Kaba struct Function ed

struct Function
    var formula: shared![Term]
    var name: string
    var params: string[]

    # constructors
    func mut __init__()
    func mut __init__(name: string, params: string[], formula: shared![Term])

    # operators
    func __str__() -> string             # str(Function) -> string
    func mut __assign__(other: Function) # Function = Function