[Haskell-cafe] parsec2 vs. parsec3... again

Bryan O'Sullivan bos at serpentine.com
Sat Jan 15 03:19:48 CET 2011

On Fri, Jan 14, 2011 at 5:54 PM, Evan Laforge <qdunkan at gmail.com> wrote:


Then I found out that
> compiling with profiling enabled makes attoparsec slow and parsec
> fast.

Yes, the SCC annotations added by GHC have a fairly high cost.

I think my short term solution is going to be remove -auto-all from
> attoparsec's cabal---I'm not profiling attoparsec and so I don't want
> my entire profile output to be internal attoparsec functions.  But
> presumably the flag was added there for a reason, so maybe there are
> people who really want that.

Yes - me :-)

I typically turn on profiling for most of my libraries while I think of them
as "under development", a period of indefinite length that comes to an end
when I deem the performance good enough. None of my libraries has actually
hit that point yet :-)

This isn't completely without basis. For instance, I made some big speed
improvements to attoparsec's very performance-sensitive takeWhile function
just the other day, thanks to -auto-all.

I might, though, see if there's a way I could enable that flag only for
myself (in a way that I wouldn't routinely forget).
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