Lambda the Ultimate

Phil seems to have made the mistake most of us make from time to time: failing to follow the classic interpreter pattern in handling the environment (from SICP, not GoF!).

It seems such a trivial thing... But if you don't handle the env correctly, it is bound to bite you in the a** sooner or later. It's one of the many things SICP and EOPL teach you without belaboring the point - so subtly in fact that you can easily fail to keep the message firmly in mind when you set up to implement your own language.

I am pretty sure I wrote here about the time I made this mistake, but I haven't managed to find that post in the archives.