Obviously you get the false every time as the dot notation for your input returns like a_list.0 when the rule you are creating is applied to a_list so it does not find the given key in your input. This behaviour looks a bit strange for me as it should check by input keys, and array_dot returns a bit strange result. You can try to create conditional validation like here http://laravel.com/docs/4.2/validation#conditionally-adding-rules.
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