mkTupleSelector :: [Id]         -- ^ The 'Id's to pattern match the tuple against
                -> Id           -- ^ The 'Id' to select
                -> Id           -- ^ A variable of the same type as the scrutinee
                -> CoreExpr     -- ^ Scrutinee
                -> CoreExpr     -- ^ Selector expression

-- mkTupleSelector [a,b,c,d] b v e
--          = case e of v {
--                (p,q) -> case p of p {
--                           (a,b) -> b }}
-- We use 'tpl' vars for the p,q, since shadowing does not matter.
--
-- In fact, it's more convenient to generate it innermost first, getting
--
--        case (case e of v
--                (p,q) -> p) of p
--          (a,b) -> b
mkTupleSelector vars the_var scrut_var scrut
  = mk_tup_sel (chunkify vars) the_var
  where
    mk_tup_sel [vars] the_var = mkSmallTupleSelector vars the_var scrut_var scrut
    mk_tup_sel vars_s the_var = mkSmallTupleSelector group the_var tpl_v $
                                mk_tup_sel (chunkify tpl_vs) tpl_v
        where
          tpl_tys = [mkBoxedTupleTy (map idType gp) | gp <- vars_s]
          tpl_vs  = mkTemplateLocals tpl_tys
          [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
                                         the_var `elem` gp ]

-- | Like 'mkTupleSelector' but for tuples that are guaranteed
-- never to be \"big\".
--
-- > mkSmallTupleSelector [x] x v e = [| e |]
-- > mkSmallTupleSelector [x,y,z] x v e = [| case e of v { (x,y,z) -> x } |]
mkTupleSelector :: [Id]         -- ^ The 'Id's to pattern match the tuple against
                -> Id           -- ^ The 'Id' to select
                -> Id           -- ^ A variable of the same type as the scrutinee
                -> CoreExpr     -- ^ Scrutinee
                -> CoreExpr
mkTupleSelector vars the_var scrut_var scrut
  = mk_tup_sel (chunkify vars) the_var
  where
    mk_tup_sel [vars] the_var = mkSmallTupleSelector vars the_var scrut_var scrut
    mk_tup_sel vars_s the_var = mkSmallTupleSelector group the_var tpl_v $
                                mk_tup_sel (chunkify tpl_vs) tpl_v
        where
          tpl_tys = [mkBoxedTupleTy (map idType gp) | gp <- vars_s]
          tpl_vs  = mkTemplateLocals tpl_tys
          [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
                                         the_var `elem` gp ]

-- | Like 'mkTupleSelector' but for tuples that are guaranteed
-- never to be \"big\".
--
-- > mkSmallTupleSelector [x] x v e = [| e |]
-- > mkSmallTupleSelector [x,y,z] x v e = [| case e of v { (x,y,z) -> x } |]
mkTupleSelector vars the_var scrut_var scrut
  = mk_tup_sel (chunkify vars) the_var
  where
    mk_tup_sel [vars] the_var = mkSmallTupleSelector vars the_var scrut_var scrut
    mk_tup_sel vars_s the_var = mkSmallTupleSelector group the_var tpl_v $
                                mk_tup_sel (chunkify tpl_vs) tpl_v
        where
          tpl_tys = [mkBoxedTupleTy (map idType gp) | gp <- vars_s]
          tpl_vs  = mkTemplateLocals tpl_tys
          [(tpl_v, group)] = [(tpl,gp) | (tpl,gp) <- zipEqual "mkTupleSelector" tpl_vs vars_s,
                                         the_var `elem` gp ]

-- | Like 'mkTupleSelector' but for tuples that are guaranteed
-- never to be \"big\".
--
-- > mkSmallTupleSelector [x] x v e = [| e |]
-- > mkSmallTupleSelector [x,y,z] x v e = [| case e of v { (x,y,z) -> x } |]