export declare function sum(arr: number[]): number;
export declare function dropWhile<T>(f: (elt: T) => boolean, arr: T[]): T[];
export declare function takeWhile<T>(f: (elt: T) => boolean, arr: T[]): T[];
export declare function timeSlow<T>(label: string, thunk: () => T): T;
export declare function groupBy<T>(inGroup: (x: T, y: T) => boolean, arr: T[]): T[][];
export declare function parseArg<T>(convert: (arg: string) => T, validate: (parsed: T) => boolean, error: string): (arg: any) => any;
export declare function unreachable(): never;