What causes "to_fixed() digits argument must be an int at {:?}" in BoundaryML/baml?

Pass an integer literal or an Int-typed variable for digits

to_fixed() digits argument must be an int at

Error message

to_fixed() digits argument must be an int at {:?}

What it means

When to_fixed receives an argument, it must be an Int (the number of decimal digits). The interpreter matches args.first() and bails on any non-Int value (float, string, bool, null, etc.), reporting the source span.

Solutions

Pass an integer literal or an Int-typed variable for digits
Convert a float digits value to int before calling (e.g. truncate/round)
Default to omitting the argument (0 digits) if no meaningful count is available

Example fix

// before (digits came from LLM as float)
let out = value.to_fixed(digits);
// after
let out = value.to_fixed(digits.ToInt());

Defensive patterns

Strategy: type-guard

Validate before calling

// digits must be int: if (d is int) { num.to_fixed(d); }

Type guard

fn is_int(v: Value) -> bool { matches!(v, Value::Int(_)) }

Try / catch

try { out = num.to_fixed(d); } catch (e) { out = num.to_fixed(0); }

Prevention

Use integer literals for precision
Truncate float digit counts first
Ensure dynamic digits come from int-typed fields

When it happens

Trigger: Calling num.to_fixed("2"), to_fixed(2.0), to_fixed(someString), or passing null where the digits count should be.

Common situations: A digits value computed from LLM output that came back as a float or string; copying code where 2 was written but a variable holding a float was substituted.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/20dc850ca2f6b5a7. Report an issue: GitHub.

Appendix: source

Thrown at engine/baml-compiler/src/thir/interpret.rs:3008

            Ok(BamlValueWithMeta::String(result, meta.clone()))
        }
        "to_fixed" => {
            let value = match receiver {
                BamlValueWithMeta::Float(v, _) => *v,
                BamlValueWithMeta::Int(v, _) => *v as f64,
                _ => bail!(
                    "to_fixed() method only available on floats and ints at {:?}",
                    meta.0
                ),
            };

            if args.len() > 1 {
                bail!("to_fixed() method takes at most 1 argument at {:?}", meta.0);
            }

            let digits = match args.first() {
                Some(BamlValueWithMeta::Int(v, _)) => *v,
                Some(_) => bail!("to_fixed() digits argument must be an int at {:?}", meta.0),
                None => 0,
            };

            let formatted = baml_vm::native::number_to_fixed(value, digits)
                .map_err(|msg| anyhow::anyhow!("{msg} at {:?}", meta.0))?;
            Ok(BamlValueWithMeta::String(formatted, meta.clone()))
        }
        _ => bail!(
            "unknown method '{}' at {:?}, should have been caught during typechecking",
            method_name,
            meta.0
        ),
    }
}

#[cfg(test)]
mod tests {
    use std::path::PathBuf;

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