First of all, thank you for making these bindings available. They are great! Much better that the bare-bones cffi wrappers I've been using for the small subset of gsl I've needed. I think there is a small bug with exceptions in the code. I usually make my own image with code that I use regularly (sbcl 1.0.14), i.e. (require 'asdf) (require 'asdf-install) (require 'cffi) (require 'gsll) (sb-ext:save-lisp-and-die "sbcl-with-slime.core") then start up sbcl with "sbcl --core sbcl-with-slime.core". In this mode of operation gsll hangs when an exception is caught, e.g. (jacobian-elliptic-functions 0.61802d0 1.5d0) just sits and the repl prompt is not returned (endless loop or something). If I just fire up sbcl and load gsll normal everything works fine and I get the expected warning that |m|>1. Hope this is a useful enough description of the problem for you to track it down. With kind regards, Jason