Lisp and Erlang are the only languages I've seen where a comment can start with a single character, but it's very common to use two (;; or %% respectively)
miniblog.
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TIL that `cargo t` and `cargo r` work as `cargo test` and `cargo run` respectively. Several keystrokes saved!
Python and JS can both execute code when loading libraries (`import foo` and `require('foo')` respectively).
Yet the Python CLI apps I've seen have to do much more work to ensure good startup performance (e.g. `myapp --help` not being slow). I'm not sure why.