Since HAIFA is dead now there are no equivalent frameworks for SOAP web services in Haskell now. So I would advise you to use some bunch of frameworks.
May be Yesod + shoap will be suitable.
I think such a tendency in domain of SOAP WS frameworks in Haskell because of smooth transition to REST/JSON technologies.
Also may be these two articles will be useful for you
http://www.cin.ufpe.br/~haskell/hwsproxygen/files/HWSProxyGen.pdf
and
http://www.jofcis.com/publishedpapers/2010_6_9_2859_2867.pdf