libghc-dual-tree-doc 0.2.2.1-1build1 (amd64 binary) in ubuntu hirsute

 Rose (n-ary) trees with both upwards- (i.e. cached) and downwards-traveling
 (i.e. accumulating) monoidal annotations.
 .
 Abstractly, a DUALTree is a rose (n-ary) tree with data at leaves, data at
 internal nodes, and two types of monoidal annotations, one travelling "up" the
 tree and one traveling "down".
 .
 This package provides the documentation for a library for the Haskell
 programming language.
 See http://www.haskell.org/ for more information on Haskell.