transcendental-lisp/src/function/builtin/cons/FIRST.java

package function.builtin.cons;

import function.*;
import sexpression.*;

public class FIRST extends LispFunction {

    private ArgumentValidator argumentValidator;

    public FIRST() {
        this.argumentValidator = new ArgumentValidator("FIRST");
        this.argumentValidator.setExactNumberOfArguments(1);
        this.argumentValidator.setEveryArgumentExpectedType(Cons.class);
    }

    public SExpression call(Cons argumentList) {
        argumentValidator.validate(argumentList);
        Cons argument = (Cons) argumentList.getFirst();

        return argument.getFirst();
    }

}