What does #+#. mean in lisp?

Question

It is almost impossible to google, hence my understanding is limited to contextual clues from reading through the slime source code: perhaps it is part of the object system in c

Answer 1

2.4.8.17 Sharpsign Plus http://www.lispworks.com/documentation/HyperSpec/Body/02_dhq.htm #+test expression Readtime macro, if test is true read expression, otherwise read it as white space.

2.4.8.6 Sharpsign Dot http://www.lispworks.com/documentation/HyperSpec/Body/02_dhf.htm The #. foo syntax performs a read-time evaluation of foo.

http://www.lispworks.com/documentation/HyperSpec/Body/02_dh.htm All the #X operators (defined by the Lisp HyperSpec)

Why does the Lisp HyperSpec have to be so hard to read? Probably because it's done by committee. I say it's one of the reasons Lisp is not popular. Also, Lisp is too academic, and the barriers-to-entry are too high (the learning curve and support community are not so great... there aren't 10 thousand little programs out there to easily get you started (in some arcane implementation you are using)).