Add support for LaTeX to MathML conversion

* lisp/org.el (org-latex-to-mathml-jar-file)
(org-latex-to-mathml-convert-command): New user-customizable
variables.
(org-format-latex-mathml-available-p, org-create-math-formula)
(org-format-latex-as-mathml): New functions.
(org-format-latex): Add a new local variable block-type that
notes the nature of the equation - inline or display.
Associate it's value to `org-latex-src-embed-type' property of
dvipng links.  Add mathml as new processing type.

Patch by Jambunathan.

lisp/org.el

@@ -16532,11 +16532,11 @@ Some of the options can be changed using the variable
 	  (plist-get (org-infile-export-plist) :latex-header-extra))
 	 (cnt 0) txt hash link beg end re e checkdir
 	 executables-checked string
-	 m n block linkfile movefile ov)
+	 m n block-type block linkfile movefile ov)
     ;; Check the different regular expressions
     (while (setq e (pop re-list))
-      (setq m (car e) re (nth 1 e) n (nth 2 e)
-	    block (if (nth 3 e) "\n\n" ""))
+      (setq m (car e) re (nth 1 e) n (nth 2 e) block-type (nth 3 e)
+	    block (if block-type "\n\n" ""))
       (when (member m matchers)
 	(goto-char (point-min))
 	(while (re-search-forward re nil t)
@@ -16565,7 +16565,7 @@ Some of the options can be changed using the variable
 				'(org-protected t))))
 		(add-text-properties (match-beginning n) (match-end n)
 				     '(org-protected t))))
-	     ((or (eq processing-type 'dvipng) t)
+	     ((eq processing-type 'dvipng)
 	      ;; Process to an image
 	      (setq txt (match-string n)
 		    beg (match-beginning n) end (match-end n)
@@ -16621,7 +16621,156 @@ Some of the options can be changed using the variable
 		(insert (org-add-props link
 			    (list 'org-latex-src
 				  (replace-regexp-in-string
-				   "\"" "" txt)))))))))))))
+				   "\"" "" txt)
+				  'org-latex-src-embed-type
+				  (if block-type 'paragraph 'character))))))
+	     ((eq processing-type 'mathml)
+	      ;; Process to MathML
+	      (unless executables-checked
+		(unless (save-match-data (org-format-latex-mathml-available-p))
+		  (error "LaTeX to MathML converter not configured"))
+		(setq executables-checked t))
+	      (setq txt (match-string n)
+		    beg (match-beginning n) end (match-end n)
+		    cnt (1+ cnt))
+	      (if msg (message msg cnt))
+	      (goto-char beg)
+	      (delete-region beg end)
+	      (insert (org-format-latex-as-mathml
+		       txt block-type prefix dir)))
+	     (t
+	      (error "Unknown conversion type %s for latex fragments"
+		     processing-type)))))))))
+
+(defcustom org-latex-to-mathml-jar-file nil
+  "Value of\"%j\" in `org-latex-to-mathml-convert-command'.
+Use this to specify additional executable file say a jar file.
+
+When using MathToWeb as the converter, specify the full-path to
+your mathtoweb.jar file."
+  :group 'org-latex
+  :type '(choice
+	  (const :tag "None" nil)
+	  (file :tag "JAR file" :must-match t)))
+
+(defcustom org-latex-to-mathml-convert-command nil
+  "Command to convert LaTeX fragments to MathML.
+Replace format-specifiers in the command as noted below and use
+`shell-command' to convert LaTeX to MathML.
+%j:     Executable file in fully expanded form as specified by
+        `org-latex-to-mathml-jar-file'.
+%I:     Input LaTeX file in fully expanded form
+%o:     Output MathML file
+This command is used by `org-create-math-formula'.
+
+When using MathToWeb as the converter, set this to
+\"java -jar %j -unicode -force -df %o %I\"."
+  :group 'org-latex
+  :type '(choice
+	  (const :tag "None" nil)
+	  (string :tag "\nShell command")))
+
+(defun org-format-latex-mathml-available-p ()
+  "Return t if `org-latex-to-mathml-convert-command' is usable."
+  (save-match-data
+    (when (and (boundp 'org-latex-to-mathml-convert-command)
+	       org-latex-to-mathml-convert-command)
+      (let ((executable (car (split-string
+			      org-latex-to-mathml-convert-command))))
+	(when (executable-find executable)
+	  (if (string-match
+	       "%j" org-latex-to-mathml-convert-command)
+	      (file-readable-p org-latex-to-mathml-jar-file)
+	    t))))))
+
+(defun org-create-math-formula (latex-frag &optional mathml-file)
+  "Convert LATEX-FRAG to MathML and store it in MATHML-FILE.
+Use `org-latex-to-mathml-convert-command'.  If the conversion is
+sucessful, return the portion between \"<math...> </math>\"
+elements otherwise return nil.  When MATHML-FILE is specified,
+write the results in to that file.  When invoked as an
+interactive command, prompt for LATEX-FRAG, with initial value
+set to the current active region and echo the results for user
+inspection."
+  (interactive (list (let ((frag (when (region-active-p)
+				   (buffer-substring-no-properties
+				    (region-beginning) (region-end)))))
+		       (read-string "LaTeX Fragment: " frag nil frag))))
+  (unless latex-frag (error "Invalid latex-frag"))
+  (let* ((tmp-in-file (file-relative-name
+		       (make-temp-name (expand-file-name "ltxmathml-in"))))
+	 (ignore (write-region latex-frag nil tmp-in-file))
+	 (tmp-out-file (file-relative-name
+			(make-temp-name (expand-file-name  "ltxmathml-out"))))
+	 (cmd (format-spec
+	       org-latex-to-mathml-convert-command
+	       `((?j . ,(shell-quote-argument
+			 (expand-file-name org-latex-to-mathml-jar-file)))
+		 (?I . ,(shell-quote-argument tmp-in-file))
+		 (?o . ,(shell-quote-argument tmp-out-file)))))
+	 mathml shell-command-output)
+    (when (org-called-interactively-p 'any)
+      (unless (org-format-latex-mathml-available-p)
+	(error "LaTeX to MathML converter not configured")))
+    (message "Running %s" cmd)
+    (setq shell-command-output (shell-command-to-string cmd))
+    (setq mathml
+	  (when (file-readable-p tmp-out-file)
+	    (with-current-buffer (find-file-noselect tmp-out-file t)
+	      (goto-char (point-min))
+	      (when (re-search-forward
+		     (concat
+		      (regexp-quote
+		       "<math xmlns=\"http://www.w3.org/1998/Math/MathML\">")
+		      "\\(.\\|\n\\)*"
+		      (regexp-quote "</math>")) nil t)
+		(prog1 (match-string 0) (kill-buffer))))))
+    (cond
+     (mathml
+      (setq mathml
+	    (concat "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" mathml))
+      (when mathml-file
+	(write-region mathml nil mathml-file))
+      (when (org-called-interactively-p 'any)
+	(message mathml)))
+     ((message "LaTeX to MathML conversion failed")
+      (message shell-command-output)))
+    (delete-file tmp-in-file)
+    (when (file-exists-p tmp-out-file)
+      (delete-file tmp-out-file))
+    mathml))
+
+(defun org-format-latex-as-mathml (latex-frag latex-frag-type
+					      prefix &optional dir)
+  "Use `org-create-math-formula' but check local cache first."
+  (let* ((absprefix (expand-file-name prefix dir))
+	 (print-length nil) (print-level nil)
+	 (formula-id (concat
+		      "formula-"
+		      (sha1
+		       (prin1-to-string
+			(list latex-frag
+			      org-latex-to-mathml-convert-command)))))
+	 (formula-cache (format "%s-%s.mathml" absprefix formula-id))
+	 (formula-cache-dir (file-name-directory formula-cache)))
+
+    (unless (file-directory-p formula-cache-dir)
+      (make-directory formula-cache-dir t))
+
+    (unless (file-exists-p formula-cache)
+      (org-create-math-formula latex-frag formula-cache))
+
+    (if (file-exists-p formula-cache)
+	;; Successful conversion.  Return the link to MathML file.
+	(org-add-props
+	    (format  "[[file:%s]]" (file-relative-name formula-cache dir))
+	    (list 'org-latex-src (replace-regexp-in-string "\"" "" latex-frag)
+		  'org-latex-src-embed-type (if latex-frag-type
+						'paragraph 'character)))
+      ;; Failed conversion.  Return the LaTeX fragment verbatim
+      (add-text-properties
+       0 (1- (length latex-frag)) '(org-protected t) latex-frag)
+      latex-frag)))
 
 ;; This function borrows from Ganesh Swami's latex2png.el
 (defun org-create-formula-image (string tofile options buffer)