\begin{code}
module TcMatches ( tcMatchesFun, tcGRHSsPat, tcMatchesCase, tcMatchLambda,
- matchCtxt,
- tcDoStmts, tcStmtsAndThen, tcStmts, tcThingWithSig,
- tcMatchPats,
- TcStmtCtxt(..), TcMatchCtxt(..)
+ tcMatchPats, matchCtxt, TcMatchCtxt(..),
+ tcStmts, tcDoStmts,
+ tcDoStmt, tcMDoStmt, tcGuardStmt,
+ tcThingWithSig
) where
#include "HsVersions.h"
-import {-# SOURCE #-} TcExpr( tcCheckRho, tcMonoExpr )
+import {-# SOURCE #-} TcExpr( tcSyntaxOp, tcCheckRho, tcInferRho, tcMonoExpr, tcCheckSigma )
-import HsSyn ( HsExpr(..), LHsExpr, HsBindGroup(..),
+import HsSyn ( HsExpr(..), LHsExpr, MatchGroup(..),
Match(..), LMatch, GRHSs(..), GRHS(..),
Stmt(..), LStmt, HsMatchContext(..), HsStmtContext(..),
- ReboundNames, LPat,
- pprMatch, isDoExpr,
- pprMatchContext, pprStmtContext, pprStmtResultContext,
- collectSigTysFromPats, glueBindsOnGRHSs
+ LPat, pprMatch, isIrrefutableHsPat,
+ pprMatchContext, pprStmtContext, pprMatchRhsContext,
+ collectPatsBinders, noSyntaxExpr
)
-import TcHsSyn ( ExprCoFn, TcDictBinds, isIdCoercion, (<$>), (<.>) )
+import TcHsSyn ( ExprCoFn, isIdCoercion, (<$>), (<.>) )
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, typeKind,
- 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 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 ( tcLocalBinds )
+import TcUnify ( Expected(..), zapExpectedType, readExpectedType,
+ unifyTauTy, subFunTys, unifyTyConApp,
+ checkSigTyVarsWrt, zapExpectedBranches, tcSubExp, tcGen,
+ unifyAppTy, zapToListTy, zapToTyConApp )
+import TcSimplify ( bindInstsOfLocalFuns )
import Name ( Name )
-import TysWiredIn ( boolTy, mkListTy, mkPArrTy )
+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 Bag
-import Util ( isSingleton, notNull )
+import Util ( isSingleton )
import Outputable
-import SrcLoc ( Located(..), noLoc )
+import SrcLoc ( Located(..) )
import List ( nub )
\end{code}
\begin{code}
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...
- 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 subFunTys does that on the fly
- tcMatches match_ctxt 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 ctxt 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 }
+ ctxt = FunRhs fun_name
+ match_ctxt = MC { mc_what = ctxt, mc_body = tcMonoExpr }
\end{code}
@tcMatchesCase@ doesn't do the argument-count check because the
\begin{code}
tcMatchesCase :: TcMatchCtxt -- Case context
- -> [LMatch Name] -- The case alternatives
+ -> TcRhoType -- Type of scrutinee
+ -> MatchGroup 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)
- = newTyVarTy openTypeKind `thenM` \ scrut_ty ->
- -- openTypeKind because the scrutinee can be an unboxed type
- 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
+ -> 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 LambdaExpr 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 }
mc_body = tcMonoExpr }
\end{code}
-\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}
-
%************************************************************************
%* *
%************************************************************************
\begin{code}
+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 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.
+ -> [Expected TcRhoType] -- Expected pattern types
+ -> Expected TcRhoType -- Expected result-type of the Match.
-> LMatch Name
-> TcM (LMatch TcId)
-tcMatch ctxt exp_ty match = wrapLocM (tc_match ctxt exp_ty) match
+tcMatch ctxt pat_tys rhs_ty match
+ = wrapLocM (tc_match ctxt pat_tys rhs_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'))
+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
- 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 <$>) e))
- lift_stmt stmt = stmt
+ lift_grhs (GRHS stmts rhs) = GRHS stmts (fmap (co_fn <$>) rhs)
+-------------
tcGRHSs :: TcMatchCtxt -> GRHSs Name
-> Expected TcRhoType
-> TcM (GRHSs TcId)
-- 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 openTypeKind `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')
+tcGRHSs ctxt (GRHSs [L loc1 (GRHS [] rhs)] binds) exp_ty
+ = do { (binds', rhs') <- tcLocalBinds binds $
+ mc_body ctxt rhs exp_ty
+ ; returnM (GRHSs [L loc1 (GRHS [] rhs')] binds') }
+
+tcGRHSs ctxt (GRHSs grhss binds) exp_ty
+ = 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
+
+ ; (binds', grhss') <- tcLocalBinds binds $
+ mappM (wrapLocM (tcGRHS ctxt exp_ty')) grhss
+
+ ; returnM (GRHSs grhss' binds') }
+
+-------------
+tcGRHS :: TcMatchCtxt -> TcRhoType
+ -> GRHS Name -> TcM (GRHS TcId)
+
+tcGRHS ctxt exp_ty' (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') }
+ where
+ match_ctxt = mc_what ctxt
+ stmt_ctxt = PatGuard match_ctxt
\end{code}
-- 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
- :: [(LPat Name, Expected TcRhoType)]
- -> Expected TcRhoType
- -> TcM a
- -> TcM ([LPat TcId], a, HsBindGroup TcId)
+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_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
+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 (C -> a -> Int).
- returnM (pats', result, HsBindGroup ex_binds [] Recursive)
+tcCheckExistentialPat pats [] pat_tys body_ty
+ = return () -- Short cut for case when there are no existentials
-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 $
- traceTc (text "tc_match_pats" <+> (ppr xve $$ ppr (map (idType . snd) xve) $$
- ppr (map (typeKind . idType . snd) xve))) `thenM_`
- 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
- )
-
-
-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))
+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
- -> [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 }
+ -> [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 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
+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
-
- -- 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 liftedTypeKind `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)
+ -> TcM ([LStmt TcId], thing)
+
+-- Note the higher-rank type. stmt_chk is applied at different
+-- types in the equations for tcStmts
+
+tcStmts ctxt stmt_chk [] thing_inside
+ = do { thing <- thing_inside
+ ; return ([], thing) }
+
+-- LetStmts are handled uniformly, regardless of context
+tcStmts ctxt stmt_chk (L loc (LetStmt binds) : stmts) thing_inside
+ = do { (binds', (stmts',thing)) <- tcLocalBinds binds $
+ tcStmts ctxt stmt_chk stmts thing_inside
+ ; return (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 [] = 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 ->
+ -- 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 (L src_loc (RecStmt stmts' later_ids rec_ids rec_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)
+ 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 <$> HsVar poly_id))
-
- -- Result statements
-tcStmtAndThen combine ctxt (L src_loc stmt@(ResultStmt exp)) thing_inside
- = addErrCtxt (stmtCtxt ctxt stmt) (sc_body ctxt exp) `thenM` \ exp' ->
- thing_inside `thenM` \ thing ->
- returnM (combine (L src_loc (ResultStmt exp')) thing)
-
-
-------------------------------
-glue_binds combine binds thing = combine (noLoc (LetStmt [binds])) thing
- -- ToDo: fix the noLoc
+ returnM (co_fn <$> 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 :: [LMatch Name] -> 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 :: LMatch Name -> Int
args_in_match (L _ (Match pats _ _)) = length pats
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)
+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)
-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
+stmtCtxt ctxt stmt = hang (ptext SLIT("In") <+> pprStmtContext ctxt <> colon)
+ 4 (ppr stmt)
-sigPatCtxt bound_tvs bound_ids tys tidy_env
+sigPatCtxt bound_ids bound_tvs tys tidy_env
= -- tys is (body_ty : pat_tys)
mapM zonkTcType tys `thenM` \ tys' ->
let
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