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1 parent 8f2e052 commit 1ac6ca030167c92eb197b0f3411732130c0a7060 Brent Yorgey committed Sep 28, 2012
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+[![Build Status](](
+Rose (n-ary) trees with both upwards- (*i.e.* cached) and
+downwards-traveling (*i.e.* accumulating) monoidal annotations. This
+is used as the core data structure underlying the
+[diagrams framework](, but
+potentially has other applications as well.
+Abstractly, a `DUALTree` is a rose (n-ary) tree with data of one type
+at leaves, data of another type at internal nodes, and two types of
+monoidal annotations, one travelling "up" the tree and
+one traveling "down".
+For a bit of background and motivation, see the paper
+[Brent Yorgey. *Monoids: Theme and Variations*.]( Haskell Symposium, 2012.
+To install,
+ cabal install dual-tree

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