gistfile1.txt

// Tested in groovy 2.4.3
import groovy.transform.TypeChecked

@TypeChecked
interface F1<A, B> {    // Function1
    abstract B f(A a);
}
@TypeChecked
interface Functor<T, A> { // Egentlig Functor<T<A>> men det går ikke i java/groovy
    abstract <A,B> T<B> map(F1<A, B> f)
}

@TypeChecked
class MyList extends ArrayList<Integer> implements Functor<List, Integer> {
    MyList(List src) {
        super(src)
    }
    List<String> map (F1 f) {
        this.collect { f.f(it) }
    }
}
def list = new MyList([1,2,3])
list.map {(it+2).toString()}
list.map {(it+2)} // So much for type safety ...