On Wed, 22 Oct 2008, Brad Bowman wrote:
The "scrap your boilerplate" scheme for generics in Haskell addresses
traversals, queries, transformations, parallel zipping and the like.
I've only briefly felt like I understood it, so I was going to
revise before trying to adapt it to Perl 6. (Any lambdacamels out there that
do understand this stuff?)
There's a paper called "Scrap your boilerplate with XPath-like combinators"
<http://homepages.cwi.nl/~ralf/popl07/> which ties
nicely into this thread. It and other SYB papers provide a
useful perspective on this traversal and matching domain,
even if the Haskell details are tricky.
SYB home: http://www.cs.vu.nl/boilerplate/
Hmm. Without reading it, I came up with the following while I was
working on a tree iterator. Basically, I figured pretty much every useful
iterator can be specified as a combination of axes, and an axis can be defined
with the following four attributes:
- bearing: this is the direction within the tree, and can be any of
"self", "descendant", "sibling", "ancestor", and "attribute".
- route: this is basically the search algorithm used; currently only
depthfirst is supported, and this is (and will remain) the default.
- direction: This is which direction you're going through the search
algorithm, and can be any of "self", "following", "preceding", and
"any". The default is "any".
- depth: the maximum depth of search to use. The default is Inf
Then there are special cases. For example, "child" is:
- bearing: descendant
- depth: 1
Anyway, you get the general idea.
But my overall aim is that you should be able to iterate over a tree
in a variety of ways, and run pretty much any Perl code on it, and that
selection should work somehow.
:)
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| Name: Tim Nelson | Because the Creator is, |
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