\section[TcMatches]{Typecheck some @Matches@}
\begin{code}
-module TcMatches ( tcMatchesFun, tcMatchesCase, tcMatchLambda,
- tcDoStmts, tcStmtsAndThen, tcGRHSs, tcThingWithSig
+module TcMatches ( tcMatchesFun, tcGRHSsPat, tcMatchesCase, tcMatchLambda,
+ matchCtxt,
+ tcDoStmts, tcStmts, tcMDoStmt, tcGuardStmt, tcThingWithSig,
+ tcMatchPats,
+ TcMatchCtxt(..)
) where
#include "HsVersions.h"
-import {-# SOURCE #-} TcExpr( tcMonoExpr )
+import {-# SOURCE #-} TcExpr( tcSyntaxOp, tcCheckRho, tcInferRho, tcMonoExpr, tcCheckSigma )
-import HsSyn ( HsExpr(..), HsBinds(..), Match(..), GRHSs(..), GRHS(..),
- MonoBinds(..), Stmt(..), HsMatchContext(..), HsStmtContext(..),
- pprMatch, getMatchLoc, isDoExpr,
- pprMatchContext, pprStmtContext, pprStmtResultContext,
- mkMonoBind, collectSigTysFromPats, andMonoBindList
+import HsSyn ( HsExpr(..), LHsExpr, MatchGroup(..),
+ Match(..), LMatch, GRHSs(..), GRHS(..),
+ Stmt(..), LStmt, HsMatchContext(..), HsStmtContext(..),
+ LPat, pprMatch, isIrrefutableHsPat,
+ pprMatchContext, pprStmtContext, pprMatchRhsContext,
+ collectPatsBinders, glueBindsOnGRHSs, noSyntaxExpr
)
-import RnHsSyn ( RenamedMatch, RenamedGRHSs, RenamedStmt,
- RenamedPat, RenamedMatchContext )
-import TcHsSyn ( TcMatch, TcGRHSs, TcStmt, TcDictBinds, TcHsBinds,
- TcMonoBinds, TcPat, TcStmt, ExprCoFn,
- isIdCoercion, (<$>), (<.>) )
+import TcHsSyn ( ExprCoFn, isIdCoercion, (<$>), (<.>) )
import TcRnMonad
-import TcMonoType ( tcAddScopedTyVars, tcHsSigType, UserTypeCtxt(..) )
-import Inst ( tcSyntaxName, tcInstCall )
-import TcEnv ( TcId, tcLookupLocalIds, tcLookupId, tcExtendLocalValEnv, tcExtendLocalValEnv2 )
-import TcPat ( tcPat, tcMonoPatBndr )
-import TcMType ( newTyVarTy, newTyVarTys, zonkTcType, zapToType )
-import TcType ( TcType, TcTyVar, TcSigmaType, TcRhoType,
- tyVarsOfType, tidyOpenTypes, tidyOpenType, isSigmaTy,
- mkFunTy, isOverloadedTy, liftedTypeKind, openTypeKind,
- mkArrowKind, mkAppTy )
+import TcHsType ( tcHsPatSigType, UserTypeCtxt(..) )
+import Inst ( tcInstCall, newMethodFromName )
+import TcEnv ( TcId, tcLookupLocalIds, tcLookupId, tcExtendIdEnv,
+ tcExtendTyVarEnv )
+import TcPat ( PatCtxt(..), tcPats )
+import TcMType ( newTyFlexiVarTy, newTyFlexiVarTys, zonkTcType )
+import TcType ( TcType, TcTyVar, TcSigmaType, TcRhoType, mkFunTys,
+ tyVarsOfTypes, tidyOpenTypes, isSigmaTy,
+ liftedTypeKind, openTypeKind, mkFunTy, mkAppTy )
import TcBinds ( tcBindsAndThen )
-import TcUnify ( unifyPArrTy,subFunTy, unifyListTy, unifyTauTy,
- checkSigTyVarsWrt, tcSubExp, tcGen )
-import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
+import TcUnify ( Expected(..), zapExpectedType, readExpectedType,
+ unifyTauTy, subFunTys, unifyTyConApp,
+ checkSigTyVarsWrt, zapExpectedBranches, tcSubExp, tcGen,
+ unifyAppTy, zapToListTy, zapToTyConApp )
+import TcSimplify ( bindInstsOfLocalFuns )
import Name ( Name )
-import PrelNames ( monadNames, mfixName )
-import TysWiredIn ( boolTy, mkListTy, mkPArrTy )
-import Id ( idType, mkSysLocal, mkLocalId )
+import TysWiredIn ( stringTy, boolTy, parrTyCon, listTyCon, mkListTy, mkPArrTy )
+import PrelNames ( bindMName, returnMName, mfixName, thenMName, failMName )
+import Id ( idType, mkLocalId )
+import TyCon ( TyCon )
import CoreFVs ( idFreeTyVars )
-import BasicTypes ( RecFlag(..) )
import VarSet
-import Var ( Id )
-import Bag
-import Util ( isSingleton, lengthExceeds, notNull, zipEqual )
+import Util ( isSingleton )
import Outputable
+import SrcLoc ( Located(..) )
import List ( nub )
\end{code}
\begin{code}
tcMatchesFun :: Name
- -> TcType -- Expected type
- -> [RenamedMatch]
- -> TcM [TcMatch]
-
-tcMatchesFun fun_name expected_ty matches@(first_match:_)
- = -- Check that they all have the same no of arguments
- -- Set the location to that of the first equation, 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...
- addSrcLoc (getMatchLoc first_match) (
- checkTc (sameNoOfArgs matches)
- (varyingArgsErr fun_name matches)
- ) `thenM_`
+ -> MatchGroup Name
+ -> Expected TcRhoType -- Expected type of function
+ -> TcM (MatchGroup TcId) -- Returns type of body
+
+tcMatchesFun fun_name matches exp_ty
+ = do { -- 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...
+ checkTc (sameNoOfArgs matches) (varyingArgsErr fun_name matches)
-- 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
- -- No need to zonk expected_ty, because subFunTy does that on the fly
- tcMatches (FunRhs fun_name) matches expected_ty
+ -- This is one of two places places we call subFunTys
+ -- The point is that if expected_y is a "hole", we want
+ -- to make pat_tys and rhs_ty as "holes" too.
+ ; exp_ty' <- zapExpectedBranches matches exp_ty
+ ; subFunTys matches exp_ty' $ \ pat_tys rhs_ty ->
+ tcMatches match_ctxt pat_tys rhs_ty matches
+ }
+ where
+ 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 :: [RenamedMatch] -- The case alternatives
- -> TcType -- Type of whole case expressions
- -> TcM (TcType, -- Inferred type of the scrutinee
- [TcMatch]) -- Translated alternatives
-
-tcMatchesCase matches expr_ty
- = newTyVarTy openTypeKind `thenM` \ scrut_ty ->
- tcMatches CaseAlt matches (mkFunTy scrut_ty expr_ty) `thenM` \ matches' ->
- returnM (scrut_ty, matches')
-
-tcMatchLambda :: RenamedMatch -> TcType -> TcM TcMatch
-tcMatchLambda match res_ty = tcMatch LambdaExpr match res_ty
+tcMatchesCase :: TcMatchCtxt -- Case context
+ -> TcRhoType -- Type of scrutinee
+ -> MatchGroup Name -- The case alternatives
+ -> Expected TcRhoType -- Type of whole case expressions
+ -> TcM (MatchGroup TcId) -- Translated alternatives
+
+tcMatchesCase ctxt scrut_ty matches exp_ty
+ = do { exp_ty' <- zapExpectedBranches matches exp_ty
+ ; tcMatches ctxt [Check scrut_ty] exp_ty' matches }
+
+tcMatchLambda :: MatchGroup Name -> Expected TcRhoType -> TcM (MatchGroup TcId)
+tcMatchLambda match exp_ty -- One branch so no unifyBranches needed
+ = subFunTys match exp_ty $ \ pat_tys rhs_ty ->
+ tcMatches match_ctxt pat_tys rhs_ty match
+ where
+ match_ctxt = MC { mc_what = LambdaExpr,
+ mc_body = tcMonoExpr }
\end{code}
+@tcGRHSsPat@ typechecks @[GRHSs]@ that occur in a @PatMonoBind@.
\begin{code}
-tcMatches :: RenamedMatchContext
- -> [RenamedMatch]
- -> TcType
- -> TcM [TcMatch]
-
-tcMatches ctxt matches expected_ty
- = -- If there is more than one branch, and expected_ty is a 'hole',
- -- all branches must be types, not type schemes, otherwise the
- -- in which we check them would affect the result.
- (if lengthExceeds matches 1 then
- zapToType expected_ty
- else
- returnM expected_ty) `thenM` \ expected_ty' ->
-
- mappM (tc_match expected_ty') matches
+tcGRHSsPat :: GRHSs Name
+ -> Expected TcRhoType
+ -> TcM (GRHSs TcId)
+tcGRHSsPat grhss exp_ty = tcGRHSs match_ctxt grhss exp_ty
where
- tc_match expected_ty match = tcMatch ctxt match expected_ty
+ match_ctxt = MC { mc_what = PatBindRhs,
+ mc_body = tcMonoExpr }
\end{code}
%************************************************************************
\begin{code}
-tcMatch :: RenamedMatchContext
- -> RenamedMatch
- -> TcType -- 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.
- -> TcM TcMatch
-
-tcMatch ctxt match@(Match pats maybe_rhs_sig grhss) expected_ty
- = addSrcLoc (getMatchLoc match) $ -- At one stage I removed this;
- addErrCtxt (matchCtxt ctxt match) $ -- I'm not sure why, so I put it back
- tcMatchPats pats expected_ty tc_grhss `thenM` \ (pats', grhss', ex_binds) ->
- returnM (Match pats' Nothing (glue_on ex_binds grhss'))
-
- where
- tc_grhss rhs_ty
- = -- Deal with the result signature
- case maybe_rhs_sig of
- 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) rhs_ty `thenM` \ (co_fn, grhss') ->
- returnM (lift_grhss co_fn rhs_ty grhss')
-
--- lift_grhss pushes the coercion down to the right hand sides,
--- because there is no convenient place to hang it otherwise.
-lift_grhss co_fn rhs_ty grhss
- | isIdCoercion co_fn = grhss
-lift_grhss co_fn rhs_ty (GRHSs grhss binds ty)
- = GRHSs (map lift_grhs grhss) binds rhs_ty -- Change the type, since the coercion does
+tcMatches :: TcMatchCtxt
+ -> [Expected TcRhoType] -- Expected pattern types
+ -> Expected TcRhoType -- Expected result-type of the Match.
+ -> MatchGroup Name
+ -> TcM (MatchGroup TcId)
+
+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 ctxt pat_tys rhs_ty (MatchGroup matches _)
+ = do { matches' <- mapM (tcMatch ctxt pat_tys rhs_ty) matches
+ ; pat_tys' <- mapM readExpectedType pat_tys
+ ; rhs_ty' <- readExpectedType rhs_ty
+ ; return (MatchGroup matches' (mkFunTys pat_tys' rhs_ty')) }
+
+-------------
+tcMatch :: TcMatchCtxt
+ -> [Expected TcRhoType] -- Expected pattern types
+ -> Expected TcRhoType -- Expected result-type of the Match.
+ -> LMatch Name
+ -> TcM (LMatch TcId)
+
+tcMatch ctxt pat_tys rhs_ty match
+ = wrapLocM (tc_match ctxt pat_tys rhs_ty) match
+
+tc_match ctxt pat_tys rhs_ty match@(Match pats maybe_rhs_sig grhss)
+ = addErrCtxt (matchCtxt (mc_what ctxt) match) $
+ do { (pats', grhss') <- tcMatchPats pats pat_tys rhs_ty $
+ tc_grhss ctxt maybe_rhs_sig grhss rhs_ty
+ ; returnM (Match pats' Nothing grhss') }
+
+
+-------------
+tc_grhss ctxt Nothing grhss rhs_ty
+ = tcGRHSs ctxt grhss rhs_ty -- No result signature
+
+tc_grhss ctxt (Just res_sig) grhss rhs_ty
+ = do { (sig_tvs, sig_ty) <- tcHsPatSigType ResSigCtxt res_sig
+ ; traceTc (text "tc_grhss" <+> ppr sig_tvs)
+ ; (co_fn, grhss') <- tcExtendTyVarEnv sig_tvs $
+ tcThingWithSig sig_ty (tcGRHSs ctxt grhss . Check) rhs_ty
+
+ -- Push the coercion down to the right hand sides,
+ -- because there is no convenient place to hang it otherwise.
+ ; if isIdCoercion co_fn then
+ return grhss'
+ else
+ return (lift_grhss co_fn grhss') }
+
+-------------
+lift_grhss co_fn (GRHSs grhss binds)
+ = GRHSs (map (fmap lift_grhs) grhss) binds
where
- lift_grhs (GRHS stmts loc) = GRHS (map lift_stmt stmts) loc
-
- lift_stmt (ResultStmt e l) = ResultStmt (co_fn <$> e) l
- lift_stmt stmt = stmt
-
--- glue_on just avoids stupid dross
-glue_on EmptyBinds grhss = grhss -- The common case
-glue_on binds1 (GRHSs grhss binds2 ty)
- = GRHSs grhss (binds1 `ThenBinds` binds2) ty
-
-
-tcGRHSs :: RenamedMatchContext -> RenamedGRHSs
- -> TcType
- -> TcM TcGRHSs
-
-tcGRHSs ctxt (GRHSs grhss binds _) expected_ty
- = tcBindsAndThen glue_on binds (tc_grhss grhss)
- where
- m_ty = (\ty -> ty, expected_ty)
-
- tc_grhss grhss
- = mappM tc_grhs grhss `thenM` \ grhss' ->
- returnM (GRHSs grhss' EmptyBinds expected_ty)
-
- tc_grhs (GRHS guarded locn)
- = addSrcLoc locn $
- tcStmts (PatGuard ctxt) m_ty guarded `thenM` \ guarded' ->
- returnM (GRHS guarded' locn)
+ lift_grhs (GRHS stmts rhs) = GRHS stmts (fmap (co_fn <$>) rhs)
+
+-------------
+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 [] rhs)] binds) exp_ty
+ = tcBindsAndThen glueBindsOnGRHSs binds $
+ mc_body ctxt rhs exp_ty `thenM` \ rhs' ->
+ returnM (GRHSs [L loc1 (GRHS [] rhs')] [])
+
+tcGRHSs ctxt (GRHSs grhss binds) exp_ty
+ = tcBindsAndThen glueBindsOnGRHSs binds $
+ do { exp_ty' <- zapExpectedType exp_ty openTypeKind
+ -- 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 match_ctxt = mc_what ctxt
+ stmt_ctxt = PatGuard match_ctxt
+ tc_grhs (GRHS guards rhs)
+ = do { (guards', rhs')
+ <- tcStmts stmt_ctxt (tcGuardStmt exp_ty') guards $
+ addErrCtxt (grhsCtxt match_ctxt rhs) $
+ tcCheckRho rhs exp_ty'
+ ; return (GRHS guards' rhs') }
+
+ ; grhss' <- mappM (wrapLocM tc_grhs) grhss
+ ; returnM (GRHSs grhss' []) }
\end{code}
\begin{code}
tcThingWithSig :: TcSigmaType -- Type signature
-> (TcRhoType -> TcM r) -- How to type check the thing inside
- -> TcRhoType -- Overall expected result type
+ -> Expected TcRhoType -- Overall expected result type
-> TcM (ExprCoFn, r)
-- Used for expressions with a type signature, and for result type signatures
-- 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) ->
+ tcInstCall InstSigOrigin 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.
%************************************************************************
\begin{code}
-tcMatchPats
- :: [RenamedPat] -> TcType
- -> (TcType -> TcM a)
- -> TcM ([TcPat], a, TcHsBinds)
+tcMatchPats :: [LPat Name]
+ -> [Expected TcSigmaType] -- Pattern types
+ -> Expected TcRhoType -- Result type;
+ -- used only to check existential escape
+ -> TcM a
+ -> TcM ([LPat TcId], a)
-- 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 expected_ty thing_inside
- = -- STEP 1: Bring pattern-signature type variables into scope
- tcAddScopedTyVars (collectSigTysFromPats pats) (
-
- -- STEP 2: Typecheck the patterns themselves, gathering all the stuff
- -- then do the thing inside
- getLIE (tc_match_pats pats expected_ty 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 expected_ty `thenM` \ ex_binds ->
- -- NB: we *must* pass "expected_ty" not "result_ty" to tcCheckExistentialPat
+tcMatchPats pats tys body_ty thing_inside
+ = do { (pats', ex_tvs, res) <- tcPats LamPat pats tys thing_inside
+ ; tcCheckExistentialPat pats' ex_tvs tys body_ty
+ ; returnM (pats', res) }
+
+tcCheckExistentialPat :: [LPat TcId] -- Patterns (just for error message)
+ -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
+ -> [Expected TcSigmaType] -- Types of the patterns
+ -> Expected TcRhoType -- Type of the body of the match
+ -- Tyvars in either of these must not escape
+ -> TcM ()
+ -- NB: we *must* pass "pats_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 (a -> Int).
+ -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
- returnM (pats', result, mkMonoBind Recursive ex_binds)
+tcCheckExistentialPat pats [] pat_tys body_ty
+ = return () -- Short cut for case when there are no existentials
-tc_match_pats [] expected_ty thing_inside
- = thing_inside expected_ty `thenM` \ answer ->
- returnM ([], emptyBag, [], [], answer)
-
-tc_match_pats (pat:pats) expected_ty thing_inside
- = subFunTy expected_ty $ \ arg_ty rest_ty ->
- -- This is the unique place we call subFunTy
- -- The point is that if expected_y is a "hole", we want
- -- to make arg_ty and rest_ty as "holes" too.
- tcPat tcMonoPatBndr pat arg_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 rest_ty 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
- )
-
-
-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
- -> TcType -- and type of the Match; vars in here must not escape
- -> TcM TcDictBinds -- LIE to float out and dict bindings
-tcCheckExistentialPat ex_tvs ex_ids ex_lie lie_req match_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 EmptyMonoBinds
-
- | otherwise
- = addErrCtxtM (sigPatCtxt tv_list ex_ids match_ty) $
-
- -- 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 ->
- checkSigTyVarsWrt (tyVarsOfType match_ty) tv_list `thenM_`
-
- returnM (dict_binds `AndMonoBinds` inst_binds)
- where
- doc = text ("existential context of a data constructor")
- tv_list = bagToList ex_tvs
- not_overloaded id = not (isOverloadedTy (idType id))
+tcCheckExistentialPat pats ex_tvs pat_tys body_ty
+ = do { tys <- mapM readExpectedType (body_ty : pat_tys)
+ ; addErrCtxtM (sigPatCtxt (collectPatsBinders pats) ex_tvs tys) $
+ checkSigTyVarsWrt (tyVarsOfTypes tys) ex_tvs }
\end{code}
%************************************************************************
\begin{code}
-tcDoStmts :: HsStmtContext Name -> [RenamedStmt] -> [Name] -> TcType
- -> TcM (TcMonoBinds, [TcStmt], [Id])
-tcDoStmts PArrComp stmts method_names res_ty
- = unifyPArrTy res_ty `thenM` \elt_ty ->
- tcStmts PArrComp (mkPArrTy, elt_ty) stmts `thenM` \ stmts' ->
- returnM (EmptyMonoBinds, stmts', [{- unused -}])
-
-tcDoStmts ListComp stmts method_names res_ty
- = unifyListTy res_ty `thenM` \ elt_ty ->
- tcStmts ListComp (mkListTy, elt_ty) stmts `thenM` \ stmts' ->
- returnM (EmptyMonoBinds, stmts', [{- unused -}])
-
-tcDoStmts do_or_mdo_expr 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_`
-
- tcStmts do_or_mdo_expr (mkAppTy m_ty, elt_ty) 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.
- --
- mapAndUnzipM (tc_syn_name m_ty)
- (zipEqual "tcDoStmts" currentMonadNames method_names) `thenM` \ (binds, ids) ->
- returnM (andMonoBindList binds, stmts', ids)
- where
- currentMonadNames = case do_or_mdo_expr of
- DoExpr -> monadNames
- MDoExpr -> monadNames ++ [mfixName]
- tc_syn_name :: TcType -> (Name,Name) -> TcM (TcMonoBinds, Id)
- tc_syn_name m_ty (std_nm, usr_nm)
- = tcSyntaxName DoOrigin m_ty std_nm usr_nm `thenM` \ (expr, expr_ty) ->
- case expr of
- HsVar v -> returnM (EmptyMonoBinds, v)
- other -> newUnique `thenM` \ uniq ->
- let
- id = mkSysLocal FSLIT("syn") uniq expr_ty
- in
- returnM (VarMonoBind id expr, id)
+tcDoStmts :: HsStmtContext Name
+ -> [LStmt Name]
+ -> LHsExpr Name
+ -> Expected TcRhoType
+ -> TcM (HsExpr TcId) -- Returns a HsDo
+tcDoStmts ListComp stmts body res_ty
+ = do { elt_ty <- zapToListTy res_ty
+ ; (stmts', body') <- tcStmts ListComp (tcLcStmt listTyCon elt_ty) stmts $
+ addErrCtxt (doBodyCtxt ListComp body) $
+ tcCheckRho body elt_ty
+ ; return (HsDo ListComp stmts' body' (mkListTy elt_ty)) }
+
+tcDoStmts PArrComp stmts body res_ty
+ = do { [elt_ty] <- zapToTyConApp parrTyCon res_ty
+ ; (stmts', body') <- tcStmts PArrComp (tcLcStmt parrTyCon elt_ty) stmts $
+ addErrCtxt (doBodyCtxt PArrComp body) $
+ tcCheckRho body elt_ty
+ ; return (HsDo PArrComp stmts' body' (mkPArrTy elt_ty)) }
+
+tcDoStmts DoExpr stmts body res_ty
+ = do { res_ty' <- zapExpectedType res_ty liftedTypeKind
+ ; (m_ty, _) <- unifyAppTy res_ty'
+ ; (stmts', body') <- tcStmts DoExpr (tcDoStmt m_ty res_ty') stmts $
+ addErrCtxt (doBodyCtxt DoExpr body) $
+ tcCheckRho body res_ty'
+ ; return (HsDo DoExpr stmts' body' res_ty') }
+
+tcDoStmts cxt@(MDoExpr _) stmts body res_ty
+ = do { res_ty' <- zapExpectedType res_ty liftedTypeKind
+ ; (m_ty, _) <- unifyAppTy res_ty'
+ ; let tc_rhs rhs = do { (rhs', rhs_ty) <- tcInferRho rhs
+ ; (n_ty, pat_ty) <- unifyAppTy rhs_ty
+ ; unifyTauTy m_ty n_ty
+ ; return (rhs', pat_ty) }
+
+ ; (stmts', body') <- tcStmts cxt (tcMDoStmt res_ty' tc_rhs) stmts $
+ addErrCtxt (doBodyCtxt cxt body) $
+ tcCheckRho body res_ty'
+
+ ; let names = [mfixName, bindMName, thenMName, returnMName, failMName]
+ ; insts <- mapM (newMethodFromName DoOrigin m_ty) names
+ ; return (HsDo (MDoExpr (names `zip` insts)) stmts' body' res_ty') }
+
+tcDoStmts ctxt stmts body res_ty = pprPanic "tcDoStmts" (pprStmtContext ctxt)
\end{code}
%* *
%************************************************************************
-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.
-
-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 do_or_lc m_ty stmts
- = ASSERT( notNull stmts )
- tcStmtsAndThen (:) do_or_lc m_ty stmts (returnM [])
-
-tcStmtsAndThen
- :: (TcStmt -> thing -> thing) -- Combiner
- -> HsStmtContext Name
- -> (TcType -> TcType, TcType) -- m, the relationship type of pat and rhs in pat <- rhs
- -- elt_ty, where type of the comprehension is (m elt_ty)
- -> [RenamedStmt]
+type TcStmtChecker
+ = forall thing. HsStmtContext Name
+ -> Stmt Name
+ -> TcM thing
+ -> TcM (Stmt TcId, thing)
+
+tcStmts :: HsStmtContext Name
+ -> TcStmtChecker -- NB: higher-rank type
+ -> [LStmt Name]
-> TcM thing
- -> TcM thing
+ -> TcM ([LStmt TcId], thing)
- -- Base case
-tcStmtsAndThen combine do_or_lc m_ty [] do_next
- = do_next
+-- Note the higher-rank type. stmt_chk is applied at different
+-- types in the equations for tcStmts
-tcStmtsAndThen combine do_or_lc m_ty (stmt:stmts) do_next
- = tcStmtAndThen combine do_or_lc m_ty stmt
- (tcStmtsAndThen combine do_or_lc m_ty stmts do_next)
+tcStmts ctxt stmt_chk [] thing_inside
+ = do { thing <- thing_inside
+ ; return ([], thing) }
- -- LetStmt
-tcStmtAndThen combine do_or_lc m_ty (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
+-- LetStmts are handled uniformly, regardless of context
+tcStmts ctxt stmt_chk (L loc (LetStmt binds) : stmts) thing_inside
+ = tcBindsAndThen -- No error context, but a binding group is
+ glue_binds -- rather a large thing for an error context anyway
binds
- thing_inside
-
-tcStmtAndThen combine do_or_lc m_ty@(m,elt_ty) stmt@(BindStmt pat exp src_loc) thing_inside
- = addSrcLoc src_loc $
- addErrCtxt (stmtCtxt do_or_lc stmt) $
- newTyVarTy liftedTypeKind `thenM` \ pat_ty ->
- tcMonoExpr exp (m pat_ty) `thenM` \ exp' ->
- tcMatchPats [pat] (mkFunTy pat_ty (m elt_ty)) (\ _ ->
- popErrCtxt thing_inside
- ) `thenM` \ ([pat'], thing, dict_binds) ->
- returnM (combine (BindStmt pat' exp' src_loc)
- (glue_binds combine dict_binds thing))
-
- -- ParStmt
-tcStmtAndThen combine do_or_lc m_ty (ParStmtOut bndr_stmts_s) thing_inside
- = loop bndr_stmts_s `thenM` \ (pairs', thing) ->
- returnM (combine (ParStmtOut pairs') thing)
+ (tcStmts ctxt stmt_chk stmts thing_inside)
where
- loop []
- = thing_inside `thenM` \ thing ->
- returnM ([], thing)
-
- loop ((bndrs,stmts) : pairs)
- = tcStmtsAndThen
- combine_par ListComp m_ty stmts
- -- Notice we pass on m_ty; 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))) `thenM` \ (stmts', (bndrs', pairs', thing)) ->
-
- returnM ((bndrs',stmts') : pairs', thing)
-
- combine_par stmt (stmts, thing) = (stmt:stmts, thing)
-
- -- RecStmt
-tcStmtAndThen combine do_or_lc m_ty (RecStmt recNames stmts _) thing_inside
- = newTyVarTys (length recNames) liftedTypeKind `thenM` \ recTys ->
- let
- mono_ids = zipWith mkLocalId recNames recTys
- in
- tcExtendLocalValEnv mono_ids $
- tcStmtsAndThen combine_rec do_or_lc m_ty stmts (
- mappM tc_ret (recNames `zip` recTys) `thenM` \ rets ->
- returnM ([], rets)
- ) `thenM` \ (stmts', rets) ->
-
- -- NB: it's the mono_ids that scope over this part
- thing_inside `thenM` \ thing ->
+ glue_binds binds (stmts, thing) = (L loc (LetStmt [binds]) : stmts, thing)
+
+
+-- For the vanilla case, handle the location-setting part
+tcStmts ctxt stmt_chk (L loc stmt : stmts) thing_inside
+ = do { (stmt', (stmts', thing)) <-
+ setSrcSpan loc $
+ addErrCtxt (stmtCtxt ctxt stmt) $
+ stmt_chk ctxt stmt $
+ popErrCtxt $
+ tcStmts ctxt stmt_chk stmts $
+ thing_inside
+ ; return (L loc stmt' : stmts', thing) }
+
+--------------------------------
+-- Pattern guards
+tcGuardStmt :: TcType -> TcStmtChecker
+tcGuardStmt res_ty ctxt (ExprStmt guard _ _) thing_inside
+ = do { guard' <- tcCheckRho guard boolTy
+ ; thing <- thing_inside
+ ; return (ExprStmt guard' noSyntaxExpr boolTy, thing) }
+
+tcGuardStmt res_ty ctxt (BindStmt pat rhs _ _) thing_inside
+ = do { (rhs', rhs_ty) <- tcInferRho rhs
+ ; (pat', thing) <- tcBindPat pat rhs_ty res_ty thing_inside
+ ; return (BindStmt pat' rhs' noSyntaxExpr noSyntaxExpr, thing) }
+
+tcGuardStmt res_ty ctxt stmt thing_inside
+ = pprPanic "tcGuardStmt: unexpected Stmt" (ppr stmt)
+
+
+--------------------------------
+-- List comprehensions and PArrays
+
+tcLcStmt :: TyCon -- The list/Parray type constructor ([] or PArray)
+ -> TcType -- The element type of the list or PArray
+ -> TcStmtChecker
+
+-- A generator, pat <- rhs
+tcLcStmt m_tc elt_ty ctxt (BindStmt pat rhs _ _) thing_inside
+ = do { (rhs', rhs_ty) <- tcInferRho rhs
+ ; [pat_ty] <- unifyTyConApp m_tc rhs_ty
+ ; (pat', thing) <- tcBindPat pat pat_ty elt_ty thing_inside
+ ; return (BindStmt pat' rhs' noSyntaxExpr noSyntaxExpr, thing) }
+
+-- A boolean guard
+tcLcStmt m_tc elt_ty ctxt (ExprStmt rhs _ _) thing_inside
+ = do { rhs' <- tcCheckRho rhs boolTy
+ ; thing <- thing_inside
+ ; return (ExprStmt rhs' noSyntaxExpr boolTy, thing) }
+
+-- A parallel set of 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.
+--
+-- 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.
+
+tcLcStmt m_tc elt_ty ctxt (ParStmt bndr_stmts_s) thing_inside
+ = do { (pairs', thing) <- loop bndr_stmts_s
+ ; return (ParStmt pairs', thing) }
+ where
+ -- loop :: [([LStmt Name], [Name])] -> TcM ([([LStmt TcId], [TcId])], thing)
+ loop [] = do { thing <- thing_inside
+ ; return ([], thing) }
+
+ loop ((stmts, names) : pairs)
+ = do { (stmts', (ids, pairs', thing))
+ <- tcStmts ctxt (tcLcStmt m_tc elt_ty) stmts $
+ do { ids <- tcLookupLocalIds names
+ ; (pairs', thing) <- loop pairs
+ ; return (ids, pairs', thing) }
+ ; return ( (stmts', ids) : pairs', thing ) }
+
+tcLcStmt m_tc elt_ty ctxt stmt thing_inside
+ = pprPanic "tcLcStmt: unexpected Stmt" (ppr stmt)
+
+--------------------------------
+-- Do-notation
+-- The main excitement here is dealing with rebindable syntax
+
+tcDoStmt :: TcType -- Monad type, m
+ -> TcType -- Result type, m b
+ -> TcStmtChecker
+ -- BindStmt
+tcDoStmt m_ty res_ty ctxt (BindStmt pat rhs bind_op fail_op) thing_inside
+ = do { -- Deal with rebindable syntax; (>>=) :: m a -> (a -> m b) -> m b
+ ; (rhs', rhs_ty) <- tcInferRho rhs
+ -- We should use type *inference* for the RHS computations, becuase of GADTs.
+ -- do { pat <- rhs; <rest> }
+ -- is rather like
+ -- case rhs of { pat -> <rest> }
+ -- We do inference on rhs, so that information about its type can be refined
+ -- when type-checking the pattern.
+
+ ; (n_ty, pat_ty) <- unifyAppTy rhs_ty
+ ; unifyTauTy m_ty n_ty
+ ; let bind_ty = mkFunTys [rhs_ty, mkFunTy pat_ty res_ty] res_ty
+
+ ; (pat', thing) <- tcBindPat pat pat_ty res_ty thing_inside
+
+ -- Rebindable syntax stuff
+ ; bind_op' <- tcSyntaxOp DoOrigin bind_op bind_ty
+ -- If (but only if) the pattern can fail,
+ -- typecheck the 'fail' operator
+ ; fail_op' <- if isIrrefutableHsPat pat'
+ then return noSyntaxExpr
+ else tcSyntaxOp DoOrigin fail_op (mkFunTy stringTy res_ty)
+ ; return (BindStmt pat' rhs' bind_op' fail_op', thing) }
+
+
+tcDoStmt m_ty res_ty ctxt (ExprStmt rhs then_op _) thing_inside
+ = do { -- Deal with rebindable syntax; (>>) :: m a -> m b -> m b
+ a_ty <- newTyFlexiVarTy liftedTypeKind
+ ; let rhs_ty = mkAppTy m_ty a_ty
+ then_ty = mkFunTys [rhs_ty, res_ty] res_ty
+ ; then_op' <- tcSyntaxOp DoOrigin then_op then_ty
+ ; rhs' <- tcCheckSigma rhs rhs_ty
+ ; thing <- thing_inside
+ ; return (ExprStmt rhs' then_op' rhs_ty, thing) }
+
+tcDoStmt m_ty res_ty ctxt stmt thing_inside
+ = pprPanic "tcDoStmt: unexpected Stmt" (ppr stmt)
+
+--------------------------------
+-- Mdo-notation
+-- The distinctive features here are
+-- (a) RecStmts, and
+-- (b) no rebindable syntax
+
+tcMDoStmt :: TcType -- Result type, m b
+ -> (LHsExpr Name -> TcM (LHsExpr TcId, TcType)) -- RHS inference
+ -> TcStmtChecker
+tcMDoStmt res_ty tc_rhs ctxt (BindStmt pat rhs bind_op fail_op) thing_inside
+ = do { (rhs', pat_ty) <- tc_rhs rhs
+ ; (pat', thing) <- tcBindPat pat pat_ty res_ty thing_inside
+ ; return (BindStmt pat' rhs' noSyntaxExpr noSyntaxExpr, thing) }
+
+tcMDoStmt res_ty tc_rhs ctxt (ExprStmt rhs then_op _) thing_inside
+ = do { (rhs', elt_ty) <- tc_rhs rhs
+ ; thing <- thing_inside
+ ; return (ExprStmt rhs' noSyntaxExpr elt_ty, thing) }
+
+tcMDoStmt res_ty tc_rhs ctxt (RecStmt stmts laterNames recNames _ _) thing_inside
+ = do { rec_tys <- newTyFlexiVarTys (length recNames) liftedTypeKind
+ ; let rec_ids = zipWith mkLocalId recNames rec_tys
+ ; tcExtendIdEnv rec_ids $ do
+ { (stmts', (later_ids, rec_rets))
+ <- tcStmts ctxt (tcMDoStmt res_ty tc_rhs) stmts $
+ -- ToDo: res_ty not really right
+ do { rec_rets <- zipWithM tc_ret recNames rec_tys
+ ; later_ids <- tcLookupLocalIds laterNames
+ ; return (later_ids, rec_rets) }
+
+ ; (thing,lie) <- tcExtendIdEnv later_ids (getLIE thing_inside)
+ -- NB: The rec_ids for the recursive things
+ -- already scope over this part. This binding may shadow
+ -- some of them with polymorphic things with the same Name
+ -- (see note [RecStmt] in HsExpr)
+ ; lie_binds <- bindInstsOfLocalFuns lie later_ids
- returnM (combine (RecStmt mono_ids stmts' rets) thing)
+ ; return (RecStmt stmts' later_ids rec_ids rec_rets lie_binds, 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 ->
+ 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 mono_ty (idType poly_id) `thenM` \ co_fn ->
- returnM (co_fn <$> HsVar poly_id)
-
- -- ExprStmt
-tcStmtAndThen combine do_or_lc m_ty@(m, res_elt_ty) stmt@(ExprStmt exp _ locn) thing_inside
- = addErrCtxt (stmtCtxt do_or_lc stmt) (
- if isDoExpr do_or_lc then
- newTyVarTy openTypeKind `thenM` \ any_ty ->
- tcMonoExpr exp (m any_ty) `thenM` \ exp' ->
- returnM (ExprStmt exp' any_ty locn)
- else
- tcMonoExpr exp boolTy `thenM` \ exp' ->
- returnM (ExprStmt exp' boolTy locn)
- ) `thenM` \ stmt' ->
-
- thing_inside `thenM` \ thing ->
- returnM (combine stmt' thing)
-
-
- -- Result statements
-tcStmtAndThen combine do_or_lc m_ty@(m, res_elt_ty) stmt@(ResultStmt exp locn) thing_inside
- = addErrCtxt (resCtxt do_or_lc stmt) (
- if isDoExpr do_or_lc then
- tcMonoExpr exp (m res_elt_ty)
- else
- tcMonoExpr exp res_elt_ty
- ) `thenM` \ exp' ->
-
- thing_inside `thenM` \ thing ->
-
- returnM (combine (ResultStmt exp' locn) thing)
-
-
-------------------------------
-glue_binds combine EmptyBinds thing = thing
-glue_binds combine other_binds thing = combine (LetStmt other_binds) thing
+ tcSubExp (Check mono_ty) (idType poly_id) `thenM` \ co_fn ->
+ returnM (co_fn <$> HsVar poly_id)
+
+tcMDoStmt res_ty tc_rhs ctxt stmt thing_inside
+ = pprPanic "tcMDoStmt: unexpected Stmt" (ppr stmt)
+
+-----------------
+tcBindPat :: LPat Name -> TcType
+ -> TcType -- Result type; used only to check existential escape
+ -> TcM a
+ -> TcM (LPat TcId, a)
+tcBindPat pat pat_ty res_ty thing_inside
+ = do { ([pat'],thing) <- tcMatchPats [pat] [Check pat_ty]
+ (Check res_ty) thing_inside
+ ; return (pat', thing) }
\end{code}
number of args are used in each equation.
\begin{code}
-sameNoOfArgs :: [RenamedMatch] -> Bool
-sameNoOfArgs matches = isSingleton (nub (map args_in_match matches))
+sameNoOfArgs :: MatchGroup Name -> Bool
+sameNoOfArgs (MatchGroup matches _)
+ = isSingleton (nub (map args_in_match matches))
where
- args_in_match :: RenamedMatch -> Int
- args_in_match (Match pats _ _) = length pats
+ args_in_match :: LMatch Name -> Int
+ args_in_match (L _ (Match pats _ _)) = length pats
\end{code}
\begin{code}
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 do_or_lc stmt = hang (ptext SLIT("In") <+> pprStmtContext do_or_lc <> colon) 4 (ppr stmt)
-resCtxt do_or_lc stmt = hang (ptext SLIT("In") <+> pprStmtResultContext do_or_lc <> colon) 4 (ppr stmt)
+matchCtxt ctxt match = hang (ptext SLIT("In") <+> pprMatchContext ctxt <> colon)
+ 4 (pprMatch ctxt match)
+
+grhsCtxt ctxt rhs = hang (ptext SLIT("In") <+> pprMatchRhsContext ctxt <> colon)
+ 4 (ppr rhs)
+
+doBodyCtxt :: HsStmtContext Name -> LHsExpr Name -> SDoc
+doBodyCtxt ctxt body = hang (ptext SLIT("In the result of") <+> pprStmtContext ctxt <> colon)
+ 4 (ppr body)
-sigPatCtxt bound_tvs bound_ids match_ty tidy_env
- = zonkTcType match_ty `thenM` \ match_ty' ->
+stmtCtxt ctxt stmt = hang (ptext SLIT("In") <+> pprStmtContext ctxt <> colon)
+ 4 (ppr stmt)
+
+sigPatCtxt bound_ids bound_tvs 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_mty) = tidyOpenType env1 match_ty'
+ (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("and whose type is") <+> ppr tidy_mty])
+ 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
+ ppr_id id ty = ppr id <+> dcolon <+> ppr ty
-- Don't zonk the types so we get the separate, un-unified versions
\end{code}
projects / ghc-hetmet.git / blobdiff