import Id ( Id )
import Type ( Type )
import ListSetOps ( equivClassesByUniq )
-import SrcLoc ( unLoc )
+import SrcLoc ( unLoc, Located(..) )
import Unique ( Uniquable(..) )
import Outputable
\end{code}
= 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 { eqn_pats = ConPatOut 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
- mappM (match_con vars ty) eqn_groups `thenDs` \ alts ->
- returnDs (mkCoAlgCaseMatchResult var ty 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
\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
-
- ; match_result <- match (arg_vars ++ vars) ty (shiftEqns eqns)
-
- ; binds <- mapM ds_binds [ bind | ConPatOut _ _ _ bind _ _ <- pats,
- not (isEmptyLHsBinds bind) ]
-
- ; let match_result' = bindInMatchResult (line_up other_pats) $
- mkCoLetsMatchResult binds match_result
-
- ; return (data_con, tvs1 ++ dicts1 ++ arg_vars, match_result') }
+ 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
- pats@(pat1 : other_pats) = map firstPat eqns
- ConPatOut data_con tvs1 dicts1 _ (PrefixCon arg_pats1) pat_ty = pat1
-
- ds_binds bind = do { prs <- dsHsNestedBinds bind; return (Rec prs) }
+ ConPatOut (L _ con) tvs1 dicts1 _ (PrefixCon arg_pats1) pat_ty = firstPat (head eqns)
- line_up pats
- | null tvs1 && null dicts1 = [] -- Common case
- | otherwise = [ pr | ConPatOut _ ts ds _ _ _ <- pats,
- pr <- (ts `zip` tvs1) ++ (ds `zip` dicts1)]
+ 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 data_con) inst_tys)
- (dataConOrigArgTys data_con)
- inst_tys | isVanillaDataCon data_con = tcTyConAppArgs pat_ty -- Newtypes opaque!
- | otherwise = mkTyVarTys tvs1
+ 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 [Existentials in shift_con_pat]