A simple F# program to concat js given an input and output file (provided sprockets exists on the system)

watcher.fs

open System;
open System.IO;
open Microsoft.FSharp.Collections;
open System.Diagnostics;

let projectDirectory = Directory.GetCurrentDirectory()
let args = Environment.GetCommandLineArgs();

let watcher = new FileSystemWatcher(projectDirectory)

let exec procName procArgs = 
    let procInfo = new ProcessStartInfo(procName, procArgs)
    procInfo.CreateNoWindow <- true
    procInfo.WindowStyle <- ProcessWindowStyle.Hidden
    Process.Start(procInfo)

let path file = projectDirectory + (string)Path.DirectorySeparatorChar + file

let concat (fargs:FileSystemEventArgs) = 
    if fargs.FullPath <> path args.[1] && fargs.FullPath <> path args.[2] then 
        exec "sprocketize" ("-I " + projectDirectory + " " + path args.[1] + " > " + path args.[2]) |> ignore

watcher.Changed.Add(concat)
watcher.Filter <- "*.js"

//read from console
let readlines = Seq.initInfinite (fun _ -> Console.ReadLine())
let readline line = if line = "q" then Some(line) else None

//run it
watcher.EnableRaisingEvents <- true;
Console.WriteLine(@"Press 'q' to quit listening")

Seq.pick readline readlines |> ignore