OCaml

Appeared in:
1996
Influenced by:
Influenced:
Paradigm:
Typing discipline:
File extensions:
.ml .mli
Versions and implementations (Collapse all | Expand all):
Programming language

OCaml is a functional language developed by Inria. The language is strongly typed, but uses type inference rather than explicit variable types. For objects, a structural typing system is used. It has a very fast garbage collector built-in, a native-code and byte-code generator, a top level for entering language constructs directly into an interpreter, and very powerful pattern matching.

Elements of syntax:

Nestable comments (* *)
Case-sensitivity Yes
Variable identifier regexp [_a-z][_a-zA-Z0-9']*
Function identifier regexp [_a-z][_a-zA-Z0-9']*
Variable declaration with assignment let variable = value {toplevel} or let variable = value in ... {local scope}
Block begin ... end or ( ... )
Physical (shallow) equality ==
Physical (shallow) inequality !=
Deep equality =
Deep inequality <>
Comparison < > <= >=
Function definition let f p1 p2 ... = ... or let f = fun p1 p2 ... -> ...
Function call f a b ...
Function call with no parameters f ()
Sequence ;
If - then if condition then ...
If - then - else if condition then ... else ...
Loop forever while true do ... done
While condition do while condition do ... done
For each value in a numeric range, 1 increment for i = 1 to 10 do ... done
For each value in a numeric range, 1 decrement for i = 10 downto 1 do ... done

OCaml logo
OCaml logo

Links:

Examples:

Hello, World!:

Example for versions OCaml 3.11

print_endline is a built-in function defined with the following type: 

string -> unit = <func>

This means that it takes 1 string as a parameter, and returns the unit type, (). 

let () = print_endline "Hello World";;

Factorial:

Example for versions OCaml 3.11

This example uses an auxiliary function fact, so that tail recursion is possible.

let rec fact n accum =
    if n <= 1 then 
        accum
    else
        fact (n-1) (accum*n);;

let factorial n =
    fact n 1;;

let () =
    for n = 0 to 16 do
        Printf.printf "%d! = %d\n" n (factorial n)
    done;

Factorial:

Example for versions OCaml 3.11

This example shows the naive way to implement the factorial function. However, it is not tail recursive, since the recursive function call is not the only statement on the line. 

let rec factorial n =
    if n <= 1 then
      1
    else
      factorial (n-1) * n;;

let () =
  for n = 0 to 16 do
    Printf.printf "%d! = %d\n" n (factorial n)
  done;

Fibonacci numbers:

Example for versions OCaml 3.11

This example uses straightforward recursive solution. Printf.printf does formatted output. 

let rec fibonacci n =
  if n < 3 then
    1
  else
    fibonacci (n-1) + fibonacci (n-2)

let () =
  for n = 1 to 16 do
    Printf.printf "%d, " (fibonacci n)
  done;
  print_endline "..."

Quadratic equation:

Example for versions OCaml 3.11

ocaml quadratic_equation.ml 3. 5. 2. 

let square x = x *. x;;

let delta  a b c = ( square b-. (4. *. a *. c ));;

let   solve a b c   =
    if a=0. 
        then Printf.printf "Not a quadratic equation\n"
            else
                if   delta a b c  >= 0.
                    then
                        let   x1=( -.b +. sqrt(delta a b c )) /. (2. *. a)
                            and x2=  (-.b -.  sqrt(delta a b c ))  /. (2. *. a)  
                        in 
                            Printf.printf "x1 =%.5f x2=%.5f \n"  x1  x2
                    else 
                        let   x= (-.b   /. (2. *. a))
                            and i=     sqrt(4. *. a *. c -. square b)  /. (2. *. a) 
                        in Printf.printf "x+ =%.5f+i%.5f  x-=%.5f-i%.5f \n"  x  i  x i
    ;;



let () =
solve (float_of_string Sys.argv.(1))( float_of_string Sys.argv.(2) )(float_of_string Sys.argv.(3))