diff --git a/boot/driver.cc b/boot/driver.cc
index 2443dbc..c9a8e58 100644
--- a/boot/driver.cc
+++ b/boot/driver.cc
@@ -117,7 +117,7 @@ namespace elna::boot
             }
             ++current_position;
         }
-        result.pop_back();
+        result.pop_back(); // Remove the terminating quote character.
 
         return result;
     }
diff --git a/boot/lexer.ll b/boot/lexer.ll
index 5ac68ff..bed3254 100644
--- a/boot/lexer.ll
+++ b/boot/lexer.ll
@@ -32,248 +32,289 @@ along with GCC; see the file COPYING3.  If not see
 
 %x IN_COMMENT
 
+ID1 [A-Za-z_]
+ID2 [A-Za-z0-9_]
+HIGIT [0-9a-fA-F]
+BIGIT [01]
+
 %%
 %{
     this->location.step();
 %}
 
 <IN_COMMENT>{
-\*\)                    BEGIN(INITIAL);
-[^*\n]+                 ; /* Eat comment in chunks. */
-\*                      ; /* Eat the lone star. */
-\n+                     {
-                            this->location.lines(yyleng);
-                            this->location.step();
-                        }
+    \*\) BEGIN(INITIAL);
+    [^*\n]+ ; /* Eat comment in chunks. */
+    \* ; /* Eat the lone star. */
+    \n+ {
+        this->location.lines(yyleng);
+        this->location.step();
+    }
 }
-\(\*                    BEGIN(IN_COMMENT);
-[ \t\r]                 {
-                            this->location.step();
+\(\* BEGIN(IN_COMMENT);
+[ \t\r] {
+    this->location.step();
+}
+\n+ {
+    this->location.lines(yyleng);
+}
+if {
+    return yy::parser::make_IF(this->location);
+}
+then {
+    return yy::parser::make_THEN(this->location);
+}
+else {
+    return yy::parser::make_ELSE(this->location);
+}
+elsif {
+    return yy::parser::make_ELSIF(this->location);
+}
+while {
+    return yy::parser::make_WHILE(this->location);
+}
+do {
+    return yy::parser::make_DO(this->location);
+}
+proc {
+    return yy::parser::make_PROCEDURE(this->location);
+}
+begin {
+    return yy::parser::make_BEGIN_BLOCK(this->location);
                         }
-\n+                     {
-                            this->location.lines(yyleng);
-                        }
-if                      {
-                            return yy::parser::make_IF(this->location);
-                        }
-then                    {
-                            return yy::parser::make_THEN(this->location);
-                        }
-else                    {
-                            return yy::parser::make_ELSE(this->location);
-                        }
-elsif                   {
-                            return yy::parser::make_ELSIF(this->location);
-                        }
-while                   {
-                            return yy::parser::make_WHILE(this->location);
-                        }
-do                      {
-                            return yy::parser::make_DO(this->location);
-                        }
-proc                    {
-                            return yy::parser::make_PROCEDURE(this->location);
-                        }
-begin                   {
-                            return yy::parser::make_BEGIN_BLOCK(this->location);
-                        }
-end                     {
-                            return yy::parser::make_END_BLOCK(this->location);
-                        }
-extern                  {
-                            return yy::parser::make_EXTERN(this->location);
-                        }
-const                   {
-                            return yy::parser::make_CONST(this->location);
-                        }
-var                     {
-                            return yy::parser::make_VAR(this->location);
-                        }
-type                    {
-                            return yy::parser::make_TYPE(this->location);
-                        }
-record                  {
-                            return yy::parser::make_RECORD(this->location);
-                        }
-union                   {
-                            return yy::parser::make_UNION(this->location);
-                        }
-true                    {
-                            return yy::parser::make_BOOLEAN(true, this->location);
-                        }
-false                   {
-                            return yy::parser::make_BOOLEAN(false, this->location);
-                        }
-nil                     {
-                            return yy::parser::make_NIL(this->location);
-                        }
-\&                      {
-                            return yy::parser::make_AND(this->location);
-                        }
-xor                     {
-                            return yy::parser::make_XOR(this->location);
-                        }
-or                     {
-                            return yy::parser::make_OR(this->location);
-                        }
-\|                      {
-                            return yy::parser::make_PIPE(this->location);
-                        }
-\~                      {
-                            return yy::parser::make_NOT(this->location);
-                        }
-return                  {
-                            return yy::parser::make_RETURN(this->location);
-                        }
-module                  {
-                            return yy::parser::make_MODULE(this->location);
-                        }
-program                 {
-                            return yy::parser::make_PROGRAM(this->location);
-                        }
-import                  {
-                            return yy::parser::make_IMPORT(this->location);
-                        }
-cast                    {
-                            return yy::parser::make_CAST(this->location);
-                        }
-defer                   {
-                            return yy::parser::make_DEFER(this->location);
-                        }
-case                    {
-                            return yy::parser::make_CASE(this->location);
-                        }
-of                      {
-                            return yy::parser::make_OF(this->location);
-                        }
-[A-Za-z_][A-Za-z0-9_]*  {
-                            return yy::parser::make_IDENTIFIER(yytext, this->location);
-                        }
-#[A-Za-z_][A-Za-z0-9_]* {
-                            return yy::parser::make_TRAIT(yytext + 1, this->location);
-                        }
-[0-9]+u                 {
-                            return yy::parser::make_WORD(strtoul(yytext, NULL, 10), this->location);
-                        }
-[0-9]+                  {
-                            return yy::parser::make_INTEGER(strtol(yytext, NULL, 10), this->location);
-                        }
-[0-9]+\.[0-9]           {
-                            return yy::parser::make_FLOAT(strtof(yytext, NULL), this->location);
-                        }
-'[[:print:]]'           {
-                            if (yytext[1] == '\\' || yytext[1] == '\'')
-                            {
-                                REJECT;
-                            }
-                            else
-                            {
-                                return yy::parser::make_CHARACTER(std::string(yytext, 1, 1), this->location);
-                            }
-                        }
-'\\x[0-9a-fA-F]{1,2}'   {
-                            char character = static_cast<char>(std::stoi(yytext + 3, nullptr, 16));
+end {
+    return yy::parser::make_END_BLOCK(this->location);
+}
+extern {
+    return yy::parser::make_EXTERN(this->location);
+}
+const {
+    return yy::parser::make_CONST(this->location);
+}
+var {
+    return yy::parser::make_VAR(this->location);
+}
+type {
+    return yy::parser::make_TYPE(this->location);
+}
+record {
+    return yy::parser::make_RECORD(this->location);
+}
+union {
+    return yy::parser::make_UNION(this->location);
+}
+true {
+    return yy::parser::make_BOOLEAN(true, this->location);
+}
+false {
+    return yy::parser::make_BOOLEAN(false, this->location);
+}
+nil {
+    return yy::parser::make_NIL(this->location);
+}
+\& {
+    return yy::parser::make_AND(this->location);
+}
+xor {
+    return yy::parser::make_XOR(this->location);
+}
+or {
+    return yy::parser::make_OR(this->location);
+}
+\| {
+    return yy::parser::make_PIPE(this->location);
+}
+\~ {
+    return yy::parser::make_NOT(this->location);
+}
+return {
+    return yy::parser::make_RETURN(this->location);
+}
+module {
+    return yy::parser::make_MODULE(this->location);
+}
+program {
+    return yy::parser::make_PROGRAM(this->location);
+}
+import {
+    return yy::parser::make_IMPORT(this->location);
+}
+cast {
+    return yy::parser::make_CAST(this->location);
+}
+defer {
+    return yy::parser::make_DEFER(this->location);
+}
+case {
+    return yy::parser::make_CASE(this->location);
+}
+of {
+    return yy::parser::make_OF(this->location);
+}
+{ID1}{ID2}* {
+    return yy::parser::make_IDENTIFIER(yytext, this->location);
+}
+#{ID1}{ID2}* {
+    return yy::parser::make_TRAIT(yytext + 1, this->location);
+}
+[[:digit:]]+u {
+    unsigned long result = strtoul(yytext, NULL, 10);
 
-                            return yy::parser::make_CHARACTER(std::string(&character, 1), this->location);
-                        }
-'\\[0nabtfrv\\'"?]'     {
-                            char escape = escape_char(yytext[2]);
-                            if (escape == escape_invalid_char)
-                            {
-                                REJECT;
-                            }
-                            return yy::parser::make_CHARACTER(std::string(&escape, 1), this->location);
-                        }
-\"[[:print:]]*\"        {
-                            std::optional<std::string> result = escape_string(yytext);
-                            if (!result.has_value())
-                            {
-                                REJECT;
-                            }
-                            return yy::parser::make_STRING(result.value(), this->location);
-                        }
-\(                      {
-                            return yy::parser::make_LEFT_PAREN(this->location);
-                        }
-\)                      {
-                            return yy::parser::make_RIGHT_PAREN(this->location);
-                        }
-\[                      {
-                            return yy::parser::make_LEFT_SQUARE(this->location);
-                        }
-\]                      {
-                            return yy::parser::make_RIGHT_SQUARE(this->location);
-                        }
-\<\<                    {
-                            return yy::parser::make_SHIFT_LEFT(this->location);
-                        }
-\>\>                    {
-                            return yy::parser::make_SHIFT_RIGHT(this->location);
-                        }
-\>=                     {
-                            return yy::parser::make_GREATER_EQUAL(this->location);
-                        }
-\<=                     {
-                            return yy::parser::make_LESS_EQUAL(this->location);
-                        }
-\>                      {
-                            return yy::parser::make_GREATER_THAN(this->location);
-                        }
-\<                      {
-                            return yy::parser::make_LESS_THAN(this->location);
-                        }
-\<\>                    {
-                            return yy::parser::make_NOT_EQUAL(this->location);
-                        }
-=                       {
-                            return yy::parser::make_EQUALS(this->location);
-                        }
-;                       {
-                            return yy::parser::make_SEMICOLON(this->location);
-                        }
-\.                      {
-                            return yy::parser::make_DOT(this->location);
-                        }
-,                       {
-                            return yy::parser::make_COMMA(this->location);
-                        }
-\+                      {
-                            return yy::parser::make_PLUS(this->location);
-                        }
-\->                     {
-                            return yy::parser::make_ARROW(this->location);
-                        }
-\-                      {
-                            return yy::parser::make_MINUS(this->location);
-                        }
-\*                      {
-                            return yy::parser::make_MULTIPLICATION(this->location);
-                        }
-\/                      {
-                            return yy::parser::make_DIVISION(this->location);
-                        }
-%                       {
-                            return yy::parser::make_REMAINDER(this->location);
-                        }
-:=                      {
-                            return yy::parser::make_ASSIGNMENT(this->location);
-                        }
-:                       {
-                            return yy::parser::make_COLON(this->location);
-                        }
-\^                      {
-                            return yy::parser::make_HAT(this->location);
-                        }
-@                       {
-                            return yy::parser::make_AT(this->location);
-                        }
-!                       {
-                            return yy::parser::make_EXCLAMATION(this->location);
-                        }
-.                       {
-                            std::stringstream ss;
+    if (errno == ERANGE)
+    {
+        REJECT;
+    }
+    else
+    {
+        return yy::parser::make_WORD(result, this->location);
+    }
+}
+[[:digit:]]+ {
+    long result = strtol(yytext, NULL, 10);
 
-                            ss << "Illegal character 0x" << std::hex << static_cast<unsigned int>(yytext[0]);
-                            driver.add_error<syntax_error>(ss.str(), driver.input_file, this->location);
-                        }
+    if (errno == ERANGE)
+    {
+        REJECT;
+    }
+    else
+    {
+        return yy::parser::make_INTEGER(result, this->location);
+    }
+}
+0x{HIGIT}+ {
+    unsigned long result = strtoul(yytext, NULL, 16);
+
+    if (errno == ERANGE)
+    {
+        REJECT;
+    }
+    else
+    {
+        return yy::parser::make_WORD(result, this->location);
+    }
+}
+0b{BIGIT}+ {
+    unsigned long result = strtoul(yytext, NULL, 2);
+
+    if (errno == ERANGE)
+    {
+        REJECT;
+    }
+    else
+    {
+        return yy::parser::make_WORD(result, this->location);
+    }
+}
+[[:digit:]]+\.[[:digit:]]+ {
+    float result = strtof(yytext, NULL);
+
+    if (errno == ERANGE)
+    {
+        REJECT;
+    }
+    else
+    {
+        return yy::parser::make_FLOAT(result, this->location);
+    }
+}
+'[[:print:]]+' {
+    std::optional<std::string> result = escape_string(yytext);
+    if (!result.has_value() || result.value().size() != 1)
+    {
+        REJECT;
+    }
+    return yy::parser::make_CHARACTER(result.value(), this->location);
+}
+\"[[:print:]]*\" {
+    std::optional<std::string> result = escape_string(yytext);
+    if (!result.has_value())
+    {
+        REJECT;
+    }
+    return yy::parser::make_STRING(result.value(), this->location);
+}
+\( {
+    return yy::parser::make_LEFT_PAREN(this->location);
+}
+\) {
+    return yy::parser::make_RIGHT_PAREN(this->location);
+}
+\[ {
+    return yy::parser::make_LEFT_SQUARE(this->location);
+}
+\] {
+    return yy::parser::make_RIGHT_SQUARE(this->location);
+}
+\<\< {
+    return yy::parser::make_SHIFT_LEFT(this->location);
+}
+\>\> {
+    return yy::parser::make_SHIFT_RIGHT(this->location);
+}
+\>= {
+    return yy::parser::make_GREATER_EQUAL(this->location);
+}
+\<= {
+    return yy::parser::make_LESS_EQUAL(this->location);
+}
+\> {
+    return yy::parser::make_GREATER_THAN(this->location);
+}
+\< {
+    return yy::parser::make_LESS_THAN(this->location);
+}
+\<\> {
+    return yy::parser::make_NOT_EQUAL(this->location);
+}
+= {
+    return yy::parser::make_EQUALS(this->location);
+}
+; {
+    return yy::parser::make_SEMICOLON(this->location);
+}
+\. {
+    return yy::parser::make_DOT(this->location);
+}
+, {
+    return yy::parser::make_COMMA(this->location);
+}
+\+ {
+    return yy::parser::make_PLUS(this->location);
+}
+\-> {
+    return yy::parser::make_ARROW(this->location);
+}
+\- {
+    return yy::parser::make_MINUS(this->location);
+}
+\* {
+    return yy::parser::make_MULTIPLICATION(this->location);
+}
+\/ {
+    return yy::parser::make_DIVISION(this->location);
+}
+% {
+    return yy::parser::make_REMAINDER(this->location);
+}
+:= {
+    return yy::parser::make_ASSIGNMENT(this->location);
+}
+: {
+    return yy::parser::make_COLON(this->location);
+}
+\^ {
+    return yy::parser::make_HAT(this->location);
+}
+@ {
+    return yy::parser::make_AT(this->location);
+}
+! {
+    return yy::parser::make_EXCLAMATION(this->location);
+}
+. {
+    std::stringstream ss;
+
+    ss << "Illegal character 0x" << std::hex << static_cast<unsigned int>(yytext[0]);
+    driver.add_error<syntax_error>(ss.str(), driver.input_file, this->location);
+}
 %%
diff --git a/source/main.elna b/source/main.elna
index 0f3d001..2da63e7 100644
--- a/source/main.elna
+++ b/source/main.elna
@@ -1074,6 +1074,12 @@ begin
   return return_code
 end;
 
+proc f();
+var x: Char;
+begin
+  x := '\x4'
+end;
+
 begin
   exit(process(count, parameters))
 end.