc splitters here (for a selector)
448 (Just (AnId sel_id) : _) = maybe_sel_ids
449 field_lbl = recordSelectorFieldLabel sel_id -- We've failed already if
450 tycon = fieldLabelTyCon field_lbl -- it's not a field label
451 data_cons = tyConDataCons tycon
452 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
454 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
457 -- Check that at least one constructor has all the named fields
458 -- i.e. has an empty set of bad fields returned by badFields
459 checkTc (any (null . badFields rbinds) data_cons)
460 (badFieldsUpd rbinds) `thenM_`
463 -- Typecheck the update bindings.
464 -- (Do this after checking for bad fields in case there's a field that
465 -- doesn't match the constructor.)
467 result_record_ty = mkTyConApp tycon result_inst_tys
469 unifyTauTy res_ty result_record_ty `thenM_`
470 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
473 -- Use the un-updated fields to find a vector of booleans saying
474 -- which type arguments must be the same in updatee and result.
476 -- WARNING: this code assumes that all data_cons in a common tycon
477 -- have FieldLabels abstracted over the same tyvars.
479 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
480 con_field_lbls_s = map dataConFieldLabels data_cons
482 -- A constructor is only relevant to this process if
483 -- it contains all the fields that are being updated
484 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
485 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
487 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
488 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
490 mk_inst_ty (tyvar, result_inst_ty)
491 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
492 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
494 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
497 -- Typecheck the expression to be updated
499 record_ty = mkTyConApp tycon inst_tys
501 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
504 -- Figure out the LIE we need. We have to generate some
505 -- dictionaries for the data type context, since we are going to
506 -- do pattern matching over the data cons.
508 -- What dictionaries do we need?
509 -- We just take the context of the type constructor
511 theta' = substTheta inst_env (tyConTheta tycon)
513 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
514 extendLIEs dicts `thenM_`
517 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
521 %************************************************************************
523 Arithmetic sequences e.g. [a,b..]
524 and their parallel-array counterparts e.g. [: a,b.. :]
527 %************************************************************************
530 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
531 = unifyListTy res_ty `thenM` \ elt_ty ->
532 tcMonoExpr expr elt_ty `thenM` \ expr' ->
534 newMethodFromName (ArithSeqOrigin seq)
535 elt_ty enumFromName `thenM` \ enum_from ->
537 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
539 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
540 = addErrCtxt (arithSeqCtxt in_expr) $
541 unifyListTy res_ty `thenM` \ elt_ty ->
542 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
543 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
544 newMethodFromName (ArithSeqOrigin seq)
545 elt_ty enumFromThenName `thenM` \ enum_from_then ->
547 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
550 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
551 = addErrCtxt (arithSeqCtxt in_expr) $
552 unifyListTy res_ty `thenM` \ elt_ty ->
553 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
554 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
555 newMethodFromName (ArithSeqOrigin seq)
556 elt_ty enumFromToName `thenM` \ enum_from_to ->
558 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
560 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
561 = addErrCtxt (arithSeqCtxt in_expr) $
562 unifyListTy res_ty `thenM` \ elt_ty ->
563 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
564 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
565 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
566 newMethodFromName (ArithSeqOrigin seq)
567 elt_ty enumFromThenToName `thenM` \ eft ->
569 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
571 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
572 = addErrCtxt (parrSeqCtxt in_expr) $
573 unifyPArrTy res_ty `thenM` \ elt_ty ->
574 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
575 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
576 newMethodFromName (PArrSeqOrigin seq)
577 elt_ty enumFromToPName `thenM` \ enum_from_to ->
579 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
581 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
582 = addErrCtxt (parrSeqCtxt in_expr) $
583 unifyPArrTy res_ty `thenM` \ elt_ty ->
584 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
585 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
586 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
587 newMethodFromName (PArrSeqOrigin seq)
588 elt_ty enumFromThenToPName `thenM` \ eft ->
590 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
592 tcMonoExpr (PArrSeqIn _) _
593 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
594 -- the parser shouldn't have generated it and the renamer shouldn't have
599 %************************************************************************
603 %************************************************************************
606 #ifdef GHCI /* Only if bootstrapped */
607 -- Rename excludes these cases otherwise
609 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
610 tcMonoExpr (HsBracket brack loc) res_ty = addSrcLoc loc (tcBracket brack res_ty)
612 tcMonoExpr (HsReify (Reify flavour name)) res_ty
613 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
614 tcMetaTy tycon_name `thenM` \ reify_ty ->
615 unifyTauTy res_ty reify_ty `thenM_`
616 returnM (HsReify (ReifyOut flavour name))
618 tycon_name = case flavour of
619 ReifyDecl -> DsMeta.declTyConName
620 ReifyType -> DsMeta.typeTyConName
621 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
626 %************************************************************************
630 %************************************************************************
633 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
637 %************************************************************************
639 \subsection{@tcApp@ typchecks an application}
641 %************************************************************************
645 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
646 -> TcType -- Expected result type of application
647 -> TcM TcExpr -- Translated fun and args
649 tcApp (HsApp e1 e2) args res_ty
650 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
652 tcApp fun args res_ty
653 = -- First type-check the function
654 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
656 addErrCtxt (wrongArgsCtxt "too many" fun args) (
657 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
658 split_fun_ty fun_ty (length args)
659 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
661 -- Unify with expected result before (was: after) type-checking the args
662 -- so that the info from res_ty (was: args) percolates to args (was actual_result_ty).
663 -- This is when we might detect a too-few args situation.
664 -- (One can think of cases when the opposite order would give
665 -- a better error message.)
666 -- [March 2003: I'm experimenting with putting this first. Here's an
667 -- example where it actually makes a real difference
668 -- class C t a b | t a -> b
669 -- instance C Char a Bool
671 -- data P t a = forall b. (C t a b) => MkP b
672 -- data Q t = MkQ (forall a. P t a)
675 -- f1 = MkQ (MkP True)
676 -- f2 = MkQ (MkP True :: forall a. P Char a)
678 -- With the change, f1 will type-check, because the 'Char' info from
679 -- the signature is propagated into MkQ's argument. With the check
680 -- in the other order, the extra signature in f2 is reqd.]
682 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
683 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
685 -- Now typecheck the args
687 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
689 returnM (co_fn <$> foldl HsApp fun' args')
692 -- If an error happens we try to figure out whether the
693 -- function has been given too many or too few arguments,
695 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
696 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
697 zonkTcType actual_res_ty `thenM` \ act_ty' ->
699 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
700 (env2, act_ty'') = tidyOpenType env1 act_ty'
701 (exp_args, _) = tcSplitFunTys exp_ty''
702 (act_args, _) = tcSplitFunTys act_ty''
704 len_act_args = length act_args
705 len_exp_args = length exp_args
707 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
708 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
709 | otherwise = appCtxt fun args
711 returnM (env2, message)
714 split_fun_ty :: TcType -- The type of the function
715 -> Int -- Number of arguments
716 -> TcM ([TcType], -- Function argument types
717 TcType) -- Function result types
719 split_fun_ty fun_ty 0
720 = returnM ([], fun_ty)
722 split_fun_ty fun_ty n
723 = -- Expect the function to have type A->B
724 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
725 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
726 returnM (arg_ty:arg_tys, final_res_ty)
730 tcArg :: RenamedHsExpr -- The function (for error messages)
731 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
732 -> TcM TcExpr -- Resulting argument and LIE
734 tcArg the_fun (arg, expected_arg_ty, arg_no)
735 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
736 tcExpr arg expected_arg_ty
740 %************************************************************************
742 \subsection{@tcId@ typchecks an identifier occurrence}
744 %************************************************************************
746 tcId instantiates an occurrence of an Id.
747 The instantiate_it loop runs round instantiating the Id.
748 It has to be a loop because we are now prepared to entertain
750 f:: forall a. Eq a => forall b. Baz b => tau
751 We want to instantiate this to
752 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
754 The -fno-method-sharing flag controls what happens so far as the LIE
755 is concerned. The default case is that for an overloaded function we
756 generate a "method" Id, and add the Method Inst to the LIE. So you get
759 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
760 If you specify -fno-method-sharing, the dictionary application
761 isn't shared, so we get
763 f = /\a (d:Num a) (x:a) -> (+) a d x x
764 This gets a bit less sharing, but
765 a) it's better for RULEs involving overloaded functions
766 b) perhaps fewer separated lambdas
769 tcId :: Name -> TcM (TcExpr, TcType)
770 tcId name -- Look up the Id and instantiate its type
771 = -- First check whether it's a DataCon
772 -- Reason: we must not forget to chuck in the
773 -- constraints from their "silly context"
774 tcLookupGlobal_maybe name `thenM` \ maybe_thing ->
775 case maybe_thing of {
776 Just (ADataCon data_con) -> inst_data_con data_con ;
779 -- OK, so now look for ordinary Ids
780 tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
783 loop (HsVar id) (idType id) -- Non-TH case
785 #else /* GHCI is on */
786 -- Check for cross-stage lifting
787 getStage `thenM` \ use_stage ->
789 Brack use_lvl ps_var lie_var
790 | use_lvl > bind_lvl && not (isExternalName name)
791 -> -- E.g. \x -> [| h x |]
792 -- We must behave as if the reference to x was
794 -- We use 'x' itself as the splice proxy, used by
795 -- the desugarer to stitch it all back together.
796 -- If 'x' occurs many times we may get many identical
797 -- bindings of the same splice proxy, but that doesn't
798 -- matter, although it's a mite untidy.
800 -- NB: During type-checking, isExernalName is true of
801 -- top level things, and false of nested bindings
802 -- Top-level things don't need lifting.
807 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
808 -- If x is polymorphic, its occurrence sites might
809 -- have different instantiations, so we can't use plain
810 -- 'x' as the splice proxy name. I don't know how to
811 -- solve this, and it's probably unimportant, so I'm
812 -- just going to flag an error for now
815 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
816 -- Put the 'lift' constraint into the right LIE
818 -- Update the pending splices
819 readMutVar ps_var `thenM` \ ps ->
820 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
822 returnM (HsVar id, id_ty))
825 checkWellStaged (quotes (ppr id)) bind_lvl use_stage `thenM_`
826 loop (HsVar id) (idType id)
831 orig = OccurrenceOf name
833 loop (HsVar fun_id) fun_ty
834 | want_method_inst fun_ty
835 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
836 newMethodWithGivenTy orig fun_id
837 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
838 loop (HsVar meth_id) tau
842 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
843 loop (inst_fn <$> fun) tau
846 = returnM (fun, fun_ty)
848 -- Hack Alert (want_method_inst)!
849 -- If f :: (%x :: T) => Int -> Int
850 -- Then if we have two separate calls, (f 3, f 4), we cannot
851 -- make a method constraint that then gets shared, thus:
852 -- let m = f %x in (m 3, m 4)
853 -- because that loses the linearity of the constraint.
854 -- The simplest thing to do is never to construct a method constraint
855 -- in the first place that has a linear implicit parameter in it.
856 want_method_inst fun_ty
857 | opt_NoMethodSharing = False
858 | otherwise = case tcSplitSigmaTy fun_ty of
859 (_,[],_) -> False -- Not overloaded
860 (_,theta,_) -> not (any isLinearPred theta)
863 -- We treat data constructors differently, because we have to generate
864 -- constraints for their silly theta, which no longer appears in
865 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
866 inst_data_con data_con
867 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
868 extendLIEs ex_dicts `thenM_`
869 returnM (mkHsDictApp (mkHsTyApp (HsVar (dataConWrapId data_con)) ty_args)
870 (map instToId ex_dicts),
871 mkFunTys arg_tys result_ty)
874 Typecheck expression which in most cases will be an Id.
875 The expression can return a higher-ranked type, such as
876 (forall a. a->a) -> Int
877 so we must create a HoleTyVarTy to pass in as the expected tyvar.
880 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
881 tcExpr_id (HsVar name) = tcId name
882 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
883 tcMonoExpr expr id_ty `thenM` \ expr' ->
884 readHoleResult id_ty `thenM` \ id_ty' ->
885 returnM (expr', id_ty')
889 %************************************************************************
891 \subsection{Record bindings}
893 %************************************************************************
895 Game plan for record bindings
896 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
897 1. Find the TyCon for the bindings, from the first field label.
899 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
901 For each binding field = value
903 3. Instantiate the field type (from the field label) using the type
906 4 Type check the value using tcArg, passing the field type as
907 the expected argument type.
909 This extends OK when the field types are universally quantified.
914 :: TyCon -- Type constructor for the record
915 -> [TcType] -- Args of this type constructor
916 -> RenamedRecordBinds
919 tcRecordBinds tycon ty_args rbinds
920 = mappM do_bind rbinds
922 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
924 do_bind (field_lbl_name, rhs)
925 = addErrCtxt (fieldCtxt field_lbl_name) $
926 tcLookupId field_lbl_name `thenM` \ sel_id ->
928 field_lbl = recordSelectorFieldLabel sel_id
929 field_ty = substTy tenv (fieldLabelType field_lbl)
931 ASSERT( isRecordSelector sel_id )
932 -- This lookup and assertion will surely succeed, because
933 -- we check that the fields are indeed record selectors
934 -- before calling tcRecordBinds
935 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
936 -- The caller of tcRecordBinds has already checked
937 -- that all the fields come from the same type
939 tcExpr rhs field_ty `thenM` \ rhs' ->
941 returnM (sel_id, rhs')
943 badFields rbinds data_con
944 = filter (not . (`elem` field_names)) (recBindFields rbinds)
946 field_names = map fieldLabelName (dataConFieldLabels data_con)
948 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
949 checkMissingFields data_con rbinds
950 | null field_labels -- Not declared as a record;
951 -- But C{} is still valid if no strict fields
952 = if any isMarkedStrict field_strs then
953 -- Illegal if any arg is strict
954 addErrTc (missingStrictFields data_con [])
958 | otherwise -- A record
959 = checkM (null missing_s_fields)
960 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
962 doptM Opt_WarnMissingFields `thenM` \ warn ->
963 checkM (not (warn && notNull missing_ns_fields))
964 (warnTc True (missingFields data_con missing_ns_fields))
968 = [ fl | (fl, str) <- field_info,
970 not (fieldLabelName fl `elem` field_names_used)
973 = [ fl | (fl, str) <- field_info,
974 not (isMarkedStrict str),
975 not (fieldLabelName fl `elem` field_names_used)
978 field_names_used = recBindFields rbinds
979 field_labels = dataConFieldLabels data_con
981 field_info = zipEqual "missingFields"
985 field_strs = dropList ex_theta (dataConStrictMarks data_con)
986 -- The 'drop' is because dataConStrictMarks
987 -- includes the existential dictionaries
988 (_, _, _, ex_theta, _, _) = dataConSig data_con
991 %************************************************************************
993 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
995 %************************************************************************
998 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1000 tcMonoExprs [] [] = returnM []
1001 tcMonoExprs (expr:exprs) (ty:tys)
1002 = tcMonoExpr expr ty `thenM` \ expr' ->
1003 tcMonoExprs exprs tys `thenM` \ exprs' ->
1004 returnM (expr':exprs')
1008 %************************************************************************
1010 \subsection{Literals}
1012 %************************************************************************
1014 Overloaded literals.
1017 tcLit :: HsLit -> TcType -> TcM TcExpr
1018 tcLit (HsLitLit s _) res_ty
1019 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1020 newDicts (LitLitOrigin (unpackFS s))
1021 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1022 extendLIEs dicts `thenM_`
1023 returnM (HsLit (HsLitLit s res_ty))
1026 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1031 %************************************************************************
1033 \subsection{Errors and contexts}
1035 %************************************************************************
1037 Boring and alphabetical:
1040 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1043 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1046 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1049 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1052 = hang (ptext SLIT("When checking the type signature of the expression:"))
1056 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1058 fieldCtxt field_name
1059 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1061 funAppCtxt fun arg arg_no
1062 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1063 quotes (ppr fun) <> text ", namely"])
1064 4 (quotes (ppr arg))
1067 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1070 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1073 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1076 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1078 the_app = foldl HsApp fun args -- Used in error messages
1080 lurkingRank2Err fun fun_ty
1081 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1082 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1083 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1086 = hang (ptext SLIT("No constructor has all these fields:"))
1087 4 (pprQuotedList (recBindFields rbinds))
1089 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1090 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1093 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1095 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1096 missingStrictFields con fields
1099 rest | null fields = empty -- Happens for non-record constructors
1100 -- with strict fields
1101 | otherwise = colon <+> pprWithCommas ppr fields
1103 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1104 ptext SLIT("does not have the required strict field(s)")
1106 missingFields :: DataCon -> [FieldLabel] -> SDoc
1107 missingFields con fields
1108 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1109 <+> pprWithCommas ppr fields
1111 polySpliceErr :: Id -> SDoc
1113 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1115 wrongArgsCtxt too_many_or_few fun args
1116 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1117 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1118 <+> ptext SLIT("arguments in the call"))
1119 4 (parens (ppr the_app))
1121 the_app = foldl HsApp fun args -- Used in error messages