very basic version of usql

usql/lexer.h

@@ -0,0 +1,113 @@
+#pragma once
+
+#include <iostream>
+#include <regex>
+#include <stdexcept>
+#include <string>
+
+namespace usql {
+
+    enum class TokenType {
+	undef,
+	identifier,
+	plus,
+	minus,
+	multiply,
+	divide,
+	equal,
+	not_equal,
+	greater,
+	greater_equal,
+	lesser,
+	lesser_equal,
+	keyword_create,
+	keyword_table,
+	keyword_where,
+	keyword_delete,
+	keyword_update,
+	keyword_load,
+	keyword_from,
+	keyword_insert,
+	keyword_into,
+	keyword_values,
+	keyword_select,
+	keyword_set,
+	keyword_copy,
+	keyword_not,
+	keyword_null,
+	keyword_int,
+	keyword_float,
+	keyword_varchar,
+	int_number,
+	double_number,
+	string_literal,
+	open_paren,
+	close_paren,
+	logical_and,
+	logical_or,
+	pipe,
+	semicolon,
+	comma,
+	newline,
+	comment,
+	eof
+    };
+
+    struct Token {
+	std::string token_string;
+	TokenType type;
+
+	Token(const std::string &token_str, TokenType typ);
+    };
+
+    class Lexer {
+    public:
+	Lexer();
+
+	void parse(const std::string &code);
+
+	void debugTokens();
+
+	Token currentToken();
+
+	Token consumeCurrentToken();
+
+	void nextToken();
+
+	void skipToken(TokenType type);
+
+	void skipTokenOptional(TokenType type);
+
+	TokenType tokenType();
+
+	TokenType nextTokenType();
+
+	TokenType prevTokenType();
+
+	static bool isRelationalOperator(TokenType token_type);
+
+	static bool isLogicalOperator(TokenType token_type);
+
+	static bool isArithmeticalOperator(TokenType token_type);
+
+    private:
+	TokenType type(const std::string &token);
+
+	std::string stringLiteral(std::string token);
+
+	static std::string typeToString(TokenType token_type);
+
+
+    private:
+	std::string m_code_str;
+	std::vector<Token> m_tokens;
+	int m_index = 0;
+
+	std::regex k_words_regex;
+	std::regex k_int_regex;
+	std::regex k_int_underscored_regex;
+	std::regex k_double_regex;
+	std::regex k_identifier_regex;
+    };
+
+}