OCaml from the Very Beginning (204pp, paperback) is now available on Amazon for $39.99 / €29.99 / £24.99, as well as an e-book from ocaml-book.com for $19.99. Here are preview chapters and a .zip of the examples and exercises.
Here's the blurb:
In OCaml from the Very Beginning John Whitington takes a no-prerequisites approach to teaching a modern general-purpose programming language. Each small, self-contained chapter introduces a new topic, building until the reader can write quite substantial programs. There are plenty of questions and, crucially, worked answers and hints.
OCaml from the Very Beginning will appeal both to new programmers, and experienced programmers eager to explore functional languages such as OCaml. It is suitable both for formal use within an undergraduate or graduate curriculum, and for the interested amateur.
Please do review the book on Amazon if you have the chance.