...

Because I want to be able to make Foo values where the parameter type isn't in Ord, too. I just want unFoo to work on specific Foo values where it is.

but your recursive function requires a recursive constraint, which your data type does not guarantee byconstruction, and which the Ord instances do not guarantee due to lack of closed classes.

Yeah. As you imply, I'm probably out of luck.

a rather pedestrian approach would record during construction whether or not all parts are in Ord (see below).

Unfortunately I need a (fully) polymorphic construction function, so this isn't possible. I'm trying to generalise the trick described at http://hsenag.livejournal.com/11803.html to arrows, but getting stuck with the "first" combinator. Thanks, Ganesh ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================