/// <summary> Recursive exploration for <see cref="Shifts"/>. </summary>
private IEnumerable <KeyValuePair <int, ParserState.RulePosition> > AllShifts(ParserState.RulePosition rulepos, HashSet <int> alreadySeenRules)
{
if (alreadySeenRules != null)
{
if (rulepos.Position == 0 && alreadySeenRules.Contains(rulepos.Rule))
{
// This rule was already seen during the recursive exploration
yield break;
}
}
var rule = Rules.GetRule(rulepos.Rule);
var pos = rulepos.Position;
// Reached the end of the rule, only reduce is allowed now
if (rule.Steps.Count == pos)
{
yield break;
}
var step = rule.Steps[pos];
// These values move us one step forward
var next = new ParserState.RulePosition(rulepos.Rule, pos + 1);
foreach (var v in step.Source)
{
yield return(new KeyValuePair <int, ParserState.RulePosition>(v, next));
}
if (step.IsTerminal)
{
yield break;
}
// Non-terminals allow stepping into any of their sub-rules, so consider
// these as well using depth-first exploration using a hashset to avoid
// infinite loops.
if (alreadySeenRules == null)
{
alreadySeenRules = new HashSet <int>();
}
if (pos == 0)
{
alreadySeenRules.Add(rulepos.Rule);
}
foreach (var v in step.Source)
{
foreach (var kv in AllShifts(new ParserState.RulePosition(v, 0), alreadySeenRules))
{
yield return(kv);
}
}
}
/// <summary> All tokens that can cause this rule to reduce. </summary>
private IEnumerable <int> Reduces(ParserState.RulePosition rulepos)
{
var rule = Rules.GetRule(rulepos.Rule);
var pos = rulepos.Position;
// Reduce only allowed at end of rule
if (rule.Steps.Count > pos)
{
return(new int[0]);
}
return(rule.ReducingTokens);
}
/// <summary> Shifts for a specific position in a rule. </summary> /// <remarks> /// The value is the result of the shift, may be in the same rule or in /// another rule. The key is the shift source, can be either a token /// (in which case the action is a true SLR shift) or a rule (a SLR goto). /// </remarks> private IEnumerable <KeyValuePair <int, ParserState.RulePosition> > Shifts(ParserState.RulePosition rulepos) => AllShifts(rulepos, null);