Sprache parser with custom fields

Question

I have a report server that needs to parse a string with some arguments controlling what is in the report.

I am using the parser library sprache to help with this. All is working fine except for one thing I'm stuck on.

I have a time filter that can be one of the following values: today, yesterday, last week, last month, none or custom.

It is custom that is giving me some grief. All of the others are just simple strings. Custom also has a from and to properties afterwards.

   private static readonly Parser<DataFilterEntity> TimeFilter =
        from filter in Parse.String("today").Return(DataFilterEntity.Today)
            .Or(Parse.String("yesterday").Return(DataFilterEntity.Yesterday)
            .Or(Parse.String("last week").Return(DataFilterEntity.LastWeek)
            .Or(Parse.String("last month").Return(DataFilterEntity.LastMonth)
            .Or(Parse.String("none").Return(DataFilterEntity.None))
            .Or(Parse.String("custom").Return(DataFilterEntity.Custom())))))
        select filter;

The custom line is the problem. I need to parse the "custom" string but then parse the from and to DateTime fields as well and pass them through to DataFilterEntity.Custom(from, to)

Any ideas much appreciated.

Answer 1

You need to create a parser for DateTime first and then a parser for your custom type. Here's a 'simplest thing that could possibly work' example. You'd probably want to make the DateTimeParser a bit more specific in the values it accepts. I don't know what the constructor for your DataFilterEntity looks like, so I guessed :)

public static readonly Parser<DateTime> DateTimeParser =
    from day in Parse.Number
    from s1 in Parse.Char('/')
    from month in Parse.Number
    from s2 in Parse.Char('/')
    from year in Parse.Number
    select new DateTime(int.Parse(year), int.Parse(month), int.Parse(day));

public static readonly Parser<DataFilterEntity> CustomParser =
    from a1 in Parse.String("custom").Token()
    from fromDateTime in DateTimeParser.Token()
    from toDateTime in DateTimeParser.Token()
    select new DataFilterEntity(fromDateTime.ToShortDateString() + " -> " + toDateTime.ToShortDateString());

public static readonly Parser<DataFilterEntity> TimeFilter =
    Parse.String("today").Return(DataFilterEntity.Today)
        .Or(Parse.String("yesterday").Return(DataFilterEntity.Yesterday)
        .Or(Parse.String("last week").Return(DataFilterEntity.LastWeek)
        .Or(Parse.String("last month").Return(DataFilterEntity.LastMonth)
        .Or(Parse.String("none").Return(DataFilterEntity.None))
        .Or(CustomParser))));

public void TestIt()
{
    var result = TimeFilter.Parse("custom 21/3/2013 10/4/2013");
    Console.Out.WriteLine("result.Value = {0}", result.Value);
}