New code The trick is to take a regular functor f and create a new functor whose fmap is lazily evaluated. Here's the usual Fix case class Fix[F[_]](inner: F[Fix[F]]) object Fix { def in[F[_]](lff: F[Fix[F]]): Fix[F] = new Fix[F](lff) def out[F[_]]: Fix[F] => F[Fix[F]] = f => f.inner

Confirmed Tikhon Jelvis tikhon@jelv.is Jeremy Gibbons jeremy.gibbons@cs.ox.ac.uk Emily Pillmore emilypi@cohomolo.gy Derek Elkins derek.a.elkins@gmail.com Susan Potter Pawel Szulc Conal Elliot https://twitter.com/conal?lang=en conal.elliott@gmail.com John Wiegley jwiegley@gmail.com