Evaluating the last expression
In the REPL, +, ++, and +++ have as values the three most recently evaluated expressions. A quick way to evaluate the previous expression, especially handy in a REPL without input history, is #.+ It’s equivalent to (eval +). (Thanks to Anton Kovalenko.)
Un-displacing an array
Here’s a function to get the underlying array on which a displaced array is based: (defun undisplace-array (array) "Return the fundamental array and the start and end positions into it of a displaced array." (let ((length (length array)) (start 0)) (loop (multiple-value-bind (to offset) (array-displacement array) (if to (setq array to ...