Ruby 1.9 brings a shorter way to define lambdas using the -> operator:

twice = -> (x) { 2 * x }
twice.call(5) # => 10

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This is equivalent to:

twice = lambda {|x| 2 * x }
twice.call(5) # => 10

Note that the syntax is subtly different from Coffeescript where you define function parameters before the arrow: (x) -> { 2 * x }.