fn f1(s string) fn (string) !string {
    return fn [s] (str string) !string {
        return s + str
    }
}

fn f2(s string) fn (string) ?string {
    return fn [s] (str string) ?string {
        return s + str
    }
}

fn f3(s string) fn (string) string {
    return fn [s] (str string) string {
        return s + str
    }
}

fn f4(s string) fn (string) ?string {
    return fn (str string) ?string {
        return none
    }
}

fn f5(s string) fn (string) !string {
    return fn (str string) !string {
        return error('test')
    }
}

fn test_call_nested_anon() {
    println(f1('V')('Lang')!)
    s1 := f1('V')('Lang')!
    println(s1)
    s2 := f1('V')('Lang') or { 'ErrLang' }
    println(s2)
    s3 := f2('V')('Lang')?
    println(s3)
    s4 := f2('V')('Lang') or { 'NoneLang' }
    println(s4)
    s := f3('V')('Lang')
    println(s)
    assert s == 'VLang'
    assert s1 == 'VLang'
    assert s2 == 'VLang'
    assert s3 == 'VLang'
    assert s4 == 'VLang'

    s5 := f4('V')('Lang') or { 'Lang++' }
    println(s5)
    assert s5 == 'Lang++'
    s6 := f5('V')('Lang') or { '${err}' }
    println(s6)
    assert s6 == 'test'
}