[MLton] printf via fold

[Vesa Karvonen]

Quoting Stephen Weeks <sweeks@sweeks.com>:
> Nice.  One minor simplification is to remove the $ from step0.
> 
>   fun step0 h = Fold.step0 (either (fn v => eval (fn () => h v), RIGHT))

Sometimes I wish there was a compiler warning (or hint) to tell me
when eta-reduction can be applied. (It is not high on my wish list,
though.)

> > (The version I have in my utility library is slightly different, though.
> > I don't use a {finish, handler} record and I use currying in step1.)
> 
> Darn.  I thought we agreed that currying in step1 doesn't make sense
> (as opposed to in the MakeFold functions, where it does).

Hmm... You are quite right. I've switched to using tupled functions.

-Vesa Karvonen