feat(furas): introduce a basic lexer

Closes: #56

furas/src/lexer.cpp

@@ -0,0 +1,91 @@
+#include "furas/lexer.hpp"
+
+#include <cctype>
+#include <unordered_map>
+
+namespace furas {
+
+using namespace std::string_literals;
+
+token_r lexer::next_token() {
+    while (m_cursor < m_content.size() && std::isspace(m_content[m_cursor]) != 0) {
+        if (m_content[m_cursor] == '\n') {
+            m_lineStart = m_cursor + 1;
+            ++m_column;
+        }
+        ++m_cursor;
+    }
+
+    // TODO: Add support for single-line comments
+    // TODO: Add support for multi-line comments
+
+    if (m_cursor >= m_content.size()) return token_r{ lexer_error{ lexer_error::EndOfFile, location() } };
+
+    // TODO: Add support for negative integers (I am positive thanks to stasiu :v:)
+    // TODO: Add support for hexadecimal and binary numeric literals
+    if (std::isdigit(m_content[m_cursor]) != 0) {
+        std::uint64_t num = 0;
+        while (m_cursor < m_content.size() && std::isdigit(m_content[m_cursor]) != 0) {
+            num *= 10;
+            num += m_content[m_cursor++] - '0';
+        }
+        return { num };
+    }
+
+    static std::unordered_map<std::string_view, enum token::type> s_tokens = {
+        { "import", token::Import },
+        { "public", token::Public },
+        { "private", token::Private },
+
+        { "push", token::Push },
+        { "array", token::Array },
+        { "get", token::Get },
+        { "drop", token::Drop },
+        { "dup", token::Dup },
+        { "clone", token::Clone },
+        { "ref", token::Ref },
+        { "add", token::Add },
+        { "sub", token::Sub },
+        { "mul", token::Mul },
+        { "div", token::Div },
+        { "mod", token::Mod },
+        { "eq", token::Eq },
+        { "neq", token::Neq },
+        { "lt", token::Lt },
+        { "gt", token::Gt },
+        { "le", token::Le },
+        { "ge", token::Ge },
+        { "ptrof", token::Ptrof },
+        { "sizeof", token::Sizeof },
+        { "lenof", token::Lenof },
+        { "load", token::Load },
+        { "store", token::Store },
+        { "call", token::Call },
+        { "jump", token::Jump },
+        { "jnz", token::Jnz },
+        { "ret", token::Ret },
+    };
+
+    if (std::isalnum(m_content[m_cursor]) != 0) {
+        std::size_t begin = m_cursor++;
+        while (m_cursor < m_content.size() && (std::isalnum(m_content[m_cursor]) != 0 || m_content[m_cursor] == '_'))
+            ++m_cursor;
+        std::string_view str = m_content.substr(begin, m_cursor - begin);
+        if (auto it = s_tokens.find(str); it != s_tokens.end()) return { it->second };
+        return { token::Identifier, str };
+    }
+
+    switch (m_content[m_cursor]) {
+    case '@': ++m_cursor; return { token::Monkey };
+    case '$': ++m_cursor; return { token::Dolar };
+    case '#': ++m_cursor; return { token::Sha256 };
+    case '%': ++m_cursor; return { token::Percent };
+    case '.': ++m_cursor; return { token::Dot };
+    default:
+        return token_r{
+            lexer_error{ lexer_error::UnknownCharacter, location(), "Unknown character '"s + m_content[m_cursor] + "'" }
+        };
+    }
+}
+
+} // namespace furas