And to add to this, the unspoken Hungarian notation rules have xs typed as a list. So the 1st instance: [x,xs] looks unprofessional and n00b-ish. It's the 2nd

And to add to this, the unspoken Hungarian notation rules have xs typed as a list. So the 1st instance: [x,xs] looks unprofessional and n00b-ish. It's the 2nd instance that's idiomatic.