On the subject: Defining Foreign Object Types at https://www.gnu.org/software/guile/manual/html_node/Defining-Foreign-Object-Types.html#Defining-Foreign-Object-Types
There is a example code snippet written in c. In the middle of that snippet: #+BEGIN_SRC c static SCM image_type image_type; #+END_SRC I think the declaration is wrong, there should be only one `image_type`. :).
