Haddock can't parse data declaration involving operator

Hi, I hope this is the right place to ask about Haddock problems? I'm using Haddock 0.6 (RedHat RPM module) under RedHat 9. When I invoke haddock on this file (Op.hs): module Op where infixl 4 := data a := b = a := b I get the error "Op.hs:Illegal data/newtype declaration". Is this a known problem? Asking more broadly - maybe there is another tool that does what I need: I just want an overview of all my modules including their exported identifiers and all type signatures (including inferred signatures). Thanks in advance, -Stefan