OCaml By Examples

Language Basics

Project Management

Advanced Ocaml

Libraries

imperative

utop

OCaml is a functional language, which is about evaluating functions. But programs are generally more complicated… One of the major feature of OCaml is the in keyword which allows to iteratively construct values that help evaluate the last expression.

 
utop # let one = 1 in
let two = one + 1 in
let four = two + two in
four + four;;
- : int = 8

But complex programs have side effects: functions that change something somewhere else, like printing to stdout or getting some input from stdin. These side-effects don't always return anything, but they can still be chained using the in keyword.

 
utop # let () = print_endline "hello" in
  let () = print_endline "world" in
  print_endline "!";;
hello
world
!
- : unit = ()

It is unatural though, and it is common to write in an imperative style by separating side-effects with a semicolon.

 
utop # print_endline "hello";
  print_endline "world";
  print_endline "!";;
hello
world
!
- : unit = ()
next: match