Review, Parcels

• Parcels represent syntactic groups of objects

    1, 2, ('hello', @a), 5/8, %h

• Parcels flatten in some contexts and itemize in others

• Parcels are immutable
• (cannot push/pop a Parcel)
• elements may be mutable

• Despite the name, the comma construct Parcels, not the parens
• ...except for empty parens

($xyz)         # not a Parcel
($xyz,2)       # a Parcel with two items
($xyz,)        # a Parcel with one item
()             # an empty Parcel