* Jan-Willem Maessen <jmaes...@alum.mit.edu> [2011-10-08 12:32:18-0400] > It seems to be a common misconception that eta-abstracting your > functions in this way will speed up or otherwise improve your code. > > Simon PJ has already provided a good explanation of why GHC eta > expands. Let me take another tack and describe why the code you wrote > without eta expansion probably doesn't provide you with any actual > benefit. Roughly speaking, you're creating a chain of closures whose > contents exactly describe the contents of your list (ie you've created > something that's isomorphic to your original list structure), and so > you should expect no benefit at all.
Thanks for the analysis. I used myFoldl as a minimal example to ask the question. Here's an example of real code where this does make a difference: https://github.com/feuerbach/regex-applicative/tree/03ca9c852f06bf9a9d51505640b8b72f07291c7d You can run the benchmark (on a POSIX system) using cd benchmark && ./runbenchmark.sh With the current version I get 2.62 seconds. If I remove -fno-do-lambda-eta-expansion for Text/Regex/Applicative/Compile.hs, the benchmark takes 2.74 seconds. What's even more interesting (and puzzling!), if remove -fno-do-lambda-eta-expansion for Text/Regex/Applicative/Types.hs, the benchmark takes 2.82 seconds. I appreciate any thoughts about this. -- Roman I. Cheplyaka :: http://ro-che.info/ _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
