[PATCH] ob-scheme.el: Fix scheme code blocks execution error in batch mode

[KDr2 <killy.draw@gmail.com>]

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The bug:
write file ~/scheme-test.org with the content below:
-------8<--------------
#+BEGIN_SRC scheme :exports results :results output raw
  (display "Hello Scheme in OrgMode")
#+END_SRC
-------8<--------------

and run:

emacs --batch --eval='(load "~/.emacs.d/init.el")' ~/scheme-test.org -f
org-html-export-to-html

you will find the bug:

`org-babel-scheme-execute-with-geiser' uses `current-message' to get the
results of scheme code blocks, but `current-message' always returns nil in
batch mode, and this patch fixes this.

-- 
-- 

KDr2, http://kdr2.com

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From cebf9fc4fe09ab22fd31ff8e5606d0f680c121e9 Mon Sep 17 00:00:00 2001
From: KDr2 <killy.draw@gmail.com>
Date: Wed, 2 Apr 2014 10:30:38 +0800
Subject: [PATCH] ob-scheme.el: Fix scheme code blocks execution error in batch
 mode

* lisp/ob-scheme.el (org-babel-scheme-capture-current-message, org-babel-scheme-execute-with-geiser): Capture scheme code results via current-message both in interactive mode and noninteractive mode.

`org-babel-scheme-execute-with-geiser' uses `current-message' to get the results of scheme code blocks, but `current-message' always returns nil in batch mode, and this patch fixes this.

Modified from a patch proposal by KDr2
---
 lisp/ob-scheme.el | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/lisp/ob-scheme.el b/lisp/ob-scheme.el
index b7117e9..3b7ceb2 100644
--- a/lisp/ob-scheme.el
+++ b/lisp/ob-scheme.el
@@ -118,6 +118,17 @@ org-babel-scheme-execute-with-geiser will use a temporary session."
 	       (name))))
     result))
 
+(defmacro org-babel-scheme-capture-current-message (&rest body)
+  "Capture current message in both interactive and noninteractive mode"
+  `(if noninteractive
+       (let ((current-message nil))
+         (flet ((message (fmt &rest args) (setq current-message (apply #'format fmt args))))
+           ,@body
+           current-message))
+     (progn
+       ,@body
+       (current-message))))
+
 (defun org-babel-scheme-execute-with-geiser (code output impl repl)
   "Execute code in specified REPL. If the REPL doesn't exist, create it
 using the given scheme implementation.
@@ -142,10 +153,11 @@ is true; otherwise returns the last value."
 			     (current-buffer)))))
 	(setq geiser-repl--repl repl-buffer)
 	(setq geiser-impl--implementation nil)
-	(geiser-eval-region (point-min) (point-max))
+	(setq result (org-babel-scheme-capture-current-message
+		      (geiser-eval-region (point-min) (point-max))))
 	(setq result
-	      (if (equal (substring (current-message) 0 3) "=> ")
-		  (replace-regexp-in-string "^=> " "" (current-message))
+	      (if (and (stringp result) (equal (substring result 0 3) "=> "))
+		  (replace-regexp-in-string "^=> " "" result)
 		"\"An error occurred.\""))
 	(when (not repl)
 	  (save-current-buffer (set-buffer repl-buffer)
-- 
1.9.1