F# defining/using a type/module in another file in the same project

I had the same problems, and you are right, the order of the files is taken in account by the compiler. Instead of the Remove and Add pattern, you can use the Move Up / Move Down items in the context menu associated to the .fs files. (Alt-Up and Alt-Down are the shortcut keys in most of the standard key-bindings)

What order are the files in the .fsproj file? Stack.fs needs to come before Program.fs for Program.fs to be able to 'see' it.

See also the start of

http://lorgonblog.spaces.live.com/blog/cns!701679AD17B6D310!444.entry

and the end of

http://lorgonblog.spaces.live.com/blog/cns!701679AD17B6D310!347.entry

All of the above are correct, but how to do this in VS2013 is another question. I had to edit my .fsproj file manually, and set the files in exact order within an ItemGroup node. In this case it would look like this:

<ItemGroup>
    <Compile Include="Stack.fs" />
    <Compile Include="Program.fs" />
    <None Include="App.config" />
</ItemGroup>

I had the same issue and it was indeed the ordering of the files. However, the links above didn't describe how to fix it in Visual Studio 2008 F# 1.9.4.19.

If you open a module, make sure your source file comes after the dependency in the solution explorer. Just right click your source and select Remove. Then re-add it. This will make it appear at the bottom of the list. Hopefully you don't have circular dependencies.