RoR "goto" function?

What's the goto function for Ruby on Rails?
Something like this:
x: y
if z goto x

Obviously that's not the proper syntax, but I don't know what is. :(

>>4,5
GOTO (5014,5000,2026,2010)KQ
        PAUSE 'NO NO'
2026 JVERB=K
        JSPK=JSPKT(JVERB)
        IF(JTWO.NE.0)GOTO 2028
        IF(JOBJ.EQ.0)GOTO 2036
2027 GOTO(9000,5066,3000,5031,2009,5031,9404,9406,5081, 5200,
        1 5200,5300,5506,5502,5504,5505)JVERB

50 INPUT A
55 IF A<1 OR A>5 THEN GOTO 50
60 GOTO 900+100*A