John Harrop himself posted on reddit awhile back that he hadn't personally used OCaml in a long time when someone asked about the book on the OCaml sub reddit.

John Harrop himself posted on reddit awhile back that he hadn't personally used OCaml in a long time when someone asked about the book on the OCaml sub reddit. His username starts with jdh I think. Honestly though, scientific computing seems to be going Julia He’s mainly converted to F# if I remember correctly. He was often in flamewars on OCaml mailing lists about multicore support. There is a bit of hype around Julia but it’s use in the real world is a rounding error compared to Python, R, MATLAB, FORTRAN etc etc. I might look at it again in 5 years or so. OCaml never gained any significant traction in scientific or numerical computing. You can try F# on https://notebooks.azure.com https://notebooks.azure.com for free