Most implementations of machine learning algorithms are based on special-purpose frameworks such as TensorFlow or PyTorch. While these frameworks are convenient to use, they introduce multi-million lines of code dependency that one has to trust, understand and potentially modify. As an alternative, this paper investigates a direct implementation of a state of the art Convolutional Neural Network (CNN) in an array language. While our implementation requires 150 lines of code to define the special-purpose operators needed for CNNs, which are readily provided through frameworks such as TensorFlow and PyTorch, our implementation outperforms these frameworks by factors 2 and 3 on a fixed set of hardware — a 64-core GPU-accelerated machine. The resulting specification is written in a rank-polymorphic data-parallel style, and it can be immediately leveraged by optimising compilers. Indeed, array languages make neural networks fast.