If you want to use getOpt, you could produce options of type 'OptDescr (Either String (Options -> Options))', that is, for a command line argument, either produce an error, or some modification of your options. It is my experience that sometimes you will need a second pass even if you do this, because there are some errors that require the value of multiple options to check. Erik On Sat, Jun 28, 2014 at 9:28 PM, Johan Larson wrote:

I've been looking at choices for parsing command line arguments, including getOpt. The examples I can find focus on string arguments, whereas I am interested in numbers. In the application at hand, it is particularly important to issue clear error messages when arguments don't parse as numbers or are out of range.

I could use getOpt as a first pass with string arguments and then turn the strings into validated numbers in a second pass, but that's a bit awkward. Alternately I could use the options records with Options -> IO Options functions. But both of these solutions treat type mismatches differently from other options errors.

Has anyone found a cleaner solution?

-- Johan Larson -- Toronto, Canada

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You can use http://hackage.haskell.org/package/uu-options, designed to parser command line options. It even allows for combining various elements on the command line into a single option field. See the second half of the paper mentioned on hackage for examples of its use. Since the parsers make use of uu-parsinglib the user gets "autocorrection" and nice error messages for free. Doaitse On 28 Jun 2014, at 21:28 , Johan Larson wrote:

I've been looking at choices for parsing command line arguments, including getOpt. The examples I can find focus on string arguments, whereas I am interested in numbers. In the application at hand, it is particularly important to issue clear error messages when arguments don't parse as numbers or are out of range.

I could use getOpt as a first pass with string arguments and then turn the strings into validated numbers in a second pass, but that's a bit awkward. Alternately I could use the options records with Options -> IO Options functions. But both of these solutions treat type mismatches differently from other options errors.

Has anyone found a cleaner solution?

-- Johan Larson -- Toronto, Canada _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe