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 -- Now typecheck the args
663 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
665 -- Unify with expected result after type-checking the args
666 -- so that the info from args percolates to actual_result_ty.
667 -- This is when we might detect a too-few args situation.
668 -- (One can think of cases when the opposite order would give
669 -- a better error message.)
670 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
671 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
673 returnM (co_fn <$> foldl HsApp fun' args')
676 -- If an error happens we try to figure out whether the
677 -- function has been given too many or too few arguments,
679 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
680 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
681 zonkTcType actual_res_ty `thenM` \ act_ty' ->
683 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
684 (env2, act_ty'') = tidyOpenType env1 act_ty'
685 (exp_args, _) = tcSplitFunTys exp_ty''
686 (act_args, _) = tcSplitFunTys act_ty''
688 len_act_args = length act_args
689 len_exp_args = length exp_args
691 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
692 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
693 | otherwise = appCtxt fun args
695 returnM (env2, message)
698 split_fun_ty :: TcType -- The type of the function
699 -> Int -- Number of arguments
700 -> TcM ([TcType], -- Function argument types
701 TcType) -- Function result types
703 split_fun_ty fun_ty 0
704 = returnM ([], fun_ty)
706 split_fun_ty fun_ty n
707 = -- Expect the function to have type A->B
708 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
709 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
710 returnM (arg_ty:arg_tys, final_res_ty)
714 tcArg :: RenamedHsExpr -- The function (for error messages)
715 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
716 -> TcM TcExpr -- Resulting argument and LIE
718 tcArg the_fun (arg, expected_arg_ty, arg_no)
719 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
720 tcExpr arg expected_arg_ty
724 %************************************************************************
726 \subsection{@tcId@ typchecks an identifier occurrence}
728 %************************************************************************
730 tcId instantiates an occurrence of an Id.
731 The instantiate_it loop runs round instantiating the Id.
732 It has to be a loop because we are now prepared to entertain
734 f:: forall a. Eq a => forall b. Baz b => tau
735 We want to instantiate this to
736 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
738 The -fno-method-sharing flag controls what happens so far as the LIE
739 is concerned. The default case is that for an overloaded function we
740 generate a "method" Id, and add the Method Inst to the LIE. So you get
743 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
744 If you specify -fno-method-sharing, the dictionary application
745 isn't shared, so we get
747 f = /\a (d:Num a) (x:a) -> (+) a d x x
748 This gets a bit less sharing, but
749 a) it's better for RULEs involving overloaded functions
750 b) perhaps fewer separated lambdas
753 tcId :: Name -> TcM (TcExpr, TcType)
754 tcId name -- Look up the Id and instantiate its type
755 = -- First check whether it's a DataCon
756 -- Reason: we must not forget to chuck in the
757 -- constraints from their "silly context"
758 tcLookupGlobal_maybe name `thenM` \ maybe_thing ->
759 case maybe_thing of {
760 Just (ADataCon data_con) -> inst_data_con data_con ;
763 -- OK, so now look for ordinary Ids
764 tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
767 loop (HsVar id) (idType id) -- Non-TH case
769 #else /* GHCI is on */
770 -- Check for cross-stage lifting
771 getStage `thenM` \ use_stage ->
773 Brack use_lvl ps_var lie_var
774 | use_lvl > bind_lvl && not (isExternalName name)
775 -> -- E.g. \x -> [| h x |]
776 -- We must behave as if the reference to x was
778 -- We use 'x' itself as the splice proxy, used by
779 -- the desugarer to stitch it all back together.
780 -- If 'x' occurs many times we may get many identical
781 -- bindings of the same splice proxy, but that doesn't
782 -- matter, although it's a mite untidy.
784 -- NB: During type-checking, isExernalName is true of
785 -- top level things, and false of nested bindings
786 -- Top-level things don't need lifting.
791 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
792 -- If x is polymorphic, its occurrence sites might
793 -- have different instantiations, so we can't use plain
794 -- 'x' as the splice proxy name. I don't know how to
795 -- solve this, and it's probably unimportant, so I'm
796 -- just going to flag an error for now
799 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
800 -- Put the 'lift' constraint into the right LIE
802 -- Update the pending splices
803 readMutVar ps_var `thenM` \ ps ->
804 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
806 returnM (HsVar id, id_ty))
809 checkWellStaged (quotes (ppr id)) bind_lvl use_stage `thenM_`
810 loop (HsVar id) (idType id)
815 orig = OccurrenceOf name
817 loop (HsVar fun_id) fun_ty
818 | want_method_inst fun_ty
819 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
820 newMethodWithGivenTy orig fun_id
821 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
822 loop (HsVar meth_id) tau
826 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
827 loop (inst_fn <$> fun) tau
830 = returnM (fun, fun_ty)
832 -- Hack Alert (want_method_inst)!
833 -- If f :: (%x :: T) => Int -> Int
834 -- Then if we have two separate calls, (f 3, f 4), we cannot
835 -- make a method constraint that then gets shared, thus:
836 -- let m = f %x in (m 3, m 4)
837 -- because that loses the linearity of the constraint.
838 -- The simplest thing to do is never to construct a method constraint
839 -- in the first place that has a linear implicit parameter in it.
840 want_method_inst fun_ty
841 | opt_NoMethodSharing = False
842 | otherwise = case tcSplitSigmaTy fun_ty of
843 (_,[],_) -> False -- Not overloaded
844 (_,theta,_) -> not (any isLinearPred theta)
847 -- We treat data constructors differently, because we have to generate
848 -- constraints for their silly theta, which no longer appears in
849 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
850 inst_data_con data_con
851 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
852 extendLIEs ex_dicts `thenM_`
853 returnM (mkHsDictApp (mkHsTyApp (HsVar (dataConWrapId data_con)) ty_args)
854 (map instToId ex_dicts),
855 mkFunTys arg_tys result_ty)
858 Typecheck expression which in most cases will be an Id.
859 The expression can return a higher-ranked type, such as
860 (forall a. a->a) -> Int
861 so we must create a HoleTyVarTy to pass in as the expected tyvar.
864 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
865 tcExpr_id (HsVar name) = tcId name
866 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
867 tcMonoExpr expr id_ty `thenM` \ expr' ->
868 readHoleResult id_ty `thenM` \ id_ty' ->
869 returnM (expr', id_ty')
873 %************************************************************************
875 \subsection{Record bindings}
877 %************************************************************************
879 Game plan for record bindings
880 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
881 1. Find the TyCon for the bindings, from the first field label.
883 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
885 For each binding field = value
887 3. Instantiate the field type (from the field label) using the type
890 4 Type check the value using tcArg, passing the field type as
891 the expected argument type.
893 This extends OK when the field types are universally quantified.
898 :: TyCon -- Type constructor for the record
899 -> [TcType] -- Args of this type constructor
900 -> RenamedRecordBinds
903 tcRecordBinds tycon ty_args rbinds
904 = mappM do_bind rbinds
906 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
908 do_bind (field_lbl_name, rhs)
909 = addErrCtxt (fieldCtxt field_lbl_name) $
910 tcLookupId field_lbl_name `thenM` \ sel_id ->
912 field_lbl = recordSelectorFieldLabel sel_id
913 field_ty = substTy tenv (fieldLabelType field_lbl)
915 ASSERT( isRecordSelector sel_id )
916 -- This lookup and assertion will surely succeed, because
917 -- we check that the fields are indeed record selectors
918 -- before calling tcRecordBinds
919 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
920 -- The caller of tcRecordBinds has already checked
921 -- that all the fields come from the same type
923 tcExpr rhs field_ty `thenM` \ rhs' ->
925 returnM (sel_id, rhs')
927 badFields rbinds data_con
928 = filter (not . (`elem` field_names)) (recBindFields rbinds)
930 field_names = map fieldLabelName (dataConFieldLabels data_con)
932 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
933 checkMissingFields data_con rbinds
934 | null field_labels -- Not declared as a record;
935 -- But C{} is still valid if no strict fields
936 = if any isMarkedStrict field_strs then
937 -- Illegal if any arg is strict
938 addErrTc (missingStrictFields data_con [])
942 | otherwise -- A record
943 = checkM (null missing_s_fields)
944 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
946 doptM Opt_WarnMissingFields `thenM` \ warn ->
947 checkM (not (warn && notNull missing_ns_fields))
948 (warnTc True (missingFields data_con missing_ns_fields))
952 = [ fl | (fl, str) <- field_info,
954 not (fieldLabelName fl `elem` field_names_used)
957 = [ fl | (fl, str) <- field_info,
958 not (isMarkedStrict str),
959 not (fieldLabelName fl `elem` field_names_used)
962 field_names_used = recBindFields rbinds
963 field_labels = dataConFieldLabels data_con
965 field_info = zipEqual "missingFields"
969 field_strs = dropList ex_theta (dataConStrictMarks data_con)
970 -- The 'drop' is because dataConStrictMarks
971 -- includes the existential dictionaries
972 (_, _, _, ex_theta, _, _) = dataConSig data_con
975 %************************************************************************
977 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
979 %************************************************************************
982 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
984 tcMonoExprs [] [] = returnM []
985 tcMonoExprs (expr:exprs) (ty:tys)
986 = tcMonoExpr expr ty `thenM` \ expr' ->
987 tcMonoExprs exprs tys `thenM` \ exprs' ->
988 returnM (expr':exprs')
992 %************************************************************************
994 \subsection{Literals}
996 %************************************************************************
1001 tcLit :: HsLit -> TcType -> TcM TcExpr
1002 tcLit (HsLitLit s _) res_ty
1003 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1004 newDicts (LitLitOrigin (unpackFS s))
1005 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1006 extendLIEs dicts `thenM_`
1007 returnM (HsLit (HsLitLit s res_ty))
1010 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1015 %************************************************************************
1017 \subsection{Errors and contexts}
1019 %************************************************************************
1021 Boring and alphabetical:
1024 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1027 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1030 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1033 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1036 = hang (ptext SLIT("When checking the type signature of the expression:"))
1040 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1042 fieldCtxt field_name
1043 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1045 funAppCtxt fun arg arg_no
1046 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1047 quotes (ppr fun) <> text ", namely"])
1048 4 (quotes (ppr arg))
1051 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1054 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1057 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1060 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1062 the_app = foldl HsApp fun args -- Used in error messages
1064 lurkingRank2Err fun fun_ty
1065 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1066 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1067 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1070 = hang (ptext SLIT("No constructor has all these fields:"))
1071 4 (pprQuotedList (recBindFields rbinds))
1073 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1074 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1077 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1079 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1080 missingStrictFields con fields
1083 rest | null fields = empty -- Happens for non-record constructors
1084 -- with strict fields
1085 | otherwise = colon <+> pprWithCommas ppr fields
1087 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1088 ptext SLIT("does not have the required strict field(s)")
1090 missingFields :: DataCon -> [FieldLabel] -> SDoc
1091 missingFields con fields
1092 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1093 <+> pprWithCommas ppr fields
1095 polySpliceErr :: Id -> SDoc
1097 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1099 wrongArgsCtxt too_many_or_few fun args
1100 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1101 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1102 <+> ptext SLIT("arguments in the call"))
1103 4 (parens (ppr the_app))
1105 the_app = foldl HsApp fun args -- Used in error messages