I'm curious if you get the same performance difference importing GHC.List instead of Data.Char? I chased some dependencies, and Data.Char imports GHC.Arr, which in turn imports GHC.List, which provides a bunch of fusion rules pragmas
Sterling Clover
Yes - the same difference: 1.33 minutes vs. 2.30 now. I was near at reporting this as a bug, but rejected that idea. What does "bug" mean here ? I am really a rookie at Haskell - this working on primefactors is nothing but an excercise (however i casually try number theoretic problems and often missed a program like this). But - as it appears to me - the dramatic advance in speed ghc has made recently is to a great extent due to improved types and their methods. What i see at haskell.org/ghc/docs/latest/html/libraries looks like huge road works to me. And then it is not a "bug", if elder libraries as the Prelude perhaps are not completely up to date. Another problem is, that my program was not completely correct. But it didn't crash and got most numbers decomposed correct. But the strange behavior disappeared with a correct version. Perhaps the Prelude will get better now. Cheers, Joost