type Grammar() =
    let mutable productionRules = []
    let mutable startSymbol  = 'A'

    member this.Grammar() =
        this.addProductionRule("A")
        this.addProductionRule("A->a")
        this.addProductionRule("A->aA")

        //this.addProductionRule("A -> ")

    member this.addProductionRule(line : string) =
        if (line.Contains("->") = false) then
           startSymbol <- line.[0]
        else
            productionRules <- List.append  [(new ProductionRule(line.[0],line.Substring(3) + "$"))]  productionRules

    member this.getRulesForSymbol(symbol : char) =
        let mutable rulesForSymbol = []
        let s = productionRules.Length - 1
        for i in 0..s do
            let rule : ProductionRule = productionRules.[i]
            if (rule.getLeftHandSide() = symbol) then
                rulesForSymbol <- List.append [rule] rulesForSymbol
        rulesForSymbol

    member this.getStartSymbol = startSymbol
    member this.isNonTerminal (symbol : char) = symbol >= 'A' && symbol <= 'Z'