I listed a number of classic papers on functional languages. I read these papers whenever I have spare time to refresh my mind.
 Can Programming Be Liberated from the von Neumann Style? A Functional Style and Its Algebra of Programs
 Why Functional Programming Matters, John Hughes, The University, Glasgow
 A tutorial on the universality and expressiveness of fold, GRAHAM HUTTON, University of Nottingham, Nottingham, UK
 Monads for functional programming, Philip Wadler, University of Glasgow
 Theorems for free, Philip Wadler, University of Glasgow
I will keep updating the list of papers here. If you think I missed an important paper, please let me know.