C is a bad choice for a new port scanner started in 2011. I've already written comments here justifying that statement. If you really think I'm wrong, it might be fun to hash out why. (I've got a fairly decent background in nmap's problem domain, for what it's worth.)
I don't have a problem with C, although if I had to do it I would use C++ for object-oriented support and more or less guaranteed portability. Possibly also to compile in a lua interpreter. That said, I'm not a domain expert and was responding to the question of whether nmap should have been coded in C rather than what the best language would be for something started NOW.
I don't know what the best alternatives would be and while I doubt I can contribute much to the discussion, I've read your other posts on security with interest and would be interested to hear which language you'd pick and why.
Personally, I think Lisp is a fantastic language to write a scanner in; you can express async state machines in it naturally, and most Lisps have very good foreign interfaces, which would allow you to just call into libpcap. Lisp is also good for DSLs --- look how Seibel did the little expression language for binary formats in his Lisp book; that's exactly the problem statement that drove me to make my own dumb language in '97 to express packet formats.
Virtually any language will work for this (which is why you should avoid C). About the only thing I'd steer you clear of is a JVM language. The JVM is ordinarily a win, but here, where you want the path-of-least-resistance to getting pcap into your program, it's a bit of a pain. So scratch Scala from the list. Other than that, have fun.
