Re: [BUG] beamer export

[Leo Butler <Leo.Butler@umanitoba.ca>]

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On Fri, Jan 26 2024, Leo Butler <Leo.Butler@umanitoba.ca> wrote:

> On Fri, Jan 26 2024, Ihor Radchenko <yantar92@posteo.net> wrote:
>
>> Leo Butler <Leo.Butler@umanitoba.ca> writes:
>>
>>>> Apparently, LaTeX has really hard time processing verbatim code inside
>>>> beamer frames.
>>>
>>> I looked again at the solution here:
>>> https://tex.stackexchange.com/questions/140719/verbatim-in-beamer-showing-error-file-ended-while-scanning-use-of-xverbatim
>>>
>>> and it errors out with a recent version of pdflatex:
>>>
>>>    This is pdfTeX, Version 3.141592653-2.6-1.40.25 (TeX Live 2023/Debian) (preloaded format=pdflatex)
>>>
>>> This is, apparently, a known problem:
>>>
>>> https://github.com/josephwright/beamer/issues/360
>>>
>>> The end of that issue report includes a work-around that we might apply
>>> in org. I have attached a patch for your feedback. The example that
>>> stimulated this discussion compiles with the patch and the testsuite
>>> shows no errors related to it.
>>
>> Thanks!
>> I have concerns about your approach though.
>>
>> You are replacing all the frame environments with custom environment
>> unconditionally. However, custom environment has downsides. For example,
>> \againframe will stop working, as pointed earlier in the linked beamer
>> thread
>> https://github.com/josephwright/beamer/issues/360#issuecomment-708705250
>
> The comment that you are citing shows how to define the custom
> environment so that \againframe works correctly. See the attachment
> `beamer-example-againframe.tex' and pdf. You can see that \againframe
> works with the custom environment.
>
>>
>> Since the problem appears only when the frame contents contains
>> \end{frame}, it may be sufficient to replace the standard frame
>> environment with the workaround only in such scenario.
>
> Yes, that might be true. But my feeling is that it would be simpler and
> more robust to use the custom frame environment in most cases.

Replying to self: Attached is a patch that adds a property,
BEAMER_FRAME, that lets the frame environment name be set on a
frame-by-frame basis. In addition, it typesets any fragile frame in the
`orgframe' environment. I am not sure if the latter is really needed,
given the former.

Comments?

Leo


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From d0117ca35405654c6adc003252eff5a1f629b67a Mon Sep 17 00:00:00 2001
From: Leo Butler <leo.butler@umanitoba.ca>
Date: Thu, 25 Jan 2024 09:48:20 -0600
Subject: [PATCH] lisp/ox-beamer.el:  customize the beamer frame environment
 name

* lisp/ox-beamer.el (org-beamer-frame-environment): A new customize
variable that contains the name of an environment that serves as an
alias for the beamer frame environment.

(org-beamer--format-frame): Introduce the new property, :BEAMER_FRAME.
If set in the headline, use that as name of the frame environment.
Otherwise, in frames marked as fragile, the name of the frame
environment is taken from `org-beamer--frame-environment'.  In all
other frames, the default name is frame.  Unless the frame name is
"frame", the name is added to the list
`org-beamer--frame-environments'.

(org-beamer--frame-environments): New variable and function.  The
variable holds a list of names of frame environments found while
formatting frames.  The function generates the LaTeX code to define
each new frame environment.

(org-beamer-template): Add a call to `org-beamer--frame-environments'
to insert the environment definitions into the beamer document.

Rationale: Code with \begin{frame} or \end{frame} cannot be embedded
in a verbatim environment inside a beamer frame due to a design
decision made by the beamer developers [1].  As suggested in that
report, defining an alias for the beamer frame environment will allow
such verbatim examples to compile correctly [2].  Since the frame
environment name is customize-able, beamer code generated by ox-beamer
can be included inside the verbatim environment, simply by changing
the frame environment name via the :BEAMER_FRAME property.

This solution also works with instances of \againframe.

Refs:
[1] https://github.com/josephwright/beamer/issues/360
[2] https://github.com/josephwright/beamer/issues/360#issuecomment-708705250
[3] https://list.orgmode.org/orgmode/87le8eg1hs.fsf@localhost/T/
---
 lisp/ox-beamer.el | 44 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/lisp/ox-beamer.el b/lisp/ox-beamer.el
index 82c8841aa..4a1e09b85 100644
--- a/lisp/ox-beamer.el
+++ b/lisp/ox-beamer.el
@@ -149,9 +149,17 @@ which is replaced with the subtitle."
   :package-version '(Org . "8.3")
   :type '(string :tag "Format string"))
 
+(defcustom org-beamer-frame-environment "orgframe"
+  "Name of the beamer frame environment."
+  :group 'org-export-beamer
+  :type '(string :tag "Beamer frame"))
+
 \f
 ;;; Internal Variables
 
+(defvar org-beamer--frame-environments '()
+  "List of beamer frame environments.")
+
 (defconst org-beamer-column-widths
   "0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.0 :ETC"
   "The column widths that should be installed as allowed property values.")
@@ -409,12 +417,17 @@ used as a communication channel."
   "Format HEADLINE as a frame.
 CONTENTS holds the contents of the headline.  INFO is a plist
 used as a communication channel."
-  (let ((fragilep
-	 ;; FRAGILEP is non-nil when HEADLINE contains an element
-	 ;; among `org-beamer-verbatim-elements'.
-	 (org-element-map headline org-beamer-verbatim-elements 'identity
-			  info 'first-match)))
-    (concat "\\begin{frame}"
+  (let* ((fragilep
+	  ;; FRAGILEP is non-nil when HEADLINE contains an element
+	  ;; among `org-beamer-verbatim-elements'.
+	  (org-element-map headline org-beamer-verbatim-elements 'identity
+			   info 'first-match))
+         (frame (or (org-element-property :BEAMER_FRAME headline)
+                    (and fragilep org-beamer-frame-environment)
+                    "frame")))
+    (unless (string= frame "frame")
+      (add-to-list 'org-beamer--frame-environments frame))
+    (concat "\\begin{" frame "}"
 	    ;; Overlay specification, if any. When surrounded by
 	    ;; square brackets, consider it as a default
 	    ;; specification.
@@ -481,7 +494,7 @@ used as a communication channel."
 	    ;; output.
 	    (if (not fragilep) contents
 	      (replace-regexp-in-string "\\`\n*" "\\& " (or contents "")))
-	    "\\end{frame}")))
+	    "\\end{" frame "}")))
 
 (defun org-beamer--format-block (headline contents info)
   "Format HEADLINE as a block.
@@ -805,6 +818,21 @@ contextual information."
 	  (org-export-get-reference radio-target info)
 	  text))
 
+;;;; Frame Environments
+;;
+;; Define any needed frame environments.
+
+(defun org-beamer--frame-environments ()
+  "Define beamer frame environments.
+This function is called once from `org-beamer-template'.  As a
+side-effect, it resets `org-beamer--frame-environments' to nil."
+  (prog1
+      (string-join
+       (mapcar
+        #'(lambda(frame)
+            (format "\\newenvironment<>{%s}[1][]{\\begin{frame}[environment=%s,#1]}{\\end{frame}}\n" frame frame))
+        org-beamer--frame-environments))
+    (setq org-beamer--frame-environments '())))
 
 ;;;; Template
 ;;
@@ -825,6 +853,8 @@ holding export options."
      (org-latex--insert-compiler info)
      ;; Document class and packages.
      (org-latex-make-preamble info)
+     ;; Define the frame environments, if needed.
+     (org-beamer--frame-environments)
      ;; Insert themes.
      (let ((format-theme
 	    (lambda (prop command)
-- 
2.43.0


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#+startup: beamer
#+LaTeX_CLASS: beamer

* A frame with =verbatim= contents
#+begin_example
\begin{frame}
  Here is a beamer frame.
\end{frame}
#+end_example

This is typeset in an =orgframe= environment, since it is marked as fragile.

* An ordinary frame
\[ z^n = x^n + y^n \]

This is typeset in a =frame= environment.

* A frame with =:BEAMER_FRAME= property set
:PROPERTIES:
:BEAMER_FRAME: special-frame
:END:
#+begin_example
\begin{orgframe}
  Here is a beamer orgframe.
\end{orgframe}
#+end_example

This is typeset in a =special-frame= environment, otherwise a LaTeX error will be thrown.