Of course I did that. I know how to do bitwise arithmetic with integers in Scheme. That's not what I was asking. _bitmask in the foreign module doesn't give me integers. It gives me lists of symbols. Moreover, I see no way of converting between the symbols and numbers manually besides doing the equivalent of defining the bitmask again. So it seems to me, from reading the documentation, that I have to use list algorithms, which to me seem to be more work for both me and the computer and less natural than using arithmetic bitwise operations on numbers. If that's the case, I see no reason to use _bitmask, other than to get a nice symbolic representation of a bitmask when a foreign function returns one. That's less important to me than actually being able to manipulate the bitmask conveniently and efficiently. <div class="gmail_quote">On Sun, Nov 15, 2009 at 10:07 AM, Jos Koot <<a href="mailto:jos.koot@telefonica.net">jos.koot@telefonica.net</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Look for bitwise in the PLT docs. Jos ----- Original Message ----- From: "Anye Li" <<a href="mailto:li.anye.0@gmail.com" target="_blank">li.anye.0@gmail.com</a>> To: <<a href="mailto:plt-scheme@list.cs.brown.edu" target="_blank">plt-scheme@list.cs.brown.edu</a>> Sent: Saturday, November 14, 2009 11:21 PM Subject: [plt-scheme] bitwise operations on scheme/foreign _bitmask <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Using the _bitmask type provided by the scheme/foreign module, is there a simple and efficient way of doing bitwise manipulations, e.g. turn off a particular set of bits from an existing set of bits? _________________________________________________ For list-related administrative tasks: <a href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme" target="_blank">http://list.cs.brown.edu/mailman/listinfo/plt-scheme</a> </blockquote> </blockquote></div>