Hello, World!
let () = print_endline "Hello, World!"main.ml
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OCaml 5.4.1Readymain.mlLn 1, Col 1Spaces: 4UTF-8
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main.ml · output appears here
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Output streams here as your program runs.
OCaml is a general-purpose, multi-paradigm programming language created in 1996 by Xavier Leroy and others at INRIA in France, evolving from the ML family. It combines functional, imperative, and object-oriented programming with a powerful static type system featuring type inference, algebraic data types, and pattern matching. OCaml is known for producing fast, safe code while letting programmers omit most type annotations thanks to inference.
On CompileBytes, OCaml is compiled with the toolchain reported as version 4.12.0. The language is widely used in compilers, theorem provers, financial systems, and static analysis tools, and it influenced languages like F# and Rust. OCaml offers both a native-code compiler and a bytecode compiler, immutable data by default, and a module system with functors that supports building large, well-structured programs with strong correctness guarantees.
main.ml is the entry point for each run.
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let () = print_endline "Hello, World!"let square n = n * n
let () = Printf.printf "%d\n" (square 5)let rec factorial n =
if n <= 1 then 1
else n * factorial (n - 1)
let () = Printf.printf "%d\n" (factorial 6)let rec sum lst =
match lst with
| [] -> 0
| x :: rest -> x + sum rest
let () = Printf.printf "%d\n" (sum [1; 2; 3; 4; 5])let nums = [1; 2; 3; 4; 5]
let () =
let squares = List.map (fun x -> x * x) nums in
List.iter (fun x -> Printf.printf "%d " x) squares;
print_newline ()type shape =
| Circle of float
| Square of float
let area s =
match s with
| Circle r -> 3.14159 *. r *. r
| Square s -> s *. s
let () = Printf.printf "%.2f\n" (area (Circle 2.0))type person = { name : string; age : int }
let () =
let p = { name = "Ada"; age = 36 } in
Printf.printf "%s is %d\n" p.name p.agelet safe_div a b =
if b = 0 then None
else Some (a / b)
let () =
match safe_div 10 2 with
| Some r -> Printf.printf "%d\n" r
| None -> print_endline "division by zero"let nums = [1; 2; 3; 4; 5]
let () =
let total = List.fold_left (+) 0 nums in
Printf.printf "Sum: %d\n" totalThe editor uses Monaco, the engine behind VS Code, with language-aware editing tools and familiar keyboard controls.
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OCaml is one of 46 single-file compiler scratchpads. Each run submits only main.ml; local sibling-file imports are not enabled.
Linked-project languages (23): Node.js, TypeScript, Deno, Python, C, Go, Dart, Swift, Rust, Ruby, PHP, Java, Kotlin, C++, C#, Nim, Crystal, Haxe, Zig, Scala, D, Bun, Objective-C.
Single-file scratchpads (46): Matplotlib, NumPy, pandas, Haskell, Clojure, Perl, Lua, Tcl, jq, Raku, Elixir, Bash, Zsh, Nushell, R, Assembly (NASM), Julia, Octave, Groovy, PowerShell, Visual Basic .NET, Odin, Pascal, Lisp, Erlang, CoffeeScript, COBOL, BASIC, V, Racket, OCaml, Prolog, AWK, Emacs Lisp, Emojicode, Forth, F#, Fortran, Assembly (NASM64), Solidity, Mojo, Ada, WASM (WAT), Gleam, Shell Script (sh), Scheme.
Download file exports the active OCaml source file.