[fine] Classes!

It's kinda amazing this works actually

fine/src/vm.rs

@@ -29,6 +29,10 @@ pub enum VMErrorCode {
     FunctionOutOfRange(usize),
     #[error("internal error: stack type mismatch ({0:?} is not function)")]
     StackExpectedFunction(StackValue),
+    #[error("internal error: stack type mismatch ({0:?} is not object)")]
+    StackExpectedObject(StackValue),
+    #[error("internal error: slot {0} was out of range for object (type {1} with {2} slots)")]
+    SlotOutOfRange(usize, Rc<str>, usize),
 }
 
 #[derive(Debug)]
@@ -45,6 +49,19 @@ pub struct Object {
     values: Box<[StackValue]>,
 }
 
+impl Object {
+    pub fn get_slot(&self, index: usize) -> Result<StackValue> {
+        match self.values.get(index) {
+            Some(v) => Ok(v.clone()),
+            None => Err(VMErrorCode::SlotOutOfRange(
+                index,
+                self.name.clone(),
+                self.values.len(),
+            )),
+        }
+    }
+}
+
 #[derive(Clone, Debug)]
 pub enum StackValue {
     Nothing,
@@ -109,6 +126,13 @@ impl Frame {
         }
     }
 
+    fn pop_object(&mut self) -> Result<Rc<Object>> {
+        match self.pop_value()? {
+            StackValue::Object(v) => Ok(v),
+            v => Err(VMErrorCode::StackExpectedObject(v)),
+        }
+    }
+
     fn push_value(&mut self, v: StackValue) {
         self.stack.push(v)
     }
@@ -410,6 +434,10 @@ fn eval_one(
 
             f.push_object(object.into());
         }
+        Instruction::LoadSlot(slot) => {
+            let obj = f.pop_object()?;
+            f.push_value(obj.get_slot(slot)?);
+        }
     }
 
     Ok(Flow::Continue)