line 20 of example.hs was:
setImportsQ [("Prelude", Nothing), ("Data.Map", Just "M")]
for this example it is:
setImportsQ [("Prelude", Nothing), ("Data.Map", Just "M"), ("Control.Proxy", Just "P")]
When run with runhaskell or compiled with ghc hint can not find the pipes package when it is install through nix.