- Tuple (col, color) with column and color index for the current node

      - A list of tuples indicating the edges between the current node and its

        parents.

    """

    seen = []

    colors = {}

    newcolor = 1

    getconf = lambda rev: {}

    for (cur, type, data, parents) in dag:

        # Compute seen and next

        if cur not in seen:

            seen.append(cur)  # new head

            colors[cur] = newcolor

            newcolor += 1

        col = seen.index(cur)

        color = colors.pop(cur)

        next = seen[:]

        # Add parents to next

        addparents = [p for p in parents if p not in next]

        next[col:col + 1] = addparents

        # Set colors for the parents

        for i, p in enumerate(addparents):

            if not i:

                colors[p] = color

            else:

                colors[p] = newcolor

                newcolor += 1

        # Add edges to the graph

        edges = []

        for ecol, eid in enumerate(seen):

            if eid in next:

                bconf = getconf(eid)

                edges.append((

                    ecol, next.index(eid), colors[eid],

                    bconf.get('width', -1),

                    bconf.get('color', '')))

            elif eid == cur:

                for p in parents:

                    bconf = getconf(p)

                    edges.append((

                        bconf.get('width', -1),

                        bconf.get('color', '')))

        # Yield and move on

        yield (cur, type, data, (col, color), edges)

        seen = next