What's magic there seemed magical at the time because even Go's creators were only just coming to see the power of interfaces then. Now, having a decompressor read from a block reader, which reads in turn from some other place, is not magical, it's just good practice.
This is from Go 1. Unfortunately, that file accumulated tons of other ugliness over time, as it dealt with the real world. I was one of the people who had to make that line less magic. Sorry Rob.
The Lambda Calculus. Invented in the 1930s it is still used today as the basis for most advanced CS research and as the foundation of many programming languages.