what wrong with this alias

[Qusatlegadus via Digitalmars-d-learn]

    auto s = 1234.to!string.map!q{a - '0'}.sum;
works fine.


but if i do an alias

    alias comb = to!string.map!q{a - '0'}

    Error: unknown, please file report on issues.dlang.org

What's wrong with this alias?