Any time people claim that Lisp is a functional programming language, I like to drag out this example posted by Joe Marshall to comp.lang.lisp[1]: (DEFUN R

Any time people claim that Lisp is a functional programming language, I like to drag out this example posted by Joe Marshall to comp.lang.lisp[1]: (DEFUN RDSYL (L DF) (PROG (LL BRAKP ANS CH) (SETQ DF (MERGEF DF '((* *) * *))) AA (SETQ LL (SETQ BRAKP () )) A (SETQ CH (OR (CAR L) #/_)) (COND ((OR (= CH #/ ) (= CH #//)) ;"/", " " (POP L) (SETQ CH (CAR L))) ((AND (= CH #/[) (NOT #%(ITSP))) ;"[" (SETQ BRAKP 'T)) ((AND (= CH #/]) (NOT #%(ITSP))) (SETQ BRAKP () )) ;"]" ((OR (= CH #/( ) (= CH #/) )) (RETURN () )) ;Cant have parens here ((= CH #/,) ;Comma (COND ((NOT BRAKP) (POP L) (GO RET)))) ((= CH #/_) (GO RET))) (PUSH CH LL) (POP L) (GO A) RET (SETQ DF (MERGEF (NAMELIST (MAKNAM (NREVERSE LL))) DF)) (SETQ ANS (NCONC ANS (LIST DF))) (AND (= CH #/,) (GO AA)) (RETURN ANS) )) There is a lot of this kind of code around in the various Lisp Machine sources (CADR is legally available for poking around in[2]). Occasionally things like this pop up in contemporary Lisp compilers or IO/concurrency libraries. Some algorithms are much easier to express with goto. [1] https://groups.google.com/forum/#!msg/comp.lang.lisp/4nwskBo3FR0/cmVlCio6s64J https://groups.google.com/forum/#!msg/comp.lang.lisp/4nwskBo... [2] http://www.unlambda.com/cadr/ http://www.unlambda.com/cadr/