diff --git a/app/Engine/Cfnpp/Expression/Expression.php b/app/Engine/Cfnpp/Expression/Expression.php
index dbd64e5..d381967 100644
--- a/app/Engine/Cfnpp/Expression/Expression.php
+++ b/app/Engine/Cfnpp/Expression/Expression.php
@@ -4,19 +4,47 @@ declare(strict_types=1);
 
 namespace App\Engine\Cfnpp\Expression;
 
+/**
+ * Expression that can be evaluated.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class Expression
 {
+	/**
+	 * List of Tokens in the expression.
+	 * @var Token[]
+	 */
 	protected $tokens;
 
+	/**
+	 * Evaluation stack.
+	 * @var mixed[]
+	 */
 	protected $stack;
 
+	/**
+	 * Variables that can be referenced in the expression.
+	 * @var array<string,mixed>
+	 */
 	protected $variables;
 
+	/**
+	 * Create a new expression.
+	 *
+	 * @param Token[] $tokens
+	 */
 	public function __construct(array $tokens)
 	{
 		$this->tokens = $tokens;
 	}
 
+	/**
+	 * Evaluate the tokens contained in this expression.
+	 *
+	 * @param  array<string,mixed> $variables variables that can be referenced
+	 * @return mixed
+	 */
 	public function evaluate(array $variables = [])
 	{
 		$this->variables = $variables;
@@ -26,6 +54,7 @@ class Expression
 		while (sizeof($tokens))
 		{
 			$token = array_shift($tokens);
+			assert(isset($token));
 
 			if ($token instanceof TokenNumericLiteral)
 			{
@@ -49,25 +78,45 @@ class Expression
 			}
 		}
 
-		if (sizeof($this->stack) != 1)
+		if (sizeof($this->stack) == 1)
 		{
-			throw new \Exception('Expression did not evaluate down to a single value');
+			return end($this->stack);
 		}
 
-		return $this->stack[0];
+		throw new \Exception('Expression did not evaluate down to a single value');
 	}
 
-	protected function evaluateTokenNumericLiteral(TokenNumericLiteral $token)
+	/**
+	 * Evaluate and mutate the stack given a numeric literal.
+	 *
+	 * @param  TokenNumericLiteral $token
+	 * @return void
+	 */
+	protected function evaluateTokenNumericLiteral(TokenNumericLiteral $token): void
 	{
 		$this->push($token->getValue());
 	}
 
-	protected function evaluateTokenStringLiteral(TokenStringLiteral $token)
+	/**
+	 * Evaluate and mutate the stack given a string literal.
+	 *
+	 * @param  TokenStringLiteral $token
+	 * @return void
+	 */
+	protected function evaluateTokenStringLiteral(TokenStringLiteral $token): void
 	{
 		$this->push($token->getValue());
 	}
 
-	protected function evaluateTokenOperator(TokenOperator $token)
+	/**
+	 * Evaluate and mutate the stack given a comparison operator.
+	 *
+	 * $this->pop() == $this->pop() is valid.
+	 * @suppress PhanPluginDuplicateExpressionBinaryOp
+	 * @param  TokenOperator $token
+	 * @return void
+	 */
+	protected function evaluateTokenOperator(TokenOperator $token): void
 	{
 		switch ($token->getOperator())
 		{
@@ -102,6 +151,12 @@ class Expression
 		}
 	}
 
+	/**
+	 * Evaluate and mutate the stack given a variable reference.
+	 *
+	 * @param  TokenVariable $token
+	 * @return void
+	 */
 	protected function evaluateTokenVariable(TokenVariable $token)
 	{
 		$name = $token->getName();
@@ -112,12 +167,28 @@ class Expression
 		$this->push($this->variables[$name]);
 	}
 
+	/**
+	 * Pop an item off the stack.
+	 *
+	 * @param  int   $offset offset from the end of the stack to pop from
+	 * @return mixed
+	 */
 	protected function pop(int $offset = 0)
 	{
+		if (sizeof($this->stack) < $offset + 1)
+		{
+			throw new \Exception('Expression stack underflow!');
+		}
 		return array_splice($this->stack, -1 * ($offset + 1), 1)[0];
 	}
 
-	protected function push($value)
+	/**
+	 * Push an item onto the end of the stack.
+	 *
+	 * @param  mixed $value
+	 * @return void
+	 */
+	protected function push($value): void
 	{
 		array_push($this->stack, $value);
 	}
diff --git a/app/Engine/Cfnpp/Expression/Parser.php b/app/Engine/Cfnpp/Expression/Parser.php
index f483438..19cec7c 100644
--- a/app/Engine/Cfnpp/Expression/Parser.php
+++ b/app/Engine/Cfnpp/Expression/Parser.php
@@ -4,8 +4,18 @@ declare(strict_types=1);
 
 namespace App\Engine\Cfnpp\Expression;
 
+/**
+ * Parse a string into a series of expression tokens.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class Parser
 {
+	/**
+	 * List of class names of tokens this parser will parse.
+	 *
+	 * @var string[]
+	 */
 	public const TOKEN_TYPES = [
 		TokenNumericLiteral::class,
 		TokenOperator::class,
@@ -13,10 +23,16 @@ class Parser
 		TokenVariable::class
 	];
 
+	/**
+	 * Parse a string into an expression.
+	 *
+	 * @param  string     $value
+	 * @return Expression
+	 */
 	public function parse(string $value): Expression
 	{
 		$original_value = $value;
-		$value = $value.' ';
+		$value .= ' ';
 		$tokens = [];
 		while (strlen($value) > 0)
 		{
diff --git a/app/Engine/Cfnpp/Expression/Token.php b/app/Engine/Cfnpp/Expression/Token.php
index e5f4c1e..75eb65d 100644
--- a/app/Engine/Cfnpp/Expression/Token.php
+++ b/app/Engine/Cfnpp/Expression/Token.php
@@ -4,6 +4,11 @@ declare(strict_types=1);
 
 namespace App\Engine\Cfnpp\Expression;
 
+/**
+ * Token representing a distinct part of an expression.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 abstract class Token
 {
 	/**
diff --git a/app/Engine/Cfnpp/Expression/TokenNumericLiteral.php b/app/Engine/Cfnpp/Expression/TokenNumericLiteral.php
index 1a4127d..1aec30c 100644
--- a/app/Engine/Cfnpp/Expression/TokenNumericLiteral.php
+++ b/app/Engine/Cfnpp/Expression/TokenNumericLiteral.php
@@ -4,25 +4,58 @@ declare(strict_types=1);
 
 namespace App\Engine\Cfnpp\Expression;
 
+/**
+ * Token representing a numeric (integer or float) literal.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class TokenNumericLiteral extends Token
 {
+	/**
+	 * Numeric value this token represents.
+	 * @var int|float
+	 */
 	protected $value;
 
+	/**
+	 * Create a new numeric literal.
+	 *
+	 * @param int|float $value
+	 */
 	public function __construct($value)
 	{
 		$this->value = $value;
 	}
 
+	/**
+	 * Get the value this token represents.
+	 *
+	 * @return int|float
+	 */
 	public function getValue()
 	{
 		return $this->value;
 	}
 
+	/**
+	 * Determine whether a numeric token can be parsed from a stream.
+	 *
+	 * @param  string $stream
+	 * @return bool
+	 */
 	public static function isToken(string $stream): bool
 	{
 		return is_numeric($stream[0]);
 	}
 
+	/**
+	 * Parse a numeric token from a stream.
+	 *
+	 * Returns token, and modifies stream to remove all consumed characters.
+	 *
+	 * @param  string $stream
+	 * @return Token
+	 */
 	public static function getToken(string &$stream): Token
 	{
 		$buffer = '';
@@ -40,6 +73,15 @@ class TokenNumericLiteral extends Token
 
 		$stream = substr($stream, strlen($buffer));
 
+		if (stristr($buffer, '.'))
+		{
+			$buffer = (float)$buffer;
+		}
+		else
+		{
+			$buffer = (int)$buffer;
+		}
+
 		return new TokenNumericLiteral($buffer);
 	}
 }
diff --git a/app/Engine/Cfnpp/Expression/TokenOperator.php b/app/Engine/Cfnpp/Expression/TokenOperator.php
index ca2c02e..cffc8e4 100644
--- a/app/Engine/Cfnpp/Expression/TokenOperator.php
+++ b/app/Engine/Cfnpp/Expression/TokenOperator.php
@@ -4,8 +4,17 @@ declare(strict_types=1);
 
 namespace App\Engine\Cfnpp\Expression;
 
+/**
+ * Token representing a comparison operator.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class TokenOperator extends Token
 {
+	/**
+	 * List of valid operators this can parse.
+	 * @var string[]
+	 */
 	public const OPERATORS = [
 		'eq',
 		'gt',
@@ -17,18 +26,38 @@ class TokenOperator extends Token
 		'or'
 	];
 
+	/**
+	 * Operator this token represents.
+	 * @var string
+	 */
 	protected $operator;
 
+	/**
+	 * Create a new operator token.
+	 *
+	 * @param string $operator
+	 */
 	public function __construct($operator)
 	{
 		$this->operator = $operator;
 	}
 
-	public function getOperator()
+	/**
+	 * Get the operator this token represents.
+	 *
+	 * @return string
+	 */
+	public function getOperator(): string
 	{
 		return $this->operator;
 	}
 
+	/**
+	 * Determine whether a operator token can be parsed from a stream.
+	 *
+	 * @param  string $stream
+	 * @return bool
+	 */
 	public static function isToken(string $stream): bool
 	{
 		foreach (static::OPERATORS as $operator)
@@ -42,6 +71,14 @@ class TokenOperator extends Token
 		return false;
 	}
 
+	/**
+	 * Parse an operator token from a stream.
+	 *
+	 * Returns token, and modifies stream to remove all consumed characters
+	 *
+	 * @param  string $stream
+	 * @return Token
+	 */
 	public static function getToken(string &$stream): Token
 	{
 		foreach (static::OPERATORS as $operator)
@@ -54,5 +91,6 @@ class TokenOperator extends Token
 				return new TokenOperator($operator);
 			}
 		}
+		throw new \Exception('Could not parse operator token!');
 	}
 }
diff --git a/app/Engine/Cfnpp/Expression/TokenStringLiteral.php b/app/Engine/Cfnpp/Expression/TokenStringLiteral.php
index 30bec17..685caaa 100644
--- a/app/Engine/Cfnpp/Expression/TokenStringLiteral.php
+++ b/app/Engine/Cfnpp/Expression/TokenStringLiteral.php
@@ -4,25 +4,58 @@ declare(strict_types=1);
 
 namespace App\Engine\Cfnpp\Expression;
 
+/**
+ * Token representing a string literal.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class TokenStringLiteral extends Token
 {
+	/**
+	 * Value of the string literal.
+	 * @var string
+	 */
 	protected $value;
 
-	public function __construct($value)
+	/**
+	 * Create a new string literal token.
+	 *
+	 * @param string $value
+	 */
+	public function __construct(string $value)
 	{
 		$this->value = $value;
 	}
 
-	public function getValue()
+	/**
+	 * Get the value of the string literal.
+	 *
+	 * @return string
+	 */
+	public function getValue(): string
 	{
 		return $this->value;
 	}
 
+	/**
+	 * Determine whether a string token can be parsed from a stream.
+	 *
+	 * @param  string $stream
+	 * @return bool
+	 */
 	public static function isToken(string $stream): bool
 	{
 		return $stream[0] == '"';
 	}
 
+	/**
+	 * Parse a string literal token from a stream.
+	 *
+	 * Returns token, and modifies stream to remove all consumed characters
+	 *
+	 * @param  string $stream
+	 * @return Token
+	 */
 	public static function getToken(string &$stream): Token
 	{
 		$buffer = '';
diff --git a/app/Engine/Cfnpp/Expression/TokenVariable.php b/app/Engine/Cfnpp/Expression/TokenVariable.php
index ea8cc1f..ed78f29 100644
--- a/app/Engine/Cfnpp/Expression/TokenVariable.php
+++ b/app/Engine/Cfnpp/Expression/TokenVariable.php
@@ -4,25 +4,58 @@ declare(strict_types=1);
 
 namespace App\Engine\Cfnpp\Expression;
 
+/**
+ * Expression token referencing a variable.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class TokenVariable extends Token
 {
+	/**
+	 * Name of the variable this token references.
+	 * @var string
+	 */
 	protected $name;
 
-	public function __construct($name)
+	/**
+	 * Create a new variable token.
+	 *
+	 * @param string $name
+	 */
+	public function __construct(string $name)
 	{
 		$this->name = $name;
 	}
 
-	public function getName()
+	/**
+	 * Get the name of the variable this token references.
+	 *
+	 * @return string
+	 */
+	public function getName(): string
 	{
 		return $this->name;
 	}
 
+	/**
+	 * Determine whether a variable name token can be parsed from a stream.
+	 *
+	 * @param  string $stream
+	 * @return bool
+	 */
 	public static function isToken(string $stream): bool
 	{
-		return preg_match('/^[A-Za-z]$/', $stream[0]);
+		return (bool)preg_match('/^[A-Za-z]$/', $stream[0]);
 	}
 
+	/**
+	 * Parse a variable token from a stream.
+	 *
+	 * Returns token, and modifies stream to remove all consumed characters.
+	 *
+	 * @param  string $stream
+	 * @return Token
+	 */
 	public static function getToken(string &$stream): Token
 	{
 		$buffer = '';
diff --git a/app/Engine/Cfnpp/Functions.php b/app/Engine/Cfnpp/Functions.php
index 8854726..51672d9 100644
--- a/app/Engine/Cfnpp/Functions.php
+++ b/app/Engine/Cfnpp/Functions.php
@@ -128,7 +128,12 @@ class Functions
 
 		$nodes = $function->getChildren();
 
-		$condition = $nodes[0]; // expects NodeValue
+		$condition = $nodes[0];
+
+		if (!($condition instanceof NodeValue))
+		{
+			throw new \Exception('!if requires scalar condition');
+		}
 		$if_true = $nodes[1];
 		$if_false = sizeof($nodes) == 3 ? $nodes[2] : null;