variablenode2.php

<?php
/**
 * @author Gerard van Helden <gerard@zicht.nl>
 * @copyright Zicht Online <http://zicht.nl>
 */
 
require_once 'vendor/autoload.php';

class MyConf implements \Symfony\Component\Config\Definition\ConfigurationInterface
{
    /**
     * Generates the configuration tree builder.
     *
     * @return \Symfony\Component\Config\Definition\Builder\TreeBuilder The tree builder
     */
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new \Symfony\Component\Config\Definition\Builder\TreeBuilder();

        $root = $treeBuilder->root('task');

        $root
            ->children()
                ->arrayNode('tasks')
                    ->prototype('array')
//                        ->children()->scalarNode('type')->end()->end()
                        ->prototype('variable')
                    ->end()
                    ->validate()
                        ->ifTrue(function($v) {
                            $params = $v;
                            unset($params['type']);

                            $isValid = false;

                            switch($v['type']) {
                                case 'a':
                                    $isValid = isset($params['param_valid_for_a']) && count($params) == 1;
                                    break;
                                case 'b':
                                    $isValid = isset($params['param_valid_for_b']) && count($params) == 1;
                                    break;
                            }

                            return !$isValid;
                        })
                        ->thenInvalid('Fail')
                        ->end()
                    ->end()
                ->end()
            ->end()
        ;

        return $treeBuilder;
    }
}

$yml = <<<EOYML
tasks:
    -
        type: "a"
        param_valid_for_a: "value1"
    -
        type: "a"
        param_valid_for_a: "value2"
#        param_valid_for_b: "value2"
    -
        type: "b"
        param_valid_for_b: "value"
EOYML;

$processor = new \Symfony\Component\Config\Definition\Processor();
$configs = array();
$configs[]= \Symfony\Component\Yaml\Yaml::parse($yml);

$result = $processor->processConfiguration(new MyConf(), $configs);
print_r($result);