Using a Lisp compiler helps a bit. * (defun foo (alpha) (flet ((beta (bar) (+ alph bar))) (bet (beta 1 2)))) The Lisp compiler,

Using a Lisp compiler helps a bit. * (defun foo (alpha) (flet ((beta (bar) (+ alph bar))) (bet (beta 1 2)))) The Lisp compiler, here SBCL with its REPL, detects in this function above: * wrong number of arguments * undefined function * undefined variable * unused variable Lisp compilers have only been made available as late as 1962, so that might explain why Lisp has no wider adoption... ; in: DEFUN FOO ; (BETA 1 2) ; ; caught WARNING: ; function called with two arguments, but wants exactly one ; See also: ; The ANSI Standard, Section 3.2.2.3 ; (SB-INT:NAMED-LAMBDA FOO ; (ALPHA) ; (BLOCK FOO ; (FLET ((BETA # ; #)) ; (BET (BETA 1 2))))) ; ; caught STYLE-WARNING: ; The variable ALPHA is defined but never used. ; in: DEFUN FOO ; (+ ALPH BAR) ; ; caught WARNING: ; undefined variable: ALPH ; (BET (BETA 1 2)) ; ; caught STYLE-WARNING: ; undefined function: BET ; ; compilation unit finished ; Undefined function: ; BET ; Undefined variable: ; ALPH ; caught 2 WARNING conditions ; caught 2 STYLE-WARNING conditions FOO