[zelphirkalt]

I found the regular expression package as a first thing to make in SML waaay too complex. You already need to have a good understanding of the elements of SML syntax to understand how it works. This is definitely not for SML beginners. I recommend "Elements of ML Programming" by Jeffrey D. Ullman for people starting to learn SML. It too has some corners, that are less great for not so mathematically inclined people, but you will definitely learn the language and have exercises.

[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