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/ast/expr.rs

@@ -0,0 +1,84 @@
+use crate::ast::stmt::Stmt;
+
+#[derive(Debug, Clone)]
+pub enum Expr {
+    /// 字面量：number / string / bool / nil
+    Literal(Literal),
+
+    /// 变量引用
+    Variable(String),
+
+    /// 赋值表达式：a = b
+    Assign {
+        name: String,
+        value: Box<Expr>,
+    },
+
+    /// 一元运算：!expr / -expr
+    Unary {
+        op: UnaryOp,
+        right: Box<Expr>,
+    },
+
+    /// 二元运算：a + b
+    Binary {
+        left: Box<Expr>,
+        op: BinaryOp,
+        right: Box<Expr>,
+    },
+
+    /// 逻辑运算：&& ||
+    Logical {
+        left: Box<Expr>,
+        op: LogicalOp,
+        right: Box<Expr>,
+    },
+
+    /// 函数调用
+    Call {
+        callee: Box<Expr>,
+        arguments: Vec<Expr>,
+    },
+
+    /// 匿名函数（为闭包预留）
+    Lambda {
+        params: Vec<String>,
+        body: Vec<Stmt>,
+    },
+}
+
+#[derive(Debug, Clone)]
+pub enum Literal {
+    Number(f64),
+    String(String),
+    Bool(bool),
+    Nil,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum UnaryOp {
+    Negate, // -
+    Not,    // !
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum BinaryOp {
+    Add,
+    Sub,
+    Mul,
+    Div,
+
+    Greater,
+    GreaterEqual,
+    Less,
+    LessEqual,
+
+    Equal,
+    NotEqual,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum LogicalOp {
+    And,
+    Or,
+}