On 2011 Mar 4, at 01:39, Marc Weber wrote:
Excerpts from Jacek Generowicz's message of Fri Mar 04 00:18:07
+0000 2011:
Prelude Data.List> groupBy (<) [1,2,3,2]
[[1,2,3,2]]
This is wired. However if you think about the algorithm always using
the
first element of a list and comparing it against the next elements you
get
1 < 2 ok, same group
1 < 3 dito
1 < 2 dito
Thus you get [[1,2,3,2]]
OK, that works, but it seems like a strange choice ...
On 2011 Mar 4, at 01:47, Daniel Fischer wrote:
On Friday 04 March 2011 01:18:07, Jacek Generowicz wrote:
What am I missing?
That groupBy expects an equivalence relation
... Bingo! Now it makes sense.
(iirc, that was documented some time, seems to be gone, there's only
a hint left at the docs for group
"equality test").
Hrrrrmph. In my opinion, explicitly including the words "equivalence
relation" would immensely improve the documentation.
Thank you for you clarifications, gentlemen.
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