[ben509]

All DI libraries can be ripped out and replaced with a bog standard main method, and it doesn't even require much skill. Most of what it's doing for you is stuff like "foo = new Foo(); bar = new Bar(foo, 33);" So there's no strict "need" for them, they help with (and enable) complexity.

What F#'s aversion to cyclic dependencies does forces you to break cycles of types referring to types referring to types. The way you do that is by writing a generic function that avoids referring to a concrete type. Because it's generic, such a function is inherently easier to test by means of a simple stub value.