How about some Groovy step definitions for Cuke4Duke?

this.metaClass.mixin(cuke4duke.GroovyDsl)

Given(~/I have entered (\d+) into the calculator/) { int number ->
  calc = new calc.Calculator()
  calc.push number
}

Groovy Step Definitions should go into features/step_definitions/*.groovy. Check out the Groovy example project to learn more.