halp.sty

% Reads one paragraph from each IOR stream #1 and #2 into boxes #3 and
% #4.  The streams must be open.
\cs_new:Npn \fncypoem_read_par:NNNN #1 #2 #3 #4 {
  \ior_if_eof:NT { #1 } {
    \typeout{!~read~error~1}
  }
  \ior_if_eof:NT { #2 } {
    \typeout{!~read~error~2}
  }

  \seq_new:N \l_parA_lines_seq
  \seq_new:N \l_parB_lines_seq

  \int_new:N \l_parA_line_no_int
  \int_new:N \l_parB_line_no_int

  % Prime line buffer to trick \bool_until_do:
  \tl_set:N \l_tmpa_tl { line }
  % Read lines into hboxes and pump them into token lists until you hit a
  % blank line or the end of the paragraph
  \bool_until_do:Nn { \tl_if_empty_p:N \l_tmpa_tl || \ior_if_eof_p:N { #1 }} {
    % Save name as TMP_B
    \tl_set:Nn \l_tmpb_tl {
      l_parA_hbox \int_use:N { \l_parA_line_no_int } _box
    }
    \box_new:c { \tl_use:N \l_tmpb_tl }

    % Read line into TMP_A
    \ior_get_str:NN { #1 } \l_tmpa_tl
    \hbox_set:cn { \tl_use:N \l_tmpb_tl }
                 { \tl_use:N \l_tmpa_tl } % does not account for long lines
    \seq_put_right:NV \l_parA_lines_seq { \use:c { \tl_use:N \l_tmpb_tl } }
  }

  \tl_set:N \l_tmpa_tl { line } % now do it for #2
  \bool_until_do:Nn { \tl_if_empty_p:N \l_tmpa_tl || \ior_if_eof_p:N { #2 }} {
    \tl_set:Nn \l_tmpb_tl { l_parA_hbox \int_use:N { \l_parA_line_no_int } _box }
    \box_new:c { \tl_use:N \l_tmpb_tl }
    \ior_get_str:NN { #1 } \l_tmpa_tl
    \hbox_set:cn { \tl_use:N \l_tmpb_tl } { \tl_use:N \l_tmpa_tl }
    \seq_put_right:NV \l_parA_lines_seq { \use:c { \l_tmpb_tl } }
  }

  % Set pack the vboxes
  \vbox_set:Nn { #3 } { \l_parA_tl } % I-have-no-idea-what-I-am-doing.jpg
  \vbox_set:Nn { #4 } { \l_parB_tl }
}