module man_or_boy
 
implicit none
 
contains
 
  recursive integer function A(k,x1,x2,x3,x4,x5) result(res)
    integer, intent(in) :: k
    interface
      recursive integer function x1()
      end function
      recursive integer function x2()
      end function
      recursive integer function x3()
      end function
      recursive integer function x4()
      end function
      recursive integer function x5()
      end function
    end interface
    integer :: m
    if ( k <= 0 ) then
      res = x4()+x5()
    else
      m = k
      res = B()
    end if
 
  contains
 
    recursive integer function B() result(res)    
      m = m-1
      res = A(m,B,x1,x2,x3,x4)
    end function B
 
  end function A
 
 
  recursive integer function one() result(res)
    res = 1
  end function
 
  recursive integer function minus_one() result(res)
    res = -1
  end function
 
  recursive integer function zero() result(res)
    res = 0
  end function
 
end module man_or_boy
 
program test
  use man_or_boy
  write (*,*) A(10,one,minus_one,minus_one,one,zero)
end program test