I think it is rather obvious that one is most productive in the language he or she knows best. So the question rather is, for language one knows well, what is t

I think it is rather obvious that one is most productive in the language he or she knows best. So the question rather is, for language one knows well, what is the more productive? Also, this is a very abstract question. In reality, availability of libraries and development tools can tweak the balance for a certain task a lot. For example, I can be very productive with tcl/tk, because the whole package lets me do certain tasks very efficiently, but I wouldn't call the language "tcl" expecially productive. But overall, I think Lisp is an extremely productive language. In the last decades, a lot of modern languages have implemented a lot of Lisp features, so getting closer in productivity, without quite reaching it. Consequentely, the productivity factor depends on which langauge you compare Lisp with. But compared to languages like C++, the productivity gain is really large. For me, beyond the overall language qualities, there are two especial productivity boosters in Lisp: the ability for incremental and interactive development and to create domain specific abstractions. There are many dynamic languages, but so far I haven't seen one which as easily allows you to do interactive development. That is the ability to update single functions while your application is running. That speeds up the cycle of changing the code and testing it by orders of magnitude.