Thanks for the explanation. Popular "modern" languages like Javascript, Ruby or Python already have many of the "FP" features mentioned in the OP and comments:

Thanks for the explanation. Popular "modern" languages like Javascript, Ruby or Python already have many of the "FP" features mentioned in the OP and comments: first class functions (though not so simple Ruby) and high level data processing functions (e.g. map, filter, select). As best I can tell the big new benefit of FP is the potential, generally not currently realized, for automatic parallelization. The cost is having to think in a new way that is, at least initially, somewhat confusing. Alternatively non-FP languages could simply import ideas from FP and gain the benefits in an evolutionary way. For example if Mads wanted to he could rewrite the Ruby interpreter to have map, filter and many other methods automatically use multiple cores. Eventually programmers using the new multi-core version would learn which structures were, such as map, or weren't, suc as for loops, going to be parallelized. There would be many language specific details to work out. For example determining if there are truly no side effects in a particular situation. This is not always so simple in non-FP languages but still not as complex as analyzing every possible for..end loop. As 4, 8, 16, 32 and more core processors become more and more common the pressure to either change to FP languages, incorporate FP feature in non-FP languages or find some other parallelization methodology (?) will become irresistible.