When do you put double semicolons in F#?

Question

This is a stupid question. I\'ve been reading a couple books on F# and can\'t find anything that explains when you put ;; after a statement, nor can I find a pattern in the

Answer 1

In F#, the only place ;; is required is to end expressions in the interactive mode.

;; is left over from the transition from OCaml, where in turn it is left over from Caml Light. Originally ;; was used to end top-level "phrases"--that is, let, type, etc. OCaml made ;; optional since the typical module consists of a series of let statements with maybe one statement at the end to call the main function. If you deviate from this pattern, you need to separate the statements with ;;. Unfortunately, in OCaml, when ;; is optional versus required is hard to learn.

However, F# introduces two relevant modifications to OCaml syntax: indentation and do. Top-level statements have to go inside a do block, and indentation is required for blocks, so F# always knows that each top-level statement begin with do and an indent and ends with an outdent. No more ;; required.

Overall, all you need to know is that [O']Caml's syntax sucks, and F# fixes a lot of its problems, but maintains a lot of confusing backward compatibility. (I believe that F# can still compile a lot of OCaml code.)

Note: This answer was based on my experience with OCaml and the link Adam Gent posted (which is unfortunately not very enlightening unless you know OCaml).