Better than a REPL - Reload!

reload.fs

// 1. Watch source files for changes.
// 2. When a change is detected, recompile.
// 3. When assembly changes are detected, reload. (katana?)
// 4. Allow editing of files in a gui (dropbox integration?)

#if INTERACTIVE
#r @"..\packages\FAKE.1.64.6\tools\FakeLib.dll"
#endif

open System
open System.IO
open Fake

let (+/) path1 path2 = Path.Combine(path1, path2)

type Agent<'a> = MailboxProcessor<'a>

let runner = Agent.Start(fun inbox -> async {
    while true do
        let! path, target = inbox.Receive()
        match Shell.Exec(path+/target, dir = path) with
        | 0 -> ()
        | code -> printfn "The program compiled but failed to run with exit code %d" code
})

let compiler = Agent.Start(fun inbox -> async {
    let fsc = @"C:\Program Files (x86)\Microsoft F#\v4.0\Fsc.exe"
    while true do
        let! path, files, target = inbox.Receive()
        match Shell.Exec(fsc, files + " --out:" + target + " --target:exe --standalone --staticlink:mscorlib --tailcalls+ --optimize+ --nologo --sig:test.fsi", path) with
        | 0 -> runner.Post (path, target)
        | code -> printfn "Compilation failed with exit code %d" code
})

let main args =
    // TODO: Move to a command line arg.
    let path = @"G:\OSS\test"
    let files = "test.fs"
    let target = "test.exe"

    if not <| Directory.Exists path then Directory.CreateDirectory path |> ignore
    let watcher = new FileSystemWatcher(path, "*.fs", EnableRaisingEvents = true, NotifyFilter = NotifyFilters.LastWrite)

    let handle (args: FileSystemEventArgs) =
        tracefn "%s\%s changed (%A)" args.FullPath args.Name args.ChangeType
        compiler.Post (path, files, target)

    // Could benefit from Distinct and Throttle from System.Reactive
    let events =
        watcher.Created
        |> Observable.merge watcher.Changed
        |> Observable.merge watcher.Deleted

    let subscriptions = [|
        yield events |> Observable.subscribe handle
        yield watcher.Renamed |> Observable.subscribe handle
    |]

    Console.WriteLine("Press any key to stop watching.")
    Console.ReadKey() |> ignore
    subscriptions |> Array.iter (fun subscription -> subscription.Dispose())

#if INTERACTIVE
main [||]
#else
[<EntryPoint>]
let entryPoint args =
    main args
    0
#endif

Better yet, just use the FscHelper built into FAKE. :)

Looks like FAKE has completely replaced the need for this thing: File Watcher