I write CL production code all the time. Basically daily. I use hash tables a lot, and those are obviously mutable (I did mention that as an exception) but most

I write CL production code all the time. Basically daily. I use hash tables a lot, and those are obviously mutable (I did mention that as an exception) but most of the rest of my code is pretty much functional, which is generally (though not uniquely) immutable. I can’t really see how it makes sense to do hash table immutably. It might just be me, but functional style tends toward immutability be default.