Function interp_environment 

fn interp_environment(
    positional: &[RValue],
    _named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Get or query the environment of a function.

@param fun function whose environment to return (optional; returns calling env if omitted) @return the environment of fun, or the calling environment if no argument given