Function call_builtin 

fn call_builtin(
    interp: &Interpreter,
    name: &str,
    implementation: &BuiltinImplementation,
    min_args: usize,
    max_args: Option<usize>,
    positional: &[RValue],
    named: &[(String, RValue)],
    env: &Environment,
) -> Result<RValue, RFlow>