I have been spending enjoyable time with gsll's (and gsl's) histogram routines.
A small bug in the code popped up. In histogram/histogram.lisp the grid:copy method calls histo-copy and histo-clone. The arguments in those calls are incorrect. This is what the method should look like:
(defmethod grid:copy ((source histogram) &key destination &allow-other-keys)
(if destination
(histo-copy source destination)
(histo-clone source)))
In the original, source and destination were swapped.