[..]

Therefore, I chose to reimplement (most of) the wheel.  I discarded
most of haskell-devscripts and just used dh_haskell_prep and made a
CDBS rule file to take care of the rest.

Here's my complete debian/rules file, using CDBS:
#!/usr/bin/make -f
include $(CURDIR)/debian/hlibrary.mk

Neat, no?  And this should work for any cabalized Haskell library.
That's the theory, at least.  The rest is mostly controlled by
debian/control.  This has been successfully tested with haskell-binary
(already in unstable) and haskell-hlist.

Cute! Are you feeding that back to CDBS so that at some point in the future Haskell (Cabal) will be supported natively by CDBS?

/M