fix SetLocal not taking into account the stack bottom

y'know, when you look for locals relative to the call frame's bottom, but then set locals relative to index 0...
boom.

closes #78

crates/haku/src/vm.rs

@@ -210,6 +210,7 @@ impl Vm {
                 .checked_sub(1)
                 .ok_or_else(|| self.create_exception("code ran for too long"))?;
 
+            #[allow(unused)]
             let pc2 = pc;
             let opcode = chunk.read_opcode(&mut pc)?;
             vmtrace!("{pc2:2} {opcode:?}");
@@ -245,7 +246,7 @@ impl Vm {
                 Opcode::SetLocal => {
                     let index = chunk.read_u8(&mut pc)? as usize;
                     let new_value = self.pop()?;
-                    *self.get_mut(index)? = new_value;
+                    *self.get_mut(bottom + index)? = new_value;
                 }
 
                 Opcode::Capture => {

crates/haku/tests/language.rs

@@ -266,3 +266,18 @@ fn system_arithmetic() {
     expect_number("1 + 2 + 3 + 4", 10.0, 0.0001);
     expect_number("(2 * 1) + 1 + (6 / 2) + (10 - 3)", 13.0, 0.0001);
 }
+
+#[test]
+fn issue_78() {
+    let code = r#"
+        f = \_ ->
+            let x = 1
+            x + x
+
+        [
+            f ()
+            f ()
+        ]
+    "#;
+    assert_eq!(eval(code).unwrap(), Value::Ref(RefId::from_u32(2)))
+}