RosettaCodeData/Task/Anonymous-recursion/Bracmat/anonymous-recursion-2.bracmat

( /(
   ' ( x
     .   $x:#:~<0
       &   ( /('(f.($f)$($f)))
           $ /(
              ' ( r
                . /(
                   ' ( n
                     .   $n:<2
                       |   (($r)$($r))$($n+-2)
                         + (($r)$($r))$($n+-1)
                     )
                   )
                )
              )
           )
         $ ($x)
     )
   )
$ 30
)