Continued sketching out code for checking states against preconditions.

It's still sketchy. I added a typestate annotation field to statements
tagged stmt_decl or stmt_expr, because a stmt_decl statement has a typestate
that's different from that of its child node. This necessitated trivial
changes to a bunch of other files all over to the compiler. I also added a
few small standard library functions, some of which I didn't actually end
up using but which I thought might be useful anyway.

src/lib/_vec.rs

@@ -1,5 +1,6 @@
 import option.none;
 import option.some;
+import util.orb;
 
 type vbuf = rustrt.vbuf;
 
@@ -230,6 +231,26 @@ fn foldl[T, U](fn (&U, &T) -> U p, &U z, &vec[T] v) -> U {
     }
 }
 
+fn unzip[T, U](&vec[tup(T, U)] v) -> tup(vec[T], vec[U]) {
+    auto sz = len[tup(T, U)](v);
+
+    if (sz == 0u) {
+        ret tup(alloc[T](0u), alloc[U](0u));
+    }
+    else {
+        auto rest = slice[tup(T, U)](v, 1u, sz);
+        auto tl   = unzip[T, U](rest);
+        auto a    = vec(v.(0)._0);
+        auto b    = vec(v.(0)._1);
+        ret tup(a + tl._0, b + tl._1);
+    }
+}
+
+fn or(&vec[bool] v) -> bool {
+    auto f = orb;
+    be _vec.foldl[bool, bool](f, false, v);
+}
+
 // Local Variables:
 // mode: rust;
 // fill-column: 78;