> Be prepared to be much less productive in Haskell; you can't just get into it and start writing code. Everything must be well thought out before you start to write a line

Something about Haskell makes people enforce this upon themselves. You most certainly can hack things together quickly with Haskell after learning as much as you would in an imperative langauge so long as you can accept it will be ugly and unmaintainable, but that's not much different than other languages.