I have searched StackOverflow (and other sources) for this answer, but can't seem to find anything.

In C#, if I had a widget definition, say:

class widget
{
    public string PrettyName() { ... do stuff here }
}

and I wanted to allow for easy printing of a list of Widgets, I might do this:

namespace ExtensionMethods
{
    public static PrintAll( this IEnumerable<Widget> widgets, TextWriter writer )
    {
        foreach(var w in widgets) { writer.WriteLine( w.PrettyName() ) }
    }  
}

How would I accomplish something similar with a record type and a collection (List or Seq preferrably in F#). I'd love to have a list of Widgest and be able to call a function right on the collection that did something like this. Assume (since it's F#) that the function would not be changing the state of the collection that it's attached to, but returning some new value.