diff --git a/src/from_json.rs b/src/from_json.rs
new file mode 100644
index 000000000..71a3f50e3
--- /dev/null
+++ b/src/from_json.rs
@@ -0,0 +1,12 @@
+use standard::*;
+
+#[macro_export]
+macro_rules! xjson {
+	( $x:expr ) => {
+		FromJson::from_json($x)
+	}
+}
+
+pub trait FromJson {
+	fn from_json(json: &Json) -> Self;
+}
diff --git a/src/misc.rs b/src/misc.rs
new file mode 100644
index 000000000..e5efd33bb
--- /dev/null
+++ b/src/misc.rs
@@ -0,0 +1,31 @@
+use common::*;
+
+#[derive(Debug,Clone,PartialEq,Eq)]
+/// Diff type for specifying a change (or not).
+pub enum Diff<T> where T: Eq {
+	Same,
+	Born(T),
+	Changed(T, T),
+	Died(T),
+}
+
+impl<T> Diff<T> where T: Eq {
+	/// Construct new object with given `pre` and `post`.
+	pub fn new(pre: T, post: T) -> Self { if pre == post { Diff::Same } else { Diff::Changed(pre, post) } }
+
+	/// Get the before value, if there is one.
+	pub fn pre(&self) -> Option<&T> { match self { &Diff::Died(ref x) | &Diff::Changed(ref x, _) => Some(x), _ => None } }
+
+	/// Get the after value, if there is one.
+	pub fn post(&self) -> Option<&T> { match self { &Diff::Born(ref x) | &Diff::Changed(_, ref x) => Some(x), _ => None } }
+
+	/// Determine whether there was a change or not.
+	pub fn is_same(&self) -> bool { match self { &Diff::Same => true, _ => false }}
+}
+
+#[derive(PartialEq,Eq,Clone,Copy)]
+/// Boolean type for clean/dirty status.
+pub enum Filth {
+	Clean,
+	Dirty,
+}