Thanks for the link. I am working my way through the book and I am up to chapter 5. I have tried entering examples from the book into Nush but it doesn't tally up too well. For example:
(sqrt 4)
works in SBCL but in Nush is gives an error "undefined symbol sort". I fished around in my Nu installation for a bit and pulled out the demo which contains
(NuMath sqrt:5)
And then
(class NSNumber
(- (id) sqrt is (NuMath sqrt:self)))
which I suppose is a category on NSNumber. And then the example goes
(2 sqrt)
which is surely a message sort to object '2'.
A tutorial really would help. Nevertheless, it does give a warm hobby tingle to the whole Nu experience and that seems rare these days.