X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FdeSugar%2FMatchCon.lhs;h=6ff502a8ae376dc5cfb56302ea1be1502156e9f8;hb=28a464a75e14cece5db40f2765a29348273ff2d2;hp=c94ce52d45eb455227bbbb1c4e2c0f7f981e6420;hpb=e7498a3ee1d0484d02a9e86633cc179c76ebf36e;p=ghc-hetmet.git diff --git a/ghc/compiler/deSugar/MatchCon.lhs b/ghc/compiler/deSugar/MatchCon.lhs index c94ce52..6ff502a 100644 --- a/ghc/compiler/deSugar/MatchCon.lhs +++ b/ghc/compiler/deSugar/MatchCon.lhs @@ -1,24 +1,32 @@ -% -% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996 + +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[MatchCon]{Pattern-matching constructors} \begin{code} -#include "HsVersions.h" - module MatchCon ( matchConFamily ) where -IMP_Ubiq() -IMPORT_DELOOPER(DsLoop) ( match ) -- break match-ish loop +#include "HsVersions.h" + +import Id( idType ) -import HsSyn ( OutPat(..), HsLit, HsExpr ) -import DsHsSyn ( outPatType ) +import {-# SOURCE #-} Match ( match ) +import HsSyn ( Pat(..), HsConDetails(..) ) +import DsBinds ( dsLHsBinds ) +import DataCon ( isVanillaDataCon, dataConInstOrigArgTys ) +import TcType ( tcTyConAppArgs ) +import Type ( mkTyVarTys ) +import CoreSyn import DsMonad import DsUtils -import Id ( isDataCon, GenId{-instances-} ) -import Util ( panic, assertPanic ) +import Id ( Id ) +import Type ( Type ) +import ListSetOps ( equivClassesByUniq ) +import SrcLoc ( unLoc, Located(..) ) +import Unique ( Uniquable(..) ) +import Outputable \end{code} We are confronted with the first column of patterns in a set of @@ -73,66 +81,94 @@ have-we-used-all-the-constructors? question; the local function @match_cons_used@ does all the real work. \begin{code} matchConFamily :: [Id] + -> Type -> [EquationInfo] - -> [EquationInfo] -- Shadows -> DsM MatchResult - -matchConFamily (var:vars) eqns_info shadows - = match_cons_used vars eqns_info shadows `thenDs` \ alts -> - mkCoAlgCaseMatchResult var alts +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 + 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 + 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. -\begin{code} -match_cons_used _ [{- no more eqns -}] _ = returnDs [] +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@. -match_cons_used vars eqns_info@(EqnInfo (ConPat data_con _ arg_pats : ps1) _ : eqns) shadows - = ASSERT(isDataCon data_con) - let - (eqns_for_this_con, eqns_not_for_this_con) = splitByCon eqns_info - (shadows_for_this_con, shadows_not_for_this_con) = splitByCon shadows - in - -- Go ahead and do the recursive call to make the alts - -- for the other ConPats in this con family... - match_cons_used vars eqns_not_for_this_con shadows_not_for_this_con `thenDs` \ rest_of_alts -> - - -- Make new vars for the con arguments; avoid new locals where possible - selectMatchVars arg_pats `thenDs` \ new_vars -> - - -- Now do the business to make the alt for _this_ ConPat ... - match (new_vars++vars) - (map shift_con_pat eqns_for_this_con) - (map shift_con_pat shadows_for_this_con) `thenDs` \ match_result -> - - returnDs ( - (data_con, new_vars, match_result) - : rest_of_alts - ) +\begin{code} +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 - splitByCon :: [EquationInfo] -> ([EquationInfo], [EquationInfo]) - splitByCon [] = ([],[]) - splitByCon (info@(EqnInfo (pat : _) _) : rest) - = case pat of - ConPat n _ _ | n == data_con -> (info:rest_yes, rest_no) - WildPat _ -> (info:rest_yes, info:rest_no) - -- WildPats will be in the shadows only, - -- and they go into both groups - other_pat -> (rest_yes, info:rest_no) - where - (rest_yes, rest_no) = splitByCon rest - - shift_con_pat :: EquationInfo -> EquationInfo - shift_con_pat (EqnInfo (ConPat _ _ pats': pats) match_result) - = EqnInfo (pats' ++ pats) match_result - shift_con_pat (EqnInfo (WildPat _: pats) match_result) -- Will only happen in shadow - = EqnInfo ([WildPat (outPatType arg_pat) | arg_pat <- arg_pats] ++ pats) match_result - shift_con_pat other = panic "matchConFamily:match_cons_used:shift_con_pat" + 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 <- dsLHsBinds 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 = dataConInstOrigArgTys con inst_tys + 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. +