Monadic parsers in Typescript/Javascript

monadic_parser.ts

const parse_int =
  then(or(match('-'), of('')), => s
  then(many(isNumber),         => digits
  of(Number(s + digits))))
  
/*
in ML-style lang, this might look like this:

parse_int = do
  s      <- match '-' <|> unit ''
  digits <- many number
  Number(s + digits)
*/