# [Haskell-cafe] Haskell Zippers on Wikibooks: teasing! :)

Peter Verswyvelen bugfact at gmail.com
Wed Jul 15 11:53:52 EDT 2009

After my colleague explained me about zippers and how one could derive the
datatype using differential rules, I had to read about it.

So I started reading
http://en.wikibooks.org/wiki/Haskell/Zippers#Mechanical_Differentiation

This page contains the sentence:  *"For a systematic construction, we need
to calculate with types. The basics of structural calculations with types
are outlined in a separate chapter **Generic
Programming*<http://en.wikibooks.org/w/index.php?title=Haskell/Generic_Programming&action=edit&redlink=1>
* and we will heavily rely on this material"*
*
*
However, the generic programming link does not exist yet :-)

So although I now have a rough idea about it, I don't understand the details
yet, e.g. notation like

[image: \mathit{Node}\,A = \mu X.\,\mathit{NodeF}_A\,X]

doesn't make much sense to me yet, although I suspect I can read the mu as a
lambda on types?

Thanks,
Peter
*
*
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