datatype expression =  Constant of int |
        Variable of string |
        Operator of string * expression |
        Pair of expression list |
        List of expression list

datatype pattern = ConstantP of int
    | VariableP of string
    | OperatorP of string * pattern
    | PairP of pattern list
    | ListP of pattern list
    | UnorderedListP of pattern list
    | Wildcard

val a = PairP([OperatorP("/", PairP([ConstantP 1, VariableP "adsfas"])), ConstantP 3])
val b = Pair([Operator("/", Pair([Constant 1, Variable "adsfas"])), Constant 3])