ToyLanguageInterpreter: Create a program from the given statements (unite them with CompundStatements)

ProgramUtils.java

public class ProgramUtils
{
    private ProgramUtils()
    {
    }
    
    public static List<Statement> generatePrograms()
    {
        return List.of(program());
    }
    
    private static Statement program()
    {
        return concatenate(
                new VariableDeclaration(new IntType(), "a"),
                new AssignStatement("a", new ValueExpression(new IntValue(3))),
                new PrintStatement(new VariableExpression("a"))
        );
    }

    private static Statement concatenate(Statement... statements)
    {
        if (statements.length > 1)
        {
            return new CompoundStatement(statements[0], concatenate(Arrays.copyOfRange(statements, 1, statements.length)));
        }
        if (statements.length == 1)
        {
            return statements[0];
        }
        return null;
    }
}