Some background for the uninitiated, this is Lambda Man, or Philip Wadler. One of the core contributors to Haskell. He also introduced monads to Haskell, which has had a huge impact on functional programming in general (https://ncatlab.org/nlab/files/WadlerMonads.pdf). His home page has so many functional programming treasures: http://homepages.inf.ed.ac.uk/wadler/. His most recent book is "Programming Language Foundations in Agda", which is available for free: https://plfa.github.io/. I have no affiliation, just a fan.
