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John Cowan  
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 More options Jan 20 2008, 3:33 pm
From: "John Cowan" <johnwco...@gmail.com>
Date: Sun, 20 Jan 2008 15:33:38 -0500
Local: Sun, Jan 20 2008 3:33 pm
Subject: Re: keyword parameters?
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On Jan 20, 2008 1:59 PM, Mark H. <mark.hoem...@gmail.com> wrote:

> On Jan 17, 7:40am, Rich Hickey <richhic...@gmail.com> wrote:
> > I've read Okasaki.

[snip]

> That's actually an interesting question -- how much optimization do
> typical SML/Haskell/Erlang compilers do on pattern matching?  But
> somehow I suspect that they won't get very far with the kind of
> matching code that does things like red-black trees.

Speaking of Okasaki and red-black trees, I just read his little paper
on them, and it's just amazing how he manages to reduce the normal
four rotations to a single transformation to be done if a newly
inserted node (colored red by default) has a red parent:

"Take the red child, the red parent, and the (black) grandparent and
locally balance these three nodes by making the smallest and largest
nodes children of the middle node. Then color the middle node red and
the other two nodes black. The middle node is linked back into the
tree in place of the former black grandparent."

If there is still a node with a red parent, then repeat the
transformation, and if you reach the root, color the root black
unconditionally (red nodes have to have black parents, so the root
can't be red).

See http://www.eecs.usma.edu/webs/people/okasaki/sigcse05.pdf , a
perfect gem which gives two pages to R/B trees and two to maxiphobic
heaps, an easier-to-understand alternative to leftist heaps.

--
GMail doesn't have rotating .sigs, but you can see mine at
http://www.ccil.org/~cowan/signatures


 
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