Lambda the Ultimate

Shriram Krishnamurthi's excellent book, Programming Languages: Application and Interpretation (PLAI), long available in PDF form, is now available in paperback.

There's also a paid download available, "in case you want to reward the author in kind". A free PDF of the latest version is still available, which "really is the entire book, with no strings attached." The book is now licensed under a Creative Commons license which allows it to be adapted ("remixed") to fit a course.

Here's an overview of the book's approach:

This book unites two approaches to teaching programming languages, one based on a survey of languages and the other on writing definitional interpreters.

Each approach has significant advantages but also huge drawbacks. The interpreter method writes programs to learn concepts, and has at its heart the fundamental belief that by teaching the computer to execute a concept we more thoroughly learn it ourselves. While this reasoning is internally consistent, it fails to recognize that understanding definitions does not imply we understand the consequences of those definitions. For instance, the difference between strict and lazy evaluation, or between static and dynamic scope, is only a few lines of interpreter code, but the consequences of these choices is enormous. The survey of languages school is better suited to understand these consequences.

The book is used as the textbook for the programming languages course at Brown University, taken primarily by 3rd and 4th year undergraduates and beginning graduate (both MS and PhD) students. It seems very accessible to smart 2nd year students too. The book has been used as a textbook at over a dozen other universities as a primary or secondary text.