Hello OCaml

print_endline "hello" prints a string and a newline. Function application is just a space: no parentheses around arguments, no commas.

A program's top-level effects are usually written let () = print_endline "hello". The () pattern says the expression returns unit, OCaml's 'no meaningful value'.

Comments are (* like this *) and they nest. There are no line comments.

Try code in utop, the interactive toplevel, ending phrases with ;;. Run a file with ocaml hello.ml, or build projects with dune build and dune exec ./hello.exe.

Misses: writing print_endline("a", "b") with a comma (that is a tuple), and using // comments.

(* hello.ml *)
let () =
  print_endline "hello";
  print_endline (string_of_int (2 + 3))