X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FdeSugar%2FMatchCon.lhs;h=a84c96d198cc08fabf27dd60782ef06d9189ab45;hb=ed75b2fd12799f62ea76ae43ebaa46d04f70db3d;hp=e828999c8af4a780fca1012ef9c64f97b15eb0e0;hpb=438596897ebbe25a07e1c82085cfbc5bdb00f09e;p=ghc-hetmet.git diff --git a/ghc/compiler/deSugar/MatchCon.lhs b/ghc/compiler/deSugar/MatchCon.lhs index e828999..a84c96d 100644 --- a/ghc/compiler/deSugar/MatchCon.lhs +++ b/ghc/compiler/deSugar/MatchCon.lhs @@ -1,4 +1,4 @@ -% + % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[MatchCon]{Pattern-matching constructors} @@ -10,16 +10,20 @@ module MatchCon ( matchConFamily ) where import {-# SOURCE #-} Match ( match ) -import HsSyn ( OutPat(..) ) - +import HsSyn ( Pat(..), HsConDetails(..), isEmptyLHsBinds ) +import DsBinds ( dsHsNestedBinds ) +import DataCon ( isVanillaDataCon, dataConTyVars, dataConOrigArgTys ) +import TcType ( tcTyConAppArgs ) +import Type ( substTys, zipTopTvSubst, mkTyVarTys ) +import CoreSyn import DsMonad import DsUtils import Id ( Id ) -import CoreSyn -import Type ( mkTyVarTys ) -import Unique ( Uniquable(..), Unique ) -import UniqFM -- Until equivClassesUniq moves to Util +import Type ( Type ) +import ListSetOps ( equivClassesByUniq ) +import SrcLoc ( unLoc, Located(..) ) +import Unique ( Uniquable(..) ) import Outputable \end{code} @@ -75,71 +79,95 @@ have-we-used-all-the-constructors? question; the local function @match_cons_used@ does all the real work. \begin{code} matchConFamily :: [Id] + -> Type -> [EquationInfo] -> DsM MatchResult - -matchConFamily (var:vars) eqns_info +matchConFamily (var:vars) ty eqns_info = let -- Sort into equivalence classes by the unique on the constructor -- All the EqnInfos should start with a ConPat - eqn_groups = equivClassesByUniq get_uniq eqns_info - get_uniq (EqnInfo _ _ (ConPat data_con _ _ _ _ : _) _) = getUnique data_con + groups = equivClassesByUniq get_uniq eqns_info + get_uniq (EqnInfo { eqn_pats = ConPatOut (L _ data_con) _ _ _ _ _ : _}) = getUnique data_con + + -- Get the wrapper from the head of each group. We're going to + -- use it as the pattern in this case expression, so we need to + -- ensure that any type variables it mentions in the pattern are + -- in scope. So we put its wrappers outside the case, and + -- zap the wrapper for it. + wraps :: [CoreExpr -> CoreExpr] + wraps = map (eqn_wrap . head) groups + + groups' = [ eqn { eqn_wrap = idWrapper } : eqns | eqn:eqns <- groups ] in -- Now make a case alternative out of each group - mapDs (match_con vars) eqn_groups `thenDs` \ alts -> - - returnDs (mkCoAlgCaseMatchResult var alts) + mappM (match_con vars ty) groups' `thenDs` \ alts -> + returnDs (adjustMatchResult (foldr (.) idWrapper wraps) $ + mkCoAlgCaseMatchResult var ty alts) \end{code} And here is the local function that does all the work. It is more-or-less the @matchCon@/@matchClause@ functions on page~94 in -Wadler's chapter in SLPJ. +Wadler's chapter in SLPJ. The function @shift_con_pats@ does what the +list comprehension in @matchClause@ (SLPJ, p.~94) does, except things +are trickier in real life. Works for @ConPats@, and we want it to +fail catastrophically for anything else (which a list comprehension +wouldn't). Cf.~@shift_lit_pats@ in @MatchLits@. \begin{code} -match_con vars all_eqns@(EqnInfo n ctx (ConPat data_con _ ex_tvs ex_dicts arg_pats : pats1) match_result1 : other_eqns) - = -- Make new vars for the con arguments; avoid new locals where possible - mapDs selectMatchVar arg_pats `thenDs` \ arg_vars -> - - -- Now do the business to make the alt for _this_ ConPat ... - match (ex_dicts ++ arg_vars ++ vars) - (map shift_con_pat all_eqns) `thenDs` \ match_result -> - - -- Substitute over the result - let - match_result' | null ex_tvs = match_result - | otherwise = adjustMatchResult subst_it match_result - in - returnDs (data_con, ex_tvs ++ ex_dicts ++ arg_vars, match_result') - where - shift_con_pat :: EquationInfo -> EquationInfo - shift_con_pat (EqnInfo n ctx (ConPat _ _ ex_tvs' ex_dicts' arg_pats: pats) match_result) - = EqnInfo n ctx (new_pats ++ pats) match_result - where - new_pats = map VarPat ex_dicts' ++ arg_pats - - -- We 'substitute' by going: (/\ tvs' -> e) tvs - subst_it e = foldr subst_one e other_eqns - subst_one (EqnInfo _ _ (ConPat _ _ ex_tvs' _ _ : _) _) e = mkTyApps (mkLams ex_tvs' e) ex_tys - ex_tys = mkTyVarTys ex_tvs - - --- Belongs in Util.lhs -equivClassesByUniq :: (a -> Unique) -> [a] -> [[a]] - -- NB: it's *very* important that if we have the input list [a,b,c], - -- where a,b,c all have the same unique, then we get back the list - -- [a,b,c] - -- not - -- [c,b,a] - -- Hence the use of foldr, plus the reversed-args tack_on below -equivClassesByUniq get_uniq xs - = eltsUFM (foldr add emptyUFM xs) +match_con vars ty eqns + = do { -- Make new vars for the con arguments; avoid new locals where possible + arg_vars <- selectMatchVars (map unLoc arg_pats1) arg_tys + ; eqns' <- mapM shift eqns + ; match_result <- match (arg_vars ++ vars) ty eqns' + ; return (con, tvs1 ++ dicts1 ++ arg_vars, match_result) } where - add a ufm = addToUFM_C tack_on ufm (get_uniq a) [a] - tack_on old new = new++old + ConPatOut (L _ con) tvs1 dicts1 _ (PrefixCon arg_pats1) pat_ty = firstPat (head eqns) + + shift eqn@(EqnInfo { eqn_wrap = wrap, + eqn_pats = ConPatOut _ tvs ds bind (PrefixCon arg_pats) _ : pats }) + = do { prs <- dsHsNestedBinds bind + ; return (eqn { eqn_wrap = wrap . wrapBinds (tvs `zip` tvs1) + . wrapBinds (ds `zip` dicts1) + . mkDsLet (Rec prs), + eqn_pats = map unLoc arg_pats ++ pats }) } + + -- Get the arg types, which we use to type the new vars + -- to match on, from the "outside"; the types of pats1 may + -- be more refined, and hence won't do + arg_tys = substTys (zipTopTvSubst (dataConTyVars con) inst_tys) + (dataConOrigArgTys con) + inst_tys | isVanillaDataCon con = tcTyConAppArgs pat_ty -- Newtypes opaque! + | otherwise = mkTyVarTys tvs1 \end{code} -Note on @shift_con_pats@ just above: does what the list comprehension in -@matchClause@ (SLPJ, p.~94) does, except things are trickier in real -life. Works for @ConPats@, and we want it to fail catastrophically -for anything else (which a list comprehension wouldn't). -Cf.~@shift_lit_pats@ in @MatchLits@. +Note [Existentials in shift_con_pat] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + data T = forall a. Ord a => T a (a->Int) + + f (T x f) True = ...expr1... + f (T y g) False = ...expr2.. + +When we put in the tyvars etc we get + + f (T a (d::Ord a) (x::a) (f::a->Int)) True = ...expr1... + f (T b (e::Ord b) (y::a) (g::a->Int)) True = ...expr2... + +After desugaring etc we'll get a single case: + + f = \t::T b::Bool -> + case t of + T a (d::Ord a) (x::a) (f::a->Int)) -> + case b of + True -> ...expr1... + False -> ...expr2... + +*** We have to substitute [a/b, d/e] in expr2! ** +Hence + False -> ....((/\b\(e:Ord b).expr2) a d).... + +Originally I tried to use + (\b -> let e = d in expr2) a +to do this substitution. While this is "correct" in a way, it fails +Lint, because e::Ord b but d::Ord a. +