[emmanueloga_]

A common recipe people quote for good software is "a) first make it work, b) then make it fast".

Haskell is very good at a), and not bad at all at b). With the help of the profiler it shouldn't be that hard to determine a program's bottlenecks/leaks and fix them, as with any other language.

BTW, since you mention http, I have this reading on my back burner [1] but from skimming it found that for certain payloads a haskell http server may perform better than nginx (1.4, circa 2013?), which is an impressive feat.

1: http://aosabook.org/en/posa/warp.html