type Record = (Description, Operator)
type EOF = (Symbol1, Symbol2)

type File = (
      Head,
      List[Record],  #[if UseList]
      Record,        #[if not UseList]
      EOF            #[if NeedEOF]
    )

Data = {
    d1 = {aa: some},
    d2 = {pa: p1; aa: a1;   use_b: true;  pb: p2; ab: a2}
}

type Attack = Magic | Melee

power: (Attack) -> int
power = (Magic) -> 5
power = (Melee) -> 4


damage: (Attack, bool, int) -> float


error Invalid(float) = SetVal(float) | SetDef

damage = (Magic, surprise, defense | Invalid) ->
       koef = 3 if surprise else 2
       effectiveness = power(Magic) * koef

       out = effectiveness - defense
       case of
            | out <= 0  =>  out = 0
            | out >= 1  =>  _
            | else          try Invalid(out) handle
                               SetVal(x) =>  out = x
                               SetDef    =>  out = 0.5
       out


damage = (Melee, surprise, defense) ->
       koef = 3 if surprise else 2
       effectiveness = power(Melee) * koef

       out = effectiveness / defense * 2
       out