Many early lisps had dynamic scoping only. It meant that this code would return 5 (defvar x 1) ; new global var (defun foo () x) ; function returns x

Many early lisps had dynamic scoping only. It meant that this code would return 5 (defvar x 1) ; new global var (defun foo () x) ; function returns x (+ (let ((x 4)) (foo)) (foo)) ; => 5 It also meant that anonymous functions weren’t closures. Later on, scheme used lexical scoping and Common Lisp used lexical scoping normally with dynamic scoping for special (typically global) variables like standard-input. At the time, implementers were worried that they wouldn’t be able to do lexical scoping efficiently. Emacs lisp only had dynamic scoping for a long time. Furthermore it had buffer-local-variables where the editor has a notion of the current buffer, buffers can have definitions of variables, and the value you get for a variable depends on what it is bound to within that buffer as well as dynamically. Over time elisp got true closures/lexical scope, first via a library and later as a language feature (if a certain buffer-local variable is set when you compile/evaluate a file, you get lexical scoping; the easy way to set it is by writing a specially formatted line in the file which allows emacs to set ‘safe’ buffer local variables on opening the file.