CachedEvaluation.groovy

def evaluator = new CachingEvaluator()

assert evaluator.evaluate("1 + 2 * 3") == 7
assert evaluator.evaluate("1 + 2 * ${3}") == 7
assert evaluator.evaluate(new String("1 + 2 * 3")) == 7
assert evaluator.compiledScriptClasses.size() == 1

class CachingEvaluator  {
    GroovyShell shell = new GroovyShell()
    Map<String, Class> compiledScriptClasses = [:]

    Object evaluate(String scriptSource) {
        Class klazz = compiledScriptClasses[scriptSource]

        if (klazz == null) {
            klazz = shell.parse(scriptSource).getClass()
            compiledScriptClasses[scriptSource] = klazz
        }

        Script script = (Script) klazz.newInstance()
        script.setBinding(shell.getContext())
        script.run()
    }
}