Arena allocate and cache type representations.

src/lib.rs

@@ -1,10 +1,15 @@
 #![feature(btree_range, collections_bound, rustc_private)]
 
-extern crate byteorder;
+// From rustc.
+extern crate arena;
 extern crate rustc;
+extern crate rustc_data_structures;
 extern crate rustc_mir;
 extern crate syntax;
 
+// From crates.io.
+extern crate byteorder;
+
 mod error;
 pub mod interpreter;
 mod memory;