why no function types?

[Antoras]

In the archive of the mailing list I found a topic which answers why 
there are no function types [1].

But I don't really understand the reason mentioned there (something 
about erased function types after type erasure). Therefore I have to ask 
again. Can someone explain me what happens when we write something like

return_value map((A -> B) f);

instead of

return_value map(Mapper<A, B> f);

I thought the first one could easily translated to the second one.

Thanks in advance


[1]: 
http://mail.openjdk.java.net/pipermail/lambda-dev/2011-December/004326.html