is there a way to alter every line of an SDoc?

[Norman Ramsey]

I'm emitting code in which I want to prettyprint the contents
of a Cmm Block as a comment, by which I mean putting `--` to the left
of *each* line of the rendered Cmm Block.  Using GHC.Utils.Outputable,
is this even possible?  How would I tackle it?  (The Haddock page
does not suggest any obvious combinators.)


Norman