error: not all control paths return a value

[electricface]

enum List {
    Cons(u32,~List),
    Nil
}

fn prepend(xs: List, value: u32) -> List {
    Cons(value, ~xs );
}

fn main(){
    let mut xs = Nil;
    xs = prepend(xs,1);
    xs = prepend(xs,2);
    xs = prepend(xs,3);
}

report error
abc.rs:7:1: 9:2 error: not all control paths return a value
abc.rs:7 fn prepend(xs: List, value: u32) -> List {
abc.rs:8 Cons(value, ~xs );
abc.rs:9 }
error: aborting due to previous error
task 'rustc' failed at 'explicit failure', /build/buildd/rust-0.9-0.9/src/libsyntax/diagnostic.rs:75
task '

' failed at 'explicit failure', /build/buildd/rust-0.9-0.9/src/librustc/lib.rs:453

If you remove the semicolon at the end of "Cons(value, ~xs );"
no error report
This is a bug?

[sfackler]

This is not a bug. Take a look at http://static.rust-lang.org/doc/master/tutorial.html#functions for more info.

[huonw]

It should work if you remove the semicolon on Cons(...);.

[electricface]

thank you