Paul Johnson wrote:
You cannot win over the entrepreneur with promises of "easier and more robust". This translates to "anyone can do it" and the valuable "trade secret" of arcane wizardry is now devalued.
I suggest reading extracts from "Beating the Averages" by Paul Graham. Then explain that Graham only wrote in Lisp because his university didn't teach Haskell.
I think a more powerful argument would be to talk about cases where Haskell is *actually being used* industrially. E.g., "these folks at Credit Suisse are using Haskell for their analytics because in their line of work, if the implementation of the code doesn't match up perfectly with the spec, their employer could lose millions of dollars, and the programmers might not notice the bug until those millions were long gone".