How far can we push things the Ruby way? Here's an elegant Ruby one-liner for the fibonacci function. I was secretly hoping that it would go on and on forever spewing out endless rows of digits until the end of time, but that was not going to happen.

kiffin@F5SL:~ $ irb
irb(main):001:0> fibonacci = Hash.new{ |h,k| h[k] = k < 2 ? k : h[k-1] + h[k-2] }
=> {}

Function defined and working...

irb(main):002:0> fibonacci[10]
=> 55

Let's go deeper ...

irb(main):003:0> fibonacci[100]
=> 354224848179261915075

And deeper ...

irb(main):004:0> fibonacci[1000]
=> 43466557686937456435688527675040625802564660517371780402481729089536555417949051890403879840079255169295922593080322634775209689623239873322471161642996440906533187938298969649928516003704476137795166849228875

Even more deeper ...

irb(main):005:0> fibonacci[5000]
=> 3878968454388325633701916308325905312082127714646245106160597214895550139044037097010822916462210669479293452858882973813483102008954982940361430156911478938364216563944106910214505634133706558656238254656700712525929903854933813928836378347518908762970712033337052923107693008518093849801803847813996748881765554653788291644268912980384613778969021502293082475666346224923071883324803280375039130352903304505842701147635242270210934637699104006714174883298422891491273104054328753298044273676822977244987749874555691907703880637046832794811358973739993110106219308149018570815397854379195305617510761053075688783766033667355445258844886241619210553457493675897849027988234351023599844663934853256411952221859563060475364645470760330902420806382584929156452876291575759142343809142302917491088984155209854432486594079793571316841692868039545309545388698114665082066862897420639323438488465240988742395873801976993820317174208932265468879364002630797780058759129671389634214252579116872755600360311370547754724604639987588046985178408674382863125

Deeper still ...

irb(main):006:0> fibonacci[10000]
SystemStackError: stack level too deep
	from /home/kiffin/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/irb/workspace.rb:86
Maybe IRB bug!
irb(main):007:0> 

Oops, we went too deep.

The moral of the story is that although Ruby is an elegant and amazing programming language with endless possibilities, even it's magical powers are not limitless.