get_entire_literal_internal Subroutine

   pure recursive subroutine get_entire_literal_internal(tree, idx, literal, res)
      use :: forgex_syntax_tree_node_m
      implicit none
      type(tree_node_t), intent(in) :: tree(:)
      integer(int32), intent(in) :: idx
      character(:), allocatable, intent(inout) :: literal
      logical, intent(inout) :: res

      type(tree_node_t) :: node
      integer :: i
      node = tree(idx)

      if (node%op == op_concat) then
         call get_entire_literal_internal(tree, node%left_i, literal, res)
         if (literal == '') return
         if (res) then
            call get_entire_literal_internal(tree, node%right_i, literal, res)
         else
            literal = ''
         end if
         if (literal == '') return

      else if (node%op == op_repeat) then
         if (node%max_repeat == node%min_repeat) then
            do i = 1, node%min_repeat
               call get_entire_literal_internal(tree, node%left_i, literal, res)
            end do
         else
            res = .false.
            literal = ''
         end if

      else if (is_literal_tree_node(node)) then

         ! This size function is safe because is_literal_function returns false
         ! if the node%c is not allocated. 
         if (size(node%c, dim=1) == 1) then

            if (node%c(1)%min == node%c(1)%max) then
               literal = literal//char_utf8(node%c(1)%min)
               res = .true.
               return
            end if
         end if
         res = .false.
         literal = ''

      else
         res = .false.
         literal = ''

      end if

   end subroutine get_entire_literal_internal