type Binary =
    Add | Sub | Mul |
    Div | Mod | Pow

type Expression =
    | Number of int
    | Variable of string
    | Operation of Binary * Expression * Expression

type Statement =
    | Read of string
    | Write of Expression
    | Assign of string * Expression
    | Sequence of Statement * Statement
    | If of Expression * t * t
    | While of Expression * t

let parseExpression l =
    match l with
    |