The reason I don't really want to work with languages that are not statically typed is that my (very well paid) projects almost always start on day #1 with 'here is 300-500k lines of code and a list of crap it doesn't do but should, cheers!'. With C#/Java, but definitely with F#/Haskell, this is not a big issue. With Python, JS, Ruby, indeed, I need callstacking like tools or it will take a lot longer. Usually the original devs already left (often they were never employees, but contractors from big firms who peddled juniors for senior prices).