I had a block for a while because I _had_ chosen a name for my language. Suddenly what I was writing was the official implementation, it had to be "right", and I got design paralysis. I found I was making further progress doing exercises outside that repository. (It's all good now, and I have a self-hosted language.)

At the function level, I'll often write the function and then rename it with F2 after I've written it.