Verse block and separations (was: [bug] `org-latex-line-break-safe' breaks the export of verse blocks to LaTeX)

[Juan Manuel Macías]

Max Nikulin writes:

> The following is irrelevant to the recent changes. I have tried
>
> ---- >8 ----
> text
>
> #+begin_verse
>
> a b
> c d
>
> e f
> g h
> #+end_verse
>
> ---- 8< ----
>
> With the fix Ihor committed today I have got
>
> ---- >8 ----
> text
> \begin{verse}
> \vspace*{1em}
> a b\\\empty
> c d\\\empty
> \vspace*{1em}
> e f\\\empty
> g h\\\empty
> \end{verse}
> ---- 8< ----
>
> My expectation was
> ---- >8 ----
> \begin{verse}
> a b\\\empty
> c d
>
> e f\\\empty
> g h
> \end{verse}
> ---- 8< ----
>
> I am surprised that \vspace is added instead of empty line between 
> stanzas. Is there a reason to override LaTeX defaults? If such reason 
> exists would not it better to add
>
>      \parskip=1em plus 0.5em minus 0.25em\relax
>
> before first verse line? Is hard coded rigid vertical space acceptable 
> when high quality output is desired? \vspace before first line looks 
> like a bug. Frankly speaking, nested calls of `replace-regexp-in-string' 
> makes the code hard to read.
>
> P.S. I have not found exact citation, but I noticed a mention: Lamport 
> expected that verse environment would get negative feedback from poets.

First of all, I'm afraid that in my previous post I mixed up two
different issues: the verse block bug and my personal opinions about the
new added constant. I should have separated these topics, sorry.

I answer here what you comment about the verse blocks and later I will
open a different thread for the other issue.

Yes, you're right: that \vspace is the normal behavior of the block when
exporting to LaTeX, and it is certainly not quite correct. In LaTeX,
both the out-of-the-box verse environment and the one provided by the
'verse' package (which, typographically speaking, is the correct way to
represent verses in LaTeX) do not add a \vspace between stanzas. In the
LaTeX input the separation between stanzas is expressed by an (at least)
empty line. In fact, that space can be controlled by the verse package
with the stanzaskip \length. I remember that I commented on this anomaly
here on the list, a long time ago, but I can't find the original
message...

In my init I have redefined the verse block like this, so that there is
a white line between stanzas, not \vspace (I have also added some things
for the verse package, so that the numbering of verses is not broken).
So your example would produce a white line under \begin{verse}, not the
current \vspace, which would be irrelevant to LaTeX. But this is only a
hack:

  (defun org-latex-verse-block (verse-block contents info)
    "Transcode a VERSE-BLOCK element from Org to LaTeX.
      CONTENTS is verse block contents.  INFO is a plist holding
      contextual information."
    (let*
        ((lin (org-export-read-attribute :attr_latex verse-block :lines))
         (latcode (org-export-read-attribute :attr_latex verse-block 
:latexcode))
         (cent (org-export-read-attribute :attr_latex verse-block :center))
         (attr (concat
                (if cent "[\\versewidth]" "")
                (if lin (format "\n\\poemlines{%s}" lin) "")
                (if latcode (format "\n%s" latcode) "")))
         (versewidth (org-export-read-attribute :attr_latex verse-block 
:versewidth))
         (vwidth (if versewidth (format "\\settowidth{\\versewidth}{%s}\n" 
versewidth) ""))
         (linreset (if lin "\n\\poemlines{0}" "")))
      (org-latex--wrap-label
       verse-block
       ;; In a verse environment, add a line break to each newline
       ;; character and change each white space at beginning of a line
       ;; into a space of 1 em.  Also change each blank line with
       ;; a vertical space of 1 em.
       (format "%s\\begin{verse}%s\n%s\\end{verse}%s"
               vwidth
               attr
               (replace-regexp-in-string
                "^[ \t]+" (lambda (m) (format "\\hspace*{%dem}" (length m)))
                (replace-regexp-in-string
                 "\\(\\\\\\\\\n\\)+\\([ \t]*\\\\\\\\\\)+" "\n"
                 (replace-regexp-in-string
                  "\\([ \t]*\\\\\\\\\\)?[ \t]*\n" "\\\\\n"
                  (setq contents
                        (if lin
                            (replace-regexp-in-string "\\(\n\\)+\\([ 
\t]*\n\\)+" "\\\\\\\\!\n\n"
                                                      contents)
                          contents)) nil t) nil t) nil t) linreset)
       info)))