[Haskell-cafe] [m..n] question

wren ng thornton wren at freegeek.org
Sun Sep 21 23:17:05 EDT 2008

ajb at spamcop.net wrote:
> Having said that, I don't know of a good reason why [5,5..5] is an
> infinte list of 5's.

I'm sure you know *why* it's an infinite list[1], but as for why that's 
useful I can't say. It has the feel of a bug in implementation, though 
it is ...consistent.

As for the OP, like Python, Perl also takes [m..n] to be [] when n < m. 
They may not be as principled as Haskell or Erlang, but it does seem to 
be the consensus view.

[1] Because the "5,5.." yields an (unfoldr (Just . (\x -> (x,x)) . (+0)) 
5) stream but the "..5" only causes termination just as soon as the 
stream is surpassing 5, which it never will.

Live well,

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