[sedachv]

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/4nwskBo...

[2] http://www.unlambda.com/cadr/