title: Get List of Files in Sub Directories for FAKE
body: <p>I'm trying to use FAKE to build F# files that are located in several sub directories. The <a href="http://fsharp.github.io/FAKE/apidocs/fake-filesystemhelper.html" rel="noreferrer">filesInDirMatching</a> is from FAKE.</p>
  
  <pre><code>#r @"packages/FAKE/tools/FakeLib.dll"
  open System.IO
  open Fake
  open Fake.FileSystemHelper
  open Fake.FscHelper
  
  let allDirs = DirectoryInfo(__SOURCE_DIRECTORY__).GetDirectories "*"
  let all = allDirs |&gt; Array.map(fun d -&gt; filesInDirMatching "Example.fs" d)
  </code></pre>
  
  <p>This all kind of works except that, in the last line, it's creating a 2-dimensional array (since filesInDirMatching creates a new FileDirectory array, I'm guessing). Is it possible to reduce the 2-dimensional array into a one-dimensional array? Or is there a better way of doing this?</p>