Improve AST nodes

Signed-off-by: CHatingPython <chatingpython@gmail.com>

furc/include/furc/front/parser.hpp

@@ -2,6 +2,8 @@
 #define FURC_FRONT_PARSER_HPP
 
 #include "furc/ast/declaration.hpp"
+#include "furc/ast/expression.hpp"
+#include "furc/ast/literal.hpp"
 #include "furc/ast/node.hpp"
 #include "furc/ast/program.hpp"
 #include "furc/front/lexer.hpp"
@@ -28,6 +30,8 @@ public:
 private:
     ast::node_handle<ast::declaration_node> parse_declaration();
     ast::node_handle<ast::statement_node>   parse_statement();
+    ast::node_handle<ast::expression_node>  parse_expression();
+    ast::node_handle<ast::literal_node>     parse_literal();
 
     ast::function_body_handle parse_body();
 private:

furc/include/furc/front/token.hpp

@@ -14,6 +14,7 @@ enum class token_t {
     None,
     Identifier,
     Keyword,
+    String,
     Integer,
     Lparen,
     Rparen,
@@ -32,6 +33,7 @@ static inline std::ostream& operator<<(std::ostream& os, token_t type) {
     case token_t::None: return os << "none";
     case token_t::Identifier: return os << "identifier";
     case token_t::Keyword: return os << "keyword";
+    case token_t::String: return os << "string";
     case token_t::Integer: return os << "integer";
     case token_t::Lparen: return os << "'('";
     case token_t::Rparen: return os << "')'";
@@ -51,6 +53,7 @@ static inline std::string operator+(const std::string& str, token_t type) {
     case token_t::None: return str + "none";
     case token_t::Identifier: return str + "identifier";
     case token_t::Keyword: return str + "keyword";
+    case token_t::String: return str + "string";
     case token_t::Integer: return str + "integer";
     case token_t::Lparen: return str + "'('";
     case token_t::Rparen: return str + "')'";
@@ -103,9 +106,10 @@ struct token {
     bool operator==(const token& rhs) const {
         if (type != rhs.type) return false;
         switch (type) {
-        case token_t::Identifier: return value == rhs.value;
-        case token_t::Keyword: return keyword == rhs.keyword;
+        case token_t::Identifier:
+        case token_t::String:
         case token_t::Integer: return value == rhs.value;
+        case token_t::Keyword: return keyword == rhs.keyword;
         case token_t::None:
         case token_t::Lparen:
         case token_t::Rparen:
@@ -124,6 +128,7 @@ struct token {
 static inline std::ostream& operator<<(std::ostream& os, const token& token) {
     switch (token.type) {
     case token_t::Identifier:
+    case token_t::String:
     case token_t::Integer: return os << token.value;
     case token_t::Keyword: return os << token.keyword;
     default: return os << token.type;