One-upping @eholk. See https://gist.github.com/eholk/3095375

gistfile1.rs

struct Hello;

impl Neg<Hello> for [Hello, ..0] {
    fn neg(&self) -> Hello { Hello }
}

impl Not<()> for Hello {
    fn not(&self) { } 
}

impl Hello {
    fn hello(&self) -> ~str { ~"hello world" }
}
 
fn foo<T>(_f:&fn()) -> Hello { Hello }
 
macro_rules! bar(
    ($_x:ident) => (
        // 19 in a row
        do foo::<~@&*()>{;!-[]}.$_x()
    )   
)

fn main() {
    println(bar!(hello));
}

Characters still missing: # % ^ = + \ | ' " / ? ,`