Re: [Caml-list] use of ";;" when teaching Ocaml

[Steve Zdancewic <stevez@cis.upenn.edu>]

At Penn we use a slightly different idiom: at the top level all 
"commands" should be _prefixed_ by ;;.  We don't think of ;; as 
terminating a declaration, instead we think of it as preceding a 
stateful operation.  This has the nice property of marking effectful 
code syntactically in the program, and students don't seem to mind. Some 
examples would be:

;; open Foo

let f x =
   let y = x ^ x in
   y ^ y

;; print_string f "x"

let g x = ...
let test () = assert_eq (g 3) 7

;; run_test "testing g" test


let main () = ...

;; main ()

--Steve

Steve Zdancewic
Professor, Dept. of Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~stevez


On 6/22/15 12:07 PM, Pippijn van Steenhoven wrote:
> On Mon, Jun 22, 2015 at 11:48:21AM -0400, Damien Doligez wrote:
>> Gerd has totally nailed it, and that's the reason why I always use ;;
>> in my code.
>> If we had another keyword for toplevel let (let without in) the
>> situation would be quite different.
> I have a rule (which I introduced recently, and thus don't yet follow
> much in my code) to use ;; to terminate all unit-returning (therefore
> effectful) functions. Pure functions or effectful functions with a proper
> return value never have the trailing-semicolon issue. An alternative
> solution is to always return () from unit-returning functions, but I
> found ;; more appealing.