(<< a b c : x y z) => (a b c (x y z))
(>> a b c : x y z) => (x y z (a b c))
then? Still looks slightly like less-than/greater-than, but this gives a visual cue for data direction, and avoids needing to care about relative precedence.
Fyi, your other comment on this thread (http://arclanguage.org/item?id=14886) is dead. It was obviously a valid post, but it apparently tripped the detector.