export type OperatorSymbol = "+" | "-" | "*" | "/";
export declare function performOperation(a: number, b: number, operator: OperatorSymbol): number;
export type CalculatorState = {
    displayValue: string;
    firstOperand: number | null;
    waitingForSecondOperand: boolean;
    operator: OperatorSymbol | null;
};
export declare const initialCalculatorState: CalculatorState;
export declare function inputDigit(state: CalculatorState, digit: string): CalculatorState;
export declare function inputDecimal(state: CalculatorState): CalculatorState;
export declare function clearAll(): CalculatorState;
export declare function applyOperator(state: CalculatorState, nextOperator: OperatorSymbol): CalculatorState;
export declare function equals(state: CalculatorState): CalculatorState;