Ruby version of Dendrogram drawing (Python recipe) from http://code.activestate.com/recipes/139422-dendrogram-drawing/

pdg.rb

def printDendrogram(t, sep=3)
 
    isPair = lambda do |t|
        return t.class == Array && t.length == 2
    end
    
    maxHeight = lambda do |t|
        if isPair.call(t)
            h = [maxHeight.call(t[0]), maxHeight.call(t[1])].max
        else
            h = t.to_s.length
        end
        return h + sep
    end

    activeLevels = {}
    
    traverse = lambda do |t, h, isFirst|
        if isPair.call(t)
            traverse.call(t[0], h-sep, 1)
            s = [" "]*(h-sep)
            s << "|"
        else
            s = t.chars
            s << (" ")
        end
        
        while s.length < h
            s << ("-")
        end
        
        if (isFirst >= 0)
            s << ("+")
            if isFirst > 0
                activeLevels[h] = 1
            else
                activeLevels.delete(h)
            end
        end
        
        a = activeLevels.keys
        a.sort!
        a.each do |l|
            if s.length < l
                while s.length < l
                    s << (" ")
                end
                s << ("|")
            end    

        end
        puts s.join("")
        
        if isPair.call(t)
            traverse.call(t[1], h-sep, 0)
        end
    end
    traverse.call(t, maxHeight.call(t), -1)
end

printDendrogram [ [ ['a' , 'b'] , 'c' ], [ [ 'd' , 'e' ], [ 'f', 'g' ] ] ]