[GHC] #7436: Derived Foldable and Traversable instances become extremely inefficient due to eta-expansion

[Simon Peyton-Jones]

It was ready to merge 3 months ago... but perhaps just got lost in the press of events.   liyang said then " Since this issue affects a large number of users and doesn't seem too contentious, could this fix be included in 7.6.2?"   

But we are where we are.  I honestly don't know if it's worth the risk, though it seems very slight, and certainly only affects 'deriving Foldable/Traversable".

Simon

|  -----Original Message-----
|  From: Ian Lynagh [mailto:ian at well-typed.com]
|  Sent: 17 April 2013 14:54
|  To: Simon Peyton-Jones; ghc-devs at haskell.org
|  Subject: Re: [GHC] #7436: Derived Foldable and Traversable instances become
|  extremely inefficient due to eta-expansion
|  
|  
|  Hi Simon,
|  
|  On Tue, Apr 16, 2013 at 03:55:16PM -0000, GHC wrote:
|  > #7436: Derived Foldable and Traversable instances become extremely
|  inefficient due
|  > to eta-expansion
|  >
|  > Comment(by simonpj):
|  >
|  >  This one is fixed, just awaiting merging into 7.6.3
|  
|  My suggestion was that we only fix #7748 in 7.6.3, as that seems to be a
|  show-stopper. There are several other fixes that we would ordinarily
|  merge into 7.6.3, but every change has a risk of causing a regression
|  (after all, 7.6.2 made #7748 worse), and we want to get 7.6.3 out as
|  quickly as possible (so as not to hold up the HP release) so we don't
|  have the luxury of being able to have a long testing/RC phase.
|  
|  But if you think it's important enough, and the fix safe enough, please
|  let me know and I'll merge it.
|  
|  
|  Thanks
|  Ian