Initialize Aster project with basic structure, including Cargo configuration, lexer, parser, interpreter, and AST definitions. Add a sample script and README documentation. Implement basic error handling and environment management for variable storage.

src/lexer/token.rs

@@ -0,0 +1,42 @@
+// lexer/token.rs
+#[derive(Debug, Clone, PartialEq)]
+pub enum TokenKind {
+    // 单字符
+    LeftParen, RightParen,
+    LeftBrace, RightBrace,
+    Comma, Semicolon,
+
+    // 运算符
+    Plus, Minus, Star, Slash,
+    Bang,
+    Equal,
+    Greater, GreaterEqual,
+    Less, LessEqual,
+    EqualEqual, BangEqual,
+    AndAnd, OrOr,
+
+    // 字面量
+    Identifier(String),
+    Number(f64),
+    String(String),
+
+    // 关键字
+    Let,
+    Fn,
+    If,
+    Else,
+    While,
+    Return,
+    True,
+    False,
+    Nil,
+
+    EOF,
+}
+
+#[derive(Debug, Clone)]
+pub struct Token {
+    pub kind: TokenKind,
+    pub line: usize,
+    pub column: usize,
+}