Initial stack typing

src/value.rs

@@ -0,0 +1,30 @@
+use Result;
+use std::convert::TryInto;
+
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum Value {
+    Int(i32),
+    HeapRef(usize),
+}
+
+impl TryInto<i32> for Value {
+    type Error = &'static str;
+
+    fn try_into(self) -> Result<i32> {
+        match self {
+            Value::Int(a) => Ok(a),
+            Value::HeapRef(_) => Err("Cannot use HeapRef as i32"),
+        }
+    }
+}
+
+impl TryInto<i32> for &Value {
+    type Error = &'static str;
+
+    fn try_into(self) -> Result<i32> {
+        match self {
+            &Value::Int(a) => Ok(a),
+            &Value::HeapRef(_) => Err("Cannot use HeapRef as i32"),
+        }
+    }
+}