Referencing snap, pipe variables from within an expression library

I’m trying to create an expression library function that needs access to both the snap and pipe variables. Can these variables be accessed directly from within the expression library function or must they be passed in as parameters?

Right now my function looks like this:

getHeader: (name) =>
   match(pipe.flags.immediate_mode) {
      true  => snap.original.load().get(name),
      _     => pipe.get("args",{}).get(name)
}

When I run this pipeline, I get the following error:

{"error":"snap is undefined.  Perhaps you meant: isNaN, jsonPath, JSON, String, _personsURL, parseInt","reason":null,"resolution":"Check the spelling of the variable"}

It looks like you have to pass in snap and probably pipe as parameters.