zippers presentation

Functional programming !Zippers!

–Gérard Huet!

“Zipper is a functional cursor into a data structure”

Often used where there is some concept of 'focus' or of moving around in some set of

data.!

Includes and generalizes the gap buffer technique

Data structure? Can be adapted to Lists, trees, and other recursively

defined data structures!

Trees, Paths and Locations

Data structure!

The current element / Zipper cursor!

The current subtree / subset!

Scalaz

NonEmptyList!

(2 3 5 7 11)

Sample list…

2 (3 5 7 11)

Traversing…

Zipper!

(2) 3 (5 7 11)

Traversing…

Zipper!

(3 2) 5 (7 11)

Traversing.…

Zipper!

Reverse???!

(3 2) 5 (7 11)

Traversing.…

Zipper!

Reverse???! Parent retrieve = 0(1)!

(5 3 2) 7 (11)

Traversing..…

Zipper!

(7 5 3 2) 11

Traversing……

Zipper!

(11 7 5 3 2)

Traversed.

Changes, Insertions and Deletions?

“Immutability”?!

“Laziness”?!

How to add an item?!How to delete an item?!

Depends on the data structure, but prefer lazy evaluations

http://scalaz.googlecode.com/svn/continuous/latest/browse.sxr/scalaz/TreeLoc.scala.html http://scalaz.googlecode.com/svn/continuous/latest/browse.sxr/scalaz/Zipper.scala.html!

Implementation