Journal of Functional Programming

Table of Contents - 2009 - Volume 19, Issue 05  

Functional Pearls

The Bird Tree

RALF HINZEa1

a1 Computing Laboratory, University of Oxford, Wolfson Building, Parks Road, Oxford, OX1 3QD, England (e-mail: ralf.hinze@comlab.ox.ac.uk)

Sadly, Richard Bird is stepping down as the editor of the ‘Functional Pearls’ column. As a farewell present, I would like to dedicate a tree to him. A woody plant is appropriate for at least two reasons: Richard has been preoccupied with trees in many of his pearls, and where else would you find a bird's nest? Actually, there is a lot of room for nests, as the tree is infinite. Figure 1 displays the first five levels. The Bird tree, whose nodes are labelled with rational numbers, enjoys several remarkable properties.