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

The double semi-colon is used to mark the end of a block of code that is ready for evaluation in F# interactive when you are typing directly into the interactive session. For example, when using it as a calculator.

This is rarely seen in F# because you typically write code into a script file, highlight it and use ALT+ENTER to have it evaluated, with Visual Studio effectively injecting the ;; at the end for you.

OCaml is the same.

Literature often quotes code written as it would appear if it had been typed into an interactive session because this is a clear way to convey not only the code but also its inferred type. For example:

> [1; 2; 3];;
val it : int list = [1; 2; 3]

This means that you type the expression [1; 2; 3] into the interactive session followed by the ;; denoting the end of a block of code that is ready to be evaluated interactively and the compiler replies with val it : int list = [1; 2; 3] describing that the expression evaluated to a value of the type int list.