start on lexer

markup/lexer.cpp

@@ -0,0 +1,14 @@
+#include "lexer.hpp"
+#include "result.hpp"
+#include <cctype>
+#include <string_view>
+
+namespace markup {
+
+auto constexpr Lexer::next() noexcept -> Result<Token, void>
+{
+    if (done())
+        return token(TokenTypes::Eof, index);
+}
+
+}

markup/lexer.hpp

@@ -0,0 +1,88 @@
+#pragma once
+
+#include "utils.hpp"
+#include <optional>
+#include <string_view>
+
+namespace markup {
+
+enum class TokenTypes {
+    Eof,
+    Whitespace,
+    MultilineComment,
+    SinglelineComment,
+
+    Name,
+    Int,
+    Float,
+    String,
+    Id, // Example = `#my_id`
+    Class, // Example = `.my_class`
+
+    True,
+    False,
+    Null,
+
+    LBrace,
+    RBrace,
+    Comma,
+    Equal,
+};
+
+struct Token {
+    TokenTypes type;
+    size_t index, length;
+    int line, column;
+};
+
+class Lexer final {
+public:
+    Lexer(std::string_view text)
+        : text { text }
+    { }
+    auto constexpr next() noexcept -> Result<Token, void>;
+    auto peek() noexcept -> Result<Token, void>
+    {
+        if (last_token)
+            return Result<Token, void>::create_ok(*last_token);
+        return {};
+    }
+
+private:
+    auto constexpr make_number() noexcept -> Result<Token, void>;
+    auto constexpr make_id() noexcept -> Result<Token, void>;
+    [[nodiscard]] auto constexpr inline token(
+        TokenTypes type, size_t begin) noexcept -> Token
+    {
+        auto token = Token { type, begin, index - begin, line, column };
+        last_token = token;
+        return token;
+    }
+    [[nodiscard]] auto constexpr inline done() const noexcept -> bool
+    {
+        return index >= text.size();
+    }
+    [[nodiscard]] auto constexpr inline current() const noexcept -> char
+    {
+        return text.at(index);
+    }
+    auto constexpr inline step() noexcept -> void
+    {
+        if (done())
+            return;
+        index++;
+        column++;
+        if (!done() and text.at(index) == '\n') {
+            column = 1;
+            line++;
+        }
+    }
+
+    std::string_view text;
+    size_t index = 0;
+    int line = 1;
+    int column = 1;
+    std::optional<Token> last_token;
+};
+
+}

markup/meson.build

@@ -1,6 +1,7 @@
 
 markup_sources = files(
     'parser.cpp',
+    'lexer.cpp',
 )
 
 markup_inc = include_directories('.')