Data.Ord.Down does roughly the same thing as your tiebreaker, I think.
(Different semantics, but sits in the same place.) Note that it has no need
to be a semigroup on its own!
On Fri, Jan 4, 2019, 7:41 AM Carter Schonwald Does the inclusion of semi groups in base give another option? ? There’s
perfectly nice left and right biased min and max semigroups. Though I think
we only provide one flavor each for min and max. Either it is useful to document the behavior as an artifact of current
implementation but not commit to the exact same semantic in future versions
so as not to preclude future innovations ? One fuzzy thought: it almost seems like there’s two semigroup structures
in play here: the aggregation / aka min or max in this case, plus
implicitly a second structure that provides the tie breaking structure in
the case of equality , which is usually a left or right bias, but could be
some other mechanism. Is there a useful notion of a semigroup transformer
or the like? On Thu, Jan 3, 2019 at 3:50 PM Ryan Reich I think this is the right way to go: undefined when the maximum is
duplicated. It is not implausible, for instance, that someone's mental
model or even an alternate implementation of this function would, say, use
the quicksort-like binary search for the maximum, and that really could
give any of the options because quicksort is not stable. There is no right answer to this question and therefore no answer should
be demanded unless there is a compelling reason of efficiency. Definitely document this, though. On Fri, Dec 28, 2018, 07:27 Eric Mertens Hello, My opinion on this issue is that code should not be relying on the
ordering of the choice made by maximumBy or minimumBy. If we changed something I’d prefer to document that it is undefined what
element is chosen when two are considered equal by the comparison function. Code that relies on a particular earlier or later bias should use a
function that makes it clear in the name that that’s what it’s doing.
Readers should not be required to memorize the behavior of minimumBy or
maximumBy in this regard to understand the code they are reading. Best regards,
Eric On Dec 28, 2018, at 7:18 AM, Johannes Waldmann <
johannes.waldmann@htwk-leipzig.de> wrote: Dear all, this was brought up on the GHC tracker (not by me) https://ghc.haskell.org/trac/ghc/ticket/15921 and it was suggested for discussion here. my summary: Data.List.maximumBy is right-biased,
minimumBy is left-biased, and none of this is documented. - J.W. _______________________________________________
Libraries mailing list
Libraries@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries _______________________________________________
Libraries mailing list
Libraries@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries _______________________________________________
Libraries mailing list
Libraries@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries _______________________________________________
Libraries mailing list
Libraries@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries