You can still get a free-of-cost copy of Programming Languages: Application and Interpretation at its original site. Actually, the book is now released under a Creative Common license, thank you Shriram!
This is, actually, old news. The book has been in paperback for quite a while, but I neglected to publish the post at that time. Today, a chat at the Esperanto meeting about Lulu (and how useful it is for Esperantists, that make books nobody wants to publish) reminded me about the post and I’m now publishing it.