[Haskell-cafe] Interesting effect of upgrading GHC

Neil Mitchell ndmitchell at gmail.com
Mon Nov 12 15:48:56 EST 2007


> I just removed GHC 6.6.1 and installed 6.8.1, and I noticed something
> rather unexpected. I recompiled an existing program (with -O2), and
> instead of taking 30 seconds to compile, it took roughly 2 seconds.

In previous releases, certain constructs took O(n^2) time to compile.
One that was a particular issue for me was:

do return ()
     return ()
     return ()

Once you got to 100 return ()'s in a row GHC was totally useless,
while Yhc and Hugs both had no problems. This particular problem was
fixed, and I think a few others were as well - if one of those had
tripped you up that may explain the speedup.



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