fn main() { let a = Some(~1); match a { Ok(a) => println!("{}",a), None => fail!() } } 

$ rustc error.rs error.rs:13:9: 13:14 error: mismatched types: expected `std::option::Option<~<ge neric integer #0>>` but found `std::result::Result<<generic #11>,<generic #12>>` (expected enum std::option::Option but found enum std::result::Result) error.rs:13 Ok(a) => println!("{}",a), ^~~~~ error: internal compiler error: unexpected failure This message reflects a bug in the Rust compiler. We would appreciate a bug report: http://static.rust-lang.org/doc/master/complem ent-bugreport.html note: the compiler hit an unexpected failure path. this is a bug task 'rustc' failed at 'index out of bounds: the len is 0 but the index is 0', D :\Heather\Contrib\P\rust\src\librustc\middle\typeck\check\vtable.rs:255 

$ rustc -v rustc.exe 0.10-pre (bf9c255 2014-01-23 19:56:35 -0800) host: i686-pc-mingw32