program dag_example

    use dag_module

    implicit none

    type(dag) :: d
    integer,dimension(:),allocatable :: order
    integer :: istat
    integer :: i

    integer,parameter :: n_nodes = 6
    character(len=*),parameter :: filetype = 'pdf'

    ! create a dag:

    call d%set_vertices(n_nodes)
    call d%set_edges(2,[1])     ! 2 depends on 1
    call d%set_edges(3,[5,1])   ! 3 depends on 5 and 1
    call d%set_edges(4,[5])     ! 4 depends on 5
    call d%set_edges(5,[2])     ! 5 depends on 2
    call d%set_edges(6,[2,4])   ! 6 depends on 2 and 4

    ! toposort:

    call d%toposort(order,istat)

    ! define some styles for the GraphViz output:

    do i = 1, n_nodes
        if (i==3 .or. i==6) then
            call d%set_vertex_info(i,attributes='shape=square,fillcolor="SlateGray1",style=filled')
        else
            call d%set_vertex_info(i,attributes='shape=circle,fillcolor="cornsilk",style=filled')
        end if
    end do

    ! generate the GraphViz output:

    call d%save_digraph('test.dot','RL',300)
    call d%destroy()
    call execute_command_line('dot -Tpdf -o test.pdf test.dot')

end program dag_example