cancelling a match programmatically

[Brannon King]

In considering the question of how to do numerical range checking, it seems that I should be able to do something like this:

 

var number = new NumberParser();

number.PreMatch += n => { double d; return double.TryParse(n.StringValue, out d) && d < 2000.0; };

 

However, I don't see any way to return whether or not that match was successful. It might also be useful to set an error message in that scenario.

[Curtis Wensley]

The way to do this would be to subclass NumericParser and override InnerParse() to do what you want.. e.g.

public class MyNumeric : NumberParser

{

public int MinValue { get; set; }

public int MaxValue { get; set; }

protected override ParseMatch InnerParse(ParseArgs args)

{

var pos = args.Scanner.Position;

var match = base.InnerParse(args);

if (match.Success)

{

var str = args.Scanner.SubString(match.Index, match.Length);

int val;

if (int.TryParse(str, out val))

{

if (val >= MinValue && val <= MaxValue)

{

return match;

}

}

}

args.Scanner.SetPosition(pos);

return args.NoMatch;

}

}

PreMatch/Match events are called after the parsing has completed..  it is an alternative to navigating the match tree manually.

[Brannon King]

Overriding InnerParse works well for doing a custom match. How do I add a custom error message to go with it?

[Curtis Wensley]

Override Parser.GetErrorMessage()