DEV: simple expressions don't leave their values on the stack.

src/build/opcode/test.rs

@@ -584,7 +584,7 @@ macro_rules! assert_parse_cases {
             let env = Rc::new(RefCell::new(Environment::new(Vec::new(), Vec::new())));
             let mut vm = VM::new(ops.clone(), env);
             vm.run().unwrap();
-            assert_eq!(vm.pop().unwrap().0, Rc::new(case.1));
+            assert_eq!(vm.last.unwrap().0, Rc::new(case.1));
         }
     };
 
@@ -769,7 +769,7 @@ fn simple_trace() {
     let env = Rc::new(RefCell::new(Environment::new(Vec::new(), Vec::new())));
     let mut vm = VM::new(ops.clone(), env);
     vm.run().unwrap();
-    assert_eq!(vm.pop().unwrap().0, Rc::new(P(Int(2))));
+    assert_eq!(vm.last.unwrap().0, Rc::new(P(Int(2))));
     let err_out = &vm.env.borrow().stderr;
     assert_eq!(
         String::from_utf8_lossy(err_out).to_owned(),

src/build/opcode/translate.rs

@@ -55,7 +55,11 @@ impl AST {
     fn translate_stmts(stmts: Vec<Statement>, mut ops: &mut PositionMap, root: &Path) {
         for stmt in stmts {
             match stmt {
-                Statement::Expression(expr) => Self::translate_expr(expr, &mut ops, root),
+                Statement::Expression(expr) => {
+                    let expr_pos = expr.pos().clone();
+                    Self::translate_expr(expr, &mut ops, root);
+                    ops.push(Op::Pop, expr_pos);
+                }
                 Statement::Assert(_, _) => {
                     unimplemented!("Assert statements are not implmented yet")
                 }

src/build/opcode/vm.rs

@@ -38,6 +38,7 @@ where
     runtime: runtime::Builtins,
     ops: OpPointer,
     pub env: Rc<RefCell<Environment<O, E>>>,
+    pub last: Option<(Rc<Value>, Position)>,
 }
 
 impl<'a, O, E> VM<O, E>
@@ -56,6 +57,7 @@ where
             runtime: runtime::Builtins::new(),
             ops: ops,
             env: env,
+            last: None,
         }
     }
 
@@ -66,6 +68,7 @@ where
             runtime: self.runtime.clone(),
             ops: self.ops.clone(),
             env: self.env.clone(),
+            last: self.last,
         }
     }
 
@@ -135,7 +138,7 @@ where
                     return Ok(());
                 }
                 Op::Pop => {
-                    self.pop()?;
+                    self.last = Some(self.pop()?);
                 }
                 Op::Typ => self.op_typ()?,
                 Op::Runtime(h) => self.op_runtime(h, pos)?,