I love this series.
Implimented my own interpreter of the back of the original series. Managed to get a type system and all sorts added.
The author was even responsive via email giving me hints on where to investigate extending it further. (belive I was trying to add lists at the time).
Having followed a ton of 'how to write a programming language / compiler / ect tutorials'.
Its the first one to really make me grok what's going on and move beyond just copy pasting examples.
So thanks Bob. Keep up the awesome work!