It really depends on the type of risk. My assertion is that most startups have most of their risk in the market bucket rather than the technical bucket. If you can move some risk from the market bucket to the technical bucket, and compensate by using Haskell, that may be a good tradeoff.
in the case where your risk is in the market bucket, you may go through many just-barely-working prototypes before you hit product-market fit. at that point, if you've saved some time using Ruby (say) because of external factors like Heroku, Bundler, and ruby-friendly services, you're ahead of the game, even if your tenth prototype sucks and needs to be rewritten.
in the case where your risk is in the market bucket, you may go through many just-barely-working prototypes before you hit product-market fit. at that point, if you've saved some time using Ruby (say) because of external factors like Heroku, Bundler, and ruby-friendly services, you're ahead of the game, even if your tenth prototype sucks and needs to be rewritten.