miniblog.

Doing another iteration on my diagnostics display. I'm reasonably happy with the bold highlighting within the error message. I'm not sure about the colour on Warning and Error though. It gives the output some visual structure, but arguably the message itself is more important.

Chekhov's repro: If a line of code is included in a bug report, it should contribute to the debugging somewhere.

I'm adding a += operator to my programming language, because writing `x = x + 1` is tedious. This opens the tricky design question of which operators should support this. Is += and -= sufficient, or do you expect things like >>= and **= to be available?