diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..48b8bf9
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+vendor/
diff --git a/bootstrap.php b/bootstrap.php
new file mode 100644
index 0000000..229c1af
--- /dev/null
+++ b/bootstrap.php
@@ -0,0 +1,12 @@
+<?php
+require('vendor/autoload.php');
+
+function ml_get_env(): MadLisp\Env
+{
+    $env = new MadLisp\Env();
+
+    $core = new MadLisp\Lib\Core();
+    $core->register($env);
+
+    return $env;
+}
diff --git a/classes.php b/classes.php
deleted file mode 100644
index 17ff3a8..0000000
--- a/classes.php
+++ /dev/null
@@ -1,93 +0,0 @@
-<?php
-
-class MadLispException extends Exception {}
-
-abstract class MLCollection
-{
-    protected array $data = [];
-
-    public function __construct(array $data = [])
-    {
-        $this->data = $data;
-    }
-
-    public function count(): int
-    {
-        return count($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");
-    }
-}
-
-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)) {
-            return $this->data[$key];
-        } elseif ($this->parent) {
-            return $this->parent->get($key);
-        }
-
-        throw new MadLispException("symbol $key not defined");
-    }
-
-    public function set(string $key, $value): void
-    {
-        $this->data[$key] = $value;
-    }
-}
-
-class MLSymbol
-{
-    protected string $name;
-
-    public function __construct(string $name)
-    {
-        $this->name = $name;
-    }
-
-    public function name(): string
-    {
-        return $this->name;
-    }
-}
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..9761dac
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,22 @@
+{
+    "name": "maddy83/madlisp",
+    "description": "Lisp interpreter for the MadLisp language.",
+    "license": "MIT",
+    "authors": [
+        {
+            "name": "Pekka Laiho",
+            "email": "pekka.i.laiho@gmail.com"
+        }
+    ],
+    "require": {
+
+    },
+    "require-dev": {
+
+    },
+    "autoload": {
+        "psr-4": {
+            "MadLisp\\": "src/"
+        }
+    }
+}
diff --git a/lib.php b/lib.php
deleted file mode 100644
index b55156a..0000000
--- a/lib.php
+++ /dev/null
@@ -1,151 +0,0 @@
-<?php
-
-require_once('classes.php');
-
-function ml_get_env(): MLEnv
-{
-    $env = new MLEnv();
-
-    // logic
-
-    $env->set('or', function (...$args) {
-        // return first true
-        for ($i = 0; $i < count($args) - 1; $i++) {
-            if ($args[$i] == true) {
-                return $args[$i];
-            }
-        }
-
-        // return last
-        return $args[count($args) - 1];
-    });
-
-    $env->set('and', function (...$args) {
-        // return first false
-        for ($i = 0; $i < count($args) - 1; $i++) {
-            if ($args[$i] == false) {
-                return $args[$i];
-            }
-        }
-
-        // return last
-        return $args[count($args) - 1];
-    });
-
-    $env->set('not', fn ($a) => !$a);
-
-    // arithmetic
-
-    $env->set('+', function (...$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) {
-        if ($a instanceof Closure) {
-            return 'function';
-        } elseif ($a instanceof MLList) {
-            return 'list';
-        } elseif ($a instanceof MLHash) {
-            return 'hash';
-        } elseif ($a instanceof MLSymbol) {
-            return 'symbol';
-        } elseif ($a === true || $a === false) {
-            return 'bool';
-        } elseif ($a === null) {
-            return 'null';
-        } elseif (is_int($a)) {
-            return 'int';
-        } elseif (is_float($a)) {
-            return 'float';
-        } else {
-            return 'string';
-        }
-    });
-
-    $env->set('fn?', fn ($a) => $a instanceof Closure);
-    $env->set('list?', fn ($a) => $a instanceof MLList);
-    $env->set('hash?', fn ($a) => $a instanceof MLHash);
-    $env->set('sym?', fn ($a) => $a instanceof MLSymbol);
-    $env->set('bool?', fn ($a) => $a === true || $a === false);
-    $env->set('true?', fn ($a) => $a == true); // not strict
-    $env->set('false?', fn ($a) => $a == false); // not strict
-    $env->set('null?', fn ($a) => $a === null);
-    $env->set('int?', fn ($a) => is_int($a));
-    $env->set('float?', fn ($a) => is_float($a));
-    $env->set('str?', fn ($a) => is_string($a));
-
-    // collections
-
-    $env->set('list', function (...$args) {
-        return new MLList($args);
-    });
-
-    $env->set('hash', function (...$args) {
-        if (count($args) % 2 == 1) {
-            throw new MadLispException('uneven number of arguments for hash');
-        }
-
-        $data = [];
-
-        for ($i = 0; $i < count($args) - 1; $i += 2) {
-            $key = $args[$i];
-            $val = $args[$i + 1];
-
-            if (!is_string($key)) {
-                throw new MadLispException('invalid key for hash (not string)');
-            }
-
-            $data[$key] = $val;
-        }
-
-        return new MLHash($data);
-    });
-
-    // for debugging!
-    $env->set('eval', fn ($a) => ml_eval($a, $env));
-
-    return $env;
-}
diff --git a/lisp.php b/lisp.php
deleted file mode 100644
index 1acd136..0000000
--- a/lisp.php
+++ /dev/null
@@ -1,210 +0,0 @@
-<?php
-
-require_once('classes.php');
-
-function ml_tokenize(string $a): array
-{
-    $tokens = [];
-    $current = '';
-    $string = false;
-    $parens = 0;
-
-    $addCurrent = function () use (&$tokens, &$current) {
-        if ($current !== '') {
-            $tokens[] = $current;
-            $current = '';
-        }
-    };
-
-    for ($i = 0; $i < strlen($a); $i++) {
-        $c = substr($a, $i, 1);
-
-        if ($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;
-            }
-        }
-    }
-
-    // Add last also
-    $addCurrent();
-
-    // Check for errors
-    if ($parens != 0) {
-        throw new MadLispException("missing closing parenthesis");
-    } elseif ($string) {
-        throw new MadLispException("unterminated string");
-    }
-
-    return $tokens;
-}
-
-function ml_read_form(array $tokens, int &$index)
-{
-    if ($tokens[$index] == '(') {
-        return ml_read_list($tokens, $index);
-    } else {
-        return ml_read_atom($tokens, $index);
-    }
-}
-
-function ml_read_list(array $tokens, int &$index): MLList
-{
-    $result = [];
-
-    // start tag
-    $index++;
-
-    while ($tokens[$index] != ')') {
-        $result[] = ml_read_form($tokens, $index);
-    }
-
-    // end tag
-    $index++;
-
-    return new MLList($result);
-}
-
-function ml_read_atom(array $tokens, int &$index)
-{
-    $a = $tokens[$index++];
-
-    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);
-        }
-    } else {
-        return new MLSymbol($a);
-    }
-}
-
-function ml_parse(array $tokens): array
-{
-    $result = [];
-    $index = 0;
-
-    while ($index < count($tokens)) {
-        $result[] = ml_read_form($tokens, $index);
-    }
-
-    return $result;
-}
-
-function ml_read(string $code): array
-{
-    $tokens = ml_tokenize($code);
-
-    $expressions = ml_parse($tokens);
-
-    return $expressions;
-}
-
-function ml_eval($expr, MLEnv $env)
-{
-    if ($expr instanceof MLList && $expr->count() > 0) {
-        // Evaluate list contents
-        $results = array_map(fn ($a) => ml_eval($a, $env), $expr->getData());
-
-        $fn = $results[0];
-
-        if ($fn instanceof Closure) {
-            // If the first item is a function, call it
-            $args = array_slice($results, 1);
-            return $fn(...$args);
-        } else {
-            // Otherwise return new list with evaluated contents
-            return new MLList($results);
-        }
-    } elseif ($expr instanceof MLHash) {
-        // Hash: return new hash with all items evaluated
-        $items = [];
-        foreach ($expr->getData() as $key => $val) {
-            $items[$key] = ml_eval($val, $env);
-        }
-        return new MLHash($items);
-    } elseif ($expr instanceof MLSymbol) {
-        return $env->get($expr->name());
-    }
-
-    return $expr;
-}
-
-function ml_print($a): string
-{
-    if ($a instanceof Closure) {
-        return '<function>';
-    } elseif ($a instanceof MLList) {
-        return '(' . implode(' ', array_map('ml_print', $a->getData())) . ')';
-    } elseif ($a instanceof MLHash) {
-        $items = [];
-        foreach ($a->getData() as $key => $val) {
-            $items[] = ml_print($key) . ':' . ml_print($val);
-        }
-        return '{' . implode(' ', $items) . '}';
-    } elseif ($a instanceof MLSymbol) {
-        return $a->name();
-    } elseif ($a === true) {
-        return 'true';
-    } elseif ($a === false) {
-        return 'false';
-    } elseif ($a === null) {
-        return 'null';
-    } elseif (is_string($a)) {
-        return '"' . $a . '"';
-    } else {
-        return $a;
-    }
-}
-
-function ml_rep(string $input, MLEnv $env): string
-{
-    $expressions = ml_read($input);
-
-    $results = array_map(fn ($expr) => ml_eval($expr, $env), $expressions);
-
-    return implode(" ", array_map('ml_print', $results));
-}
diff --git a/repl.php b/repl.php
index 3d9cfd4..3302b01 100644
--- a/repl.php
+++ b/repl.php
@@ -1,15 +1,14 @@
 <?php
-
-require_once('lib.php');
-require_once('lisp.php');
+require('bootstrap.php');
 
 $env = ml_get_env();
+$lisp = new MadLisp\Lisp();
 
 while (true) {
     $input = readline('> ');
 
     try {
-        print(ml_rep($input, $env));
+        $lisp->rep($input, $env);
     } catch (MadLispException $ex) {
         print('error: ' . $ex->getMessage());
     }
diff --git a/src/Collection.php b/src/Collection.php
new file mode 100644
index 0000000..0a59b4c
--- /dev/null
+++ b/src/Collection.php
@@ -0,0 +1,27 @@
+<?php
+namespace MadLisp;
+
+abstract class Collection
+{
+    protected array $data = [];
+
+    public function __construct(array $data = [])
+    {
+        $this->data = $data;
+    }
+
+    public function count(): int
+    {
+        return count($this->data);
+    }
+
+    public function has(string $key): bool
+    {
+        return array_key_exists($key, $this->data);
+    }
+
+    public function getData(): array
+    {
+        return $this->data;
+    }
+}
diff --git a/src/Env.php b/src/Env.php
new file mode 100644
index 0000000..eb3a368
--- /dev/null
+++ b/src/Env.php
@@ -0,0 +1,28 @@
+<?php
+namespace MadLisp;
+
+class Env extends Hash
+{
+    protected ?Env $parent;
+
+    public function __construct(?Env $parent = null)
+    {
+        $this->parent = $parent;
+    }
+
+    public function get(string $key)
+    {
+        if ($this->has($key)) {
+            return $this->data[$key];
+        } elseif ($this->parent) {
+            return $this->parent->get($key);
+        }
+
+        throw new MadLispException("symbol $key not defined in env");
+    }
+
+    public function set(string $key, $value): void
+    {
+        $this->data[$key] = $value;
+    }
+}
diff --git a/src/Hash.php b/src/Hash.php
new file mode 100644
index 0000000..0b4bcc0
--- /dev/null
+++ b/src/Hash.php
@@ -0,0 +1,14 @@
+<?php
+namespace MadLisp;
+
+class Hash extends Collection
+{
+    public function get(string $key)
+    {
+        if ($this->has($key)) {
+            return $this->data[$key];
+        }
+
+        throw new MadLispException("hash does not contain key $key");
+    }
+}
diff --git a/src/Lib/Core.php b/src/Lib/Core.php
new file mode 100644
index 0000000..4ea88a7
--- /dev/null
+++ b/src/Lib/Core.php
@@ -0,0 +1,156 @@
+<?php
+namespace MadLisp\Lib;
+
+use Closure;
+use MadLisp\Env;
+use MadLisp\Hash;
+use MadLisp\MList;
+use MadLisp\Symbol;
+use MadLisp\MadLispException;
+
+class Core implements ILib
+{
+    public function register(Env $env): void
+    {
+        // logic
+
+        $env->set('or', function (...$args) {
+            // return first true
+            for ($i = 0; $i < count($args) - 1; $i++) {
+                if ($args[$i] == true) {
+                    return $args[$i];
+                }
+            }
+
+            // return last
+            return $args[count($args) - 1];
+        });
+
+        $env->set('and', function (...$args) {
+            // return first false
+            for ($i = 0; $i < count($args) - 1; $i++) {
+                if ($args[$i] == false) {
+                    return $args[$i];
+                }
+            }
+
+            // return last
+            return $args[count($args) - 1];
+        });
+
+        $env->set('not', fn ($a) => !$a);
+
+        // arithmetic
+
+        $env->set('+', function (...$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) {
+            if ($a instanceof Closure) {
+                return 'function';
+            } elseif ($a instanceof MList) {
+                return 'list';
+            } elseif ($a instanceof Hash) {
+                return 'hash';
+            } elseif ($a instanceof Symbol) {
+                return 'symbol';
+            } elseif ($a === true || $a === false) {
+                return 'bool';
+            } elseif ($a === null) {
+                return 'null';
+            } elseif (is_int($a)) {
+                return 'int';
+            } elseif (is_float($a)) {
+                return 'float';
+            } else {
+                return 'string';
+            }
+        });
+
+        $env->set('fn?', fn ($a) => $a instanceof Closure);
+        $env->set('list?', fn ($a) => $a instanceof MList);
+        $env->set('hash?', fn ($a) => $a instanceof Hash);
+        $env->set('sym?', fn ($a) => $a instanceof Symbol);
+        $env->set('bool?', fn ($a) => $a === true || $a === false);
+        $env->set('true?', fn ($a) => $a == true); // not strict
+        $env->set('false?', fn ($a) => $a == false); // not strict
+        $env->set('null?', fn ($a) => $a === null);
+        $env->set('int?', fn ($a) => is_int($a));
+        $env->set('float?', fn ($a) => is_float($a));
+        $env->set('str?', fn ($a) => is_string($a));
+
+        // collections
+
+        $env->set('list', function (...$args) {
+            return new MList($args);
+        });
+
+        $env->set('hash', function (...$args) {
+            if (count($args) % 2 == 1) {
+                throw new MadLispException('uneven number of arguments for hash');
+            }
+
+            $data = [];
+
+            for ($i = 0; $i < count($args) - 1; $i += 2) {
+                $key = $args[$i];
+                $val = $args[$i + 1];
+
+                if (!is_string($key)) {
+                    throw new MadLispException('invalid key for hash (not string)');
+                }
+
+                $data[$key] = $val;
+            }
+
+            return new Hash($data);
+        });
+
+        // for debugging!
+        $env->set('eval', fn ($a) => ml_eval($a, $env));
+    }
+}
diff --git a/src/Lib/ILib.php b/src/Lib/ILib.php
new file mode 100644
index 0000000..2dfdd35
--- /dev/null
+++ b/src/Lib/ILib.php
@@ -0,0 +1,9 @@
+<?php
+namespace MadLisp\Lib;
+
+use MadLisp\Env;
+
+interface ILib
+{
+    public function register(Env $env): void;
+}
diff --git a/src/Lisp.php b/src/Lisp.php
new file mode 100644
index 0000000..3988dfe
--- /dev/null
+++ b/src/Lisp.php
@@ -0,0 +1,222 @@
+<?php
+namespace MadLisp;
+
+use Closure;
+
+class Lisp
+{
+    public function tokenize(string $a): array
+    {
+        $tokens = [];
+        $current = '';
+        $string = false;
+        $parens = 0;
+
+        $addCurrent = function () use (&$tokens, &$current) {
+            if ($current !== '') {
+                $tokens[] = $current;
+                $current = '';
+            }
+        };
+
+        for ($i = 0; $i < strlen($a); $i++) {
+            $c = substr($a, $i, 1);
+
+            if ($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;
+                }
+            }
+        }
+
+        // Add last also
+        $addCurrent();
+
+        // Check for errors
+        if ($parens != 0) {
+            throw new MadLispException("missing closing parenthesis");
+        } elseif ($string) {
+            throw new MadLispException("unterminated string");
+        }
+
+        return $tokens;
+    }
+
+    public function parse(array $tokens): array
+    {
+        $result = [];
+        $index = 0;
+
+        while ($index < count($tokens)) {
+            $result[] = $this->readForm($tokens, $index);
+        }
+
+        return $result;
+    }
+
+    public function read(string $code): array
+    {
+        $tokens = $this->tokenize($code);
+
+        $expressions = $this->parse($tokens);
+
+        return $expressions;
+    }
+
+    public function eval($expr, Env $env)
+    {
+        if ($expr instanceof MList && $expr->count() > 0) {
+            // Evaluate list contents
+            $results = array_map(fn ($a) => $this->eval($a, $env), $expr->getData());
+
+            $fn = $results[0];
+
+            if ($fn instanceof Closure) {
+                // If the first item is a function, call it
+                $args = array_slice($results, 1);
+                return $fn(...$args);
+            } else {
+                // Otherwise return new list with evaluated contents
+                return new MList($results);
+            }
+        } elseif ($expr instanceof Hash) {
+            // Hash: return new hash with all items evaluated
+            $items = [];
+            foreach ($expr->getData() as $key => $val) {
+                $items[$key] = $this->eval($val, $env);
+            }
+            return new Hash($items);
+        } elseif ($expr instanceof Symbol) {
+            return $env->get($expr->name());
+        }
+
+        return $expr;
+    }
+
+    public function print($a): string
+    {
+        $result = $a;
+
+        if ($a instanceof Closure) {
+            $result = '<function>';
+        } elseif ($a instanceof MList) {
+            $items = [];
+            foreach ($a->getData() as $val) {
+                $items[] = $this->print($val);
+            }
+            $result = '(' . implode(' ', $items) . ')';
+        } elseif ($a instanceof Hash) {
+            $items = [];
+            foreach ($a->getData() as $key => $val) {
+                $items[] = $this->print($key) . ':' . $this->print($val);
+            }
+            $result = '{' . implode(' ', $items) . '}';
+        } elseif ($a instanceof Symbol) {
+            $result = $a->name();
+        } elseif ($a === true) {
+            $result = 'true';
+        } elseif ($a === false) {
+            $result = 'false';
+        } elseif ($a === null) {
+            $result = 'null';
+        } elseif (is_string($a)) {
+            $result = '"' . $a . '"';
+        }
+
+        return $result;
+    }
+
+    public function rep(string $input, Env $env): void
+    {
+        $expressions = $this->read($input);
+
+        $results = array_map(fn ($expr) => $this->eval($expr, $env), $expressions);
+
+        $output = array_map(fn ($res) => $this->print($res), $results);
+
+        print(implode(' ', $output));
+    }
+
+    private function readForm(array $tokens, int &$index)
+    {
+        if ($tokens[$index] == '(') {
+            return $this->readList($tokens, $index);
+        } else {
+            return $this->readAtom($tokens, $index);
+        }
+    }
+
+    private function readList(array $tokens, int &$index): MList
+    {
+        $result = [];
+
+        // start tag
+        $index++;
+
+        while ($tokens[$index] != ')') {
+            $result[] = $this->readForm($tokens, $index);
+        }
+
+        // end tag
+        $index++;
+
+        return new MList($result);
+    }
+
+    private function readAtom(array $tokens, int &$index)
+    {
+        $a = $tokens[$index++];
+
+        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);
+            }
+        } else {
+            return new Symbol($a);
+        }
+    }
+}
diff --git a/src/MList.php b/src/MList.php
new file mode 100644
index 0000000..74e296b
--- /dev/null
+++ b/src/MList.php
@@ -0,0 +1,14 @@
+<?php
+namespace MadLisp;
+
+class MList extends Collection
+{
+    public function get(int $index)
+    {
+        if ($this->has($index)) {
+            return $this->data[$index];
+        }
+
+        throw new MadLispException("list does not contain index $index");
+    }
+}
diff --git a/src/MadLispException.php b/src/MadLispException.php
new file mode 100644
index 0000000..5715647
--- /dev/null
+++ b/src/MadLispException.php
@@ -0,0 +1,7 @@
+<?php
+namespace MadLisp;
+
+class MadLispException extends \Exception
+{
+
+}
diff --git a/src/Symbol.php b/src/Symbol.php
new file mode 100644
index 0000000..5c86017
--- /dev/null
+++ b/src/Symbol.php
@@ -0,0 +1,17 @@
+<?php
+namespace MadLisp;
+
+class Symbol
+{
+    protected string $name;
+
+    public function __construct(string $name)
+    {
+        $this->name = $name;
+    }
+
+    public function name(): string
+    {
+        return $this->name;
+    }
+}