cmdline.sh

user@note ~/soft/mine/rust $ rustc example.rs && ./example 
example.rs:13:32: 13:43 error: failed to find an implementation of interface core::to_str::to_str for some_enum
example.rs:13             foo(nest) { "foo" + nest.to_str() }
                                              ^~~~~~~~~~~

example.rs

import io::*;
import to_str::*;

enum some_enum {
    foo(~[some_enum]),
    bar
}

impl to_str for some_enum {
    fn to_str() -> str {
        alt self {
            bar       { "bar"                 }
            foo(nest) { "foo" + nest.to_str() }
        }
    }
}

// working, but not as neat
/*
impl to_str for some_enum {
    fn to_str() -> str {
        alt self {
            bar       { "bar"                                         }
            foo(nest) { "foo" + nest.map(|x| { x.to_str() }).to_str() }
        }
    }
}
*/

fn main() {
    println(foo(~[bar,bar,bar]).to_str());
}