rt: prevent deadlock in recursive functions

src/rt/mod.rs

@@ -88,9 +88,15 @@ impl Node {
                 },
                 &stmt.body,
             ),
-            Node::CallExpr(_, expr) => expr.func.eval(scope)?.as_fn(|func, capture| {
-                exec_fn(scope, capture, &func.body, &func.params, &expr.params)
-            })?,
+            Node::CallExpr(_, expr) => {
+                // we don't execute the function within the callback because
+                // (1) that would block the mutex for way longer than necessary and
+                // (2) recursive function calls would cause a deadlock (ask me how i know)
+                let (func, mut capture) = expr.func.eval(scope)?.as_fn(|func, capture| {
+                    (func.clone(), capture.clone())
+                })?;
+                exec_fn(scope, &mut capture, &func.body, &func.params, &expr.params)
+            },
             Node::ArrayExpr(pos, expr) => expr.array.eval(scope)?.as_array(|array| {
                 expr.index.eval(scope)?.as_int(|index| {
                     if *index >= 0 && *index < array.len() as i128 {