public PartialRule(PartialRule rule, int start = 0, int?length = null)
: this(rule.Rule, start + rule.Start, length ?? (rule.Length - start))
{
if (length.HasValue && length.Value > rule.Length)
{
throw new ArgumentOutOfRangeException(nameof(length), length, "must be in range of " + nameof(rule));
}
}
/// <summary>
/// Recursively gathers a set of <see cref="Symbol"/> lists which could form the remainder after consuming
/// a <paramref name="prefixToken"/>
/// </summary>
private void GatherPostTokenSuffixes(
Token prefixToken,
PartialRule rule,
ImmutableStack <Symbol> suffix,
ISet <IReadOnlyList <Symbol> > result)
{
if (rule.Symbols.Count == 0)
{
if (!suffix.IsEmpty)
{
var nextSuffixSymbol = suffix.Peek();
if (nextSuffixSymbol is Token)
{
if (nextSuffixSymbol == prefixToken)
{
result.Add(suffix.Skip(1).ToArray());
}
}
else
{
var newSuffix = suffix.Pop();
var innerRules = this.rules[(NonTerminal)nextSuffixSymbol]
.Where(r => this.firstFollow.NextOf(r).Contains(prefixToken));
foreach (var innerRule in innerRules)
{
this.GatherPostTokenSuffixes(prefixToken, new PartialRule(innerRule), newSuffix, result);
}
}
}
else
{
throw new NotSupportedException("can't remove prefix from empty");
}
}
else if (rule.Symbols[0] is Token)
{
if (rule.Symbols[0] == prefixToken)
{
result.Add(rule.Symbols.Skip(1).Concat(suffix).ToArray());
}
return;
}
else
{
// the new suffix adds the rest of the current rule, from back to front
// to preserve ordering
var newSuffix = suffix;
for (var i = rule.Symbols.Count - 1; i > 0; --i)
{
newSuffix = newSuffix.Push(rule.Symbols[i]);
}
var innerRules = this.rules[(NonTerminal)rule.Symbols[0]]
.Where(r => this.firstFollow.NextOf(r).Contains(prefixToken));
foreach (var innerRule in innerRules)
{
this.GatherPostTokenSuffixes(prefixToken, new PartialRule(innerRule), newSuffix, result);
}
}
}
// to support initial prefix, we'll just add the ability to pass a null rule plus a suffix stack
private ISet <IReadOnlyList <Symbol> > GatherPostTokenSuffixes(Token prefixToken, PartialRule rule)
{
var result = new HashSet <IReadOnlyList <Symbol> >();
this.GatherPostTokenSuffixes(prefixToken, rule, ImmutableStack <Symbol> .Empty, result);
return(result);
}
public ParseRuleNode(PartialRule rule)
{
this.Rule = rule;
}
public static IImmutableSet <Token> NextOf(this IFirstFollowProvider provider, PartialRule partialRule)
{
var firsts = provider.FirstOf(partialRule.Symbols);
return(firsts.ContainsDefault()
? firsts.RemoveDefault().Union(provider.FollowOf(partialRule.Rule))
: firsts);
}
