BoundaryML/baml · error

No runtime loaded, it should be impossible to call an LLM fu

Error message

No runtime loaded, it should be impossible to call an LLM function

What it means

Defensive invariant check: the REPL branch that invokes LLM functions should only be reachable when a runtime is loaded. If the runtime Option is None at call time, this error fires, signaling an internal state violation rather than a user-caused problem.

Source

Thrown at engine/baml-runtime/src/cli/repl.rs:602

                                    output_tokens: resp.metadata.output_tokens,
                                    total_tokens: resp.metadata.total_tokens,
                                    cached_input_tokens: resp.metadata.cached_input_tokens,
                                };
                                let _ = tx.send(LlmStatusEvent::Finished(run_id, Some(usage)));
                            } else {
                                let _ = tx.send(LlmStatusEvent::Finished(run_id, None));
                            }
                        }
                        match function_result.parsed() {
                            Some(Ok(response_baml_value)) => Ok(response_baml_value
                                .clone()
                                .0
                                .map_meta_owned(|_| (Span::fake(), None))),
                            Some(Err(e)) => Err(anyhow!("Failed to parse function result: {}", e)),
                            None => Err(anyhow!("No parsed result available from function call")),
                        }
                    }
                    None => Err(anyhow!(
                        "No runtime loaded, it should be impossible to call an LLM function"
                    )),
                }
            }
        };
        // REPL watch handler: collect notifications
        let watch_notifications = Arc::new(Mutex::new(Vec::new()));
        let watch_notifications_clone = watch_notifications.clone();
        let watch_handler = shared_handler(move |notification| {
            watch_notifications_clone
                .lock()
                .unwrap()
                .push(format!("{notification}"));
        });

        let eval_result = interpret_thir(
            "repl".to_string(),
            thir.clone(),

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Load BAML sources first with :load <path-to-baml_src> before calling functions
2. Restart the REPL if a :reset or failed :load left the runtime unloaded
3. Check that the initial baml_src load succeeded (watch for earlier load errors)
4. File a bug if it occurs with a successfully loaded runtime

Example fix

// before (REPL input)
MyFn(1)            // no sources loaded
// after
:load ./baml_src
MyFn(1)

// Guard in embedding code before evaluating function calls
if repl_runtime_is_none() {
    return Err(anyhow!(":load baml sources before calling functions"));
}

match result { Err(e) if e.to_string().contains("No runtime loaded") => eprintln!("Run :load <baml_src> first"), other => { let _ = other; } }

When it happens

Trigger: parse_and_evaluate_baml_expression_with_status reaches the function-call arm while self.runtime is None — evaluating a function-call expression before any BAML sources were loaded.

Common situations: Starting the REPL and immediately calling a function without :load, a race where the runtime was reset mid-session, or a bug in runtime initialization.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• No BAML sources loaded. Use :load <path> to load sources.
• Type error: {}
• LLM Function {} not found
• Failed to parse function result: {}
• No parsed result available from function call

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/6280426023a19959. Report an issue: GitHub.