// Computes set of expected terms in a parser state. While there may be extended list of symbols expected at some point,
// we want to reorganize and reduce it. For example, if the current state expects all arithmetic operators as an input,
// it would be better to not list all operators (+, -, *, /, etc) but simply put "operator" covering them all.
// To achieve this grammar writer can group operators (or any other terminals) into named groups using Grammar's methods
// AddTermReportGroup, AddNoReportGroup etc. Then instead of reporting each operator separately, Irony would include
// a single "group name" to represent them all.
// The "expected report set" is not computed during parser construction (it would bite considerable time), but on demand during parsing,
// when error is detected and the expected set is actually needed for error message.
// Multi-threading concerns. When used in multi-threaded environment (web server), the LanguageData would be shared in
// application-wide cache to avoid rebuilding the parser data on every request. The LanguageData is immutable, except
// this one case - the expected sets are constructed late by CoreParser on the when-needed basis.
// We don't do any locking here, just compute the set and on return from this function the state field is assigned.
// We assume that this field assignment is an atomic, concurrency-safe operation. The worst thing that might happen
// is "double-effort" when two threads start computing the same set around the same time, and the last one to finish would
// leave its result in the state field.
#endregion
internal static StringSet ComputeGroupedExpectedSetForState(Grammar grammar, ParserState state)
{
var terms = new TerminalSet();
terms.UnionWith(state.ExpectedTerminals);
var result = new StringSet();
//Eliminate no-report terminals
foreach (var group in grammar.TermReportGroups)
{
if (group.GroupType == TermReportGroupType.DoNotReport)
{
terms.ExceptWith(group.Terminals);
}
}
//Add normal and operator groups
foreach (var group in grammar.TermReportGroups)
{
if ((group.GroupType == TermReportGroupType.Normal || group.GroupType == TermReportGroupType.Operator) &&
terms.Overlaps(group.Terminals))
{
result.Add(group.Alias);
terms.ExceptWith(group.Terminals);
}
}
//Add remaining terminals "as is"
foreach (var terminal in terms)
{
result.Add(terminal.ErrorAlias);
}
return(result);
}
internal static StringSet ComputeGroupedExpectedSetForState(Grammar grammar, ParserState state)
{
var terms = new TerminalSet();
terms.UnionWith(state.ExpectedTerminals);
var result = new StringSet();
//Eliminate no-report terminals
foreach(var group in grammar.TermReportGroups)
if (group.GroupType == TermReportGroupType.DoNotReport)
terms.ExceptWith(group.Terminals);
//Add normal and operator groups
foreach(var group in grammar.TermReportGroups)
if((group.GroupType == TermReportGroupType.Normal || group.GroupType == TermReportGroupType.Operator) &&
terms.Overlaps(group.Terminals)) {
result.Add(group.Alias);
terms.ExceptWith(group.Terminals);
}
//Add remaining terminals "as is"
foreach(var terminal in terms)
result.Add(terminal.ErrorAlias);
return result;
}