diff --git a/zjit/src/main.rs b/zjit/src/main.rs
index ec2311e448..e4fe75d2da 100644
--- a/zjit/src/main.rs
+++ b/zjit/src/main.rs
@@ -1,3 +1,24 @@
+#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
+pub struct InsnId(usize);
+#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
+pub struct BlockId(usize);
+
+enum Insn {
+    Param { idx: usize },
+}
+
+#[derive(Debug)]
+struct Block {
+    params: Vec<InsnId>,
+    insns: Vec<InsnId>,
+}
+
+#[derive(Debug)]
+struct Function {
+    name: String,
+    entry_block: BlockId,
+}
+
 fn main() {
     println!("zjit");
 }