unique_recursive.jl

function unique_recursive(itr)
    T = Base._default_eltype(typeof(itr))
    out = Vector{T}()
    seen = Set{T}()
    i = start(itr)
    if done(itr, i)
        return out
    end
    x, i = next(itr, i)
    if !isleaftype(T)
        T = typeof(x)
        return unique_recursive(itr, Set{T}(), Vector{T}(), x, i)
    end
    push!(seen, x)
    push!(out, x)
    while !done(itr, i)
        x, i = next(itr, i)
        S = typeof(x)
        if !(S === T || S <: T)
            T = typejoin(S, T)
            return unique_recursive(itr, convert(Set{T}, seen), convert(Vector{T}, out), x, i)
        end
        if !in(x, seen)
            push!(seen, x)
            push!(out, x)
        end
    end
    return out
end

function unique_recursive{T}(itr, seen, out::Vector{T}, x, i)
    if !in(x, seen)
        push!(seen, x)
        push!(out, x)
    end
    while !done(itr, i)
        x, i = next(itr, i); S = typeof(x)
        if !(S === T || S <: T)
            R = typejoin(S, T)
            return unique_recursive(itr, convert(Set{R}, seen), convert(Vector{R}, out), x, i)
        end
        if !in(x, seen)
            push!(seen, x)
            push!(out, x)
        end
    end
    return out
end