Indeed, and it does when you call compose directly. The good news is that if you name the string it works as expected.
arc> (= s "abc")
"abc"
arc> (prn:s 1)
b
#\b
The reader splits expressions such as (prn:"foo":[idfn _] 2) into (prn: "foo" : (make-br-fn (idfn _) 2). You could check for trailing : in the car or a leading : in the cadr, and if found then wrap strings and tables in id fns. Stash them (as well as literal fns and make-br-fns) under a uniq name. Finally, add the uniq name to the end of the head symbol and repeat if necessary. This would be done before expand-ssyntax. I'm not sure it's worth the effort.
I think the final result would be very cool, mostly to allow things like (prn:[_ 3] "hello").
