proc ShowTree(List);
int  List, NestLevel, I;
[NestLevel:= 0;
for I:= 0 to -1>>1 do
    [while List(I) < NestLevel do
        [ChOut(0, ^]);  NestLevel:= NestLevel-1];
    if List(I) = 0 then [CrLf(0);  return];
    if I # 0 then Text(0, ", ");
    while List(I) > NestLevel do
        [ChOut(0, ^[);  NestLevel:= NestLevel+1];
    IntOut(0, NestLevel);
    ];
];

[ShowTree([0]);
ShowTree([1, 2, 4, 0]);
ShowTree([3, 1, 3, 1, 0]);
ShowTree([1, 2, 3, 1, 0]);
ShowTree([3, 2, 1, 3, 0]);
ShowTree([3, 3, 3, 1, 1, 3, 3, 3, 0]);
ShowTree([1, 2, 4, 2, 2, 1, 0]);
]