Re: Help debugging R source code block output problem with :session

[Jack Kamm <jackkamm@gmail.com>]

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Hi Dylan,

> The patch does fix that issue -- but it introduces a different bug 
> for code blocks with ~:session~: the R block now only produces 
> output from the last statement evaluated.

Of course, you're right. Good catch.

Here's another attempt. It fixes the issue by modifying the R comint
regular expression, requiring it to match at the beginning of the line.

I think this should fix most cases, including the examples you
sent. Still, it's not totally robust -- for example, it will still
mangle multiline strings, if one of the lines starts with a substring
that looks like a prompt.

I'd be interested to hear if the attached patch works for the common
cases you encounter, such as with tibbles.

As an aside, I personally use an alternative implementation of ob-R
sessions that doesn't suffer from this issue, and also provides some
other benefits like async evaluation [1]. I'm planning to submit these
changes to org-mode someday, but am not ready yet. But you may want to
check it out, it was able to solve the issue in the other thread I
linked as well.

[1] https://github.com/jackkamm/ob-session-async


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From 9eaf81d708f88d06f14f9b6b9cf4182dd0fbb997 Mon Sep 17 00:00:00 2001
From: Jack Kamm <jackkamm@gmail.com>
Date: Sat, 29 Aug 2020 00:07:58 -0700
Subject: [PATCH] ob-R: Fix prompt mangling in session output

* lisp/ob-R.el (org-babel-R-evaluate-session): Force comint prompt
regexp to start at beginning of line, to prevent
org-babel-comint-with-output from splitting mid-line.

Fixes https://orgmode.org/list/875zgjh8wn.fsf@gmail.com/ and
https://orgmode.org/list/87r1rqled0.fsf@havana/
---
 lisp/ob-R.el | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/lisp/ob-R.el b/lisp/ob-R.el
index 5e9d35f58..10b3b6fe3 100644
--- a/lisp/ob-R.el
+++ b/lisp/ob-R.el
@@ -450,11 +450,13 @@ (defun org-babel-R-evaluate-session
 		      (car (split-string line "\n")))
 		     (substring line (match-end 1))
 		   line))
-	       (org-babel-comint-with-output (session org-babel-R-eoe-output)
-		 (insert (mapconcat 'org-babel-chomp
-				    (list body org-babel-R-eoe-indicator)
-				    "\n"))
-		 (inferior-ess-send-input)))))) "\n"))))
+	       (with-current-buffer session
+		 (let ((comint-prompt-regexp (concat "^" comint-prompt-regexp)))
+		   (org-babel-comint-with-output (session org-babel-R-eoe-output)
+		     (insert (mapconcat 'org-babel-chomp
+					(list body org-babel-R-eoe-indicator)
+					"\n"))
+		     (inferior-ess-send-input)))))))) "\n"))))
 
 (defun org-babel-R-process-value-result (result column-names-p)
   "R-specific processing of return value.
-- 
2.28.0