%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1994
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[TcMatches]{Typecheck some @Matches@}
\begin{code}
+module TcMatches ( tcMatchesFun, tcGRHSsPat, tcMatchesCase, tcMatchLambda,
+ matchCtxt,
+ tcDoStmts, tcStmtsAndThen, tcStmts, tcThingWithSig,
+ tcMatchPats,
+ TcStmtCtxt(..), TcMatchCtxt(..)
+ ) where
+
#include "HsVersions.h"
-module TcMatches ( tcMatchesFun, tcMatchesCase, tcMatch ) where
-
-import TcMonad -- typechecking monad machinery
-import TcMonadFns ( mkIdsWithOpenTyVarTys )
-import AbsSyn -- the stuff being typechecked
-
-import AbsPrel ( mkFunTy )
-import AbsUniType ( isTyVarTy, maybeUnpackFunTy )
-import E ( E, growE_LVE, LVE(..), GVE(..) )
-#if USE_ATTACK_PRAGMAS
-import CE
-import TCE
-#endif
-import Errors ( varyingArgsErr, Error(..), UnifyErrContext(..) )
-import LIE ( LIE, plusLIE )
-import Maybes ( Maybe(..) )
-import TcGRHSs ( tcGRHSsAndBinds )
-import TcPat ( tcPat )
-import Unify ( unifyTauTy, unifyTauTyList )
-import Util
+import {-# SOURCE #-} TcExpr( tcCheckRho, tcMonoExpr )
+
+import HsSyn ( HsExpr(..), LHsExpr, HsBindGroup(..),
+ Match(..), LMatch, GRHSs(..), GRHS(..),
+ Stmt(..), LStmt, HsMatchContext(..), HsStmtContext(..),
+ ReboundNames, LPat,
+ pprMatch, isDoExpr,
+ pprMatchContext, pprStmtContext, pprStmtResultContext,
+ collectSigTysFromPats, glueBindsOnGRHSs
+ )
+import TcHsSyn ( ExprCoFn, TcDictBinds, isIdCoercion, (<$>), (<.>) )
+
+import TcRnMonad
+import TcHsType ( tcAddScopedTyVars, tcHsSigType, UserTypeCtxt(..) )
+import Inst ( tcSyntaxName, tcInstCall )
+import TcEnv ( TcId, tcLookupLocalIds, tcLookupId, tcExtendLocalValEnv, tcExtendLocalValEnv2 )
+import TcPat ( tcPat, tcMonoPatBndr )
+import TcMType ( newTyVarTy, newTyVarTys, zonkTcType )
+import TcType ( TcType, TcTyVar, TcSigmaType, TcRhoType,
+ tyVarsOfTypes, tidyOpenTypes, isSigmaTy,
+ mkFunTy, isOverloadedTy, liftedTypeKind, openTypeKind,
+ mkArrowKind, mkAppTy )
+import TcBinds ( tcBindsAndThen )
+import TcUnify ( Expected(..), newHole, zapExpectedType, zapExpectedBranches, readExpectedType,
+ unifyTauTy, subFunTys, unifyPArrTy, unifyListTy, unifyFunTy,
+ checkSigTyVarsWrt, tcSubExp, tcGen )
+import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
+import Name ( Name )
+import TysWiredIn ( boolTy, mkListTy, mkPArrTy )
+import Id ( idType, mkLocalId )
+import CoreFVs ( idFreeTyVars )
+import BasicTypes ( RecFlag(..) )
+import VarSet
+import Bag
+import Util ( isSingleton, notNull )
+import Outputable
+import SrcLoc ( Located(..), noLoc )
+
+import List ( nub )
\end{code}
+%************************************************************************
+%* *
+\subsection{tcMatchesFun, tcMatchesCase}
+%* *
+%************************************************************************
+
@tcMatchesFun@ typechecks a @[Match]@ list which occurs in a
@FunMonoBind@. The second argument is the name of the function, which
is used in error messages. It checks that all the equations have the
same number of arguments before using @tcMatches@ to do the work.
\begin{code}
-tcMatchesFun :: E -> Name
- -> UniType -- Expected type
- -> [RenamedMatch]
- -> TcM ([TypecheckedMatch], LIE)
-
-tcMatchesFun e fun_name expected_ty matches@(first_match:_)
- = -- Set the location to that of the first equation, so that
+tcMatchesFun :: Name
+ -> [LMatch Name]
+ -> Expected TcRhoType -- Expected type
+ -> TcM [LMatch TcId]
+
+tcMatchesFun fun_name matches@(first_match:_) expected_ty
+ = -- Check that they all have the same no of arguments
+ -- Location is in the monad, set the caller so that
-- any inter-equation error messages get some vaguely
-- sensible location. Note: we have to do this odd
-- ann-grabbing, because we don't always have annotations in
-- hand when we call tcMatchesFun...
-
- addSrcLocTc (get_Match_loc first_match) (
-
- -- Check that they all have the same no of arguments
- checkTc (not (all_same (noOfArgs matches)))
- (varyingArgsErr fun_name matches) `thenTc_`
+ checkTc (sameNoOfArgs matches)
+ (varyingArgsErr fun_name matches) `thenM_`
-- ToDo: Don't use "expected" stuff if there ain't a type signature
-- because inconsistency between branches
-- may show up as something wrong with the (non-existent) type signature
- -- We need to substitute so that we can see as much about the type as possible
- applyTcSubstToTy expected_ty `thenNF_Tc` \ expected_ty' ->
- tcMatchesExpected e expected_ty' (\ m -> FunMonoBindsCtxt fun_name [m]) matches
-
- )
+ -- No need to zonk expected_ty, because subFunTys does that on the fly
+ tcMatches match_ctxt matches expected_ty
where
- all_same :: [Int] -> Bool
- all_same [] = True -- Should never happen (ToDo: panic?)
- all_same [x] = True
- all_same (x:xs) = all ((==) x) xs
+ match_ctxt = MC { mc_what = FunRhs fun_name,
+ mc_body = tcMonoExpr }
\end{code}
@tcMatchesCase@ doesn't do the argument-count check because the
parser guarantees that each equation has exactly one argument.
\begin{code}
-tcMatchesCase :: E -> [RenamedMatch]
- -> TcM ([TypecheckedMatch], LIE, UniType)
-
-tcMatchesCase e matches
- =
+tcMatchesCase :: TcMatchCtxt -- Case context
+ -> [LMatch Name] -- The case alternatives
+ -> Expected TcRhoType -- Type of whole case expressions
+ -> TcM (TcRhoType, -- Inferred type of the scrutinee
+ [LMatch TcId]) -- Translated alternatives
+
+tcMatchesCase ctxt matches (Check expr_ty)
+ = -- This case is a bit yukky, because it prevents the
+ -- scrutinee being higher-ranked, which might just possible
+ -- matter if we were seq'ing on it. But it's awkward to fix.
+ newTyVarTy openTypeKind `thenM` \ scrut_ty ->
+ tcMatches ctxt matches (Check (mkFunTy scrut_ty expr_ty)) `thenM` \ matches' ->
+ returnM (scrut_ty, matches')
+
+tcMatchesCase ctxt matches (Infer hole)
+ = newHole `thenM` \ fun_hole ->
+ tcMatches ctxt matches (Infer fun_hole) `thenM` \ matches' ->
+ readMutVar fun_hole `thenM` \ fun_ty ->
+ -- The result of tcMatches is bound to be a function type
+ unifyFunTy fun_ty `thenM` \ (scrut_ty, res_ty) ->
+ writeMutVar hole res_ty `thenM_`
+ returnM (scrut_ty, matches')
+
+
+tcMatchLambda :: LMatch Name -> Expected TcRhoType -> TcM (LMatch TcId)
+tcMatchLambda match res_ty = tcMatch match_ctxt res_ty match
+ where
+ match_ctxt = MC { mc_what = LambdaExpr,
+ mc_body = tcMonoExpr }
+\end{code}
- -- Typecheck them
- tcMatches e matches `thenTc` \ (matches', lie, tys@(first_ty:_)) ->
+@tcGRHSsPat@ typechecks @[GRHSs]@ that occur in a @PatMonoBind@.
- -- Set the location to that of the first equation, so that
- -- any inter-equation error messages get some vaguely sensible location
- addSrcLocTc (get_Match_loc (head matches)) (
- unifyTauTyList tys (CaseBranchesCtxt matches)
- ) `thenTc_`
+\begin{code}
+tcGRHSsPat :: GRHSs Name
+ -> Expected TcRhoType
+ -> TcM (GRHSs TcId)
+tcGRHSsPat grhss exp_ty = tcGRHSs match_ctxt grhss exp_ty
+ where
+ match_ctxt = MC { mc_what = PatBindRhs,
+ mc_body = tcMonoExpr }
+\end{code}
- returnTc (matches', lie, first_ty)
+\begin{code}
+data TcMatchCtxt -- c.f. TcStmtCtxt, also in this module
+ = MC { mc_what :: HsMatchContext Name, -- What kind of thing this is
+ mc_body :: LHsExpr Name -- Type checker for a body of an alternative
+ -> Expected TcRhoType
+ -> TcM (LHsExpr TcId) }
+
+tcMatches :: TcMatchCtxt
+ -> [LMatch Name]
+ -> Expected TcRhoType
+ -> TcM [LMatch TcId]
+
+tcMatches ctxt matches exp_ty
+ = -- If there is more than one branch, and exp_ty is a 'hole',
+ -- all branches must be types, not type schemes, otherwise the
+ -- order in which we check them would affect the result.
+ zapExpectedBranches matches exp_ty `thenM` \ exp_ty' ->
+ mappM (tcMatch ctxt exp_ty') matches
\end{code}
+%************************************************************************
+%* *
+\subsection{tcMatch}
+%* *
+%************************************************************************
+
\begin{code}
-tcMatchesExpected :: E
- -> UniType
- -> (RenamedMatch -> UnifyErrContext)
- -> [RenamedMatch]
- -> TcM ([TypecheckedMatch], LIE)
-
-tcMatchesExpected e expected_ty err_ctxt_fn [match]
- = addSrcLocTc (get_Match_loc match) (
- tcMatchExpected e expected_ty (err_ctxt_fn match) match
- ) `thenTc` \ (match', lie) ->
- returnTc ([match'], lie)
-
-tcMatchesExpected e expected_ty err_ctxt_fn ms@(match1 : matches)
- = addSrcLocTc (get_Match_loc match1) (
- tcMatchExpected e expected_ty (err_ctxt_fn match1) match1
- ) `thenTc` \ (match1', lie1) ->
- tcMatchesExpected e expected_ty err_ctxt_fn matches `thenTc` \ (matches', lie2) ->
- returnTc (match1' : matches', plusLIE lie1 lie2)
-
-tcMatches :: E -> [RenamedMatch] -> TcM ([TypecheckedMatch], LIE, [UniType])
-
-tcMatches e [match]
- = tcMatch e match `thenTc` \ (match', lie, ty) ->
- returnTc ([match'], lie, [ty])
-
-tcMatches e ms@(match1 : matches)
- = addSrcLocTc (get_Match_loc match1) (
- tcMatch e match1
- ) `thenTc` \ (match1', lie1, match1_ty) ->
- tcMatches e matches `thenTc` \ (matches', lie2, matches_ty) ->
- returnTc (match1' : matches', plusLIE lie1 lie2, match1_ty : matches_ty)
+tcMatch :: TcMatchCtxt
+ -> Expected TcRhoType -- Expected result-type of the Match.
+ -- Early unification with this guy gives better error messages
+ -- We regard the Match as having type
+ -- (ty1 -> ... -> tyn -> result_ty)
+ -- where there are n patterns.
+ -> LMatch Name
+ -> TcM (LMatch TcId)
+
+tcMatch ctxt exp_ty match = wrapLocM (tc_match ctxt exp_ty) match
+
+tc_match ctxt expected_ty match@(Match pats maybe_rhs_sig grhss)
+ = addErrCtxt (matchCtxt (mc_what ctxt) match) $ -- I'm not sure why, so I put it back
+ subFunTys pats expected_ty $ \ pats_w_tys rhs_ty ->
+ -- This is the unique place we call subFunTys
+ -- The point is that if expected_y is a "hole", we want
+ -- to make arg_ty and rest_ty as "holes" too.
+ tcMatchPats pats_w_tys rhs_ty (tc_grhss rhs_ty) `thenM` \ (pats', grhss', ex_binds) ->
+ returnM (Match pats' Nothing (glueBindsOnGRHSs ex_binds grhss'))
+
+ where
+ tc_grhss rhs_ty
+ = case maybe_rhs_sig of -- Deal with the result signature
+ Nothing -> tcGRHSs ctxt grhss rhs_ty
+
+ Just sig -> tcAddScopedTyVars [sig] $
+ -- Bring into scope the type variables in the signature
+ tcHsSigType ResSigCtxt sig `thenM` \ sig_ty ->
+ tcThingWithSig sig_ty (tcGRHSs ctxt grhss . Check) rhs_ty `thenM` \ (co_fn, grhss') ->
+
+ -- Pushes the coercion down to the right hand sides,
+ -- because there is no convenient place to hang it otherwise.
+ if isIdCoercion co_fn then
+ returnM grhss'
+ else
+ readExpectedType rhs_ty `thenM` \ rhs_ty' ->
+ returnM (lift_grhss co_fn rhs_ty' grhss')
+
+lift_grhss co_fn rhs_ty (GRHSs grhss binds ty)
+ = GRHSs (map (fmap lift_grhs) grhss) binds rhs_ty -- Change the type, since the coercion does
+ where
+ lift_grhs (GRHS stmts) = GRHS (map lift_stmt stmts)
+
+ lift_stmt (L loc (ResultStmt e)) = L loc (ResultStmt (fmap (co_fn <$>) e))
+ lift_stmt stmt = stmt
+
+tcGRHSs :: TcMatchCtxt -> GRHSs Name
+ -> Expected TcRhoType
+ -> TcM (GRHSs TcId)
+
+ -- Special case when there is just one equation with a degenerate
+ -- guard; then we pass in the full Expected type, so that we get
+ -- good inference from simple things like
+ -- f = \(x::forall a.a->a) -> <stuff>
+ -- This is a consequence of the fact that tcStmts takes a TcType,
+ -- not a Expected TcType, a decision we could revisit if necessary
+tcGRHSs ctxt (GRHSs [L loc1 (GRHS [L loc2 (ResultStmt rhs)])] binds _) exp_ty
+ = tcBindsAndThen glueBindsOnGRHSs binds $
+ mc_body ctxt rhs exp_ty `thenM` \ rhs' ->
+ readExpectedType exp_ty `thenM` \ exp_ty' ->
+ returnM (GRHSs [L loc1 (GRHS [L loc2 (ResultStmt rhs')])] [] exp_ty')
+
+tcGRHSs ctxt (GRHSs grhss binds _) exp_ty
+ = tcBindsAndThen glueBindsOnGRHSs binds $
+ zapExpectedType exp_ty `thenM` \ exp_ty' ->
+ -- Even if there is only one guard, we zap the RHS type to
+ -- a monotype. Reason: it makes tcStmts much easier,
+ -- and even a one-armed guard has a notional second arm
+ let
+ stmt_ctxt = SC { sc_what = PatGuard (mc_what ctxt),
+ sc_rhs = tcCheckRho,
+ sc_body = sc_body,
+ sc_ty = exp_ty' }
+ sc_body body = mc_body ctxt body (Check exp_ty')
+
+ tc_grhs (GRHS guarded)
+ = tcStmts stmt_ctxt guarded `thenM` \ guarded' ->
+ returnM (GRHS guarded')
+ in
+ mappM (wrapLocM tc_grhs) grhss `thenM` \ grhss' ->
+ returnM (GRHSs grhss' [] exp_ty')
\end{code}
+
\begin{code}
-tcMatchExpected
- :: E
- -> UniType -- This gives the expected
- -- result-type of the Match. Early unification
- -- with this guy gives better error messages
- -> UnifyErrContext
- -> RenamedMatch
- -> TcM (TypecheckedMatch,LIE)
- -- NB No type returned, because it was passed
- -- in instead!
-
-tcMatchExpected e expected_ty err_ctxt the_match@(PatMatch pat match)
- = case maybeUnpackFunTy expected_ty of
-
- Nothing -> -- Not a function type (eg type variable)
- -- So use tcMatch instead
- tcMatch e the_match `thenTc` \ (match', lie_match, match_ty) ->
- unifyTauTy match_ty expected_ty err_ctxt `thenTc_`
- returnTc (match', lie_match)
-
- Just (arg_ty,rest_ty) -> -- It's a function type!
- let binders = collectPatBinders pat
- in
- mkIdsWithOpenTyVarTys binders `thenNF_Tc` \ lve ->
- let e' = growE_LVE e lve
- in
- tcPat e' pat `thenTc` \ (pat', lie_pat, pat_ty) ->
-
- unifyTauTy arg_ty pat_ty err_ctxt `thenTc_`
- tcMatchExpected e' rest_ty err_ctxt match `thenTc` \ (match', lie_match) ->
- returnTc (PatMatch pat' match',
- plusLIE lie_pat lie_match)
-
-tcMatchExpected e expected_ty err_ctxt (GRHSMatch grhss_and_binds)
- = tcGRHSsAndBinds e grhss_and_binds `thenTc` \ (grhss_and_binds', lie, grhss_ty) ->
- unifyTauTy grhss_ty expected_ty err_ctxt `thenTc_`
- returnTc (GRHSMatch grhss_and_binds', lie)
-
-tcMatch :: E
- -> RenamedMatch
- -> TcM (TypecheckedMatch,LIE,UniType)
-
-tcMatch e (PatMatch pat match)
- = let binders = collectPatBinders pat
- in
- mkIdsWithOpenTyVarTys binders `thenNF_Tc` \ lve ->
- let e' = growE_LVE e lve
- in
- tcPat e' pat `thenTc` \ (pat', lie_pat, pat_ty) ->
- tcMatch e' match `thenTc` \ (match', lie_match, match_ty) ->
+tcThingWithSig :: TcSigmaType -- Type signature
+ -> (TcRhoType -> TcM r) -- How to type check the thing inside
+ -> Expected TcRhoType -- Overall expected result type
+ -> TcM (ExprCoFn, r)
+-- Used for expressions with a type signature, and for result type signatures
+
+tcThingWithSig sig_ty thing_inside res_ty
+ | not (isSigmaTy sig_ty)
+ = thing_inside sig_ty `thenM` \ result ->
+ tcSubExp res_ty sig_ty `thenM` \ co_fn ->
+ returnM (co_fn, result)
+
+ | otherwise -- The signature has some outer foralls
+ = -- Must instantiate the outer for-alls of sig_tc_ty
+ -- else we risk instantiating a ? res_ty to a forall-type
+ -- which breaks the invariant that tcMonoExpr only returns phi-types
+ tcGen sig_ty emptyVarSet thing_inside `thenM` \ (gen_fn, result) ->
+ tcInstCall SignatureOrigin sig_ty `thenM` \ (inst_fn, inst_sig_ty) ->
+ tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
+ returnM (co_fn <.> inst_fn <.> gen_fn, result)
+ -- Note that we generalise, then instantiate. Ah well.
+\end{code}
--- We don't do this any more, do we?
--- applyTcSubstToTy pat_ty `thenNF_Tc`\ pat_ty' ->
- returnTc (PatMatch pat' match',
- plusLIE lie_pat lie_match,
- mkFunTy pat_ty match_ty)
+%************************************************************************
+%* *
+\subsection{tcMatchPats}
+%* *
+%************************************************************************
+
+\begin{code}
+tcMatchPats
+ :: [(LPat Name, Expected TcRhoType)]
+ -> Expected TcRhoType
+ -> TcM a
+ -> TcM ([LPat TcId], a, HsBindGroup TcId)
+-- Typecheck the patterns, extend the environment to bind the variables,
+-- do the thing inside, use any existentially-bound dictionaries to
+-- discharge parts of the returning LIE, and deal with pattern type
+-- signatures
+
+tcMatchPats pats_w_tys body_ty thing_inside
+ = -- STEP 1: Bring pattern-signature type variables into scope
+ tcAddScopedTyVars (collectSigTysFromPats (map fst pats_w_tys)) (
+
+ -- STEP 2: Typecheck the patterns themselves, gathering all the stuff
+ -- then do the thing inside
+ getLIE (tc_match_pats pats_w_tys thing_inside)
+
+ ) `thenM` \ ((pats', ex_tvs, ex_ids, ex_lie, result), lie_req) ->
+
+ -- STEP 4: Check for existentially bound type variables
+ -- Do this *outside* the scope of the tcAddScopedTyVars, else checkSigTyVars
+ -- complains that 'a' is captured by the inscope 'a'! (Test (d) in checkSigTyVars.)
+ --
+ -- I'm a bit concerned that lie_req1 from an 'inner' pattern in the list
+ -- might need (via lie_req2) something made available from an 'outer'
+ -- pattern. But it's inconvenient to deal with, and I can't find an example
+ tcCheckExistentialPat ex_tvs ex_ids ex_lie lie_req
+ pats_w_tys body_ty `thenM` \ ex_binds ->
+ -- NB: we *must* pass "pats_w_tys" not just "body_ty" to tcCheckExistentialPat
+ -- For example, we must reject this program:
+ -- data C = forall a. C (a -> Int)
+ -- f (C g) x = g x
+ -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
+
+ returnM (pats', result, HsBindGroup ex_binds [] Recursive)
+
+tc_match_pats [] thing_inside
+ = thing_inside `thenM` \ answer ->
+ returnM ([], emptyBag, [], [], answer)
+
+tc_match_pats ((pat,pat_ty):pats) thing_inside
+ = tcPat tcMonoPatBndr pat pat_ty `thenM` \ (pat', ex_tvs, pat_bndrs, ex_lie) ->
+ let
+ xve = bagToList pat_bndrs
+ ex_ids = [id | (_, id) <- xve]
+ -- ex_ids is all the pattern-bound Ids, a superset
+ -- of the existential Ids used in checkExistentialPat
+ in
+ tcExtendLocalValEnv2 xve $
+ tc_match_pats pats thing_inside `thenM` \ (pats', exs_tvs, exs_ids, exs_lie, answer) ->
+ returnM ( pat':pats',
+ ex_tvs `unionBags` exs_tvs,
+ ex_ids ++ exs_ids,
+ ex_lie ++ exs_lie,
+ answer
+ )
-tcMatch e (GRHSMatch grhss_and_binds)
- = tcGRHSsAndBinds e grhss_and_binds `thenTc` \ (grhss_and_binds', lie, grhss_ty) ->
- returnTc (GRHSMatch grhss_and_binds', lie, grhss_ty)
+
+tcCheckExistentialPat :: Bag TcTyVar -- Existentially quantified tyvars bound by pattern
+ -> [TcId] -- Ids bound by this pattern; used
+ -- (a) by bindsInstsOfLocalFuns
+ -- (b) to generate helpful error messages
+ -> [Inst] -- and context
+ -> [Inst] -- Required context
+ -> [(pat,Expected TcRhoType)] -- Types of the patterns
+ -> Expected TcRhoType -- Type of the body of the match
+ -- Tyvars in either of these must not escape
+ -> TcM TcDictBinds -- LIE to float out and dict bindings
+tcCheckExistentialPat ex_tvs ex_ids ex_lie lie_req pats_w_tys body_ty
+ | isEmptyBag ex_tvs && all not_overloaded ex_ids
+ -- Short cut for case when there are no existentials
+ -- and no polymorphic overloaded variables
+ -- e.g. f :: (forall a. Ord a => a -> a) -> Int -> Int
+ -- f op x = ....
+ -- Here we must discharge op Methods
+ = ASSERT( null ex_lie )
+ extendLIEs lie_req `thenM_`
+ returnM emptyBag
+
+ | otherwise
+ = -- Read the by-now-filled-in expected types
+ mapM readExpectedType (body_ty : map snd pats_w_tys) `thenM` \ tys ->
+ addErrCtxtM (sigPatCtxt tv_list ex_ids tys) $
+
+ -- In case there are any polymorpic, overloaded binders in the pattern
+ -- (which can happen in the case of rank-2 type signatures, or data constructors
+ -- with polymorphic arguments), we must do a bindInstsOfLocalFns here
+ getLIE (bindInstsOfLocalFuns lie_req ex_ids) `thenM` \ (inst_binds, lie) ->
+
+ -- Deal with overloaded functions bound by the pattern
+ tcSimplifyCheck doc tv_list ex_lie lie `thenM` \ dict_binds ->
+
+ -- Check for type variable escape
+ checkSigTyVarsWrt (tyVarsOfTypes tys) tv_list `thenM_`
+
+ returnM (dict_binds `unionBags` inst_binds)
+ where
+ doc = text ("existential context of a data constructor")
+ tv_list = bagToList ex_tvs
+ not_overloaded id = not (isOverloadedTy (idType id))
\end{code}
-@noOfArgs@ takes a @[RenamedMatch]@ and returns a list telling how
-many arguments were used in each of the equations. This is used to
-report a sensible error message when different equations have
-different numbers of arguments.
+%************************************************************************
+%* *
+\subsection{@tcDoStmts@ typechecks a {\em list} of do statements}
+%* *
+%************************************************************************
\begin{code}
-noOfArgs :: [RenamedMatch] -> [Int]
+tcDoStmts :: HsStmtContext Name
+ -> [LStmt Name] -> ReboundNames Name
+ -> TcRhoType -- To keep it simple, we don't have an "expected" type here
+ -> TcM ([LStmt TcId], ReboundNames TcId)
+tcDoStmts PArrComp stmts method_names res_ty
+ = unifyPArrTy res_ty `thenM` \elt_ty ->
+ tcComprehension PArrComp mkPArrTy elt_ty stmts `thenM` \ stmts' ->
+ returnM (stmts', [{- unused -}])
+
+tcDoStmts ListComp stmts method_names res_ty
+ = unifyListTy res_ty ` thenM` \ elt_ty ->
+ tcComprehension ListComp mkListTy elt_ty stmts `thenM` \ stmts' ->
+ returnM (stmts', [{- unused -}])
+
+tcDoStmts do_or_mdo stmts method_names res_ty
+ = newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenM` \ m_ty ->
+ newTyVarTy liftedTypeKind `thenM` \ elt_ty ->
+ unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenM_`
+ let
+ ctxt = SC { sc_what = do_or_mdo,
+ sc_rhs = \ rhs rhs_elt_ty -> tcCheckRho rhs (mkAppTy m_ty rhs_elt_ty),
+ sc_body = \ body -> tcCheckRho body res_ty,
+ sc_ty = res_ty }
+ in
+ tcStmts ctxt stmts `thenM` \ stmts' ->
+
+ -- Build the then and zero methods in case we need them
+ -- It's important that "then" and "return" appear just once in the final LIE,
+ -- not only for typechecker efficiency, but also because otherwise during
+ -- simplification we end up with silly stuff like
+ -- then = case d of (t,r) -> t
+ -- then = then
+ -- where the second "then" sees that it already exists in the "available" stuff.
+ mapM (tcSyntaxName DoOrigin m_ty) method_names `thenM` \ methods ->
+
+ returnM (stmts', methods)
+
+tcComprehension do_or_lc mk_mty elt_ty stmts
+ = tcStmts ctxt stmts
+ where
+ ctxt = SC { sc_what = do_or_lc,
+ sc_rhs = \ rhs rhs_elt_ty -> tcCheckRho rhs (mk_mty rhs_elt_ty),
+ sc_body = \ body -> tcCheckRho body elt_ty, -- Note: no mk_mty!
+ sc_ty = mk_mty elt_ty }
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{tcStmts}
+%* *
+%************************************************************************
+
+Typechecking statements is rendered a bit tricky by parallel list comprehensions:
+
+ [ (g x, h x) | ... ; let g v = ...
+ | ... ; let h v = ... ]
+
+It's possible that g,h are overloaded, so we need to feed the LIE from the
+(g x, h x) up through both lots of bindings (so we get the bindInstsOfLocalFuns).
+Similarly if we had an existential pattern match:
+
+ data T = forall a. Show a => C a
+
+ [ (show x, show y) | ... ; C x <- ...
+ | ... ; C y <- ... ]
+
+Then we need the LIE from (show x, show y) to be simplified against
+the bindings for x and y.
-noOfArgs ms = map args_in_match ms
+It's difficult to do this in parallel, so we rely on the renamer to
+ensure that g,h and x,y don't duplicate, and simply grow the environment.
+So the binders of the first parallel group will be in scope in the second
+group. But that's fine; there's no shadowing to worry about.
+
+\begin{code}
+tcStmts ctxt stmts
+ = ASSERT( notNull stmts )
+ tcStmtsAndThen (:) ctxt stmts (returnM [])
+
+data TcStmtCtxt
+ = SC { sc_what :: HsStmtContext Name, -- What kind of thing this is
+ sc_rhs :: LHsExpr Name -> TcType -> TcM (LHsExpr TcId), -- Type checker for RHS computations
+ sc_body :: LHsExpr Name -> TcM (LHsExpr TcId), -- Type checker for return computation
+ sc_ty :: TcType } -- Return type; used *only* to check
+ -- for escape in existential patterns
+tcStmtsAndThen
+ :: (LStmt TcId -> thing -> thing) -- Combiner
+ -> TcStmtCtxt
+ -> [LStmt Name]
+ -> TcM thing
+ -> TcM thing
+
+ -- Base case
+tcStmtsAndThen combine ctxt [] thing_inside
+ = thing_inside
+
+tcStmtsAndThen combine ctxt (stmt:stmts) thing_inside
+ = tcStmtAndThen combine ctxt stmt $
+ tcStmtsAndThen combine ctxt stmts $
+ thing_inside
+
+ -- LetStmt
+tcStmtAndThen combine ctxt (L _ (LetStmt binds)) thing_inside
+ = tcBindsAndThen -- No error context, but a binding group is
+ (glue_binds combine) -- rather a large thing for an error context anyway
+ binds
+ thing_inside
+
+ -- BindStmt
+tcStmtAndThen combine ctxt (L src_loc stmt@(BindStmt pat exp)) thing_inside
+ = addSrcSpan src_loc $
+ addErrCtxt (stmtCtxt ctxt stmt) $
+ newTyVarTy liftedTypeKind `thenM` \ pat_ty ->
+ sc_rhs ctxt exp pat_ty `thenM` \ exp' ->
+ tcMatchPats [(pat, Check pat_ty)] (Check (sc_ty ctxt)) (
+ popErrCtxt thing_inside
+ ) `thenM` \ ([pat'], thing, dict_binds) ->
+ returnM (combine (L src_loc (BindStmt pat' exp'))
+ (glue_binds combine dict_binds thing))
+
+ -- ExprStmt
+tcStmtAndThen combine ctxt (L src_loc stmt@(ExprStmt exp _)) thing_inside
+ = addSrcSpan src_loc (
+ addErrCtxt (stmtCtxt ctxt stmt) $
+ if isDoExpr (sc_what ctxt)
+ then -- do or mdo; the expression is a computation
+ newTyVarTy openTypeKind `thenM` \ any_ty ->
+ sc_rhs ctxt exp any_ty `thenM` \ exp' ->
+ returnM (L src_loc (ExprStmt exp' any_ty))
+ else -- List comprehensions, pattern guards; expression is a boolean
+ tcCheckRho exp boolTy `thenM` \ exp' ->
+ returnM (L src_loc (ExprStmt exp' boolTy))
+ ) `thenM` \ stmt' ->
+
+ thing_inside `thenM` \ thing ->
+ returnM (combine stmt' thing)
+
+
+ -- ParStmt
+tcStmtAndThen combine ctxt (L src_loc (ParStmt bndr_stmts_s)) thing_inside
+ = loop bndr_stmts_s `thenM` \ (pairs', thing) ->
+ returnM (combine (L src_loc (ParStmt pairs')) thing)
where
- args_in_match :: RenamedMatch -> Int
- args_in_match (GRHSMatch _) = 0
- args_in_match (PatMatch _ match) = 1 + args_in_match match
+ loop [] = thing_inside `thenM` \ thing ->
+ returnM ([], thing)
+
+ loop ((stmts, bndrs) : pairs)
+ = tcStmtsAndThen combine_par ctxt stmts $
+ -- Notice we pass on ctxt; the result type is used only
+ -- to get escaping type variables for checkExistentialPat
+ tcLookupLocalIds bndrs `thenM` \ bndrs' ->
+ loop pairs `thenM` \ (pairs', thing) ->
+ returnM (([], bndrs') : pairs', thing)
+
+ combine_par stmt ((stmts, bndrs) : pairs , thing) = ((stmt:stmts, bndrs) : pairs, thing)
+
+ -- RecStmt
+tcStmtAndThen combine ctxt (L src_loc (RecStmt stmts laterNames recNames _)) thing_inside
+ = newTyVarTys (length recNames) liftedTypeKind `thenM` \ recTys ->
+ let
+ rec_ids = zipWith mkLocalId recNames recTys
+ in
+ tcExtendLocalValEnv rec_ids $
+ tcStmtsAndThen combine_rec ctxt stmts (
+ mappM tc_ret (recNames `zip` recTys) `thenM` \ rec_rets ->
+ tcLookupLocalIds laterNames `thenM` \ later_ids ->
+ returnM ([], (later_ids, rec_rets))
+ ) `thenM` \ (stmts', (later_ids, rec_rets)) ->
+
+ tcExtendLocalValEnv later_ids $
+ -- NB: The rec_ids for the recursive things
+ -- already scope over this part
+ thing_inside `thenM` \ thing ->
+
+ returnM (combine (L src_loc (RecStmt stmts' later_ids rec_ids rec_rets)) thing)
+ where
+ combine_rec stmt (stmts, thing) = (stmt:stmts, thing)
+
+ -- Unify the types of the "final" Ids with those of "knot-tied" Ids
+ tc_ret (rec_name, mono_ty)
+ = tcLookupId rec_name `thenM` \ poly_id ->
+ -- poly_id may have a polymorphic type
+ -- but mono_ty is just a monomorphic type variable
+ tcSubExp (Check mono_ty) (idType poly_id) `thenM` \ co_fn ->
+ returnM (L src_loc (co_fn <$> HsVar poly_id))
+
+ -- Result statements
+tcStmtAndThen combine ctxt (L src_loc stmt@(ResultStmt exp)) thing_inside
+ = addErrCtxt (stmtCtxt ctxt stmt) (sc_body ctxt exp) `thenM` \ exp' ->
+ thing_inside `thenM` \ thing ->
+ returnM (combine (L src_loc (ResultStmt exp')) thing)
+
+
+------------------------------
+glue_binds combine binds thing = combine (noLoc (LetStmt [binds])) thing
+ -- ToDo: fix the noLoc
\end{code}
-@get_Match_loc@ takes a @RenamedMatch@ and returns the
-source-location gotten from the GRHS inside.
-THis is something of a nuisance, but no more.
+
+%************************************************************************
+%* *
+\subsection{Errors and contexts}
+%* *
+%************************************************************************
+
+@sameNoOfArgs@ takes a @[RenamedMatch]@ and decides whether the same
+number of args are used in each equation.
+
+\begin{code}
+sameNoOfArgs :: [LMatch Name] -> Bool
+sameNoOfArgs matches = isSingleton (nub (map args_in_match matches))
+ where
+ args_in_match :: LMatch Name -> Int
+ args_in_match (L _ (Match pats _ _)) = length pats
+\end{code}
\begin{code}
-get_Match_loc :: RenamedMatch -> SrcLoc
-
-get_Match_loc (PatMatch _ m) = get_Match_loc m
-get_Match_loc (GRHSMatch (GRHSsAndBindsIn (g:_) _))
- = get_GRHS_loc g
- where
- get_GRHS_loc (OtherwiseGRHS _ locn) = locn
- get_GRHS_loc (GRHS _ _ locn) = locn
+varyingArgsErr name matches
+ = sep [ptext SLIT("Varying number of arguments for function"), quotes (ppr name)]
+
+matchCtxt ctxt match = hang (ptext SLIT("In") <+> pprMatchContext ctxt <> colon)
+ 4 (pprMatch ctxt match)
+
+stmtCtxt ctxt stmt = hang (ptext SLIT("In") <+> pp_ctxt (sc_what ctxt) <> colon) 4 (ppr stmt)
+ where
+ pp_ctxt = case stmt of
+ ResultStmt _ -> pprStmtResultContext
+ other -> pprStmtContext
+
+sigPatCtxt bound_tvs bound_ids tys tidy_env
+ = -- tys is (body_ty : pat_tys)
+ mapM zonkTcType tys `thenM` \ tys' ->
+ let
+ (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
+ (_env2, tidy_body_ty : tidy_pat_tys) = tidyOpenTypes env1 tys'
+ in
+ returnM (env1,
+ sep [ptext SLIT("When checking an existential match that binds"),
+ nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
+ ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
+ ptext SLIT("The body has type:") <+> ppr tidy_body_ty
+ ])
+ where
+ show_ids = filter is_interesting bound_ids
+ is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
+
+ ppr_id id ty = ppr id <+> dcolon <+> ppr ty
+ -- Don't zonk the types so we get the separate, un-unified versions
\end{code}
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