Ramat Gan Rabbi Yaakov Ariel was asked on the Yeshiva site whether it is permissible during the intermediate days of the festival called Chol Hamoed to write for the purpose of summarizing a Torah lesson or writing a dedication for a book. Writing during Chol HaMoed is generally prohibited.
Rabbi Ariel replied there are differences between various types and purposes of writing.
"Writing is forbidden on Chol HaMoed. Writing on a computer without printing is permitted because it is not viable writing. Also, writing is permitted for the purpose of the holiday or where loss may be incurred," Rabbi Ariel noted.
The rabbi added, "If you create Torah novellae and fear you may forget them, you are permitted to write them. Writing on a computer is preferable for the above-stated reason."
Rabbi Ariel's response may be read in the original Hebrew here.