Welcome to HCODX Online Compiler
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Compile and run F# code online instantly with HCODX. Our free cloud-based F# compiler supports real-time execution, standard input, syntax highlighting, and code download. No installation or configuration required. Start coding in F# now.
Run F# instantly without installing any IDEs or configuring environments. Our cloud-based F# handles libraries, runtimes, and dependencies automatically so you can focus on writing code.
Whether you are studying algorithms in F#, practicing data structures in F#, or exploring functional programming, our tool provides real-time stdout/stderr feedback with interactive standard input support.
HCODX is a free online compiler and code runner: write code in your browser, execute it on a cloud sandbox, and interact with your program through a live terminal. Students use it for coursework and interview practice; developers use it to test snippets in 85+ languages without setting up a local environment.
F# is Microsoft's answer to the question 'what if ML met .NET?' Designed by Don Syme at Microsoft Research and now developed in the open, F# delivers succinct functional-first code — immutability by default, algebraic data types, pattern matching, the pipeline operator — with full access to the entire .NET ecosystem. F# 9 shipped alongside .NET 9 (November 2024) with nullable reference type interop and performance work. Production users include fintech and energy-trading firms, and features F# pioneered (records, pattern matching) have steadily migrated into C#. This variant compiles your code as a .NET program. The terminal on this page is fully interactive: Console.ReadLine waits for your real keystrokes while output streams live.
open System
printf "What's your name? "
let name = Console.ReadLine()
printfn "Hello, %s!" name
printf "Enter numbers separated by spaces: "
let numbers =
Console.ReadLine().Split(' ', StringSplitOptions.RemoveEmptyEntries)
|> Array.map float
numbers
|> Array.map (fun x -> x * x)
|> Array.sum
|> printfn "Sum of squares: %g"
let parity n = if n % 2 = 0 then "an even" else "an odd"
printfn "You entered %d values - %s count." numbers.Length (parity numbers.Length)F# appeals to two overlapping groups: .NET developers who want functional programming without leaving their platform, and functional programmers who need .NET's libraries and jobs. Practicing here covers what F# interviews and coursework emphasize — pipelines, discriminated unions, records, recursion, and Option handling — without installing the .NET SDK. It's also useful for C# developers evaluating F# for a data-processing or domain-modeling component, a common adoption path since both compile to the same IL and interoperate freely in one solution. HCODX is a free online F# editor, runner and interpreter — an IDE-grade compiler and playground to write and run code online, execute code with live output and live preview, no downloads or web server required.
Yes. The compiled program runs attached to a live terminal, so Console.ReadLine blocks until you type a line, and printf/printfn output appears as it executes. You can chain several prompts — read a name, then numbers, then options — and watch each pipeline stage respond in real time.
This variant compiles your file as a .NET program and runs the resulting binary — full compilation, matching how production F# ships. The fsi variant evaluates your code through F# Interactive's script engine instead, which skips the build step. Same language and same results for typical code; choose fsi for quicker iteration.
No — execution is a single file with no NuGet restore, so external packages aren't available. What you do get is substantial: the entire .NET base class library (System.*, collections, LINQ from F#, regex, math) plus F#'s own FSharp.Core with List, Array, Seq, Map, Option, and Result modules.
Your current code will be replaced with the default sample. This cannot be undone — download your code first if you want to keep it.
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