Consider one particular case, where we need to read in a gig of data (made of many records), filter out some records, compute some stream of transformed version

Consider one particular case, where we need to read in a gig of data (made of many records), filter out some records, compute some stream of transformed versions of those records, and then write out the rolling average. This actually sounds pretty nice to write as a shell pipeline (and that's a really good way to do it), but really, it's likely that you'd end up writing some code like main() { q = queue(5); avg = 0; while(!eof) { r, eof = get_record(); t = transform(r); if(q.size() >= 5){ avg -= q.pop(); } avg += t; q.push(t); print avg/q.size(); } } or something, but it'd actually be annoying to extract out the logic for handling the rolling average and split it out from the looping code, at least if you want to maintain constant memory use, and if you had to do something similar in a few places, you'd end up duplicating code. I claim that it's possible to factor that code nicely out in Haskell, and still get the compiler to generate the same machine code as the C loop. This doesn't particularly use first class functions, and more relies on the combo of sufficiently smart compiler and sufficiently strong guarantees about what code will do. I also take slight offense at calling C-style languages "plain old algebraic style", since it'd be really strange in algebra to say both x=5 and x=6. I would not hesitate to call FP languages where you can substitute equals for equals and such the algebraic languages.