When defining the following two functions:
(defun double (f)
(lambda (arg)
(f (f arg))))
(defun inc (n)
(+ n 1))
And calling double with itself as an argument:
(((double (double double)) inc) 5)
It should evaluate to:
(((double (double (double (double inc))))) 5)
Effectively, ((2*2*2*2*1)+5) = 16+5 = 21.
However, it causes a Stack Overflow when SL is compiled with -DSL_DEBUG_MAX_CALLSTACK=10000. This happens in the latest commit, 7c4f3ba, but it's known to have happened since c6415e2.