parse Subroutine

  subroutine parse(self, source, error)
  !< Parse file either from the self source data or from a source string.
  class(file_ini),        intent(inout)   :: self      !< File data.
  type(string),           intent(in)      :: source    !< String source.
  integer(I4P), optional, intent(out)     :: error     !< Error code.
  integer(I4P)                            :: errd      !< Error code.
  type(string), allocatable               :: tokens(:) !< Options strings tokenized.
  type(string)                            :: dummy     !< Dummy string for parsing sections.
  integer(I4P)                            :: Ns        !< Counter.
  integer(I4P)                            :: s         !< Counter.
  integer(I4P)                            :: ss        !< Counter.

  errd = err_source_missing
  call source%split(tokens=tokens, sep=new_line('a'))

  Ns = 0
  s = 0
  do while (s+1<=size(tokens, dim=1))
    s = s + 1
    if (scan(adjustl(tokens(s)), comments) == 1) cycle
    if (index(trim(adjustl(tokens(s))), "[") == 1) then
      Ns = Ns + 1
      dummy = trim(adjustl(tokens(s)))//new_line('a')
      ss = s
      do while (ss+1<=size(tokens, dim=1))
        ss = ss + 1
        if (index(trim(adjustl(tokens(ss))), "[") == 1) then
          ! new section... go back
          exit
        else
          ! continuation of current section
          dummy = trim(adjustl(dummy))//new_line('a')//trim(adjustl(tokens(ss)))
          tokens(ss) = comments ! forcing skip this in the following scan
        endif
      enddo
      tokens(s) = trim(adjustl(dummy))
    endif
  enddo

  if (Ns>0) then
    if (allocated(self%sections)) deallocate(self%sections) ; allocate(self%sections(1:Ns))
    s = 0
    ss = 0
    do while (s+1<=size(tokens, dim=1))
      s = s + 1
      if (scan(adjustl(tokens(s)), comments) == 1) cycle
      if (index(trim(adjustl(tokens(s))), "[") == 1) then
        ss = ss + 1
        call self%sections(ss)%parse(sep=self%opt_sep, source=tokens(s), error=errd)
      endif
    enddo
  endif
  self%Ns = Ns

  if (present(error)) error = errd
  endsubroutine parse