[jallmann]

The way I always think about it is in terms of scope. With:

  let x = v in expr

`x` is now available for use in `expr`

In essence, an OCaml program is a giant recursive expression, because `expr` can have its own set of let definitions.

In the REPL, this is where the double semicolons come in, as a sort of hint to continue processing after the expression.