plus-mutator-infection.php

<?php
class Plus implements Mutator
{
    public function mutate(Node $node)
    {
        return new BinaryOp\Minus($node->left, $node->right, $node->getAttributes());
    }

    public function shouldMutate(Node $node) : bool
    {
        if (!($node instanceof BinaryOp\Plus)) {
            return false;
        }

        if ($node->left instanceof Array_ && $node->right instanceof Array_) {
            return false;
        }

        return true;
    }
}