Bad example or bug in new parser implementation?

[Steve-OH]

The example given at https://docopt.github.io/docopt.net/dev/#help-in-a-external-file has this code:

return Docopt.CreateParser(help)
             .WithVersion("Naval Fate 2.0")
             .Parse(args)
             .Match(Run,
                    result => ShowHelp(result.Help),
                    result => ShowVersion(result.Version),
                    result => OnError(result.Usage));

but there is no public parser variation with a Match method that takes three functions for help, version and usage. It's not clear to me from looking at the source code in Parser.cs whether this is an oversight or working as designed (i.e., there is an IHelpFeaturingParser and an IVersionFeaturingParser but no IHelpAndVersionFeaturingParser).

[atifaziz]

but there is no public parser variation with a Match method that takes three functions for help, version and usage.

You can find the variation nested under IParser<> in Parser.cs:

docopt.net/src/DocoptNet/Parser.cs

Lines 29 to 32 in cc1258e

	TResult Match<TResult>(Func<T, TResult> args,
	Func<IHelpResult, TResult> help,
	Func<IVersionResult, TResult> version,
	Func<IInputErrorResult, TResult> error);

Bear in mind that the Match method changes its arity depending on the API composition. This is pointed out in the API section of the documentation:

The version using Match provides stronger guarantees because the arity of the Match method will change depending on the requested options. For example, if the call to WithVersion is commented-out, the code will fail to compile unless the second argument to Match is also removed or commented-out:

return Docopt.CreateParser(help)
          // .WithVersion("Naval Fate 2.0")
             .Parse(args)
             .Match(Run,
                    result => ShowHelp(result.Help),
                 // result => ShowVersion(result.Version),
                    result => OnError(result.Usage));

In contrast, the version using the switch expression and pattern-matching will never produce a compile-time error but the switch arm for IVersionResult will simply never match at run-time.

[Steve-OH]

I see what the problem was: This is in a project that was migrated from the Old Way, where it wasn't necessary to explicitly list the help option in the usage:

Usage:
    ...
    avi.exe (-h | --help)     <= not needed previously

Options:
    -h --help   Show this screen.
    ...

Without that line, the source generator creates an IBaselineParser instead of an IHelpFeaturingParser.