Hi Eliot While working on a way to use the RB-AST with the standard compiler I think I found a problem in your code. To reproduce evaluate the following expression: [ :a | ] value: 1 According to my understanding that should return nil, not the first argument 1. The generated bytecode is: pushTemp: 0 blockReturn I think it should be: pushConstant nil blockReturn Cheers, Lukas -- Lukas Renggli http://www.lukas-renggli.ch