Single hyphen/dash argument for indicating stdin about optparse-applicative HOT 5 CLOSED

I'm thinking, if there were a mechanism for specifying expected constants, one could use that to both expect a single dash - argument and even support other advanced syntax in the style of ./foo rename <from> to <target>.

I noticed eitherReader. Maybe that combined with argument and metavar could be used to fake what I'm going for...

from optparse-applicative.

For now, I ended up going with:

data PathArg path = StdinArg | PathArg path

Opt.argument
  (Opt.maybeReader parsePathArg)
  (mconcat [Opt.metavar "(-|<csv-path>)"])

parsePathArg "-" = Just StdinArg
parsePathArg path = Just (PathArg path)

from optparse-applicative.

That's more or less what I would have suggested.

from optparse-applicative.

There's a solution to this which you've figured out for yourself, but obviously this could be better documented.

I'll add a page to the wiki for it when I get some time.

from optparse-applicative.

Thanks! And a built-in constant parser may be useful in the future, too, as my solution is rather verbose.

from optparse-applicative.