feat: 添加函数定义和类型表达式支持，重构解析器以处理新语法(函数定义)

src/Parser/TypeExprParser.cpp

@@ -0,0 +1,56 @@
+/*!
+    @file src/Parser/TypeExprParser.cpp
+    @brief 类型表达式解析器实现
+    @author PuqiAR (im@puqiar.top)
+    @date 2026-02-25
+*/
+
+#pragma once
+
+#include <Parser/Parser.hpp>
+
+namespace Fig
+{
+    Result<NamedTypeExpr *, Error> Parser::parseNamedTypeExpr() // 当前token为identifier
+    {
+        StateProtector p(this, {State::ParsingNamedTypeExpr});
+
+        SourceLocation location = makeSourceLocation(currentToken());
+
+        DynArray<String> path;
+        while (true)
+        {
+            const Token  &subPathTok = consumeToken();
+            const String &subPath    = srcManager.GetSub(subPathTok.index, subPathTok.length);
+            path.push_back(subPath);
+
+            if (match(TokenType::Dot))
+            {
+                if (!currentToken().isIdentifier())
+                {
+                    return std::unexpected(
+                        makeUnexpectTokenError("named type expr", "identifier", currentToken()));
+                }
+            }
+            else 
+            {
+                break;
+            }
+        }
+        NamedTypeExpr *namedTypeExpr = new NamedTypeExpr(path, location);
+        return namedTypeExpr;
+    }
+
+    Result<TypeExpr *, Error> Parser::parseTypeExpr()
+    {
+        // TODO: 泛型表达式解析
+        if (currentToken().isIdentifier())
+        {
+            return parseNamedTypeExpr();
+        }
+        else
+        {
+            return std::unexpected(makeUnexpectTokenError("type expr", "name/...", currentToken()));
+        }
+    }
+}; // namespace Fig