F# · version 10

Run F# 10 online

F# 10 — run it in a Firecracker microVM on ls-judge. Real toolchain, no wrapper.

Starter code

What you get in F# 10

Clicking "Run now" opens the playground with this exact code and a matching test case — passes on first Run.

f#
F# 10
[<EntryPoint>]
let main _ =
    let n = System.Console.ReadLine().Trim() |> int
    printfn "%d" (n * 2)
    0
stdin →21
expected →42
How it runs

How ls-judge runs F# 10

Every submission is compiled and executed inside its own Firecracker microVM — the same isolation primitive AWS Lambda uses. No shared container, no shared kernel with other users' code. The F# 10toolchain shipped with the microVM is the real thing (not a browser-side emulation): syscalls behave the way they do in production, and the compile / runtime behaviour matches what you would see on your own machine with that version installed.

Feed stdin from the Tests panel, watch verdicts stream per test case over a WebSocket. Free to use, no sign-up, works from any browser.

Other F# versions
F# 9F# 8all F# →