diff --git a/ablescript/src/interpret.rs b/ablescript/src/interpret.rs
index a2239e2..ba9191f 100644
--- a/ablescript/src/interpret.rs
+++ b/ablescript/src/interpret.rs
@@ -87,6 +87,21 @@ impl ExecEnv {
         }
     }
 
+    /// Create a new Scope with predefined variables
+    pub fn new_with_vars<I>(vars: I) -> Self
+    where
+        I: IntoIterator<Item = (String, Variable)>,
+    {
+        let scope = Scope {
+            variables: ablescript_consts().into_iter().chain(vars).collect(),
+        };
+
+        Self {
+            stack: vec![scope],
+            read_buf: Default::default(),
+        }
+    }
+
     /// Execute a set of Statements in the root stack frame. Return an
     /// error if one or more of the Stmts failed to evaluate, or if a
     /// `break` or `hopback` statement occurred at the top level.
@@ -224,7 +239,9 @@ impl ExecEnv {
                         instructions: code.to_owned(),
                         tape_len: tape_len
                             .as_ref()
-                            .map(|tape_len| self.eval_expr(tape_len).map(|v| v.into_isize() as usize))
+                            .map(|tape_len| {
+                                self.eval_expr(tape_len).map(|v| v.into_isize() as usize)
+                            })
                             .unwrap_or(Ok(crate::brian::DEFAULT_TAPE_SIZE_LIMIT))?,
                     }),
                 );