This library provides an asynchronous DNS resolver on top of GNU ADNS http://www.chiark.greenend.org.uk/~ian/adns/. Not all options are supported, but A, MX, and PTR lookups work nicely. There is also support for retrieving generic RR types, CNAMEs, and for NSEC zone walking. The library can be expected to work with fine ADNS 1.4 or later. It might also work with version ADNS 1.3, but that hasn't been tested.
The example program adns-reverse-lookup.hs demonstrates how the resolver is used. Given a list of host names on the command line, it performs an A/PTR double-lookup and checks whether the records are consistent. The output is printed in the order in which the DNS responses arrive:
$ ./adns-reverse-lookup cryp.to localhost www.example.com OK: localhost <-> 127.0.0.1 FAIL: cryp.to -> 22.214.171.124 -> ["zuse.cryp.to"] OK: www.example.com <-> 126.96.36.199