I think best to contact the hpodder author for help on fixing this
(ie with getting it to build with ghc-7.4).
Newer (latest) HaXml seems to build ok with ghc-7.4 (f19),
but current hpodder does not seem happy with it:
Commands/Ls.hs:86:11:
Could not deduce (PrintfType (m a0))
arising from the ambiguity check for `printep'
from the context (Monad m, PrintfType (m ()), PrintfType (m a))
Ah I think someone has probably already done the work:
see
https://github.com/jgoerzen/hpodder/pull/10