STRONGLY RECOMMENDED
Your vade mecum for the programming language of this course. The Cornell book store has copies available. The publisher offers a free preview of the first chapter.
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If you appreciate Zen koans and would like to deepen your understanding of recursion and types in functional programming, consider this book. I have retyped the majority of the original SML examples in OCaml for your convenience. The first chapter is available in Amazon's viewable excerpt.