size of an IO list

[Joe Armstrong (AL/EAB)]

 How about a BIF to compute the size of an I/O list?

 Why?

 I have made a deep list that I want to output (guess what's it's HTML :-)

 I need to make an HTTP header element  "Content-Length: ..."

 Which is the size of the flattened deep list , but I don't want to flatten it (horrors)
 or traverse it (in Erlang) to find the length.

 Suitable case for a BIF?

  /Joe