public static IParsingProduct TryAlternativeParse(
this IEnumerable <IExpressionParser> parsers,
ISourceCode src,
ParsingAlternationType parsingAlternationType = ParsingAlternationType.TakeFirst,
ParsingOptions options = DefaultParsingOptions)
{
if (parsingAlternationType == ParsingAlternationType.TakeFirst)
{
return(parsers.Select(p => p.TryParse(src, options)).FirstNotNullOrDefault());
}
if (parsingAlternationType != ParsingAlternationType.TakeLongest &&
parsingAlternationType != ParsingAlternationType.TakeShortest)
{
throw new NotSupportedException($"{parsingAlternationType} is not supported.");
}
var shortest = parsingAlternationType == ParsingAlternationType.TakeShortest;
var replaceCmp = shortest ? -1 : 1;
IParsingContextStream selectedCtx = null;
IParsingProduct result = null;
foreach (var parser in parsers)
{
var ctx = src.GetFurtherContext();
var res = parser.TryParse(src, options);
if (res != null && (result == null || replaceCmp == ctx.CompareTo(selectedCtx)))
{
selectedCtx?.Dispose();
selectedCtx = ctx;
result = res;
}
}
selectedCtx?.Accept();
return(result);
}