What's the reason of marking a recursive function as rec in F#?

Question

I am not sure if this is a stupid question but I was going through the tutorial that comes with VS 2010 and there is a function like this:

let rec factorial          


        

Answer 1

According to the MSDN, it's only a syntatic necessity:

Recursive functions, functions that call themselves, are identified explicitly in the F# language. This makes the identifer that is being defined available in the scope of the function.

http://msdn.microsoft.com/en-us/library/dd233232.aspx