package sexpression; @DisplayName("s-expression") public abstract class SExpression { public boolean isNull() { return false; } public boolean isAtom() { return false; } public boolean isCons() { return false; } public boolean isList() { return (isCons() || isNull()); } public boolean isNumber() { return false; } public boolean isSymbol() { return false; } public boolean isFunction() { return false; } public boolean isString() { return false; } }