Answer by Tarmil for FParsec and postfix modifiers to parsed items

I think you can use opt to allow parseCount to not find a count if there isn't one:

let parseCount =    parseTerm    .>>. opt (choice [ skipChar '*'>>% (MinCount 0)                       skipChar '+'>>% (MinCount 1)                       skipChar '?'>>% (RangeCount(0, 1)) ])    |>> function    | term, None -> term    | term, Some count -> Count (term, count)let parseTerms =    many parseCount .>> eof