Re-add !expr function

app/Cfnpp/Functions.php

@@ -215,23 +215,38 @@ class Functions
 	 * @param  NodeFunction $function
 	 * @return ?Node
 	 */
-	/*
-	 * TODO: Reimplement
 	public function f_expr(Node $node, NodeFunction $function): ?Node
 	{
 		if (!($function instanceof NodeFunctionValue))
 		{
-			throw new \Exception('!if requires scalar argument');
+			throw new \Exception('!expr requires scalar argument');
 		}
 
-		$parser = new \App\Cfnpp\Expression\Parser();
-		$expression = $parser->parse($function->getValue());
-		$result = $expression->evaluate($this->options->getVariables());
+		$expression = new \App\Cfnpp\Expression\Expression($function->getValue(), $this->options);
 
-		$result = Node::fromPhp($result);
-		$result->setName($node->hasName() ? $node->getName() : null);
+		if ($expression->isComplete())
+		{
+			// If we computed a final value/set of values, we can just insert those
+			// directly.
+			if ($expression->count() == 1)
+			{
+				$solution_node = Node::fromPhp($expression->getValue());
+			}
+			else
+			{
+				$solution_node = Node::fromPhp($expression->toArray());
+			}
+		}
+		else
+		{
+			// Otherwise let's convert it to cfn intrinsics
+			$solution_node = Node::fromPhp($expression->toCloudformation());
+		}
 
-		return $result;
+		if ($node->hasName())
+		{
+			$solution_node->setName($node->getName());
+		}
+		return $solution_node;
 	}
-	 */
 }