diff --git a/docs/ytd 12-bit computer.md b/docs/ytd 12-bit computer.md
index fc2d846..1d81b0f 100644
--- a/docs/ytd 12-bit computer.md	
+++ b/docs/ytd 12-bit computer.md	
@@ -114,8 +114,44 @@ unsigned    int         fixed       float
 
 Number Literals
 
+```
+number ::=  decinteger | bininteger | octinteger | hexinteger | pointfloat | exponentfloat
+decinteger ::=  nonzerodigit (["_"] digit)* | "0"+ (["_"] "0")*
+bininteger ::=  "0" ("b" | "B") (["_"] bindigit)+
+octinteger ::=  "0" ("o" | "O") (["_"] octdigit)+
+hexinteger ::=  "0" ("x" | "X") (["_"] hexdigit)+
+nonzerodigit ::=  "1"..."9"
+digit ::=  "0"..."9"
+bindigit ::=  "0" | "1"
+octdigit ::=  "0"..."7"
+hexdigit ::=  digit | "a"..."f" | "A"..."F"
+pointfloat    ::=  ([digitpart] fraction) | (digitpart ".")
+exponentfloat ::=  (digitpart | pointfloat) exponent
+digitpart     ::=  digit (["_"] digit)*
+fraction      ::=  "." digitpart
+exponent      ::=  ("e" | "E") ["+" | "-"] digitpart
+```
+
+Character Literals
+
+Character Literals must be on one line and begin and end with `'`. They can only
+have one printable ascii character or escape code.
+
 String Literals
 
+String Literals must be on one line and begin and end with `"`. They can have a
+unspecified number of printable ascii characters and escape codes.
+
+Escape Codes
+
+| Code | Meaning |
+| - | - |
+| `\n` | Line Feed |
+| `\r` | Return Carriage |
+| `\0` | Null Character |
+| `\'` | Single Quotation Mark (In char literals) |
+| `\"` | Double Quotation Mark (In str literals) |
+
 #### Punctuation
 
 ```
@@ -168,3 +204,20 @@ String Literals
 {       }       [       ]       ;
 :
 ```
+
+#### Escape Codes
+
+| Code | Meaning |
+| - | - |
+| `\0` | Null Character |
+| `\a` | Alert (Beep, Bell) |
+| `\b` | Backspace |
+| `\e` | Escape Character |
+| `\f` | Formfeed Page Break* |
+| `\n` | Line Feed |
+| `\r` | Return Carriage |
+| `\t` | Horizontal Tab |
+| `\v` | Vertical Tab* |
+| `\\` | Backslash |
+| `\'` | Single Quotation Mark (In char literals) |
+| `\"` | Double Quotation Mark (In str literals) |
diff --git a/pytd12dk/compiler/lexer.py b/pytd12dk/compiler/lexer.py
index e93d8f3..dded81d 100644
--- a/pytd12dk/compiler/lexer.py
+++ b/pytd12dk/compiler/lexer.py
@@ -2,7 +2,7 @@
 # Feb 2024
 
 from enum import Enum
-from typing import ClassVar, Sequence, TextIO
+from typing import ClassVar, Sequence
 
 from .compiler_types import CompilerError, FileInfo
 
@@ -19,6 +19,16 @@ class _InterTokenType(Enum):
     Punctuation = 'Punctuation'
 
 
+class _NumberLiteralType(Enum):
+    Number = 'Number'
+    Real = 'Real'
+    Exp = 'Exp'
+    Base = 'Base'
+    Binary = 'Binary'
+    Octal = 'Octal'
+    Hex = 'Hex'
+
+
 _OnlyNewLineTerminatedTokens = (
     _InterTokenType.Directive,
     _InterTokenType.SingleLineComment,
@@ -49,9 +59,59 @@ _Keywords = (
 
 _Num_Start = "0123456789"
 
-_Num_Second = _Num_Start + "box._Ee"
+_Num_Start_Next = {
+    _NumberLiteralType.Number: {
+        '.': _NumberLiteralType.Real,
+        '0': _NumberLiteralType.Base,
+    }
+}
 
-_Num_Continue = _Num_Start + "._" "ABCDEF" "abcdef"
+_Num_Second = {
+    _NumberLiteralType.Number: _Num_Start + ".eE_",
+    _NumberLiteralType.Real: _Num_Start + "eE_",
+    _NumberLiteralType.Base: "bBoOxX",
+}
+
+_Num_Second_Next = {
+    _NumberLiteralType.Number: {
+        '.': _NumberLiteralType.Real,
+        'e': _NumberLiteralType.Exp,
+        'E': _NumberLiteralType.Exp,
+    },
+    _NumberLiteralType.Real: {
+        'e': _NumberLiteralType.Exp,
+        'E': _NumberLiteralType.Exp,
+    },
+    _NumberLiteralType.Base: {
+        'b': _NumberLiteralType.Binary,
+        'B': _NumberLiteralType.Binary,
+        'o': _NumberLiteralType.Octal,
+        'O': _NumberLiteralType.Octal,
+        'x': _NumberLiteralType.Hex,
+        'X': _NumberLiteralType.Hex,
+    }
+}
+
+_Num_Continue = {
+    _NumberLiteralType.Number: _Num_Start + ".eE_",
+    _NumberLiteralType.Real: _Num_Start + "eE_",
+    _NumberLiteralType.Exp: _Num_Start + "_",
+    _NumberLiteralType.Binary: "01_",
+    _NumberLiteralType.Octal: "01234567_",
+    _NumberLiteralType.Hex: _Num_Start + "abcdefABCDEF_",
+}
+
+_Num_Continue_Next = {
+    _NumberLiteralType.Number: {
+        '.': _NumberLiteralType.Real,
+        'e': _NumberLiteralType.Exp,
+        'E': _NumberLiteralType.Exp,
+    },
+    _NumberLiteralType.Real: {
+        'e': _NumberLiteralType.Exp,
+        'E': _NumberLiteralType.Exp,
+    }
+}
 
 _Punctuation_Any = "@$+-*/%~&|^<>=!?{}[]().->,;:"
 
@@ -95,14 +155,13 @@ class StringLiteral(Token): _type = 'StringLiteral'
 class Punctuation(Token): _type = 'Punctuation'
 
 
-def lexer(file: str | TextIO, filename: str) -> Sequence[Token]:
-    if not isinstance(file, str):
-        file = file.read()
+def lexer(file: str, filename: str) -> Sequence[Token]:
     tokens: list[Token] = []
     current: str = ""
     current_line: int = 0
     current_col: int = 0
     escaped: bool = False
+    number_type: _NumberLiteralType = _NumberLiteralType.Number
     token_type: _InterTokenType = _InterTokenType.Generic
 
     for line, line_str in enumerate(file.splitlines()):
@@ -149,11 +208,14 @@ def lexer(file: str | TextIO, filename: str) -> Sequence[Token]:
                         tokens.append(Identifier(current, fi))
                 token_type = _InterTokenType.Generic
             elif token_type is _InterTokenType.NumberLiteral:
-                if (
-                    (len(current) == 2 and char in _Num_Second) ^
-                    (char in _Num_Continue)
-                ):
+                if len(current) == 2 and char in _Num_Second[number_type]:
                     current += char
+                    if char in _Num_Second_Next[number_type]:
+                        number_type = _Num_Second_Next[number_type][char]
+                elif char in _Num_Continue:
+                    current += char
+                    if char in _Num_Continue_Next[number_type]:
+                        number_type = _Num_Continue_Next[number_type][char]
                 else:
                     fi = FileInfo(
                         filename, current_line, current_col, len(current))
@@ -214,10 +276,17 @@ def lexer(file: str | TextIO, filename: str) -> Sequence[Token]:
                     token_type = _InterTokenType.MultiLineComment
                 elif char in _ID_Start:
                     token_type = _InterTokenType.Word
-                elif char == '.' and line_str[col+1] in _Num_Second:
+                elif (
+                    char == '.' and
+                    line_str[col+1] in _Num_Second[_NumberLiteralType.Real]
+                ):
                     token_type = _InterTokenType.NumberLiteral
+                    if char in _Num_Start_Next[number_type]:
+                        number_type = _Num_Start_Next[number_type][char]
                 elif char in _Num_Start:
                     token_type = _InterTokenType.NumberLiteral
+                    if char in _Num_Start_Next[number_type]:
+                        number_type = _Num_Start_Next[number_type][char]
                 elif char == "'":
                     token_type = _InterTokenType.CharLiteral
                 elif char == '"':