Ray Vernagus has posted an introduction to using F# with ArcGIS through ArcObjects

One of the things I like most about F# is how it allows typed functional programming to be applied to data-rich domains such as Machine Learning, Computer Aided Design (CAD) and Geographical Information Systems (GIS). GIS is of particular interest to me as I learned a lot about this area back in my undergraduate days, and because of the ever-enduring appeal of maps and simulation. Like Kean Wamsley's F# and AutoCAD examples, it's just amazing how easy it is to get going with F# and ArcInfo.

Ray also has a few other useful posts:

Easy Testing in F#

Functional Programming Patterns

Purely Functional Data Structures: an F# Stack

Purely Functional Data Structures: An F# Binary Tree

and a useful update to a code sample in Expert F#:

Kill That Annoying Flicker