[jstrieb]

This is valid criticism, and I agree. The regular expression example is not made easier by his use of non-standard regex syntax.

I have not read Dr. Harper's book cover to cover; I treat it as a reference. For that, it is quite useful.

The same criticism of his SML book could also be made of his Practical Foundations for Programming Languages book. It's a massive, dense tome that is probably great for other professors to use as the basis for a course, but (in my opinion) serves as a mediocre introduction if you have never seen the material before.

https://www.cs.cmu.edu/~rwh/pfpl.html