2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcMatches]{Typecheck some @Matches@}
7 module TcMatches ( tcMatchesFun, tcMatchesCase, tcMatchLambda,
8 tcStmts, tcStmtsAndThen, tcGRHSs
11 #include "HsVersions.h"
13 import {-# SOURCE #-} TcExpr( tcExpr )
15 import HsSyn ( HsBinds(..), Match(..), GRHSs(..), GRHS(..),
16 MonoBinds(..), Stmt(..), HsMatchContext(..), HsDoContext(..),
17 pprMatch, getMatchLoc, pprMatchContext, isDoExpr,
18 mkMonoBind, nullMonoBinds, collectSigTysFromPats
20 import RnHsSyn ( RenamedMatch, RenamedGRHSs, RenamedStmt, RenamedPat, RenamedHsType,
21 RenamedMatchContext, extractHsTyVars )
22 import TcHsSyn ( TcMatch, TcGRHSs, TcStmt, TcDictBinds, TypecheckedPat )
25 import TcMonoType ( kcHsSigTypes, tcScopedTyVars, checkSigTyVars, tcHsSigType, UserTypeCtxt(..), sigPatCtxt )
26 import Inst ( LIE, isEmptyLIE, plusLIE, emptyLIE, plusLIEs, lieToList )
27 import TcEnv ( TcId, tcLookupLocalIds, tcExtendLocalValEnv, tcExtendGlobalTyVars,
29 import TcPat ( tcPat, tcMonoPatBndr, polyPatSig )
30 import TcMType ( newTyVarTy, unifyFunTy, unifyTauTy )
31 import TcType ( tyVarsOfType, isTauTy, mkFunTy, isOverloadedTy,
32 liftedTypeKind, openTypeKind )
33 import TcBinds ( tcBindsAndThen )
34 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
36 import TysWiredIn ( boolTy )
38 import BasicTypes ( RecFlag(..) )
47 %************************************************************************
49 \subsection{tcMatchesFun, tcMatchesCase}
51 %************************************************************************
53 @tcMatchesFun@ typechecks a @[Match]@ list which occurs in a
54 @FunMonoBind@. The second argument is the name of the function, which
55 is used in error messages. It checks that all the equations have the
56 same number of arguments before using @tcMatches@ to do the work.
59 tcMatchesFun :: [(Name,Id)] -- Bindings for the variables bound in this group
61 -> TcType -- Expected type
63 -> TcM ([TcMatch], LIE)
65 tcMatchesFun xve fun_name expected_ty matches@(first_match:_)
66 = -- Check that they all have the same no of arguments
67 -- Set the location to that of the first equation, so that
68 -- any inter-equation error messages get some vaguely
69 -- sensible location. Note: we have to do this odd
70 -- ann-grabbing, because we don't always have annotations in
71 -- hand when we call tcMatchesFun...
72 tcAddSrcLoc (getMatchLoc first_match) (
73 checkTc (sameNoOfArgs matches)
74 (varyingArgsErr fun_name matches)
77 -- ToDo: Don't use "expected" stuff if there ain't a type signature
78 -- because inconsistency between branches
79 -- may show up as something wrong with the (non-existent) type signature
81 -- No need to zonk expected_ty, because unifyFunTy does that on the fly
82 tcMatches xve (FunRhs fun_name) matches expected_ty
85 @tcMatchesCase@ doesn't do the argument-count check because the
86 parser guarantees that each equation has exactly one argument.
89 tcMatchesCase :: [RenamedMatch] -- The case alternatives
90 -> TcType -- Type of whole case expressions
91 -> TcM (TcType, -- Inferred type of the scrutinee
92 [TcMatch], -- Translated alternatives
95 tcMatchesCase matches expr_ty
96 = newTyVarTy openTypeKind `thenNF_Tc` \ scrut_ty ->
97 tcMatches [] CaseAlt matches (mkFunTy scrut_ty expr_ty) `thenTc` \ (matches', lie) ->
98 returnTc (scrut_ty, matches', lie)
100 tcMatchLambda :: RenamedMatch -> TcType -> TcM (TcMatch, LIE)
101 tcMatchLambda match res_ty = tcMatch [] LambdaExpr match res_ty
106 tcMatches :: [(Name,Id)]
107 -> RenamedMatchContext
110 -> TcM ([TcMatch], LIE)
112 tcMatches xve fun_or_case matches expected_ty
113 = mapAndUnzipTc tc_match matches `thenTc` \ (matches, lies) ->
114 returnTc (matches, plusLIEs lies)
116 tc_match match = tcMatch xve fun_or_case match expected_ty
120 %************************************************************************
124 %************************************************************************
127 tcMatch :: [(Name,Id)]
128 -> RenamedMatchContext
130 -> TcType -- Expected result-type of the Match.
131 -- Early unification with this guy gives better error messages
132 -> TcM (TcMatch, LIE)
134 tcMatch xve1 ctxt match@(Match sig_tvs pats maybe_rhs_sig grhss) expected_ty
135 = tcAddSrcLoc (getMatchLoc match) $ -- At one stage I removed this;
136 tcAddErrCtxt (matchCtxt ctxt match) $ -- I'm not sure why, so I put it back
138 tcMatchPats pats expected_ty tc_grhss `thenTc` \ ((pats', grhss'), lie, ex_binds) ->
139 returnTc (Match [] pats' Nothing (glue_on Recursive ex_binds grhss'), lie)
142 tc_grhss pats' rhs_ty
143 = -- Check that the remaining "expected type" is not a rank-2 type
144 -- If it is it'll mess up the unifier when checking the RHS
145 checkTc (isTauTy rhs_ty) lurkingRank2SigErr `thenTc_`
147 -- Deal with the result signature
148 tc_result_sig maybe_rhs_sig (
150 -- Typecheck the body
151 tcExtendLocalValEnv xve1 $
152 tcGRHSs ctxt grhss rhs_ty `thenTc` \ (grhss', lie) ->
153 returnTc ((pats', grhss'), lie)
156 tc_result_sig Nothing thing_inside
158 tc_result_sig (Just sig) thing_inside
159 = tcAddScopedTyVars [sig] $
160 tcHsSigType ResSigCtxt sig `thenTc` \ sig_ty ->
162 -- Check that the signature isn't a polymorphic one, which
163 -- we don't permit (at present, anyway)
164 checkTc (isTauTy sig_ty) (polyPatSig sig_ty) `thenTc_`
165 unifyTauTy expected_ty sig_ty `thenTc_`
169 -- glue_on just avoids stupid dross
170 glue_on _ EmptyMonoBinds grhss = grhss -- The common case
171 glue_on is_rec mbinds (GRHSs grhss binds ty)
172 = GRHSs grhss (mkMonoBind mbinds [] is_rec `ThenBinds` binds) ty
174 tcGRHSs :: RenamedMatchContext -> RenamedGRHSs
176 -> TcM (TcGRHSs, LIE)
178 tcGRHSs ctxt (GRHSs grhss binds _) expected_ty
179 = tcBindsAndThen glue_on binds (tc_grhss grhss)
182 = mapAndUnzipTc tc_grhs grhss `thenTc` \ (grhss', lies) ->
183 returnTc (GRHSs grhss' EmptyBinds expected_ty, plusLIEs lies)
185 tc_grhs (GRHS guarded locn)
187 tcStmts ctxt (\ty -> ty, expected_ty) guarded `thenTc` \ (guarded', lie) ->
188 returnTc (GRHS guarded' locn, lie)
192 %************************************************************************
194 \subsection{tcMatchPats}
196 %************************************************************************
200 :: [RenamedPat] -> TcType
201 -> ([TypecheckedPat] -> TcType -> TcM (a, LIE))
202 -> TcM (a, LIE, TcDictBinds)
203 -- Typecheck the patterns, extend the environment to bind the variables,
204 -- do the thing inside, use any existentially-bound dictionaries to
205 -- discharge parts of the returning LIE, and deal with pattern type
208 tcMatchPats pats expected_ty thing_inside
209 = -- STEP 1: Bring pattern-signature type variables into scope
210 tcAddScopedTyVars (collectSigTysFromPats pats) (
212 -- STEP 2: Typecheck the patterns themselves, gathering all the stuff
213 tc_match_pats pats expected_ty `thenTc` \ (rhs_ty, pats', lie_req1, ex_tvs, pat_bndrs, lie_avail) ->
215 -- STEP 3: Extend the environment, and do the thing inside
217 xve = bagToList pat_bndrs
218 pat_ids = map snd xve
220 tcExtendLocalValEnv xve (thing_inside pats' rhs_ty) `thenTc` \ (result, lie_req2) ->
222 returnTc (rhs_ty, lie_req1, ex_tvs, pat_ids, lie_avail, result, lie_req2)
223 ) `thenTc` \ (rhs_ty, lie_req1, ex_tvs, pat_ids, lie_avail, result, lie_req2) ->
225 -- STEP 4: Check for existentially bound type variables
226 -- Do this *outside* the scope of the tcAddScopedTyVars, else checkSigTyVars
227 -- complains that 'a' is captured by the inscope 'a'! (Test (d) in checkSigTyVars.)
229 -- I'm a bit concerned that lie_req1 from an 'inner' pattern in the list
230 -- might need (via lie_req2) something made available from an 'outer'
231 -- pattern. But it's inconvenient to deal with, and I can't find an example
232 tcCheckExistentialPat pat_ids ex_tvs lie_avail lie_req2 rhs_ty `thenTc` \ (lie_req2', ex_binds) ->
234 returnTc (result, lie_req1 `plusLIE` lie_req2', ex_binds)
236 tcAddScopedTyVars :: [RenamedHsType] -> TcM a -> TcM a
237 -- Find the not-already-in-scope signature type variables,
238 -- kind-check them, and bring them into scope
240 -- We no longer specify that these type variables must be univerally
241 -- quantified (lots of email on the subject). If you want to put that
242 -- back in, you need to
243 -- a) Do a checkSigTyVars after thing_inside
244 -- b) More insidiously, don't pass in expected_ty, else
245 -- we unify with it too early and checkSigTyVars barfs
246 -- Instead you have to pass in a fresh ty var, and unify
247 -- it with expected_ty afterwards
248 tcAddScopedTyVars sig_tys thing_inside
249 = tcGetEnv `thenNF_Tc` \ env ->
251 all_sig_tvs = foldr (unionNameSets . extractHsTyVars) emptyNameSet sig_tys
252 sig_tvs = filter not_in_scope (nameSetToList all_sig_tvs)
253 not_in_scope tv = not (tcInLocalScope env tv)
255 tcScopedTyVars sig_tvs (kcHsSigTypes sig_tys) thing_inside
257 tcCheckExistentialPat :: [TcId] -- Ids bound by this pattern
258 -> Bag TcTyVar -- Existentially quantified tyvars bound by pattern
259 -> LIE -- and context
260 -> LIE -- Required context
261 -> TcType -- and result type; vars in here must not escape
262 -> TcM (LIE, TcDictBinds) -- LIE to float out and dict bindings
263 tcCheckExistentialPat ids ex_tvs lie_avail lie_req result_ty
264 | isEmptyBag ex_tvs && all not_overloaded ids
265 -- Short cut for case when there are no existentials
266 -- and no polymorphic overloaded variables
267 -- e.g. f :: (forall a. Ord a => a -> a) -> Int -> Int
269 -- Here we must discharge op Methods
270 = ASSERT( isEmptyLIE lie_avail )
271 returnTc (lie_req, EmptyMonoBinds)
274 = tcExtendGlobalTyVars (tyVarsOfType result_ty) $
275 tcAddErrCtxtM (sigPatCtxt tv_list ids) $
277 -- In case there are any polymorpic, overloaded binders in the pattern
278 -- (which can happen in the case of rank-2 type signatures, or data constructors
279 -- with polymorphic arguments), we must do a bindInstsOfLocalFns here
280 bindInstsOfLocalFuns lie_req ids `thenTc` \ (lie1, inst_binds) ->
282 -- Deal with overloaded functions bound by the pattern
283 tcSimplifyCheck doc tv_list (lieToList lie_avail) lie1 `thenTc` \ (lie2, dict_binds) ->
284 checkSigTyVars tv_list emptyVarSet `thenTc_`
286 returnTc (lie2, dict_binds `AndMonoBinds` inst_binds)
288 doc = text ("the existential context of a data constructor")
289 tv_list = bagToList ex_tvs
290 not_overloaded id = not (isOverloadedTy (idType id))
292 tc_match_pats [] expected_ty
293 = returnTc (expected_ty, [], emptyLIE, emptyBag, emptyBag, emptyLIE)
295 tc_match_pats (pat:pats) expected_ty
296 = unifyFunTy expected_ty `thenTc` \ (arg_ty, rest_ty) ->
297 tcPat tcMonoPatBndr pat arg_ty `thenTc` \ (pat', lie_req, pat_tvs, pat_ids, lie_avail) ->
298 tc_match_pats pats rest_ty `thenTc` \ (rhs_ty, pats', lie_reqs, pats_tvs, pats_ids, lie_avails) ->
301 lie_req `plusLIE` lie_reqs,
302 pat_tvs `unionBags` pats_tvs,
303 pat_ids `unionBags` pats_ids,
304 lie_avail `plusLIE` lie_avails
309 %************************************************************************
313 %************************************************************************
315 Typechecking statements is rendered a bit tricky by parallel list comprehensions:
317 [ (g x, h x) | ... ; let g v = ...
318 | ... ; let h v = ... ]
320 It's possible that g,h are overloaded, so we need to feed the LIE from the
321 (g x, h x) up through both lots of bindings (so we get the bindInstsOfLocalFuns).
322 Similarly if we had an existential pattern match:
324 data T = forall a. Show a => C a
326 [ (show x, show y) | ... ; C x <- ...
329 Then we need the LIE from (show x, show y) to be simplified against
330 the bindings for x and y.
332 It's difficult to do this in parallel, so we rely on the renamer to
333 ensure that g,h and x,y don't duplicate, and simply grow the environment.
334 So the binders of the first parallel group will be in scope in the second
335 group. But that's fine; there's no shadowing to worry about.
338 tcStmts do_or_lc m_ty stmts
339 = tcStmtsAndThen (:) do_or_lc m_ty stmts (returnTc ([], emptyLIE))
342 :: (TcStmt -> thing -> thing) -- Combiner
343 -> RenamedMatchContext
344 -> (TcType -> TcType, TcType) -- m, the relationship type of pat and rhs in pat <- rhs
345 -- elt_ty, where type of the comprehension is (m elt_ty)
351 tcStmtsAndThen combine do_or_lc m_ty [] do_next
354 tcStmtsAndThen combine do_or_lc m_ty (stmt:stmts) do_next
355 = tcStmtAndThen combine do_or_lc m_ty stmt
356 (tcStmtsAndThen combine do_or_lc m_ty stmts do_next)
359 tcStmtAndThen combine do_or_lc m_ty (LetStmt binds) thing_inside
360 = tcBindsAndThen -- No error context, but a binding group is
361 (glue_binds combine) -- rather a large thing for an error context anyway
365 tcStmtAndThen combine do_or_lc m_ty@(m,elt_ty) stmt@(BindStmt pat exp src_loc) thing_inside
366 = tcAddSrcLoc src_loc $
367 tcAddErrCtxt (stmtCtxt do_or_lc stmt) $
368 newTyVarTy liftedTypeKind `thenNF_Tc` \ pat_ty ->
369 tcExpr exp (m pat_ty) `thenTc` \ (exp', exp_lie) ->
370 tcMatchPats [pat] (mkFunTy pat_ty (m elt_ty)) (\ [pat'] _ ->
372 thing_inside `thenTc` \ (thing, lie) ->
373 returnTc ((BindStmt pat' exp' src_loc, thing), lie)
374 ) `thenTc` \ ((stmt', thing), lie, dict_binds) ->
375 returnTc (combine stmt' (glue_binds combine Recursive dict_binds thing),
376 lie `plusLIE` exp_lie)
380 tcStmtAndThen combine do_or_lc m_ty (ParStmtOut bndr_stmts_s) thing_inside
381 = loop bndr_stmts_s `thenTc` \ ((pairs', thing), lie) ->
382 returnTc (combine (ParStmtOut pairs') thing, lie)
385 = thing_inside `thenTc` \ (thing, stmts_lie) ->
386 returnTc (([], thing), stmts_lie)
388 loop ((bndrs,stmts) : pairs)
390 combine_par (DoCtxt ListComp) m_ty stmts
391 -- Notice we pass on m_ty; the result type is used only
392 -- to get escaping type variables for checkExistentialPat
393 (tcLookupLocalIds bndrs `thenNF_Tc` \ bndrs' ->
394 loop pairs `thenTc` \ ((pairs', thing), lie) ->
395 returnTc (([], (bndrs', pairs', thing)), lie)) `thenTc` \ ((stmts', (bndrs', pairs', thing)), lie) ->
397 returnTc ( ((bndrs',stmts') : pairs', thing), lie)
399 combine_par stmt (stmts, thing) = (stmt:stmts, thing)
402 tcStmtAndThen combine do_or_lc m_ty@(m, res_elt_ty) stmt@(ExprStmt exp _ locn) thing_inside
403 = tcSetErrCtxt (stmtCtxt do_or_lc stmt) (
404 if isDoExpr do_or_lc then
405 newTyVarTy openTypeKind `thenNF_Tc` \ any_ty ->
406 tcExpr exp (m any_ty) `thenNF_Tc` \ (exp', lie) ->
407 returnTc (ExprStmt exp' any_ty locn, lie)
409 tcExpr exp boolTy `thenNF_Tc` \ (exp', lie) ->
410 returnTc (ExprStmt exp' boolTy locn, lie)
411 ) `thenTc` \ (stmt', stmt_lie) ->
413 thing_inside `thenTc` \ (thing, stmts_lie) ->
415 returnTc (combine stmt' thing, stmt_lie `plusLIE` stmts_lie)
419 tcStmtAndThen combine do_or_lc m_ty@(m, res_elt_ty) stmt@(ResultStmt exp locn) thing_inside
420 = tcSetErrCtxt (stmtCtxt do_or_lc stmt) (
421 if isDoExpr do_or_lc then
422 tcExpr exp (m res_elt_ty)
424 tcExpr exp res_elt_ty
425 ) `thenTc` \ (exp', stmt_lie) ->
427 thing_inside `thenTc` \ (thing, stmts_lie) ->
429 returnTc (combine (ResultStmt exp' locn) thing,
430 stmt_lie `plusLIE` stmts_lie)
433 ------------------------------
434 glue_binds combine is_rec binds thing
435 | nullMonoBinds binds = thing
436 | otherwise = combine (LetStmt (mkMonoBind binds [] is_rec)) thing
440 %************************************************************************
442 \subsection{Errors and contexts}
444 %************************************************************************
446 @sameNoOfArgs@ takes a @[RenamedMatch]@ and decides whether the same
447 number of args are used in each equation.
450 sameNoOfArgs :: [RenamedMatch] -> Bool
451 sameNoOfArgs matches = length (nub (map args_in_match matches)) == 1
453 args_in_match :: RenamedMatch -> Int
454 args_in_match (Match _ pats _ _) = length pats
458 matchCtxt ctxt match = hang (pprMatchContext ctxt <> colon) 4 (pprMatch ctxt match)
459 stmtCtxt do_or_lc stmt = hang (pprMatchContext do_or_lc <> colon) 4 (ppr stmt)
461 varyingArgsErr name matches
462 = sep [ptext SLIT("Varying number of arguments for function"), quotes (ppr name)]
465 = ptext SLIT("Too few explicit arguments when defining a function with a rank-2 type")