Re: Recursive type synonyms

[wadler]

Mark suggests that Mu types might be better that recursive type
synonyms.  I think of them as pretty much equivalent, and it's
simply a question of whether one makes the `mu' syntax accessible
to the user.  One certainly needs `mu' or an equivalent internally
for doing the typechecking.  The advantage of the way I put it
is that it makes for a minimal change from the current language:
just get rid of one restriction.  -- P