diff options
Diffstat (limited to 'lib/compiler/src')
| -rw-r--r-- | lib/compiler/src/beam_dead.erl | 18 | ||||
| -rw-r--r-- | lib/compiler/src/beam_except.erl | 8 | ||||
| -rw-r--r-- | lib/compiler/src/beam_jump.erl | 50 | ||||
| -rw-r--r-- | lib/compiler/src/beam_receive.erl | 3 | ||||
| -rw-r--r-- | lib/compiler/src/beam_utils.erl | 20 | ||||
| -rw-r--r-- | lib/compiler/src/beam_validator.erl | 108 | ||||
| -rw-r--r-- | lib/compiler/src/v3_codegen.erl | 46 |
7 files changed, 162 insertions, 91 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl index dd42add433..b01f58f683 100644 --- a/lib/compiler/src/beam_dead.erl +++ b/lib/compiler/src/beam_dead.erl @@ -262,7 +262,7 @@ backward([{select,select_val,Reg,{f,Fail0},List0}|Is], D, Acc) -> backward([{jump,{f,To0}},{move,Src,Reg}=Move|Is], D, Acc) -> To = shortcut_select_label(To0, Reg, Src, D), Jump = {jump,{f,To}}, - case beam_utils:is_killed_at(Reg, To, D) of + case is_killed_at(Reg, To, D) of false -> backward([Move|Is], D, [Jump|Acc]); true -> backward([Jump|Is], D, Acc) end; @@ -420,7 +420,7 @@ comp_op_find_shortcut(To0, Reg, Val, D) -> To0 -> not_possible(); To -> - case beam_utils:is_killed_at(Reg, To, D) of + case is_killed_at(Reg, To, D) of false -> not_possible(); true -> To end @@ -863,3 +863,17 @@ get_literal(nil) -> get_literal({literal,_}=Lit) -> Lit; get_literal({_,_}) -> error. + + +%%% +%%% Removing stores to Y registers is not always safe +%%% if there is an instruction that causes an exception +%%% within a catch. In practice, there are few or no +%%% opportunities for removing stores to Y registers anyway +%%% if sys_core_fold has been run. +%%% + +is_killed_at({x,_}=Reg, Lbl, D) -> + beam_utils:is_killed_at(Reg, Lbl, D); +is_killed_at({y,_}, _, _) -> + false. diff --git a/lib/compiler/src/beam_except.erl b/lib/compiler/src/beam_except.erl index cb3a6b79de..4a181c1923 100644 --- a/lib/compiler/src/beam_except.erl +++ b/lib/compiler/src/beam_except.erl @@ -133,10 +133,12 @@ translate_exception(_, _, _, _) -> no. fix_block(Is, 0) -> reverse(Is); fix_block(Is, Words) -> - fix_block_1(reverse(Is), Words). + reverse(fix_block_1(Is, Words)). -fix_block_1([{set,[],[],{alloc,Live,{F1,F2,Needed,F3}}}|Is], Words) -> - [{set,[],[],{alloc,Live,{F1,F2,Needed-Words,F3}}}|Is]; +fix_block_1([{set,[],[],{alloc,Live,{F1,F2,Needed0,F3}}}|Is], Words) -> + Needed = Needed0 - Words, + true = Needed >= 0, %Assertion. + [{set,[],[],{alloc,Live,{F1,F2,Needed,F3}}}|Is]; fix_block_1([I|Is], Words) -> [I|fix_block_1(Is, Words)]. diff --git a/lib/compiler/src/beam_jump.erl b/lib/compiler/src/beam_jump.erl index 359248c6af..09cd3aa2d4 100644 --- a/lib/compiler/src/beam_jump.erl +++ b/lib/compiler/src/beam_jump.erl @@ -266,17 +266,17 @@ extract_seq_1(_, _) -> no. %%% (3) (4) (5) (6) Jump and unreachable code optimizations. %%% --record(st, {fc, %Label for function class errors. - entry, %Entry label (must not be moved). - mlbl, %Moved labels. - labels :: cerl_sets:set() %Set of referenced labels. - }). - -opt([{label,Fc}|_]=Is0, CLabel) -> - Lbls = initial_labels(Is0), +-record(st, + { + entry, %Entry label (must not be moved). + mlbl, %Moved labels. + labels :: cerl_sets:set() %Set of referenced labels. + }). + +opt(Is0, CLabel) -> find_fixpoint(fun(Is) -> - St = #st{fc=Fc,entry=CLabel,mlbl=#{}, - labels=Lbls}, + Lbls = initial_labels(Is), + St = #st{entry=CLabel,mlbl=#{},labels=Lbls}, opt(Is, [], St) end, Is0). @@ -327,7 +327,8 @@ opt([{label,Lbl}=I|Is], Acc, #st{mlbl=Mlbl}=St0) -> %% since we will rescan the inserted labels. We MUST rescan. St = St0#st{mlbl=maps:remove(Lbl, Mlbl)}, insert_labels([Lbl|Lbls], Is, Acc, St); - error -> opt(Is, [I|Acc], St0) + error -> + opt(Is, [I|Acc], St0) end; opt([{jump,{f,_}=X}|[{label,_},{jump,X}|_]=Is], Acc, St) -> opt(Is, Acc, St); @@ -362,12 +363,19 @@ opt([I|Is], Acc, #st{labels=Used0}=St0) -> true -> skip_unreachable(Is, [I|Acc], St); false -> opt(Is, [I|Acc], St) end; -opt([], Acc, #st{fc=Fc,mlbl=Mlbl}) -> +opt([], Acc, #st{mlbl=Mlbl}) -> Code = reverse(Acc), - case maps:find(Fc, Mlbl) of - {ok,Lbls} -> insert_fc_labels(Lbls, Mlbl, Code); - error -> Code - end. + insert_fc_labels(Code, Mlbl). + +insert_fc_labels([{label,L}=I|Is0], Mlbl) -> + case maps:find(L, Mlbl) of + error -> + [I|insert_fc_labels(Is0, Mlbl)]; + {ok,Lbls} -> + Is = [{label,Lb} || Lb <- Lbls] ++ Is0, + [I|insert_fc_labels(Is, maps:remove(L, Mlbl))] + end; +insert_fc_labels([_|_]=Is, _) -> Is. maps_append_list(K,Vs,M) -> case M of @@ -375,16 +383,6 @@ maps_append_list(K,Vs,M) -> _ -> M#{K => Vs} end. -insert_fc_labels([L|Ls], Mlbl, Acc0) -> - Acc = [{label,L}|Acc0], - case maps:find(L, Mlbl) of - error -> - insert_fc_labels(Ls, Mlbl, Acc); - {ok,Lbls} -> - insert_fc_labels(Lbls++Ls, Mlbl, Acc) - end; -insert_fc_labels([], _, Acc) -> Acc. - collect_labels(Is, #st{entry=Entry}) -> collect_labels_1(Is, Entry, []). diff --git a/lib/compiler/src/beam_receive.erl b/lib/compiler/src/beam_receive.erl index c593184746..89cafe27ce 100644 --- a/lib/compiler/src/beam_receive.erl +++ b/lib/compiler/src/beam_receive.erl @@ -177,7 +177,8 @@ opt_recv([I|Is], D, R0, L0, Acc) -> no; false -> opt_recv(Is, D, R, L, [I|Acc]) - end. + end; +opt_recv([], _, _, _, _) -> no. opt_update_regs({block,Bl}, R, L) -> {opt_update_regs_bl(Bl, R),L}; diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl index 47703b4aa3..a15ecf633e 100644 --- a/lib/compiler/src/beam_utils.erl +++ b/lib/compiler/src/beam_utils.erl @@ -167,8 +167,7 @@ bif_to_test(is_record, [_,_,_]=Ops, Fail) -> {test,is_record,Fail,Ops}. %% is_pure_test({test,Op,Fail,Ops}) -> true|false. %% Return 'true' if the test instruction does not modify any -%% registers and/or bit syntax matching state, nor modifies -%% any bit syntax matching state. +%% registers and/or bit syntax matching state. %% is_pure_test({test,is_eq,_,[_,_]}) -> true; is_pure_test({test,is_ne,_,[_,_]}) -> true; @@ -180,6 +179,8 @@ is_pure_test({test,is_nil,_,[_]}) -> true; is_pure_test({test,is_nonempty_list,_,[_]}) -> true; is_pure_test({test,test_arity,_,[_,_]}) -> true; is_pure_test({test,has_map_fields,_,[_|_]}) -> true; +is_pure_test({test,is_bitstr,_,[_]}) -> true; +is_pure_test({test,is_function2,_,[_,_]}) -> true; is_pure_test({test,Op,_,Ops}) -> erl_internal:new_type_test(Op, length(Ops)). @@ -324,8 +325,11 @@ check_liveness(R, [{deallocate,_}|Is], St) -> {y,_} -> {killed,St}; _ -> check_liveness(R, Is, St) end; -check_liveness(R, [return|_], St) -> - check_liveness_live_ret(R, 1, St); +check_liveness({x,_}=R, [return|_], St) -> + case R of + {x,0} -> {used,St}; + {x,_} -> {killed,St} + end; check_liveness(R, [{call,Live,_}|Is], St) -> case R of {x,X} when X < Live -> {used,St}; @@ -534,14 +538,6 @@ check_liveness_at(R, Lbl, #live{lbl=Ll,res=ResMemorized}=St0) -> check_liveness_ret(R, R, St) -> {used,St}; check_liveness_ret(_, _, St) -> {killed,St}. -check_liveness_live_ret({x,R}, Live, St) -> - if - R < Live -> {used,St}; - true -> {killed,St} - end; -check_liveness_live_ret({y,_}, _, St) -> - {killed,St}. - check_liveness_fail(_, _, _, 0, St) -> {killed,St}; check_liveness_fail(R, Op, Args, Fail, St) -> diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl index faff9940ec..13aa31b7c9 100644 --- a/lib/compiler/src/beam_validator.erl +++ b/lib/compiler/src/beam_validator.erl @@ -161,6 +161,13 @@ validate_0(Module, [{function,Name,Ar,Entry,Code}|Fs], Ft) -> % in the module (those that start with bs_start_match2). }). +%% Match context type. +-record(ms, + {id=make_ref() :: reference(), %Unique ID. + valid=0 :: non_neg_integer(), %Valid slots + slots=0 :: non_neg_integer() %Number of slots + }). + validate_1(Is, Name, Arity, Entry, Ft) -> validate_2(labels(Is), Name, Arity, Entry, Ft). @@ -274,7 +281,7 @@ valfun_1({bs_context_to_binary,Ctx}, #vst{current=#st{x=Xs}}=Vst) -> case Ctx of {Tag,X} when Tag =:= x; Tag =:= y -> Type = case gb_trees:lookup(X, Xs) of - {value,{match_context,_,_}} -> term; + {value,#ms{}} -> term; _ -> get_term_type(Ctx, Vst) end, set_type_reg(Type, Ctx, Vst); @@ -575,7 +582,7 @@ valfun_4({test,bs_start_match2,{f,Fail},Live,[Ctx,NeedSlots],Ctx}, Vst0) -> verify_live(Live, Vst0), Vst1 = prune_x_regs(Live, Vst0), BranchVst = case CtxType of - {match_context,_,_} -> + #ms{} -> %% The failure branch will never be taken when Ctx %% is a match context. Therefore, the type for Ctx %% at the failure label must not be match_context @@ -828,7 +835,7 @@ kill_state_1(Vst) -> %% The stackframe must be initialized. %% The instruction will return to the instruction following the call. call(Name, Live, #vst{current=St}=Vst) -> - verify_live(Live, Vst), + verify_call_args(Name, Live, Vst), verify_y_init(Vst), case return_type(Name, Vst) of Type when Type =/= exception -> @@ -840,44 +847,74 @@ call(Name, Live, #vst{current=St}=Vst) -> %% Tail call. %% The stackframe must have a known size and be initialized. %% Does not return to the instruction following the call. -tail_call(Name, Live, Vst) -> +tail_call(Name, Live, Vst0) -> + verify_y_init(Vst0), + Vst = deallocate(Vst0), verify_call_args(Name, Live, Vst), - verify_y_init(Vst), verify_no_ct(Vst), kill_state(Vst). verify_call_args(_, 0, #vst{}) -> ok; verify_call_args({f,Lbl}, Live, Vst) when is_integer(Live)-> - Verify = fun(R) -> - case get_move_term_type(R, Vst) of - {match_context,_,_} -> - verify_call_match_context(Lbl, Vst); - _ -> - ok - end - end, - verify_call_args_1(Live, Verify, Vst); + verify_local_call(Lbl, Live, Vst); verify_call_args(_, Live, Vst) when is_integer(Live)-> - Verify = fun(R) -> get_term_type(R, Vst) end, - verify_call_args_1(Live, Verify, Vst); + verify_call_args_1(Live, Vst); verify_call_args(_, Live, _) -> error({bad_number_of_live_regs,Live}). -verify_call_args_1(0, _, _) -> ok; -verify_call_args_1(N, Verify, Vst) -> +verify_call_args_1(0, _) -> ok; +verify_call_args_1(N, Vst) -> X = N - 1, - Verify({x,X}), - verify_call_args_1(X, Verify, Vst). + get_term_type({x,X}, Vst), + verify_call_args_1(X, Vst). + +verify_local_call(Lbl, Live, Vst) -> + case all_ms_in_x_regs(Live, Vst) of + [{R,Ctx}] -> + %% Verify that there is a suitable bs_start_match2 instruction. + verify_call_match_context(Lbl, R, Vst), + + %% Since the callee has consumed the match context, + %% there must be no additional copies in Y registers. + #ms{id=Id} = Ctx, + case ms_in_y_regs(Id, Vst) of + [] -> + ok; + [_|_]=Ys -> + error({multiple_match_contexts,[R|Ys]}) + end; + [_,_|_]=Xs0 -> + Xs = [R || {R,_} <- Xs0], + error({multiple_match_contexts,Xs}); + [] -> + ok + end. + +all_ms_in_x_regs(0, _Vst) -> + []; +all_ms_in_x_regs(Live0, Vst) -> + Live = Live0 - 1, + R = {x,Live}, + case get_move_term_type(R, Vst) of + #ms{}=M -> + [{R,M}|all_ms_in_x_regs(Live, Vst)]; + _ -> + all_ms_in_x_regs(Live, Vst) + end. + +ms_in_y_regs(Id, #vst{current=#st{y=Ys0}}) -> + Ys = gb_trees:to_list(Ys0), + [Y || {Y,#ms{id=OtherId}} <- Ys, OtherId =:= Id]. -verify_call_match_context(Lbl, #vst{ft=Ft}) -> +verify_call_match_context(Lbl, Ctx, #vst{ft=Ft}) -> case gb_trees:lookup(Lbl, Ft) of none -> error(no_bs_start_match2); {value,[{test,bs_start_match2,_,_,[Ctx,_],Ctx}|_]} -> ok; - {value,[{test,bs_start_match2,_,_,[Bin,_,_],Ctx}|_]} -> - error({binary_and_context_regs_different,Bin,Ctx}) + {value,[{test,bs_start_match2,_,_,_,_}=I|_]} -> + error({unsuitable_bs_start_match2,I}) end. allocate(Zero, Stk, Heap, Live, #vst{current=#st{numy=none}=St}=Vst0) -> @@ -1009,7 +1046,7 @@ assert_unique_map_keys([_,_|_]=Ls) -> %%% bsm_match_state(Slots) -> - {match_context,0,Slots}. + #ms{slots=Slots}. bsm_validate_context(Reg, Vst) -> _ = bsm_get_context(Reg, Vst), @@ -1017,7 +1054,7 @@ bsm_validate_context(Reg, Vst) -> bsm_get_context({x,X}=Reg, #vst{current=#st{x=Xs}}=_Vst) when is_integer(X) -> case gb_trees:lookup(X, Xs) of - {value,{match_context,_,_}=Ctx} -> Ctx; + {value,#ms{}=Ctx} -> Ctx; _ -> error({no_bsm_context,Reg}) end; bsm_get_context(Reg, _) -> error({bad_source,Reg}). @@ -1029,8 +1066,8 @@ bsm_save(Reg, {atom,start}, Vst) -> Vst; bsm_save(Reg, SavePoint, Vst) -> case bsm_get_context(Reg, Vst) of - {match_context,Bits,Slots} when SavePoint < Slots -> - Ctx = {match_context,Bits bor (1 bsl SavePoint),Slots}, + #ms{valid=Bits,slots=Slots}=Ctxt0 when SavePoint < Slots -> + Ctx = Ctxt0#ms{valid=Bits bor (1 bsl SavePoint),slots=Slots}, set_type_reg(Ctx, Reg, Vst); _ -> error({illegal_save,SavePoint}) end. @@ -1042,7 +1079,7 @@ bsm_restore(Reg, {atom,start}, Vst) -> Vst; bsm_restore(Reg, SavePoint, Vst) -> case bsm_get_context(Reg, Vst) of - {match_context,Bits,Slots} when SavePoint < Slots -> + #ms{valid=Bits,slots=Slots} when SavePoint < Slots -> case Bits band (1 bsl SavePoint) of 0 -> error({illegal_restore,SavePoint,not_set}); _ -> Vst @@ -1123,7 +1160,7 @@ assert_term(Src, Vst) -> %% Thus 'exception' is never stored as type descriptor %% for a register. %% -%% {match_context,_,_} A matching context for bit syntax matching. We do allow +%% #ms{} A match context for bit syntax matching. We do allow %% it to moved/to from stack, but otherwise it must only %% be accessed by bit syntax matching instructions. %% @@ -1230,7 +1267,7 @@ get_term_type(Src, Vst) -> initialized -> error({unassigned,Src}); {catchtag,_} -> error({catchtag,Src}); {trytag,_} -> error({trytag,Src}); - {match_context,_,_} -> error({match_context,Src}); + #ms{} -> error({match_context,Src}); Type -> Type end. @@ -1382,11 +1419,12 @@ merge_types(bool, {atom,A}) -> merge_bool(A); merge_types({atom,A}, bool) -> merge_bool(A); -merge_types({match_context,B0,Slots},{match_context,B1,Slots}) -> - {match_context,B0 bor B1,Slots}; -merge_types({match_context,_,_}=M, _) -> +merge_types(#ms{id=Id,valid=B0,slots=Slots}=M, + #ms{id=Id,valid=B1,slots=Slots}) -> + M#ms{valid=B0 bor B1,slots=Slots}; +merge_types(#ms{}=M, _) -> M; -merge_types(_, {match_context,_,_}=M) -> +merge_types(_, #ms{}=M) -> M; merge_types(T1, T2) when T1 =/= T2 -> %% Too different. All we know is that the type is a 'term'. @@ -1510,7 +1548,6 @@ bif_type(node, [_], _) -> {atom,[]}; bif_type(hd, [_], _) -> term; bif_type(tl, [_], _) -> term; bif_type(get, [_], _) -> term; -bif_type(raise, [_,_], _) -> exception; bif_type(Bif, _, _) when is_atom(Bif) -> term. is_bif_safe('/=', 2) -> true; @@ -1524,6 +1561,7 @@ is_bif_safe('>=', 2) -> true; is_bif_safe(is_atom, 1) -> true; is_bif_safe(is_boolean, 1) -> true; is_bif_safe(is_binary, 1) -> true; +is_bif_safe(is_bitstring, 1) -> true; is_bif_safe(is_float, 1) -> true; is_bif_safe(is_function, 1) -> true; is_bif_safe(is_integer, 1) -> true; diff --git a/lib/compiler/src/v3_codegen.erl b/lib/compiler/src/v3_codegen.erl index f531056591..f5f3c73793 100644 --- a/lib/compiler/src/v3_codegen.erl +++ b/lib/compiler/src/v3_codegen.erl @@ -1089,6 +1089,23 @@ protected_cg(Ts, Rs, _Fail, I, Vdb, Bef, St0) -> %% test_cg(TestName, Args, Fail, I, Vdb, Bef, St) -> {[Ainstr],Aft,St}. %% Generate test instruction. Use explicit fail label here. +test_cg(is_map, [A], Fail, I, Vdb, Bef, St) -> + %% We must avoid creating code like this: + %% + %% move x(0) y(0) + %% is_map Fail [x(0)] + %% make_fun => x(0) %% Overwrite x(0) + %% put_map_assoc y(0) ... + %% + %% The code is safe, but beam_validator does not understand that. + %% Extending beam_validator to handle such (rare) code as the + %% above would make it slower for all programs. Instead, change + %% the code generator to always prefer the Y register for is_map() + %% and put_map_assoc() instructions, ensuring that they use the + %% same register. + Arg = cg_reg_arg_prefer_y(A, Bef), + Aft = clear_dead(Bef, I, Vdb), + {[{test,is_map,{f,Fail},[Arg]}],Aft,St}; test_cg(Test, As, Fail, I, Vdb, Bef, St) -> Args = cg_reg_args(As, Bef), Aft = clear_dead(Bef, I, Vdb), @@ -1155,19 +1172,15 @@ call_cg(Func, As, Rs, Le, Vdb, Bef, St0) -> %% Inside a guard. The only allowed function call is to %% erlang:error/1,2. We will generate the following code: %% - %% jump FailureLabel %% move {atom,ok} DestReg - %% - %% The 'move' instruction will never be executed, but we - %% generate it anyway in case the beam_validator is run - %% on unoptimized code. + %% jump FailureLabel {remote,{atom,erlang},{atom,error}} = Func, %Assertion. [{var,DestVar}] = Rs, Int0 = clear_dead(Bef, Le#l.i, Vdb), Reg = put_reg(DestVar, Int0#sr.reg), Int = Int0#sr{reg=Reg}, Dst = fetch_reg(DestVar, Reg), - {[{jump,{f,Fail}},{move,{atom,ok},Dst}], + {[{move,{atom,ok},Dst},{jump,{f,Fail}}], clear_dead(Int, Le#l.i, Vdb),St0}; #cg{} -> %% Ordinary function call in a function body. @@ -1545,7 +1558,7 @@ set_cg([{var,R}], {map,Op,Map,[{map_pair,{var,_}=K,V}]}, Le, Vdb, Bef, Fail = {f,Bfail}, {Sis,Int0} = maybe_adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb, St), - SrcReg = cg_reg_arg(Map,Int0), + SrcReg = cg_reg_arg_prefer_y(Map, Int0), Line = line(Le#l.a), List = [cg_reg_arg(K,Int0),cg_reg_arg(V,Int0)], @@ -1572,7 +1585,7 @@ set_cg([{var,R}], {map,Op,Map,Es}, Le, Vdb, Bef, Fail = {f,Bfail}, {Sis,Int0} = maybe_adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb, St), - SrcReg = cg_reg_arg(Map,Int0), + SrcReg = cg_reg_arg_prefer_y(Map, Int0), Line = line(Le#l.a), %% fetch registers for values to be put into the map @@ -1845,6 +1858,9 @@ cg_reg_args(As, Bef) -> [cg_reg_arg(A, Bef) || A <- As]. cg_reg_arg({var,V}, Bef) -> fetch_var(V, Bef); cg_reg_arg(Literal, _) -> Literal. +cg_reg_arg_prefer_y({var,V}, Bef) -> fetch_var_prefer_y(V, Bef); +cg_reg_arg_prefer_y(Literal, _) -> Literal. + %% cg_setup_call([Arg], Bef, Cur, Vdb) -> {[Instr],Aft}. %% Do the complete setup for a call/enter. @@ -2086,6 +2102,12 @@ fetch_var(V, Sr) -> error -> fetch_stack(V, Sr#sr.stk) end. +fetch_var_prefer_y(V, #sr{reg=Reg,stk=Stk}) -> + case find_stack(V, Stk) of + {ok,R} -> R; + error -> fetch_reg(V, Reg) + end. + load_vars(Vs, Regs) -> foldl(fun ({var,V}, Rs) -> put_reg(V, Rs) end, Regs, Vs). @@ -2159,11 +2181,11 @@ fetch_stack(Var, Stk) -> fetch_stack(Var, Stk, 0). fetch_stack(V, [{V}|_], I) -> {yy,I}; fetch_stack(V, [_|Stk], I) -> fetch_stack(V, Stk, I+1). -% find_stack(Var, Stk) -> find_stack(Var, Stk, 0). +find_stack(Var, Stk) -> find_stack(Var, Stk, 0). -% find_stack(V, [{V}|Stk], I) -> {ok,{yy,I}}; -% find_stack(V, [O|Stk], I) -> find_stack(V, Stk, I+1); -% find_stack(V, [], I) -> error. +find_stack(V, [{V}|_], I) -> {ok,{yy,I}}; +find_stack(V, [_|Stk], I) -> find_stack(V, Stk, I+1); +find_stack(_, [], _) -> error. on_stack(V, Stk) -> keymember(V, 1, Stk). |