-1 on retaining this. Part of the implied contract of Data.List is that all
functions be as lazy as possible. Besides, a change that potentially breaks
old programs that use foldl' seems like a bad idea unless there's a really
strong reason for it. I don't have an existing example offhand, but it
seems at least possible that something like
last = foldl' (flip const) undefined
is out there...
On Fri, Jun 10, 2016 at 5:29 AM David Feuer
The semantics of foldl' for lists were changed between base 4.7 and base 4.8. Specifically, foldl' became strict in the initial value of its accumulator. I opened http://ghc.haskell.org/trac/ghc/ticket/12173 to report this. The change was entirely accidental, according to Joachim Breitner. However, Duncan Coutts indicated he is pleased with the change. I don't personally have a dog in this race, but I feel very strongly about three things:
1. The strictness should be fully documented, both in Haddock and the next Haskell Report (the Haskell 2010 Report does not go into sufficient detail to support either choice).
2. There should be *one* meaning of foldl' in base. Thus the default Foldable instance should match the ones for lists and arrays.
3. The containers package should be consistent with base in this regard. _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries