I'd say it's more similar to Javascript. In fact all of the examples are valid JS if you replace `fn` with `function`. (Although JS doesn't have implicit returns.)
At a guess, the author chose the syntax because it's familiar and easy to parse. Go's syntax is... eccentric where it differs from typical C-style languages.
Author here. Yes, that's exactly right. I wanted to show how to write a parser/interpreter for something that you encounter every day. JavaScript-like syntax, with curly braces and `if`/`else` is just that.
At a guess, the author chose the syntax because it's familiar and easy to parse. Go's syntax is... eccentric where it differs from typical C-style languages.