diff --git a/.clang-format b/.clang-format
index 0a15f56..09e9f78 100644
--- a/.clang-format
+++ b/.clang-format
@@ -33,13 +33,13 @@ AllowShortBlocksOnASingleLine: true
 AllowShortCaseLabelsOnASingleLine: true
 
 # 允许短的函数放在同一行: None, InlineOnly(定义在类中), Empty(空函数), Inline(定义在类中，空函数), All
-AllowShortFunctionsOnASingleLine: Inline
+AllowShortFunctionsOnASingleLine: Empty
 
 # 允许短的if语句保持在同一行
-AllowShortIfStatementsOnASingleLine: true
+AllowShortIfStatementsOnASingleLine: false
 
 # 允许短的循环保持在同一行
-AllowShortLoopsOnASingleLine: true
+AllowShortLoopsOnASingleLine: false
 
 # 总是在返回类型后换行: None, All, TopLevel(顶级函数，不包括在类中的函数), 
 # AllDefinitions(所有的定义，不包括声明), TopLevelDefinitions(所有的顶级函数的定义)
diff --git a/.gitignore b/.gitignore
index 0239152..55f9b92 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,4 +6,6 @@ build/
 .DS_Store
 
 .vscode
-.VSCodeCounter
\ No newline at end of file
+.VSCodeCounter
+
+/test.fig
\ No newline at end of file
diff --git a/src/Core/SourceLocations.hpp b/src/Core/SourceLocations.hpp
index 2722cfd..b72b51e 100644
--- a/src/Core/SourceLocations.hpp
+++ b/src/Core/SourceLocations.hpp
@@ -1,7 +1,6 @@
 #pragma once
 
 #include <Deps/Deps.hpp>
-#include <format>
 
 namespace Fig
 {
diff --git a/src/Deps/Deps.hpp b/src/Deps/Deps.hpp
index 241b69b..25bd1fc 100644
--- a/src/Deps/Deps.hpp
+++ b/src/Deps/Deps.hpp
@@ -3,11 +3,18 @@
 #include <Core/CoreInfos.hpp>
 #include <Deps/HashMap/HashMap.hpp>
 #include <Deps/String/String.hpp>
+#include <Deps/String/CharUtils.hpp>
+
+#include <expected>
 
 namespace Fig
 {
     #ifdef __FCORE_LINK_DEPS
         using Deps::String;
         using Deps::HashMap;
+        using Deps::CharUtils;
+
+        template<class _Tp, class _Err>
+        using Result = std::expected<_Tp, _Err>;
     #endif
 };
\ No newline at end of file
diff --git a/src/Deps/String/String.hpp b/src/Deps/String/String.hpp
index ab308cc..c5cf6c1 100644
--- a/src/Deps/String/String.hpp
+++ b/src/Deps/String/String.hpp
@@ -17,7 +17,8 @@ namespace Fig::Deps
         {
             for (size_t i = 0; i < n; ++i)
             {
-                if (static_cast<unsigned char>(data[i]) >= 128) return false;
+                if (static_cast<unsigned char>(data[i]) >= 128)
+                    return false;
             }
             return true;
         }
@@ -26,7 +27,8 @@ namespace Fig::Deps
         {
             for (size_t i = 0; i < n; ++i)
             {
-                if (data[i] >= 128) return false;
+                if (data[i] >= 128)
+                    return false;
             }
             return true;
         }
@@ -100,8 +102,14 @@ namespace Fig::Deps
             _length = other._length;
             mode = other.mode;
 
-            if (mode == Mode::ASCII_SSO) { memcpy(sso, other.sso, sizeof(unsigned char) * _length); }
-            else if (mode == Mode::ASCII_HEP) { new (&ascii) std::vector<unsigned char>(other.ascii); }
+            if (mode == Mode::ASCII_SSO)
+            {
+                memcpy(sso, other.sso, sizeof(unsigned char) * _length);
+            }
+            else if (mode == Mode::ASCII_HEP)
+            {
+                new (&ascii) std::vector<unsigned char>(other.ascii);
+            }
             else
             {
                 new (&utf32) std::vector<u32>(other.utf32);
@@ -134,24 +142,33 @@ namespace Fig::Deps
             {
                 // pass
             }
-            if (mode == Mode::ASCII_HEP) { ascii.~vector(); }
-            if (mode == Mode::UTF32_HEP) { utf32.~vector(); }
+            if (mode == Mode::ASCII_HEP)
+            {
+                ascii.~vector();
+            }
+            if (mode == Mode::UTF32_HEP)
+            {
+                utf32.~vector();
+            }
         }
 
         void ensure_utf32()
         {
-            if (mode == Mode::UTF32_HEP) return;
+            if (mode == Mode::UTF32_HEP)
+                return;
 
             std::vector<u32> tmp;
             tmp.reserve(_length);
 
             if (mode == Mode::ASCII_SSO)
             {
-                for (size_t i = 0; i < _length; ++i) tmp.push_back(static_cast<u32>(sso[i]));
+                for (size_t i = 0; i < _length; ++i)
+                    tmp.push_back(static_cast<u32>(sso[i]));
             }
             else // ASCII_HEP
             {
-                for (unsigned char c : ascii) tmp.push_back(static_cast<u32>(c));
+                for (unsigned char c : ascii)
+                    tmp.push_back(static_cast<u32>(c));
             }
 
             destroy();
@@ -166,7 +183,8 @@ namespace Fig::Deps
 
             std::vector<unsigned char> tmp;
             tmp.reserve(_length);
-            for (size_t i = 0; i < _length; ++i) tmp.push_back(sso[i]);
+            for (size_t i = 0; i < _length; ++i)
+                tmp.push_back(sso[i]);
 
             mode = Mode::ASCII_HEP;
             new (&ascii) std::vector<unsigned char>(std::move(tmp));
@@ -223,7 +241,8 @@ namespace Fig::Deps
         {
             assert(data);
             size_t n = 0;
-            while (data[n] != 0) ++n;
+            while (data[n] != 0)
+                ++n;
             init(data, n);
         }
 
@@ -236,7 +255,8 @@ namespace Fig::Deps
             if (n <= SSO_SIZE && StringUtils::is_pure_ascii(data, n))
             {
                 mode = Mode::ASCII_SSO;
-                for (size_t i = 0; i < n; ++i) sso[i] = static_cast<unsigned char>(data[i]);
+                for (size_t i = 0; i < n; ++i)
+                    sso[i] = static_cast<unsigned char>(data[i]);
                 return;
             }
 
@@ -245,7 +265,8 @@ namespace Fig::Deps
                 mode = Mode::ASCII_HEP;
                 new (&ascii) std::vector<unsigned char>();
                 ascii.reserve(n);
-                for (size_t i = 0; i < n; ++i) ascii.push_back(static_cast<unsigned char>(data[i]));
+                for (size_t i = 0; i < n; ++i)
+                    ascii.push_back(static_cast<unsigned char>(data[i]));
                 return;
             }
 
@@ -255,10 +276,19 @@ namespace Fig::Deps
         }
 
     public:
-        size_t length() const noexcept { return _length; }
-        size_t size() const noexcept { return _length; }
+        size_t length() const noexcept
+        {
+            return _length;
+        }
+        size_t size() const noexcept
+        {
+            return _length;
+        }
 
-        bool empty() const noexcept { return _length == 0; }
+        bool empty() const noexcept
+        {
+            return _length == 0;
+        }
         void reserve(size_t n)
         {
             if (mode == Mode::ASCII_HEP)
@@ -274,7 +304,10 @@ namespace Fig::Deps
             {
                 // pass
             }
-            if (mode == Mode::ASCII_HEP) { ascii.clear(); }
+            if (mode == Mode::ASCII_HEP)
+            {
+                ascii.clear();
+            }
             else
             {
                 utf32.clear();
@@ -283,34 +316,71 @@ namespace Fig::Deps
 
         void shrink_to_fit() noexcept
         {
-            if (mode == Mode::ASCII_HEP) { ascii.shrink_to_fit(); }
+            if (mode == Mode::ASCII_HEP)
+            {
+                ascii.shrink_to_fit();
+            }
             else
             {
                 utf32.shrink_to_fit();
             }
         }
 
-        ~String() noexcept { destroy(); }
+        ~String() noexcept
+        {
+            destroy();
+        }
         String() noexcept
         {
             mode = Mode::ASCII_SSO;
             _length = 0;
         }
-        String(const String &other) noexcept { copyfrom(other); }
-        String(String &&other) noexcept { movefrom(std::move(other)); }
-        String(const char *str) { init(str); }
-        String(const char32_t *str) { init(str); }
-        String(const std::string &s) { init(s.data(), s.size()); }
+        String(const String &other) noexcept
+        {
+            copyfrom(other);
+        }
+        String(String &&other) noexcept
+        {
+            movefrom(std::move(other));
+        }
+        String(const char *str)
+        {
+            init(str);
+        }
+        String(const char32_t *str)
+        {
+            init(str);
+        }
+        String(char32_t c)
+        {
+            init("");
+            push_back(c);
+        }
+        String(char c)
+        {
+            init("");
+            push_back(static_cast<char32_t>(c));
+        }
+        String(const std::string &s)
+        {
+            init(s.data(), s.size());
+        }
 
         static String fromPureAscii(const char *str)
         {
             String string;
             string._length = std::strlen(str);
-            if (string._length <= SSO_SIZE) { memcpy(string.sso, str, string._length); }
+            if (string._length <= SSO_SIZE)
+            {
+                memcpy(string.sso, str, string._length);
+            }
             else
             {
                 string.ascii.reserve(string._length);
-                for (size_t i = 0; i < string._length; ++i) { string.ascii.push_back(str[i]); }
+                for (size_t i = 0; i < string._length; ++i)
+                {
+                    string.ascii.push_back(str[i]);
+                }
             }
 
             return string;
@@ -328,13 +398,15 @@ namespace Fig::Deps
 
         String &operator=(String &&other) noexcept
         {
-            if (this != &other) movefrom(std::move(other));
+            if (this != &other)
+                movefrom(std::move(other));
             return *this;
         }
 
         String &operator+=(const String &rhs)
         {
-            if (rhs._length == 0) return *this;
+            if (rhs._length == 0)
+                return *this;
 
             // 两边都是 ASCII
             bool this_ascii = (mode == Mode::ASCII_SSO || mode == Mode::ASCII_HEP);
@@ -356,7 +428,8 @@ namespace Fig::Deps
                     return *this;
                 }
 
-                if (mode == Mode::ASCII_SSO) promote_sso_ascii_to_heap();
+                if (mode == Mode::ASCII_SSO)
+                    promote_sso_ascii_to_heap();
 
                 // 追加
                 if (rhs.mode == Mode::ASCII_SSO)
@@ -377,11 +450,13 @@ namespace Fig::Deps
 
                 if (mode == Mode::ASCII_SSO)
                 {
-                    for (size_t i = 0; i < _length; ++i) tmp.push_back(static_cast<u32>(sso[i]));
+                    for (size_t i = 0; i < _length; ++i)
+                        tmp.push_back(static_cast<u32>(sso[i]));
                 }
                 else // ASCII_HEP
                 {
-                    for (unsigned char c : ascii) tmp.push_back(static_cast<u32>(c));
+                    for (unsigned char c : ascii)
+                        tmp.push_back(static_cast<u32>(c));
                 }
 
                 destroy();
@@ -389,14 +464,19 @@ namespace Fig::Deps
                 new (&utf32) std::vector<u32>(std::move(tmp));
             }
 
-            if (rhs.mode == Mode::UTF32_HEP) { utf32.insert(utf32.end(), rhs.utf32.begin(), rhs.utf32.end()); }
+            if (rhs.mode == Mode::UTF32_HEP)
+            {
+                utf32.insert(utf32.end(), rhs.utf32.begin(), rhs.utf32.end());
+            }
             else if (rhs.mode == Mode::ASCII_SSO)
             {
-                for (size_t i = 0; i < rhs._length; ++i) utf32.push_back(static_cast<u32>(rhs.sso[i]));
+                for (size_t i = 0; i < rhs._length; ++i)
+                    utf32.push_back(static_cast<u32>(rhs.sso[i]));
             }
             else // ASCII_HEP
             {
-                for (unsigned char c : rhs.ascii) utf32.push_back(static_cast<u32>(c));
+                for (unsigned char c : rhs.ascii)
+                    utf32.push_back(static_cast<u32>(c));
             }
 
             _length = utf32.size();
@@ -425,7 +505,8 @@ namespace Fig::Deps
                     return;
                 }
 
-                if (mode == Mode::ASCII_SSO) promote_sso_ascii_to_heap();
+                if (mode == Mode::ASCII_SSO)
+                    promote_sso_ascii_to_heap();
 
                 if (mode == Mode::ASCII_HEP)
                 {
@@ -477,7 +558,8 @@ namespace Fig::Deps
 
         String &append(size_t count, u32 cp)
         {
-            for (size_t i = 0; i < count; ++i) push_back(cp);
+            for (size_t i = 0; i < count; ++i)
+                push_back(cp);
             return *this;
         }
 
@@ -523,7 +605,10 @@ namespace Fig::Deps
             // UTF32_HEP -> UTF-8 encode
             for (u32 cp : utf32)
             {
-                if (cp <= 0x7F) { out.push_back(static_cast<char>(cp)); }
+                if (cp <= 0x7F)
+                {
+                    out.push_back(static_cast<char>(cp));
+                }
                 else if (cp <= 0x7FF)
                 {
                     out.push_back(static_cast<char>(0xC0 | (cp >> 6)));
@@ -547,18 +632,24 @@ namespace Fig::Deps
 
             return out;
         }
-        friend std::ostream &operator<<(std::ostream &os, const String &s) { return os << s.toStdString(); }
+        friend std::ostream &operator<<(std::ostream &os, const String &s)
+        {
+            return os << s.toStdString();
+        }
 
         friend bool operator==(const String &a, const String &b) noexcept
         {
-            if (a._length != b._length) return false;
+            if (a._length != b._length)
+                return false;
 
             // 同模式
             if (a.mode == b.mode)
             {
-                if (a.mode == Mode::ASCII_SSO) return std::memcmp(a.sso, b.sso, a._length) == 0;
+                if (a.mode == Mode::ASCII_SSO)
+                    return std::memcmp(a.sso, b.sso, a._length) == 0;
 
-                if (a.mode == Mode::ASCII_HEP) return a.ascii == b.ascii;
+                if (a.mode == Mode::ASCII_HEP)
+                    return a.ascii == b.ascii;
 
                 return a.utf32 == b.utf32;
             }
@@ -582,18 +673,23 @@ namespace Fig::Deps
             if (ascii_str.mode == Mode::ASCII_SSO)
             {
                 for (size_t i = 0; i < ascii_str._length; ++i)
-                    if (static_cast<u32>(ascii_str.sso[i]) != utf32_str.utf32[i]) return false;
+                    if (static_cast<u32>(ascii_str.sso[i]) != utf32_str.utf32[i])
+                        return false;
             }
             else
             {
                 for (size_t i = 0; i < ascii_str._length; ++i)
-                    if (static_cast<u32>(ascii_str.ascii[i]) != utf32_str.utf32[i]) return false;
+                    if (static_cast<u32>(ascii_str.ascii[i]) != utf32_str.utf32[i])
+                        return false;
             }
 
             return true;
         }
 
-        friend bool operator!=(const String &a, const String &b) noexcept { return !(a == b); }
+        friend bool operator!=(const String &a, const String &b) noexcept
+        {
+            return !(a == b);
+        }
         // std::hash
         friend struct std::hash<String>;
 
@@ -602,34 +698,41 @@ namespace Fig::Deps
         {
             assert(i < _length);
 
-            if (mode == Mode::ASCII_SSO) return static_cast<u32>(sso[i]);
-            if (mode == Mode::ASCII_HEP) return static_cast<u32>(ascii[i]);
+            if (mode == Mode::ASCII_SSO)
+                return static_cast<u32>(sso[i]);
+            if (mode == Mode::ASCII_HEP)
+                return static_cast<u32>(ascii[i]);
             return utf32[i];
         }
         u32 at(size_t i) const
         {
-            if (i >= _length) throw std::out_of_range("String::at");
+            if (i >= _length)
+                throw std::out_of_range("String::at");
             return (*this)[i];
         }
 
         bool starts_with(const String &prefix) const
         {
-            if (prefix._length > _length) return false;
+            if (prefix._length > _length)
+                return false;
 
             for (size_t i = 0; i < prefix._length; ++i)
-                if ((*this)[i] != prefix[i]) return false;
+                if ((*this)[i] != prefix[i])
+                    return false;
 
             return true;
         }
 
         bool ends_with(const String &suffix) const
         {
-            if (suffix._length > _length) return false;
+            if (suffix._length > _length)
+                return false;
 
             size_t offset = _length - suffix._length;
 
             for (size_t i = 0; i < suffix._length; ++i)
-                if ((*this)[offset + i] != suffix[i]) return false;
+                if ((*this)[offset + i] != suffix[i])
+                    return false;
 
             return true;
         }
@@ -639,27 +742,32 @@ namespace Fig::Deps
             if (mode == Mode::ASCII_SSO)
             {
                 for (size_t i = 0; i < _length; ++i)
-                    if (sso[i] == cp) return true;
+                    if (sso[i] == cp)
+                        return true;
                 return false;
             }
 
             if (mode == Mode::ASCII_HEP)
             {
-                if (cp >= 128) return false;
+                if (cp >= 128)
+                    return false;
                 for (unsigned char c : ascii)
-                    if (c == cp) return true;
+                    if (c == cp)
+                        return true;
                 return false;
             }
 
             for (u32 c : utf32)
-                if (c == cp) return true;
+                if (c == cp)
+                    return true;
 
             return false;
         }
 
         String substr(size_t pos, size_t count = size_t(-1)) const
         {
-            if (pos >= _length) return String();
+            if (pos >= _length)
+                return String();
 
             size_t len = (_length - pos < count) ? (_length - pos) : count;
 
@@ -710,7 +818,8 @@ namespace Fig::Deps
 
         String &erase(size_t pos, size_t count = size_t(-1))
         {
-            if (pos >= _length) return *this;
+            if (pos >= _length)
+                return *this;
 
             size_t len = (_length - pos < count) ? (_length - pos) : count;
 
@@ -735,8 +844,10 @@ namespace Fig::Deps
 
         String &insert(size_t pos, const String &other)
         {
-            if (pos > _length) pos = _length;
-            if (other._length == 0) return *this;
+            if (pos > _length)
+                pos = _length;
+            if (other._length == 0)
+                return *this;
 
             bool this_ascii = (mode != Mode::UTF32_HEP);
             bool other_ascii = (other.mode != Mode::UTF32_HEP);
@@ -759,7 +870,8 @@ namespace Fig::Deps
                     return *this;
                 }
 
-                if (mode == Mode::ASCII_SSO) promote_sso_ascii_to_heap();
+                if (mode == Mode::ASCII_SSO)
+                    promote_sso_ascii_to_heap();
 
                 if (other.mode == Mode::ASCII_SSO)
                     ascii.insert(ascii.begin() + pos, other.sso, other.sso + other._length);
@@ -794,17 +906,21 @@ namespace Fig::Deps
             {
                 u32 a = (*this)[i];
                 u32 b = other[i];
-                if (a != b) return (a < b) ? -1 : 1;
+                if (a != b)
+                    return (a < b) ? -1 : 1;
             }
 
-            if (_length == other._length) return 0;
+            if (_length == other._length)
+                return 0;
             return (_length < other._length) ? -1 : 1;
         }
 
         size_t find(const String &needle, size_t pos = 0) const
         {
-            if (needle._length == 0) return pos <= _length ? pos : size_t(-1);
-            if (needle._length > _length || pos >= _length) return size_t(-1);
+            if (needle._length == 0)
+                return pos <= _length ? pos : size_t(-1);
+            if (needle._length > _length || pos >= _length)
+                return size_t(-1);
 
             size_t limit = _length - needle._length;
 
@@ -812,9 +928,11 @@ namespace Fig::Deps
             {
                 size_t j = 0;
                 for (; j < needle._length; ++j)
-                    if ((*this)[i + j] != needle[j]) break;
+                    if ((*this)[i + j] != needle[j])
+                        break;
 
-                if (j == needle._length) return i;
+                if (j == needle._length)
+                    return i;
             }
 
             return size_t(-1);
@@ -822,16 +940,20 @@ namespace Fig::Deps
 
         size_t rfind(const String &needle) const
         {
-            if (needle._length == 0) return _length;
-            if (needle._length > _length) return size_t(-1);
+            if (needle._length == 0)
+                return _length;
+            if (needle._length > _length)
+                return size_t(-1);
 
             for (size_t i = _length - needle._length + 1; i-- > 0;)
             {
                 size_t j = 0;
                 for (; j < needle._length; ++j)
-                    if ((*this)[i + j] != needle[j]) break;
+                    if ((*this)[i + j] != needle[j])
+                        break;
 
-                if (j == needle._length) return i;
+                if (j == needle._length)
+                    return i;
             }
 
             return size_t(-1);
@@ -839,7 +961,8 @@ namespace Fig::Deps
 
         String &replace(size_t pos, size_t len, const String &repl)
         {
-            if (pos >= _length) return *this;
+            if (pos >= _length)
+                return *this;
 
             size_t erase_len = (_length - pos < len) ? (_length - pos) : len;
 
@@ -865,7 +988,8 @@ namespace Fig::Deps
                     return *this;
                 }
 
-                if (mode == Mode::ASCII_SSO) promote_sso_ascii_to_heap();
+                if (mode == Mode::ASCII_SSO)
+                    promote_sso_ascii_to_heap();
 
                 ascii.erase(ascii.begin() + pos, ascii.begin() + pos + erase_len);
 
@@ -948,7 +1072,10 @@ namespace std
     struct std::formatter<Fig::Deps::String, char>
     {
         // 不支持自定义格式说明符
-        constexpr auto parse(std::format_parse_context &ctx) { return ctx.begin(); }
+        constexpr auto parse(std::format_parse_context &ctx)
+        {
+            return ctx.begin();
+        }
 
         template <typename FormatContext>
         auto format(const Fig::Deps::String &s, FormatContext &ctx) const
diff --git a/src/Error/Error.cpp b/src/Error/Error.cpp
index 52742bd..551f592 100644
--- a/src/Error/Error.cpp
+++ b/src/Error/Error.cpp
@@ -36,8 +36,14 @@ namespace Fig
             case ErrorType::MayBeNull: return "MaybeNull";
 
             case ErrorType::UnterminatedString: return "UnterminatedString";
+            case ErrorType::UnterminatedComments: return "UnterminatedComments";
+            case ErrorType::InvalidNumberLiteral: return "InvalidNumberLiteral";
+            case ErrorType::InvalidCharacter: return "InvalidCharacter";
+            case Fig::ErrorType::InvalidSymbol: return "InvalidSymbol";
+
             case ErrorType::SyntaxError: return "SyntaxError";
-            default: return "Some one forgot to add case to `ErrorTypeToString`";
+
+            // default: return "Some one forgot to add case to `ErrorTypeToString`";
         }
     }
 
@@ -76,8 +82,9 @@ namespace Fig
 
         const SourceLocation &location = error.location;
 
-        err << TC::DarkGray << "  ┌─> " << TC::Cyan << location.fileName << " " << TC::DarkGray << location.sp.line
-            << ":" << location.sp.column << '\n';
+        err << TC::DarkGray << "  ┌─> Fn " << TC::Cyan << '\'' << location.packageName << '.' << location.functionName
+            << '\'' << " " << location.fileName << " (" << TC::DarkGray << location.sp.line << ":" << location.sp.column
+            << TC::Cyan << ')' << TC::Reset << '\n';
         err << TC::DarkGray << "  │" << '\n' << "  │" << TC::Reset << '\n';
 
         // 尝试打印上3行 下2行
diff --git a/src/Error/Error.hpp b/src/Error/Error.hpp
index 97fa942..75748ca 100644
--- a/src/Error/Error.hpp
+++ b/src/Error/Error.hpp
@@ -20,6 +20,11 @@ namespace Fig
         MayBeNull = 1001,
 
         UnterminatedString = 2001,
+        UnterminatedComments,
+        InvalidNumberLiteral,
+        InvalidCharacter,
+        InvalidSymbol,
+
         SyntaxError,
     };
 
diff --git a/src/Lexer/Lexer.cpp b/src/Lexer/Lexer.cpp
index 1f26d28..290a7c9 100644
--- a/src/Lexer/Lexer.cpp
+++ b/src/Lexer/Lexer.cpp
@@ -2,5 +2,280 @@
 
 namespace Fig
 {
-    
-};
\ No newline at end of file
+    /*
+        总则：
+            Lexer不涉及语义部分，语义为Parser及之后的部分确定！
+            确定边界 --> 分词
+            无法确定 --> 错误的源，报错
+
+    */
+
+    Result<Token, Error> Lexer::scanComments()
+    {
+        Token tok(rd.currentIndex(), 2, TokenType::Comments);
+        rd.skip(2); // 跳过 //
+        do
+        {
+            tok.length++;
+            if (rd.current() == U'\n')
+            {
+                rd.next(); // skip '\n'
+                break;
+            }
+            rd.next();
+        } while (rd.hasNext());
+        return tok;
+    }
+
+    Result<Token, Error> Lexer::scanMultilineComments()
+    {
+        Token tok(rd.currentIndex(), 2, TokenType::Comments);
+        SourcePosition startPos = rd.currentPosition();
+        rd.skip(2); // 跳过 / *
+        while (true)
+        {
+            if (rd.isAtEnd())
+            {
+                return std::unexpected(Error(ErrorType::UnterminatedComments,
+                                             "unterminated multiline comments",
+                                             "insert '*/'",
+                                             makeSourceLocation(startPos)));
+            }
+            if (rd.current() == U'*' && rd.peekIf() == U'/')
+            {
+                rd.skip(2);
+                break;
+            }
+            tok.length++;
+            rd.next();
+        }
+        return tok;
+    }
+
+    Result<Token, Error> Lexer::scanIdentifierOrKeyword()
+    {
+        Token tok(rd.currentIndex(), 1, TokenType::Identifier);
+        String value;                  // 用于判断是标识符还是关键字
+        value.push_back(rd.produce()); // 加入第一个
+
+        while (CharUtils::isIdentifierContinue(rd.current())) // continue: _ / 0-9 / aA - zZ
+        {
+            tok.length++;
+            value.push_back(rd.produce());
+            if (rd.isAtEnd())
+            {
+                break;
+            }
+        }
+
+        if (Token::keywordMap.contains(value))
+        {
+            tok.type = Token::keywordMap.at(value);
+        }
+        return tok;
+    }
+
+    Result<Token, Error> Lexer::scanNumberLiteral()
+    {
+        Token tok(rd.currentIndex(), 0, TokenType::LiteralNumber);
+        state = State::ScanDec;
+
+        if (rd.current() == U'0')
+        {
+            char32_t _peek = std::tolower(rd.peekIf());
+            if (_peek == U'b')
+            {
+                state = State::ScanBin;
+                rd.skip(2); // 跳过 0b
+                tok.length += 2;
+            }
+            else if (_peek == U'x')
+            {
+                state = State::ScanHex;
+                rd.skip(2); // 跳过 0x
+                tok.length += 2;
+            }
+            // else
+            // {
+            //     return std::unexpected(Error(ErrorType::InvalidNumberLiteral,
+            //                                  std::format("bad number postfix 0{}", String(_peek)),
+            //                                  "correct it",
+            //                                  makeSourceLocation(rd.currentPosition())));
+                
+            // }
+        }
+
+        do
+        {
+            char32_t current = rd.current();
+            if (state == State::ScanDec && !CharUtils::isDigit(current))
+            {
+                break;
+            }
+            if (state == State::ScanHex && !CharUtils::isHexDigit(current))
+            {
+                break;
+            }
+            if (state == State::ScanBin && current != U'0' && current != U'1')
+            {
+                // return std::unexpected(
+                //     Error(ErrorType::InvalidNumberLiteral,
+                //           std::format("invalid binary number literal, scanning '{}'", String(&current)),
+                //           "correct it",
+                //           makeSourceLocation(rd.currentPosition())));
+                break;
+            }
+            tok.length++;
+            rd.next();
+        } while (!rd.isAtEnd());
+
+        // 科学计数法
+        while (!rd.isAtEnd() && state == State::ScanDec
+               && (rd.current() == U'e' || rd.current() == U'E' || rd.current() == U'_' || rd.current() == U'+'
+                   || rd.current() == U'-' || CharUtils::isDigit(rd.current())))
+        {
+            tok.length++;
+            rd.next();
+        }
+
+        return tok;
+    }
+    Result<Token, Error> Lexer::scanStringLiteral()
+    {
+        state = (rd.current() == U'"' ? State::ScanStringDQ : Lexer::State::ScanStringSQ);
+
+        SourcePosition startPos = rd.currentPosition();
+
+        rd.next(); // skip " / '
+        Token tok(rd.currentIndex(), 0, TokenType::LiteralString);
+
+        while (true)
+        {
+            if (state == State::ScanStringDQ && rd.current() == U'"')
+            {
+                rd.next(); // skip '"'
+                break;
+            }
+            else if (state == State::ScanStringSQ && rd.current() == U'\'')
+            {
+                rd.next(); // skip `'`
+                break;
+            }
+            else if (rd.isAtEnd())
+            {
+                return std::unexpected(
+                    Error(ErrorType::UnterminatedString,
+                          "unterminated string literal",
+                          std::format("insert '{}'", String((state == State::ScanStringDQ ? "\"" : "'"))),
+                          makeSourceLocation(startPos)));
+            }
+            else
+            {
+                tok.length++;
+                rd.next();
+            }
+        }
+        return tok;
+    }
+    Result<Token, Error> Lexer::scanPunct()
+    {
+        Token tok(rd.currentIndex(), 0, TokenType::Illegal);
+
+        auto startsWith = [&](const String &prefix) -> bool {
+            for (const auto &p : Token::punctMap)
+            {
+                const String &op = p.first;
+                if (op.starts_with(prefix))
+                    return true;
+            }
+            return false;
+        };
+
+        String sym;
+
+        do
+        {
+            String candidate = sym + rd.current();
+            if (startsWith(candidate))
+            {
+                rd.next();
+                tok.length++;
+                sym = candidate;
+            }
+            else
+            {
+                break;
+            }
+        } while (!rd.isAtEnd() && CharUtils::isPunct(rd.current()));
+
+        if (!Token::punctMap.contains(sym))
+        {
+            return std::unexpected(Error(ErrorType::InvalidSymbol,
+                                         std::format("invalid symbol `{}`", sym),
+                                         "correct it",
+                                         makeSourceLocation(rd.currentPosition())));
+        }
+        tok.type = Token::punctMap.at(sym);
+        return tok;
+    }
+
+    void Lexer::skipWhitespaces()
+    {
+        while (!rd.isAtEnd())
+        {
+            char32_t current = rd.current();
+            if (current == EOF || !CharUtils::isAsciiSpace(current)) // 检查 EOF
+                break;
+            rd.next();
+        }
+    }
+
+    Result<Token, Error> Lexer::NextToken()
+    {
+        if (rd.isAtEnd())
+        {
+            return Token(rd.currentIndex(), 0, TokenType::EndOfFile);
+        }
+        if (rd.current() == U'\0')
+        {
+            return Token(rd.currentIndex(), 1, TokenType::EndOfFile);
+        }
+        if (rd.current() == U'/' && rd.peekIf() == U'/')
+        {
+            return scanComments();
+        }
+        else if (rd.current() == U'/' && rd.peekIf() == U'*')
+        {
+            return scanMultilineComments();
+        }
+        else if (CharUtils::isIdentifierStart(rd.current()))
+        {
+            return scanIdentifierOrKeyword();
+        }
+        else if (CharUtils::isDigit(rd.current()))
+        {
+            return scanNumberLiteral();
+        }
+        else if (rd.current() == U'"' || rd.current() == U'\'')
+        {
+            return scanStringLiteral();
+        }
+        else if (CharUtils::isPunct(rd.current()))
+        {
+            return scanPunct();
+        }
+        else if (CharUtils::isSpace(rd.current()))
+        {
+            skipWhitespaces();
+            return NextToken();
+        }
+        else
+        {
+            return std::unexpected(Error(
+                ErrorType::InvalidCharacter,
+                std::format("invalid character '{}' (U+{})", String(rd.current()), static_cast<int>(rd.current())),
+                "correct it",
+                makeSourceLocation(rd.currentPosition())));
+        }
+    }
+}; // namespace Fig
\ No newline at end of file
diff --git a/src/Lexer/Lexer.hpp b/src/Lexer/Lexer.hpp
index 842f958..b29b8bc 100644
--- a/src/Lexer/Lexer.hpp
+++ b/src/Lexer/Lexer.hpp
@@ -10,6 +10,7 @@
 #include <Deps/Deps.hpp>
 #include <Token/Token.hpp>
 #include <Core/SourceLocations.hpp>
+#include <Error/Error.hpp>
 
 namespace Fig
 {
@@ -25,13 +26,13 @@ namespace Fig
         SourceReader()
         {
             index = 0;
-            pos.line = pos.column = 0;
+            pos.line = pos.column = 1;
         }
         SourceReader(const String &_source) // copy
         {
             source = _source;
             index = 0;
-            pos.line = pos.column = 0;
+            pos.line = pos.column = 1;
         }
 
         SourcePosition &currentPosition() { return pos; }
@@ -42,7 +43,16 @@ namespace Fig
             return source[index];
         }
 
-        inline bool hasNext() const { return index < source.length(); }
+        inline char32_t currentIf() const
+        {
+            if (index >= source.length())
+            {
+                return U'\0';
+            }
+            return source[index];
+        }
+
+        inline bool hasNext() const { return index < source.length() - 1; }
 
         inline char32_t peek() const
         {
@@ -66,10 +76,10 @@ namespace Fig
 
         inline void next()
         {
-            assert(hasNext() && "SrcReader: next failed, need more runes");
-            ++index;
+            char32_t consumed = currentIf();
 
-            if (current() == U'\n')
+            ++index;
+            if (consumed == U'\n')
             {
                 ++pos.line;
                 pos.column = 1;
@@ -80,18 +90,38 @@ namespace Fig
             }
         }
 
+        inline void skip(size_t n)
+        {
+            for (size_t i = 0; i < n; ++i) { next(); }
+        }
+
         inline size_t currentIndex() const { return index; }
 
-        inline bool isAtEnd() const { return index == source.length() - 1; }
+        inline bool isAtEnd() const { return index >= source.length(); }
     };
 
     class Lexer
     {
     public:
-        enum State : uint8_t
+        enum class State : uint8_t
         {
-            Normal,
-            Error
+            Error,
+            Standby,
+            End,
+
+            ScanComments,          // 单行注释
+            ScanMultilineComments, // 多行注释
+            ScanIdentifier,        // 关键字也算
+
+            ScanDec,      // 十进制数字, 如 1.2 31, 3.14e+3, 1_000_0000
+            ScanBin,      // 二进制数字, 如 0b0001 / 0B0001
+            ScanHex,      // 十六进制数字, 如 0xABCD / 0XabCd
+            ScanStringDQ, // 双引号字符串, 如 "hello, world!"
+            ScanStringSQ, // 单引号字符串, 如 'hello'
+            ScanBool,     // 布尔字面量, true / false
+            ScanNull,     // 空值字面量, null
+
+            ScanPunct, // 符号
         };
 
     private:
@@ -99,17 +129,22 @@ namespace Fig
         SourceReader rd;
 
     protected:
-        Token scanComments();
-        Token scanIdentifierOrKeyword();
+        Result<Token, Error> scanComments();
+        Result<Token, Error> scanMultilineComments();
 
-        Token scanNumberLiteral();
-        Token scanStringLiteral();
-        Token scanBoolLiteral();
-        Token scanLiteralNull();
+        Result<Token, Error> scanIdentifierOrKeyword();
+
+        Result<Token, Error> scanNumberLiteral();
+        Result<Token, Error> scanStringLiteral(); // 支持多行
+        // Result<Token, Error> scanBoolLiteral(); 由 scanIdentifier...扫描
+        // Result<Token, Error> scanLiteralNull(); 由 scanIdentifier...扫描
+
+        Result<Token, Error> scanPunct();
+
+        void skipWhitespaces();
 
-        Token scanPunct();
     public:
-        State state = Normal;
+        State state = State::Standby;
 
         Lexer() {}
         Lexer(const String &source, String _fileName)
@@ -118,6 +153,12 @@ namespace Fig
             fileName = std::move(_fileName);
         }
 
-        Token NextToken();
+        SourceLocation makeSourceLocation(const SourcePosition &current_pos)
+        {
+            return SourceLocation(
+                current_pos, fileName, "[internal lexer]", String(magic_enum::enum_name(state).data()));
+        }
+
+        Result<Token, Error> NextToken();
     };
 }; // namespace Fig
\ No newline at end of file
diff --git a/src/Lexer/LexerTest.cpp b/src/Lexer/LexerTest.cpp
new file mode 100644
index 0000000..35d68ca
--- /dev/null
+++ b/src/Lexer/LexerTest.cpp
@@ -0,0 +1,43 @@
+#include <Error/Error.hpp>
+#include <Token/Token.hpp>
+#include <Lexer/Lexer.hpp>
+
+#include <iostream>
+
+int main()
+{
+    using namespace Fig;
+
+    String fileName = "test.fig";
+    String filePath = "T:/Files/Maker/Code/MyCodingLanguage/The Fig Project/Fig/test.fig";
+
+    SourceManager manager(filePath);
+    manager.Read();
+
+    if (!manager.read)
+    {
+        std::cerr << "Couldn't read file";
+        return 1;
+    }
+
+    Lexer lexer(manager.GetSource(), fileName);
+
+    while (true)
+    {
+        const auto &result = lexer.NextToken();
+        if (!result.has_value())
+        {
+            ReportError(result.error(), manager);
+            break;
+        }
+        const Token &token = *result;
+        const String &lexeme = manager.GetSub(token.index, token.length);
+        const auto &type = magic_enum::enum_name(token.type);
+        if (token.type == TokenType::EndOfFile)
+        {
+            std::cout << "EOF: " << type << '\n';
+            break;
+        }
+        std::cout << lexeme << " --> " << type << '\n';
+    }
+}
\ No newline at end of file
diff --git a/src/SourceManager/SourceManager.hpp b/src/SourceManager/SourceManager.hpp
index 655b164..fed79a3 100644
--- a/src/SourceManager/SourceManager.hpp
+++ b/src/SourceManager/SourceManager.hpp
@@ -52,5 +52,10 @@ namespace Fig
         {
             return source.substr(_index_start, _length);
         }
+
+        const String &GetSource() const
+        {
+            return source;
+        }
     };
 };
\ No newline at end of file
diff --git a/src/Token/Token.cpp b/src/Token/Token.cpp
index 210179c..7524959 100644
--- a/src/Token/Token.cpp
+++ b/src/Token/Token.cpp
@@ -2,7 +2,7 @@
 
 namespace Fig
 {
-    const HashMap<String, TokenType> Token::symbolMap = {
+    const HashMap<String, TokenType> Token::punctMap = {
         // 三字符
         {String("..."), TokenType::TripleDot},
         // 双字符
@@ -83,5 +83,8 @@ namespace Fig
         {String("throw"), TokenType::Throw},
         {String("Finally"), TokenType::Finally},
         {String("as"), TokenType::As},
+        {String("true"), TokenType::LiteralTrue},
+        {String("false"), TokenType::LiteralFalse},
+        {String("null"), TokenType::LiteralNull},
     };
 };
\ No newline at end of file
diff --git a/src/Token/Token.hpp b/src/Token/Token.hpp
index 6f94011..a62f25c 100644
--- a/src/Token/Token.hpp
+++ b/src/Token/Token.hpp
@@ -54,11 +54,13 @@ namespace Fig
         // TypeBool,   // Bool
         // TypeDouble, // Double
 
-        /* Literal Types (not keyword)*/
+        /* Literal Types */
         LiteralNumber, // number (int,float...)
         LiteralString, // string
-        LiteralBool,   // bool (true/false)
-        LiteralNull,   // null (Null unique instance)
+
+        LiteralTrue,  // true  <-- keyword
+        LiteralFalse, // false <-- keyword
+        LiteralNull,  // null (Null unique instance) <-- keyword
 
         /* Punct */
         Plus,       // +
@@ -121,12 +123,12 @@ namespace Fig
     class Token final
     {
     public:
-        static const HashMap<String, TokenType> symbolMap;
+        static const HashMap<String, TokenType> punctMap;
         static const HashMap<String, TokenType> keywordMap;
 
-        const size_t index, length;
+        size_t index, length;
         //      源文件中的下标 Token长度
-        const TokenType type;
+        TokenType type;
 
         Token() : index(0), length(0), type(TokenType::Illegal) {};
         Token(size_t _index, size_t _length, TokenType _type) : index(_index), length(_length), type(_type) {}
@@ -138,8 +140,8 @@ namespace Fig
         bool isIdentifier() const { return type == TokenType::Identifier; }
         bool isLiteral() const
         {
-            return type == TokenType::LiteralNull || type == TokenType::LiteralBool || type == TokenType::LiteralNumber
-                   || type == TokenType::LiteralString;
+            return type == TokenType::LiteralNull || type == TokenType::LiteralTrue || type == TokenType::LiteralFalse
+                   || type == TokenType::LiteralNumber || type == TokenType::LiteralString;
         }
     };
 } // namespace Fig
\ No newline at end of file
diff --git a/src/main.cpp b/src/main.cpp
index 55158e0..e69de29 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,15 +0,0 @@
-#include <Error/Error.hpp>
-#include <Token/Token.hpp>
-
-int main()
-{
-    using namespace Fig;
-    Error error{ErrorType::MayBeNull,
-                "unterminated string literal",
-                "terminated it",
-                SourceLocation{2, 4, 5, "main.cpp", "main", "main"}};
-    SourceManager manager = SourceManager("T:/Files/Maker/Code/MyCodingLanguage/The Fig Project/Fig/src/main.cpp");
-    manager.Read();
-
-    ReportError(error, manager);
-}
\ No newline at end of file
diff --git a/xmake.lua b/xmake.lua
index fe965a2..8b475d2 100644
--- a/xmake.lua
+++ b/xmake.lua
@@ -28,6 +28,13 @@ add_defines("__FCORE_COMPILE_TIME=\"" .. os.date("%Y-%m-%d %H:%M:%S") .. "\"")
 target("StringTest")
     add_files("src/Deps/String/StringTest.cpp")
     
+target("LexerTest")
+    add_files("src/Core/*.cpp")
+    add_files("src/Token/Token.cpp")
+    add_files("src/Error/Error.cpp")
+    add_files("src/Lexer/Lexer.cpp")
+
+    add_files("src/Lexer/LexerTest.cpp")
 target("Fig")
     add_files("src/Core/*.cpp")
     add_files("src/Token/Token.cpp")