Expose an RNG (the one used by our runtime) to Rust via std.

src/lib/rand.rs

@@ -0,0 +1,25 @@
+/**
+ * Bindings the runtime's random number generator (ISAAC).
+ */
+
+native "rust" mod rustrt {
+  type rctx;
+  fn rand_new() -> rctx;
+  fn rand_next(rctx c) -> u32;
+  fn rand_free(rctx c);
+}
+
+type rng = obj { fn next() -> u32; };
+
+fn mk_rng() -> rng {
+  obj rt_rng(rustrt.rctx c) {
+    fn next() -> u32 {
+      ret rustrt.rand_next(c);
+    }
+    drop {
+      rustrt.rand_free(c);
+    }
+  }
+
+  ret rt_rng(rustrt.rand_new());
+}