diff --git a/classes.php b/classes.php
index d99e032..7c35663 100644
--- a/classes.php
+++ b/classes.php
@@ -2,21 +2,69 @@
 
 class MadLispException extends Exception {}
 
-class Env
+abstract class MLCollection
 {
-    private array $data = [];
-    private ?Env $parent;
+    protected array $data = [];
 
-    public function __construct(?Env $parent = null)
+    public function __construct(array $data = [])
     {
-        $this->parent = $parent;
+        $this->data = $data;
     }
 
-    public function has(string $key)
+    public function count(): int
+    {
+        return count($this->data);
+    }
+
+    public function has(string $key): bool
     {
         return array_key_exists($key, $this->data);
     }
 
+    public function getData(): array
+    {
+        return $this->data;
+    }
+}
+
+class MLList extends MLCollection
+{
+    public function get(int $index)
+    {
+        if ($this->has($index)) {
+            return $this->data[$index];
+        }
+
+        throw new MadLispException("list does not contain index $index");
+    }
+}
+
+class MLHash extends MLCollection
+{
+    public function get(string $key)
+    {
+        if ($this->has($key)) {
+            return $this->data[$key];
+        }
+
+        throw new MadLispException("hash does not contain key $key");
+    }
+
+    public function set(string $key, $value): void
+    {
+        $this->data[$key] = $value;
+    }
+}
+
+class MLEnv extends MLHash
+{
+    protected ?MLEnv $parent;
+
+    public function __construct(?MLEnv $parent = null)
+    {
+        $this->parent = $parent;
+    }
+
     public function get(string $key)
     {
         if ($this->has($key)) {
@@ -27,9 +75,19 @@ class Env
 
         throw new MadLispException("symbol $key not defined");
     }
+}
 
-    public function set(string $key, $value): void
+class MLSymbol
+{
+    protected string $name;
+
+    public function __construct(string $name)
     {
-        $this->data[$key] = $value;
+        $this->name = $name;
+    }
+
+    public function name(): string
+    {
+        return $this->name;
     }
 }
diff --git a/lib.php b/lib.php
index 3eda6dd..f68e953 100644
--- a/lib.php
+++ b/lib.php
@@ -2,16 +2,62 @@
 
 require_once('classes.php');
 
-function ml_get_env(): Env
+function ml_get_env(): MLEnv
 {
-    $env = new Env();
+    $env = new MLEnv();
 
     // basic arithmetic
-    $env->set('+', fn (...$args) => array_sum($args));
-    $env->set('-', fn ($a, $b) => $a - $b);
-    $env->set('*', fn ($a, $b) => $a * $b);
-    $env->set('/', fn ($a, $b) => $a / $b);
-    $env->set('%', fn ($a, $b) => $a % $b);
+
+    $env->set('+', function (...$args) {
+        return array_sum($args);
+    });
+
+    $env->set('-', function (...$args) {
+        $result = $args[0] ?? null;
+        for ($i = 1; $i < count($args); $i++) {
+            $result -= $args[$i];
+        }
+        return $result;
+    });
+
+    $env->set('*', function (...$args) {
+        $result = $args[0] ?? null;
+        for ($i = 1; $i < count($args); $i++) {
+            $result *= $args[$i];
+        }
+        return $result;
+    });
+
+    $env->set('/', function (...$args) {
+        $result = $args[0] ?? null;
+        for ($i = 1; $i < count($args); $i++) {
+            $result /= $args[$i];
+        }
+        return $result;
+    });
+
+    $env->set('%', function (...$args) {
+        $result = $args[0] ?? null;
+        for ($i = 1; $i < count($args); $i++) {
+            $result %= $args[$i];
+        }
+        return $result;
+    });
+
+    // comparison
+
+    $env->set('=', fn ($a, $b) => $a == $b);
+    $env->set('<', fn ($a, $b) => $a < $b);
+    $env->set('>', fn ($a, $b) => $a > $b);
+    $env->set('<=', fn ($a, $b) => $a <= $b);
+    $env->set('>=', fn ($a, $b) => $a >= $b);
+    $env->set('!=', fn ($a, $b) => $a != $b);
+
+    // types
+
+    $env->set('type?', function ($a) {
+        return gettype($a);
+    });
 
     return $env;
 }
diff --git a/lisp.php b/lisp.php
index bdcb558..b7784a7 100644
--- a/lisp.php
+++ b/lisp.php
@@ -2,16 +2,6 @@
 
 require_once('classes.php');
 
-// types
-define("SYMBOL", "SYMBOL");
-define("STRING", "STRING");
-define("NUMBER", "NUMBER");
-define("START", "START");
-define("END", "END");
-
-// special sign for symbols
-define("MAGIC", "§");
-
 function ml_tokenize(string $a): array
 {
     $tokens = [];
@@ -19,21 +9,9 @@ function ml_tokenize(string $a): array
     $string = false;
     $parens = 0;
 
-    $addCurrent = function ($string = false) use (&$tokens, &$current) {
-        if ($current !== '' || $string) {
-            if ($string) {
-                $tokens[] = [STRING, $current];
-            } elseif ($current == 'true') {
-                $tokens[] = [true];
-            } elseif ($current == 'false') {
-                $tokens[] = [false];
-            } elseif ($current == 'null') {
-                $tokens[] = [null];
-            } elseif (is_numeric($current)) {
-                $tokens[] = [NUMBER, $current];
-            } else {
-                $tokens[] = [SYMBOL, $current];
-            }
+    $addCurrent = function () use (&$tokens, &$current) {
+        if ($current !== '') {
+            $tokens[] = $current;
             $current = '';
         }
     };
@@ -41,36 +19,43 @@ function ml_tokenize(string $a): array
     for ($i = 0; $i < strlen($a); $i++) {
         $c = substr($a, $i, 1);
 
-        if ($c == '"') {
-            if ($string) {
-                // End of string
-                $addCurrent(true);
-                $string = false;
-            } else {
-                // Start of string
-                $string = true;
-            }
-        } elseif ($c == ' ' || $c == "\t" || $c == "\n" || $c == "\r") {
-            if ($string) {
-                // Include whitespace only inside strings
-                $current .= $c;
-            } else {
-                $addCurrent();
-            }
-        } elseif ($c == '(') {
-            $addCurrent();
-            $tokens[] = [START];
-            $parens++;
-        } elseif ($c == ')') {
-            if ($parens == 0) {
-                throw new MadLispException("unexpected closing parenthesis");
-            }
-            $addCurrent();
-            $tokens[] = [END];
-            $parens--;
-        } else {
-            // All other characters are included normally
+        if ($string) {
+            // Inside string, add all characters
             $current .= $c;
+
+            // Stop at "
+            if ($c == '"') {
+                $addCurrent();
+                $string = false;
+            }
+        } else {
+            // Not inside string
+
+            if ($c == '"') {
+                // Start of string
+                $addCurrent();
+                $current .= $c;
+                $string = true;
+            } elseif ($c == ' ' || $c == "\t" || $c == "\n" || $c == "\r") {
+                // Whitespace is ignored
+                $addCurrent();
+            } elseif ($c == '(') {
+                // Start of list
+                $addCurrent();
+                $tokens[] = '(';
+                $parens++;
+            } elseif ($c == ')') {
+                // End of list
+                if ($parens == 0) {
+                    throw new MadLispException("unexpected closing parenthesis");
+                }
+                $addCurrent();
+                $tokens[] = ')';
+                $parens--;
+            } else {
+                // All other characters
+                $current .= $c;
+            }
         }
     }
 
@@ -89,48 +74,51 @@ function ml_tokenize(string $a): array
 
 function ml_read_form(array $tokens, int &$index)
 {
-    $a = $tokens[$index];
-
-    if ($a[0] == START) {
+    if ($tokens[$index] == '(') {
         return ml_read_list($tokens, $index);
     } else {
         return ml_read_atom($tokens, $index);
     }
 }
 
-function ml_read_list(array $tokens, int &$index): array
+function ml_read_list(array $tokens, int &$index): MLList
 {
     $result = [];
 
     // start tag
     $index++;
 
-    while ($tokens[$index][0] != END) {
+    while ($tokens[$index] != ')') {
         $result[] = ml_read_form($tokens, $index);
     }
 
     // end tag
     $index++;
 
-    return $result;
+    return new MLList($result);
 }
 
 function ml_read_atom(array $tokens, int &$index)
 {
     $a = $tokens[$index++];
 
-    if ($a[0] == STRING) {
-        return $a[1];
-    } elseif ($a[0] == SYMBOL) {
-        return MAGIC . $a[1];
-    } elseif ($a[0] == NUMBER) {
-        if (filter_var($a[1], FILTER_VALIDATE_INT) !== false) {
-            return intval($a[1]);
+    if ($a === 'true') {
+        return true;
+    } elseif ($a === 'false') {
+        return false;
+    } elseif ($a === 'null') {
+        return null;
+    } elseif (substr($a, 0, 1) === '"') {
+        // string
+        return substr($a, 1, strlen($a) - 2);
+    } elseif (is_numeric($a)) {
+        if (filter_var($a, FILTER_VALIDATE_INT) !== false) {
+            return intval($a);
         } else {
-            return floatval($a[1]);
+            return floatval($a);
         }
     } else {
-        return $a[0];
+        return new MLSymbol($a);
     }
 }
 
@@ -146,16 +134,6 @@ function ml_parse(array $tokens): array
     return $result;
 }
 
-function ml_is_symbol($a)
-{
-    return substr($a, 0, strlen(MAGIC)) === MAGIC;
-}
-
-function ml_strip_symbol($a)
-{
-    return substr($a, strlen(MAGIC));
-}
-
 function ml_read(string $code): array
 {
     $tokens = ml_tokenize($code);
@@ -165,20 +143,22 @@ function ml_read(string $code): array
     return $expressions;
 }
 
-function ml_eval($expr, Env $env)
+function ml_eval($expr, MLEnv $env)
 {
-    if (is_array($expr)) {
-        // Evaluate list items
-        $expr = array_map(fn ($a) => ml_eval($a, $env), $expr);
+    if ($expr instanceof MLList && $expr->count() > 0) {
+        // Evaluate list contents
+        $results = array_map(fn ($a) => ml_eval($a, $env), $expr->getData());
 
-        // If the first item is a function, call it
-        $fn = $expr[0] ?? null;
-        if ($fn && $fn instanceof Closure) {
-            $args = array_slice($expr, 1);
-            return $fn(...$args);
+        if ($results[0] instanceof Closure) {
+            // If the first item is a function, call it
+            $args = array_slice($results, 1);
+            return ($results[0])(...$args);
+        } else {
+            // Otherwise return new list with evaluated contents
+            return new MLList($results);
         }
-    } elseif (ml_is_symbol($expr)) {
-        return $env->get(ml_strip_symbol($expr));
+    } elseif ($expr instanceof MLSymbol) {
+        return $env->get($expr->name());
     }
 
     return $expr;
@@ -188,16 +168,16 @@ function ml_print($a): string
 {
     if ($a instanceof Closure) {
         return '<function>';
-    } elseif (is_array($a)) {
-        return '(' . implode(' ', array_map('ml_print', $a)) . ')';
+    } elseif ($a instanceof MLList) {
+        return '(' . implode(' ', array_map('ml_print', $a->getData())) . ')';
+    } elseif ($a instanceof MLSymbol) {
+        return $a->name();
     } elseif ($a === true) {
         return 'true';
     } elseif ($a === false) {
         return 'false';
     } elseif ($a === null) {
         return 'null';
-    } elseif (ml_is_symbol($a)) {
-        return ml_strip_symbol($a);
     } elseif (is_string($a)) {
         return '"' . $a . '"';
     } else {
@@ -205,7 +185,7 @@ function ml_print($a): string
     }
 }
 
-function ml_rep(string $input, Env $env): string
+function ml_rep(string $input, MLEnv $env): string
 {
     $expressions = ml_read($input);