How to display only the program output in utop on the VS Code terminal and not all the instructions one after the other

Question

(*redefining the power function for integers*)
let rec ( ** ) v n = if n = 0 then 1 else v * (( ** ) v (n-1));;

let rec sommation n = 
   if n = 0 then 0 else -1**(n/3) * n**(2+ (-1)**n) + sommation (n-1);;

print_int (sommation 7);;

When I run the above program in VS Code by selecting all lines of code then press Ctrl+Enter, this is what displays in the terminal:

                                                  └──────────────────────────────────────────────────────────────┘

Type #utop_help for help about using utop.

─( 17:07:51 )─< command 0 >───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────{ counter: 0 }─utop # (*redefining the power function for integers*)
let rec ( ** ) v n = if n = 0 then 1 else v * (( ** ) v (n-1));;
val ( ** ) : int -> int -> int = <fun>
─( 17:07:51 )─< command 1 >───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────{ counter: 0 }─utop # 
let rec sommation n =
  if n = 0 then 0 else -1**(n/3) * n**(2+ (-1)**n) + sommation (n-1);;
val sommation : int -> int = <fun>
─( 17:07:54 )─< command 2 >───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────{ counter: 0 }─utop # 
print_int (sommation 7);;
160- : unit = ()
─( 17:07:54 )─< command 3 >───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────{ counter: 0 }─

As you can see, it displays the lines of my program one after the other, which makes it take a long time to display the output which is 160

How can I fix this problem?

Answer 1

Once you start writing large programs rather than testing short snippets in the toplevel, it probably makes sense to save them as a file, and execute that file. If you go beyond one file, you should probably investigate using Dune to manage the build process.

Consider your example. Rather than a bunch of expressions separated by ;; tokens, let's put that into a file test.ml.

(*redefining the power function for integers*)
let rec ( ** ) v n = 
  if n = 0 then 1 
  else v * (( ** ) v (n-1))

let rec sommation n = 
  if n = 0 then 0 
  else -1**(n/3) * n**(2+ (-1)**n) + sommation (n-1)

let () =
  print_int (sommation 7)

In a program, your last expression would not be valid. At the top level of a program, we cannot have bare expressions, so we bind it to ().

Now you can execute this as ocaml test.ml in your shell or compile it with ocamlc or ocamlopt.