cpp interpreter

1. token ✔
2. lexer ✔
3. parser ✔
4. ast ✔
5. object ✔
6. environment (unifinish stuff)

parser

$ Welcome to the simple Interpreter in C++.
$ Enter expressions or commands.
>> let x = 1 * 2 * 3 * 4 * 5
let x = ((((1 * 2) * 3) * 4) * 5);
>> x * y / 2 + 3 * 8 - 123
((((x * y) / 2) + (3 * 8)) - 123)
>> true == false
(true == false)
>>

7. evaluator ? // 需要修改一下node 增加类型识别