example.jl

for i in Sequence([(1, 2, 3, 4, 5), (6, 5, 4, 3), (-3, -3, -3 )])
    println(i)
end

sequence.jl

immutable Sequence
    iter :: Any
end

Base.start(s :: Sequence) = (1, 1, 0)

#this is helper function, returns pair of states for iterator s1, s2, and inner_iter (inner list iterator)
function skip_to_next(iter, s1, s2)
    (inner_iter, s1_) = next(iter, s1)
    while done(inner_iter, s2)
        s1 = s1_
        if done(iter, s1)
            break
        end
        (inner_iter, s1_) = next(iter, s1)
        s2 = start(inner_iter)
    end
    (s1, s2, inner_iter)
end

function Base.done(s :: Sequence, state) 
    (s1, s2, _) = state
    if done(s.iter, s1) 
        true
    else
        (s1, s2, inner_iter) = skip_to_next(s.iter, s1, s2)
        done(inner_iter, s2)
    end
end


function Base.next(s :: Sequence, state)
    (s1, s2, l) = state
    (inner_iter, s1_) = next(s.iter, s1)
    if done(inner_iter, s2)
        (s1, s2, inner_iter) = skip_to_next(s.iter, s1, s2)
        (el, _) = next(inner_iter, s2)
        return ((el+l)/2.0, (s1, s2, el))
    end
    
    (el, s2) = next(inner_iter, s2)
    (el, (s1, s2, el))
end


Base.eltype(:: Type{Sequence}) = Int 
Base.length(s :: Sequence) = sum(map(x->length(x)+1, s.iter)) - 1