Functional Programming—–what is it good for? Programming is the writing of programs. Judging from the papers and most books on functional programming, functional programming excels as a tool for writing short programs—–up to a hundred lines maybe. We also know that there are large functional code bases at large companies, and folklore has it that this also works quite well. Yet there is precious little literature on how to go from a hundred lines to a million lines of functional code. This hinders the adoption of functional program by newcomers, who ask questions like: Successful practitioners rely on folklore and experience for the answers to these questions, but precious little is written down in findable places and accessible formats. This paper is a call to action: The functional programming community needs to do a better job at outreach—find the gaps in our published knowledge, write down what is undocumented and talk to other communities who deal with large-scale software development.