Introduce a registry into the conversion to intermediate format.

src/intermediate/registry.rs

@@ -0,0 +1,24 @@
+use std::collections::HashMap;
+
+type IdCounter = u16;
+
+pub(crate) struct Registry<'p> {
+    id_counter: IdCounter,
+    targets: HashMap<&'p str, String>,
+}
+
+impl<'p> Registry<'p> {
+    pub(crate) fn new() -> Registry<'p> {
+        Registry {
+            id_counter: 0,
+            targets: HashMap::new(),
+        }
+    }
+
+    pub(crate) fn get_target<'b>(&'b mut self, body: &'p str) -> &'b String {
+        self.targets.entry(body).or_insert_with(|| {
+            self.id_counter += 1;
+            format!("target_{}", self.id_counter)
+        })
+    }
+}