This code was published on
http://fhtr.blogspot.com/2008/12/drawing-tree-with-haskell-and-cairo.html

You can compile it by doing
ghc --make tree.hs canvas.hs -o tree

make sure to have haskell-cairo package and haskel-gtk bindings installed on your system

for ubuntu 10.4 those are libghc6-cairo-dev and libghc6-gtk-dev