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 -- It "wraps" the rest of the body typecheck because it may
149 -- bring into scope the type variables in the signature
150 tc_result_sig maybe_rhs_sig rhs_ty $
152 -- Typecheck the body
153 tcExtendLocalValEnv xve1 $
154 tcGRHSs ctxt grhss rhs_ty `thenTc` \ (grhss', lie) ->
155 returnTc ((pats', grhss'), lie)
157 tc_result_sig Nothing rhs_ty thing_inside
159 tc_result_sig (Just sig) rhs_ty thing_inside
160 = tcAddScopedTyVars [sig] $
161 tcHsSigType ResSigCtxt sig `thenTc` \ sig_ty ->
163 -- Check that the signature isn't a polymorphic one, which
164 -- we don't permit (at present, anyway)
165 checkTc (isTauTy sig_ty) (polyPatSig sig_ty) `thenTc_`
166 unifyTauTy sig_ty rhs_ty `thenTc_`
170 -- glue_on just avoids stupid dross
171 glue_on _ EmptyMonoBinds grhss = grhss -- The common case
172 glue_on is_rec mbinds (GRHSs grhss binds ty)
173 = GRHSs grhss (mkMonoBind mbinds [] is_rec `ThenBinds` binds) ty
175 tcGRHSs :: RenamedMatchContext -> RenamedGRHSs
177 -> TcM (TcGRHSs, LIE)
179 tcGRHSs ctxt (GRHSs grhss binds _) expected_ty
180 = tcBindsAndThen glue_on binds (tc_grhss grhss)
183 = mapAndUnzipTc tc_grhs grhss `thenTc` \ (grhss', lies) ->
184 returnTc (GRHSs grhss' EmptyBinds expected_ty, plusLIEs lies)
186 tc_grhs (GRHS guarded locn)
188 tcStmts ctxt (\ty -> ty, expected_ty) guarded `thenTc` \ (guarded', lie) ->
189 returnTc (GRHS guarded' locn, lie)
193 %************************************************************************
195 \subsection{tcMatchPats}
197 %************************************************************************
201 :: [RenamedPat] -> TcType
202 -> ([TypecheckedPat] -> TcType -> TcM (a, LIE))
203 -> TcM (a, LIE, TcDictBinds)
204 -- Typecheck the patterns, extend the environment to bind the variables,
205 -- do the thing inside, use any existentially-bound dictionaries to
206 -- discharge parts of the returning LIE, and deal with pattern type
209 tcMatchPats pats expected_ty thing_inside
210 = -- STEP 1: Bring pattern-signature type variables into scope
211 tcAddScopedTyVars (collectSigTysFromPats pats) (
213 -- STEP 2: Typecheck the patterns themselves, gathering all the stuff
214 tc_match_pats pats expected_ty `thenTc` \ (rhs_ty, pats', lie_req1, ex_tvs, pat_bndrs, lie_avail) ->
216 -- STEP 3: Extend the environment, and do the thing inside
218 xve = bagToList pat_bndrs
219 pat_ids = map snd xve
221 tcExtendLocalValEnv xve (thing_inside pats' rhs_ty) `thenTc` \ (result, lie_req2) ->
223 returnTc (rhs_ty, lie_req1, ex_tvs, pat_ids, lie_avail, result, lie_req2)
224 ) `thenTc` \ (rhs_ty, lie_req1, ex_tvs, pat_ids, lie_avail, result, lie_req2) ->
226 -- STEP 4: Check for existentially bound type variables
227 -- Do this *outside* the scope of the tcAddScopedTyVars, else checkSigTyVars
228 -- complains that 'a' is captured by the inscope 'a'! (Test (d) in checkSigTyVars.)
230 -- I'm a bit concerned that lie_req1 from an 'inner' pattern in the list
231 -- might need (via lie_req2) something made available from an 'outer'
232 -- pattern. But it's inconvenient to deal with, and I can't find an example
233 tcCheckExistentialPat pat_ids ex_tvs lie_avail lie_req2 rhs_ty `thenTc` \ (lie_req2', ex_binds) ->
235 returnTc (result, lie_req1 `plusLIE` lie_req2', ex_binds)
237 tcAddScopedTyVars :: [RenamedHsType] -> TcM a -> TcM a
238 -- Find the not-already-in-scope signature type variables,
239 -- kind-check them, and bring them into scope
241 -- We no longer specify that these type variables must be univerally
242 -- quantified (lots of email on the subject). If you want to put that
243 -- back in, you need to
244 -- a) Do a checkSigTyVars after thing_inside
245 -- b) More insidiously, don't pass in expected_ty, else
246 -- we unify with it too early and checkSigTyVars barfs
247 -- Instead you have to pass in a fresh ty var, and unify
248 -- it with expected_ty afterwards
249 tcAddScopedTyVars sig_tys thing_inside
250 = tcGetEnv `thenNF_Tc` \ env ->
252 all_sig_tvs = foldr (unionNameSets . extractHsTyVars) emptyNameSet sig_tys
253 sig_tvs = filter not_in_scope (nameSetToList all_sig_tvs)
254 not_in_scope tv = not (tcInLocalScope env tv)
256 tcScopedTyVars sig_tvs (kcHsSigTypes sig_tys) thing_inside
258 tcCheckExistentialPat :: [TcId] -- Ids bound by this pattern
259 -> Bag TcTyVar -- Existentially quantified tyvars bound by pattern
260 -> LIE -- and context
261 -> LIE -- Required context
262 -> TcType -- and result type; vars in here must not escape
263 -> TcM (LIE, TcDictBinds) -- LIE to float out and dict bindings
264 tcCheckExistentialPat ids ex_tvs lie_avail lie_req result_ty
265 | isEmptyBag ex_tvs && all not_overloaded ids
266 -- Short cut for case when there are no existentials
267 -- and no polymorphic overloaded variables
268 -- e.g. f :: (forall a. Ord a => a -> a) -> Int -> Int
270 -- Here we must discharge op Methods
271 = ASSERT( isEmptyLIE lie_avail )
272 returnTc (lie_req, EmptyMonoBinds)
275 = tcExtendGlobalTyVars (tyVarsOfType result_ty) $
276 tcAddErrCtxtM (sigPatCtxt tv_list ids) $
278 -- In case there are any polymorpic, overloaded binders in the pattern
279 -- (which can happen in the case of rank-2 type signatures, or data constructors
280 -- with polymorphic arguments), we must do a bindInstsOfLocalFns here
281 bindInstsOfLocalFuns lie_req ids `thenTc` \ (lie1, inst_binds) ->
283 -- Deal with overloaded functions bound by the pattern
284 tcSimplifyCheck doc tv_list (lieToList lie_avail) lie1 `thenTc` \ (lie2, dict_binds) ->
285 checkSigTyVars tv_list emptyVarSet `thenTc_`
287 returnTc (lie2, dict_binds `AndMonoBinds` inst_binds)
289 doc = text ("the existential context of a data constructor")
290 tv_list = bagToList ex_tvs
291 not_overloaded id = not (isOverloadedTy (idType id))
293 tc_match_pats [] expected_ty
294 = returnTc (expected_ty, [], emptyLIE, emptyBag, emptyBag, emptyLIE)
296 tc_match_pats (pat:pats) expected_ty
297 = unifyFunTy expected_ty `thenTc` \ (arg_ty, rest_ty) ->
298 tcPat tcMonoPatBndr pat arg_ty `thenTc` \ (pat', lie_req, pat_tvs, pat_ids, lie_avail) ->
299 tc_match_pats pats rest_ty `thenTc` \ (rhs_ty, pats', lie_reqs, pats_tvs, pats_ids, lie_avails) ->
302 lie_req `plusLIE` lie_reqs,
303 pat_tvs `unionBags` pats_tvs,
304 pat_ids `unionBags` pats_ids,
305 lie_avail `plusLIE` lie_avails
310 %************************************************************************
314 %************************************************************************
316 Typechecking statements is rendered a bit tricky by parallel list comprehensions:
318 [ (g x, h x) | ... ; let g v = ...
319 | ... ; let h v = ... ]
321 It's possible that g,h are overloaded, so we need to feed the LIE from the
322 (g x, h x) up through both lots of bindings (so we get the bindInstsOfLocalFuns).
323 Similarly if we had an existential pattern match:
325 data T = forall a. Show a => C a
327 [ (show x, show y) | ... ; C x <- ...
330 Then we need the LIE from (show x, show y) to be simplified against
331 the bindings for x and y.
333 It's difficult to do this in parallel, so we rely on the renamer to
334 ensure that g,h and x,y don't duplicate, and simply grow the environment.
335 So the binders of the first parallel group will be in scope in the second
336 group. But that's fine; there's no shadowing to worry about.
339 tcStmts do_or_lc m_ty stmts
340 = tcStmtsAndThen (:) do_or_lc m_ty stmts (returnTc ([], emptyLIE))
343 :: (TcStmt -> thing -> thing) -- Combiner
344 -> RenamedMatchContext
345 -> (TcType -> TcType, TcType) -- m, the relationship type of pat and rhs in pat <- rhs
346 -- elt_ty, where type of the comprehension is (m elt_ty)
352 tcStmtsAndThen combine do_or_lc m_ty [] do_next
355 tcStmtsAndThen combine do_or_lc m_ty (stmt:stmts) do_next
356 = tcStmtAndThen combine do_or_lc m_ty stmt
357 (tcStmtsAndThen combine do_or_lc m_ty stmts do_next)
360 tcStmtAndThen combine do_or_lc m_ty (LetStmt binds) thing_inside
361 = tcBindsAndThen -- No error context, but a binding group is
362 (glue_binds combine) -- rather a large thing for an error context anyway
366 tcStmtAndThen combine do_or_lc m_ty@(m,elt_ty) stmt@(BindStmt pat exp src_loc) thing_inside
367 = tcAddSrcLoc src_loc $
368 tcAddErrCtxt (stmtCtxt do_or_lc stmt) $
369 newTyVarTy liftedTypeKind `thenNF_Tc` \ pat_ty ->
370 tcExpr exp (m pat_ty) `thenTc` \ (exp', exp_lie) ->
371 tcMatchPats [pat] (mkFunTy pat_ty (m elt_ty)) (\ [pat'] _ ->
373 thing_inside `thenTc` \ (thing, lie) ->
374 returnTc ((BindStmt pat' exp' src_loc, thing), lie)
375 ) `thenTc` \ ((stmt', thing), lie, dict_binds) ->
376 returnTc (combine stmt' (glue_binds combine Recursive dict_binds thing),
377 lie `plusLIE` exp_lie)
381 tcStmtAndThen combine do_or_lc m_ty (ParStmtOut bndr_stmts_s) thing_inside
382 = loop bndr_stmts_s `thenTc` \ ((pairs', thing), lie) ->
383 returnTc (combine (ParStmtOut pairs') thing, lie)
386 = thing_inside `thenTc` \ (thing, stmts_lie) ->
387 returnTc (([], thing), stmts_lie)
389 loop ((bndrs,stmts) : pairs)
391 combine_par (DoCtxt ListComp) m_ty stmts
392 -- Notice we pass on m_ty; the result type is used only
393 -- to get escaping type variables for checkExistentialPat
394 (tcLookupLocalIds bndrs `thenNF_Tc` \ bndrs' ->
395 loop pairs `thenTc` \ ((pairs', thing), lie) ->
396 returnTc (([], (bndrs', pairs', thing)), lie)) `thenTc` \ ((stmts', (bndrs', pairs', thing)), lie) ->
398 returnTc ( ((bndrs',stmts') : pairs', thing), lie)
400 combine_par stmt (stmts, thing) = (stmt:stmts, thing)
403 tcStmtAndThen combine do_or_lc m_ty@(m, res_elt_ty) stmt@(ExprStmt exp _ locn) thing_inside
404 = tcSetErrCtxt (stmtCtxt do_or_lc stmt) (
405 if isDoExpr do_or_lc then
406 newTyVarTy openTypeKind `thenNF_Tc` \ any_ty ->
407 tcExpr exp (m any_ty) `thenNF_Tc` \ (exp', lie) ->
408 returnTc (ExprStmt exp' any_ty locn, lie)
410 tcExpr exp boolTy `thenNF_Tc` \ (exp', lie) ->
411 returnTc (ExprStmt exp' boolTy locn, lie)
412 ) `thenTc` \ (stmt', stmt_lie) ->
414 thing_inside `thenTc` \ (thing, stmts_lie) ->
416 returnTc (combine stmt' thing, stmt_lie `plusLIE` stmts_lie)
420 tcStmtAndThen combine do_or_lc m_ty@(m, res_elt_ty) stmt@(ResultStmt exp locn) thing_inside
421 = tcSetErrCtxt (stmtCtxt do_or_lc stmt) (
422 if isDoExpr do_or_lc then
423 tcExpr exp (m res_elt_ty)
425 tcExpr exp res_elt_ty
426 ) `thenTc` \ (exp', stmt_lie) ->
428 thing_inside `thenTc` \ (thing, stmts_lie) ->
430 returnTc (combine (ResultStmt exp' locn) thing,
431 stmt_lie `plusLIE` stmts_lie)
434 ------------------------------
435 glue_binds combine is_rec binds thing
436 | nullMonoBinds binds = thing
437 | otherwise = combine (LetStmt (mkMonoBind binds [] is_rec)) thing
441 %************************************************************************
443 \subsection{Errors and contexts}
445 %************************************************************************
447 @sameNoOfArgs@ takes a @[RenamedMatch]@ and decides whether the same
448 number of args are used in each equation.
451 sameNoOfArgs :: [RenamedMatch] -> Bool
452 sameNoOfArgs matches = length (nub (map args_in_match matches)) == 1
454 args_in_match :: RenamedMatch -> Int
455 args_in_match (Match _ pats _ _) = length pats
459 matchCtxt ctxt match = hang (pprMatchContext ctxt <> colon) 4 (pprMatch ctxt match)
460 stmtCtxt do_or_lc stmt = hang (pprMatchContext do_or_lc <> colon) 4 (ppr stmt)
462 varyingArgsErr name matches
463 = sep [ptext SLIT("Varying number of arguments for function"), quotes (ppr name)]
466 = ptext SLIT("Too few explicit arguments when defining a function with a rank-2 type")