fun foo(a: Int, s: (Int) -> String = { a ->
    """c$a
    :${a + 1}d"""
}): String {
    val x = """_${s(a)}_"""
    val y = "_$a:${a + 1}d_"
    val z = """_c$a:${a + 1}d_"""
    val u = "_c$a\n:${a + 1}d_"
    return """ab${s(a)}ef"""
}