BoundaryML/baml · error

error parsing function result: {e}

Error message

error parsing function result: {e}

What it means

The function result did have a parsed slot, but the inner parse operation failed with error e. The runtime wraps that error as 'error parsing function result: {e}', meaning the LLM output could not be coerced into the declared output type.

Source

Thrown at engine/baml-runtime/src/async_vm_runtime.rs:1351

        BamlValue::Media(media) => Ok(vm.alloc_media(media.clone())),
    }
}

fn try_vm_value_from_function_result(
    vm: &mut Vm,
    resolved_class_names: &HashMap<String, ObjectIndex>,
    resolved_enums_names: &HashMap<String, ObjectIndex>,
    result: anyhow::Result<FunctionResult>,
) -> anyhow::Result<baml_vm::Value> {
    let fn_result = result.context("failed to get function result")?;

    // TODO: Return type of .parsed() sucks.
    let baml_value = fn_result
        .parsed()
        .as_ref()
        .ok_or_else(|| anyhow!("no parsed result available from function call"))?
        .as_ref()
        .map_err(|e| anyhow!("error parsing function result: {e}"))?
        .clone()
        .0
        .value();

    try_vm_value_from_baml_value(vm, resolved_class_names, resolved_enums_names, &baml_value)
}

impl crate::runtime_interface::InternalRuntimeInterface for BamlAsyncVmRuntime {
    fn features(&self) -> crate::internal::ir_features::IrFeatures {
        self.llm_runtime.features()
    }

    fn diagnostics(&self) -> &internal_baml_core::internal_baml_diagnostics::Diagnostics {
        self.llm_runtime.diagnostics()
    }

    fn orchestration_graph(
        &self,

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Inspect the wrapped inner error e to see which field/shape failed
2. Tighten the prompt/schema, or make fields optional/nullable where the model may omit them
3. Enable BAML's retry policy or output 'repair' behaviors for malformed JSON
4. Increase max output tokens if truncation is the cause

if let Some(parsed) = fn_result.parsed() { if parsed.is_err() { handle_parse_failure(parsed.unwrap_err()); } }

Err(e) if e.to_string().starts_with("error parsing function result:") => { /* read inner cause, adjust schema/prompt, retry */ }

When it happens

Trigger: baml function call where the model's raw response fails jsonish parsing against the output format — invalid JSON, wrong shape, truncated output, or missing required fields.

Common situations: Models returning markdown-fenced or truncated JSON; output type expecting fields the model omitted; very long responses cut off by max token limits.

Understand the failure class

Background: "Invalid JSON response" and "Failed to parse response" errors: when an API answers 200 but the body isn't the JSON your library expected — this error's family across 28 libraries.

Related errors

• expected `true` or `false`, got `{raw}`
• expected `null`, got `{raw}`
• Expected {expected}, got {actual}
• Parse response error: {0}
• Jsonish error: {0}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/5a656bec8731df9e. Report an issue: GitHub.