Human-pipelined functions

[dbarowy]

data.automan_map { e => foo(e) }.automan_map { e=> bar(e) }

if pipelined, would allow us to compute bar(foo(e)) without having to block after the first map before the second could start. We can do this if we lazily evaluate the entire expression. Choosing when to evaluate is tricky, though, since we don't want to wait too long.