feat: basic lexer + parser with basic example

include/lexer.hpp

@@ -0,0 +1,136 @@
+#pragma once
+#include <iostream>
+#include <cctype>
+
+#include "string.hpp"
+
+enum TokenType
+{
+    Eof = 256,
+    Id,
+    IntLiteral,
+
+    Unknown,
+};
+
+struct Token
+{
+    TokenType token;
+    long int_number;
+    // null-terminated
+    char* string;
+    long line_number;
+    long offset_start;
+    long offset_end;
+public:
+    Token(TokenType t) : token(t) {}
+    Token(TokenType t, long lnumber, long soffset, long eoffset)
+        : token(t), line_number(lnumber), offset_start(soffset), offset_end(eoffset) {}
+    Token() : token(Unknown) {}
+};
+
+class Lexer
+{
+public:
+    const Token& token() { return m_token; }
+public:
+    Lexer(char* filename, StringView code)
+        : m_filename(filename), m_code(code) {}
+
+    Lexer(const Lexer&) = delete;
+    Lexer(Lexer&& other)
+    {
+        m_code = other.m_code;
+        other.m_code = StringView();
+    }
+public:
+    bool NextToken()
+    {
+        if (m_pos >= m_code.size)
+        {
+            m_token = Token(TokenType::Eof);
+            return false;
+        }
+
+        char c = m_code.data[m_pos++];
+
+        while(std::isspace(c)) {
+            if (c == '\n')
+            {
+                m_line++;
+                m_last_newline = m_pos;
+            }
+            c = m_code.data[m_pos++];
+        }
+
+        if (std::isalpha(c) != 0)
+        {
+            StringBuilder s;
+            long offset_start = m_pos - m_last_newline;
+            s.PushChar(c);
+            // id
+            while (std::isalpha(m_code.data[m_pos]) != 0)
+            {
+                s.PushChar(m_code.data[m_pos++]);
+            }
+            s.PushChar('\0');
+            m_token = Token(Id, m_line, offset_start, m_pos - m_last_newline);
+            m_token.string = s.data;
+            return true;
+        }
+
+        if (std::isdigit(c) != 0)
+        {
+            StringBuilder s;
+            long offset_start = m_pos - m_last_newline;
+            bool hex = c == '0' && m_code.data[m_pos] == 'x';
+            s.PushChar(c);
+            // integer (could be hex)
+            while (std::isdigit(m_code.data[m_pos]) != 0 || (hex && std::isalpha(m_code.data[m_pos]) != 0))
+            {
+                s.PushChar(m_code.data[m_pos++]);
+            }
+            s.PushChar('\0');
+            m_token = Token(IntLiteral, m_line, offset_start, m_pos - m_last_newline);
+            m_token.int_number = std::strtol(s.data, nullptr, hex ? 16 : 10);
+            m_token.string = s.data;
+            return true;
+        }
+        
+        m_token = Token((TokenType)c, m_line, m_pos - m_last_newline, m_pos - m_last_newline + 1);
+        return true;
+    }
+
+    void Eat(TokenType expected)
+    {
+        if (!NextToken())
+        {
+            fprintf(stderr, "%s:%d:%d: ERROR: expected %ld, but got EOF", m_filename, 0, 0, expected);
+            Exit(1);
+        }
+        if (token().token != expected)
+        {
+            fprintf(stderr, "%s:%d:%d: ERROR: expected %ld, but got %ld", m_filename, token().line_number, token().offset_start, expected);
+            Exit(1);
+        }
+    }
+
+    void Eat(char expected)
+    {
+        Eat((TokenType)expected);
+    }
+private:
+    void Exit(int status)
+    {
+        std::exit(status);
+    }
+private:
+    StringView m_code;
+    char* m_filename;
+
+    Token m_token;
+
+    size_t m_pos = 0;
+    size_t m_line = 1;
+    size_t m_last_newline = 0;
+};