Environment honouring newlines and add stuff before empty lines

Question

I need an environment in which newlines are treated as newlines and that adds something at the end of lines followed by an empty line. Alltt is changing too many things, and even the font therefore i do not use it.

I provide my mwe, and an illustration done in lowriter. As I have no idea how to do it, i have not done anything for the new environment.

\documentclass[a4paper]{article}
\usepackage{fancyhdr}
\setlength{\parindent}{0pt}
\fancyhead[C]{lipsum text (dummy text)}
\begin{document}
lipsum text \ (dummy text)
\begin{myenv}
Laborum molestias nam
possimus omnis. Libero sit
maiores quas asperiores nobis
est nulla. Culpa sequi iste deserunt. ||
Adipisci fuga et quis dicta est et
odit. Illo aut nulla qui incidunt
necessitatibus nulla qui. Sunt
cumque voluptatem quasi quam  ||
\textbf{the peacock says ...}
commodi culpa quaerat sunt.
Debitis accusantium et porro et
libero nulla ut est. Asperiores sed
exercitationem aut. Ex sapiente  ||
\textbf{the elephant says ...}
Debitis nobis fugiat doloremque
voluptates enim ratione. Unde ||
magni beatae magni. Unde
voluptatum qui odio corporis quia.  ||
\end{myenv}
\end{document}

\z as defined here is the stuff I need to add at the end of each line followed by an empty line:

\newcounter{versenum}\setcounter{versenum}{1}
\newcommand{\z}{\arabic{versenum}\addtocounter{versenum}{1}}

Answer 1

I've done this by making a custom \obeylines macro which peeks ahead looking for blank lines and handles the special case when the userverse environment finishes.

Features

• Uses LaTeX \list environment to control vertical spacing above and below and indent within other list environments.
• Places each verse in a \vtox box to prevent page breaks within verses.
• Uses \devanagaridigits to print verse numbers

% TeX Program = xelatex
\documentclass{article}
\usepackage{lipsum}
\usepackage{multicol}
\usepackage{fontspec}
\usepackage{polyglossia}
\setmainlanguage{english}
\setotherlanguage{hindi}
\setmainfont{Noto Serif}
\newfontfamily\hindifont[Script=Devanagari]{Noto Serif Devanagari}
\ExplSyntaxOn
% Configuration
\dim_new:N \l__user_verse_left_margin_dim
\dim_set:Nn \l__user_verse_left_margin_dim { 3em }
\dim_new:N \l__user_verse_indent_dim
\dim_set:Nn \l__user_verse_indent_dim { 2em }
\skip_new:N \l__user_verse_skip
\skip_set:Nn \l__user_verse_skip { \medskipamount }
% Box to hold each verse to so page breaks are suppressed
\box_new:N \l__user_verse_box
% Counter to hold the verse number
\int_new:N \g__user_verse_number_int
% Increment verse number and output in required format
\cs_new_protected:Nn \__user_number_verse:
  {
    \int_gincr:N \g__user_verse_number_int
    \quad $\|$ ~
    \texthindi
      {
        \devanagaridigits { \int_use:N \g__user_verse_number_int }
      }
  }
% Set up custom \obeylines macro which calls \_user_do_obeylines:
\group_begin:
  \char_set_catcode_active:N \^^M
  \cs_gset_protected_nopar:Nn \__user_obeylines: %
    {%
      \char_set_catcode_active:N \^^M%
      \cs_set_eq:NN ^^M \__user_do_obeylines:%
    }%
\group_end:
\cs_new_protected:Npn \__user_vbox_set_top:Nw #1
  {
    \tex_setbox:D #1 \tex_vtop:D
      \c_group_begin_token
        \color_group_begin:
  }
% Use box maintaining spacing
% Adapted from https://tex.stackexchange.com/a/463739/87678
\cs_new_protected:Nn \__user_box_use_drop:N
  {
    \vbox_set_top:Nn \l_tmpa_box { \vbox_unpack:N #1 }
    \vbox_set:Nn \l_tmpb_box { \vbox_unpack_drop:N #1 }
    \dim_set:Nn \l_tmpa_dim { \box_dp:N \l_tmpa_box - \box_dp:N \l_tmpb_box }
    \box_set_dp:Nn \l_tmpa_box { \box_dp:N \l_tmpb_box }
    \box_use_drop:N \l_tmpa_box
    \vspace* \l_tmpa_dim
  }
% Look ahead at the end of each line
\cs_new_protected:Nn \__user_do_obeylines:
  {
    \peek_meaning:NTF \__user_do_obeylines:
      {
%       add verse number and extra space if blank line found
        \__user_number_verse:
        \vbox_set_end:
        \mode_leave_vertical:
        \__user_box_use_drop:N \l__user_verse_box
        \obeyedline
        \penalty \c_zero_int
        \vspace \l__user_verse_skip
        \__user_vbox_set_top:Nw \l__user_verse_box
        \dim_set_eq:NN \hsize \linewidth
      }
      {
%       no extra space if at end of verse environment, otherwise end paragraph
        \peek_meaning:NTF \end
          { \__user_number_verse: }
          { \obeyedline }
      }
  }
% Format verses
\NewDocumentEnvironment { userverse } { }
  {
    \int_gzero:N \g__user_verse_number_int
%   User a list environment to easily set indent and handle vertical spacing
    \list { }
      {
        \skip_zero:N \parsep
        \dim_set:Nn \leftmargin
          { \l__user_verse_left_margin_dim + \l__user_verse_indent_dim }
      }
    \item
    \relax
    \__user_obeylines:
    \__user_vbox_set_top:Nw \l__user_verse_box
    \dim_set_eq:NN \hsize \linewidth
  }
  {
    \vbox_set_end:
    \box_set_wd:Nn \l__user_verse_box \linewidth
    \mode_leave_vertical:
    \__user_box_use_drop:N \l__user_verse_box
    \endlist
  }
% Outdent and format verse intros 
\NewDocumentCommand \verseintro { m }
  {
    \hspace { -\l__user_verse_indent_dim }
    \textbf {#1}
  }
\ExplSyntaxOff
\begin{document}
\lipsum[11]
\begin{userverse}
  Laborum molestias nam
  possimus omnis. Libero sit
  maiores quas asperiores nobis
  est nulla. Culpa sequi iste deserunt.
Adipisci fuga et quis dicta est et
  odit. Illo aut nulla qui incidunt
  necessitatibus nulla qui. Sunt
  cumque voluptatem quasi quam
\verseintro{the peacock says\ldots}
  commodi culpa quaerat sunt.
  Debitis accusantium et porro et
  libero nulla ut est. Asperiores sed
  exercitationem aut. Ex sapiente
\verseintro{the elephant says\ldots}
  Debitis nobis fugiat doloremque
  voluptates enim ratione. Unde
magni beatae magni. Unde
  voluptatum qui odio corporis quia.
\end{userverse}
\lipsum[11]
\selectlanguage{hindi}
\begin{multicols}{2}
  \begin{userverse}
    अअअअअअ
    अअअअअअ
अअअअअअ
अअअअअअ

अअअअअअ
अअअअअअ

अअअअअअ
अअअअअअ

\end{userverse}
\end{multicols}
\selectlanguage{english}
\lipsum[11]
\end{document}

Answer 2

You can do it with regex replacement.

I inject \obeylines in the myenv environment prior to the reading of the argument, so each endline is transformed into an active ^^M.

Then initial ^^M tokens are removed; similarly, trailing ^^M are replaced by \addstanzanumber. Next, sequences of two or more ^^M are replaced by \addstanzanumber\par. The remaining ^^M are replaced by \\ and the resulting token list is fed to verse.

Initial or trailing blank lines in myenv are therefore ignored.

\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\ExplSyntaxOn
% a trick to set a token list to the active endline character
\group_begin:
\char_set_catcode_active:n { 13 }
\tl_const:Nn \c_myenv_blank_line_tl { ^^M }
\group_end:
\cs_generate_variant:Nn \seq_set_split:Nnn { NV }
\tl_new:N \l_myenv_body_tl
\NewDocumentEnvironment{myenv}{+b}
 {
  \setcounter{stanzanumber}{0}
  \myenv_make:n { #1 }
  \begin{verse} \tl_use:N \l_myenv_body_tl \end{verse}

 }
 {}
\cs_new_protected:Nn \myenv_make:n
 {
  \tl_set:Nn \l_myenv_body_tl { #1 }
  % remove any number of ^^M at the beginning
  \regex_replace_once:nnN { \A \u{c_myenv_blank_line_tl}* } { } \l_myenv_body_tl
  % replace any number of ^^M at the end with \addstanzanumber
  \regex_replace_once:nnN { \u{c_myenv_blank_line_tl}* \Z } { \c{addstanzanumber} } \l_myenv_body_tl
  % replace any number greater than two of ^^M with \addstanzanumber
  \regex_replace_all:nnN
   { \u{c_myenv_blank_line_tl}{2,} }% pairs ^^M^^M
   { \c{addstanzanumber}\c{par} } % replace with \addstanzanumber\par
   \l_myenv_body_tl
  % replace any remaining ^^M with \
  \regex_replace_all:nnN
   { \u{c_myenv_blank_line_tl} } % single ^^M
   { \c{\} } % replace with \
   \l_myenv_body_tl
 }
\ExplSyntaxOff
\AtBeginEnvironment{myenv}{\obeylines}
\newcounter{stanzanumber}
\newcommand{\addstanzanumber}{~||~\stepcounter{stanzanumber}\thestanzanumber}
\newcommand{\says}[1]{\hspace{-2em}\textbf{#1}}
\begin{document}
\begin{myenv}
Laborum molestias nam
possimus omnis. Libero sit
maiores quas asperiores nobis
est nulla. Culpa sequi iste deserunt.
Adipisci fuga et quis dicta est et
odit. Illo aut nulla qui incidunt
necessitatibus nulla qui. Sunt
cumque voluptatem quasi quam
\says{the peacock says\dots}
commodi culpa quaerat sunt.
Debitis accusantium et porro et
libero nulla ut est. Asperiores sed
exercitationem aut. Ex sapiente
\says{the elephant says\dots}
Debitis nobis fugiat doloremque
voluptates enim ratione. Unde
magni beatae magni. Unde
voluptatum qui odio corporis quia. 
\end{myenv}
\end{document}