OCaml is an interesting functional language. There are lots learning materials on the Internet. I compile a list of resources for OCaml learning and reference.
Recommended OCaml learning and reference material
Online book of Real World OCaml by Yaron Minsky, Anil Madhavapeddy, Jason Hickey.
A very good tutorial by Jason Hickey: http://www.cs.caltech.edu/courses/cs134/cs134b/book.pdf.
OCaml Style Guides
Other OCaml learning materials
OCaml Homepage: http://caml.inria.fr/
Introduction to OCaml on Wikipedia: https://en.wikipedia.org/wiki/OCaml
Introducing OCaml: http://www.ffconsultancy.com/products/ocaml_journal/free/introduction.html
The Harvard CS51 course which is introduced with OCaml.
A Concise Introduction to Objective Caml by David Matuszek
A good “why OCaml”: https://www.cs.ubc.ca/~murphyk/Software/Ocaml/why_ocaml.html
A very very good introduction to OCaml:
Some claim that OCaml sucks: http://sds.podval.org/ocaml-sucks.html