feat: L Language v0.1 编译器完整实现

5 阶段编译流水线: 词法分析 → 语法分析(Pratt) → 语义分析(类型推断) → LLVM IR → .exe

模块:
- lexer: 手写状态机, 40 种 Token, // 和 /* */ 注释
- parser: Pratt 表达式解析(9 级优先级) + 递归下降语句/函数
- ast: 14 种节点类型 + 工厂函数
- sema: 作用域链符号表 + 类型推断 + 类型检查
- codegen: AST → LLVM-C API, print_i64/f64/bool 内建
- driver: 命令行 + 流水线串联 + 错误报告
- util: Arena bump allocator (8MB)

测试: 65 单元测试(词法41+语法15+语义9) + 5 集成测试 全部通过

语言特性: i64/f64/bool/void, let不可变变量, if/else, while, 递归函数

src/ast/ast.h

@@ -0,0 +1,96 @@
+#ifndef AST_H
+#define AST_H
+
+#include "l_lang.h"
+#include <stddef.h>
+
+typedef enum {
+    AST_PROGRAM,
+    AST_FUNCTION,
+    AST_PARAMETER,
+    AST_BLOCK,
+    AST_LET_STMT,
+    AST_IF_STMT,
+    AST_WHILE_STMT,
+    AST_RETURN_STMT,
+    AST_EXPR_STMT,
+    AST_BINARY_EXPR,
+    AST_UNARY_EXPR,
+    AST_CALL_EXPR,
+    AST_LITERAL_EXPR,
+    AST_IDENT_EXPR,
+} AstKind;
+
+typedef enum {
+    OP_ADD, OP_SUB, OP_MUL, OP_DIV, OP_MOD,
+    OP_EQ, OP_NE, OP_LT, OP_GT, OP_LE, OP_GE,
+    OP_AND, OP_OR,
+    OP_NEG, OP_NOT,
+} BinaryOp;
+
+// 类型信息（语义分析阶段填充）
+typedef struct {
+    TypeKind kind;
+} TypeInfo;
+
+// AST 节点
+struct AstNode {
+    AstKind   kind;
+    TypeInfo  type;         // 语义分析后填充，默认为 TYPE_UNKNOWN
+    int       line;         // 源文件行号
+    int       col;          // 源文件列号
+
+    // 节点特有数据（按 kind 解释）
+    union {
+        // AST_PROGRAM
+        struct { struct AstNode** functions; size_t fn_count; } program;
+        // AST_FUNCTION
+        struct { const char* name; struct AstNode** params; size_t param_count;
+                 TypeKind return_type; struct AstNode* body; } function;
+        // AST_PARAMETER
+        struct { const char* name; TypeKind type; } parameter;
+        // AST_BLOCK
+        struct { struct AstNode** stmts; size_t stmt_count; } block;
+        // AST_LET_STMT
+        struct { const char* name; TypeKind annot_type; bool has_type_annot; struct AstNode* init; } let_stmt;
+        // AST_IF_STMT
+        struct { struct AstNode* cond; struct AstNode* then_block; struct AstNode* else_block; } if_stmt;
+        // AST_WHILE_STMT
+        struct { struct AstNode* cond; struct AstNode* body; } while_stmt;
+        // AST_RETURN_STMT
+        struct { struct AstNode* expr; } return_stmt;
+        // AST_EXPR_STMT
+        struct { struct AstNode* expr; } expr_stmt;
+        // AST_BINARY_EXPR
+        struct { BinaryOp op; struct AstNode* left; struct AstNode* right; } binary;
+        // AST_UNARY_EXPR
+        struct { BinaryOp op; struct AstNode* operand; } unary;
+        // AST_CALL_EXPR
+        struct { const char* name; struct AstNode** args; size_t arg_count; } call;
+        // AST_LITERAL_EXPR
+        struct { TypeKind lit_type; union { int64_t i64_val; double f64_val; bool bool_val; }; } literal;
+        // AST_IDENT_EXPR
+        struct { const char* name; } ident;
+    } as;
+};
+
+// 创建节点的辅助函数（内存来自 arena，通过 void* 传递避免循环依赖）
+AstNode* ast_make_program(void* alloc, AstNode** fns, size_t count, int line, int col);
+AstNode* ast_make_function(void* alloc, const char* name, AstNode** params, size_t pcount,
+                           TypeKind ret, AstNode* body, int line, int col);
+AstNode* ast_make_parameter(void* alloc, const char* name, TypeKind type, int line, int col);
+AstNode* ast_make_block(void* alloc, AstNode** stmts, size_t count, int line, int col);
+AstNode* ast_make_let(void* alloc, const char* name, TypeKind annot_type, bool has_type_annot, AstNode* init, int line, int col);
+AstNode* ast_make_if(void* alloc, AstNode* cond, AstNode* then_b, AstNode* else_b, int line, int col);
+AstNode* ast_make_while(void* alloc, AstNode* cond, AstNode* body, int line, int col);
+AstNode* ast_make_return(void* alloc, AstNode* expr, int line, int col);
+AstNode* ast_make_expr_stmt(void* alloc, AstNode* expr, int line, int col);
+AstNode* ast_make_binary(void* alloc, BinaryOp op, AstNode* left, AstNode* right, int line, int col);
+AstNode* ast_make_unary(void* alloc, BinaryOp op, AstNode* operand, int line, int col);
+AstNode* ast_make_call(void* alloc, const char* name, AstNode** args, size_t count, int line, int col);
+AstNode* ast_make_literal_i64(void* alloc, int64_t val, int line, int col);
+AstNode* ast_make_literal_f64(void* alloc, double val, int line, int col);
+AstNode* ast_make_literal_bool(void* alloc, bool val, int line, int col);
+AstNode* ast_make_ident(void* alloc, const char* name, int line, int col);
+
+#endif