private static IEnumerable <Production <SYMBOL_ENUM, TREE_NODE> > unfoldIdentityProductions(StringRep <SYMBOL_ENUM> symbolsRep,
IEnumerable <Production <SYMBOL_ENUM, TREE_NODE> > productions,
SYMBOL_ENUM eofSymbol, SYMBOL_ENUM syntaxErrorSymbol)
{
var used_aliases = new HashSet <SYMBOL_ENUM>();
while (true)
{
var result = new Productions <SYMBOL_ENUM, TREE_NODE>(symbolsRep, productions, eofSymbol, syntaxErrorSymbol, s => {});
List <Production <SYMBOL_ENUM, TREE_NODE> > new_productions = null;
CoverSets <SYMBOL_ENUM> cover_sets = new BuilderCoverSets <SYMBOL_ENUM, TREE_NODE>(result, lookaheadWidth: 1).ComputeCoverSets();
foreach (SYMBOL_ENUM non_term in result.NonTerminals)
{
if (!used_aliases.Contains(non_term) &&
!cover_sets.IsRecursive(non_term) &&
result.isAlias(non_term))
{
used_aliases.Add(non_term);
// todo: this won't work for multi-param alias rules
SYMBOL_ENUM[] expansions = result.FilterByLhs(non_term).Select(it => it.RhsSymbols.Single()).ToArray();
new_productions = new List <Production <SYMBOL_ENUM, TREE_NODE> >();
UnAliasing change = UnAliasing.NoChange;
foreach (Production <SYMBOL_ENUM, TREE_NODE> p in productions.Where(it => !it.LhsNonTerminal.Equals(non_term)))
{
new_productions.AddRange(
unAliasProductionRhs(non_term, expansions, p, result.StartSymbol, syntaxErrorSymbol, ref change)
.Select(rhs => new Production <SYMBOL_ENUM, TREE_NODE>(
symbolsRep,
p.LhsNonTerminal,
p.Recursive,
rhs,
p.UserAction,
// todo: this won't work for multi-param alias rules
p.IdentityOuterFunctionParamIndex)));
// we need to break right-away, otherwise "change" variable could be changed in next expansion to "expanded"
if (change == UnAliasing.Forbidden)
{
break;
}
}
if (change == UnAliasing.Expansion)
{
break;
}
else
{
new_productions = null;
}
}
}
// all non terminals checked or productions were expanded
if (new_productions == null)
{
break;
}
else
{
productions = new_productions;
}
}
return(productions);
}
private static IEnumerable <Production <SYMBOL_ENUM, TREE_NODE> > unfoldErrorProductions_NOT_USED(StringRep <SYMBOL_ENUM> symbolsRep,
IEnumerable <Production <SYMBOL_ENUM, TREE_NODE> > productions,
SYMBOL_ENUM eofSymbol, SYMBOL_ENUM syntaxErrorSymbol)
{
var result = new Productions <SYMBOL_ENUM, TREE_NODE>(symbolsRep, productions, eofSymbol, syntaxErrorSymbol, s => { });
var new_productions = new List <Production <SYMBOL_ENUM, TREE_NODE> >();
// compute all non-terminals that serve as aliases for terminals
// alias is a symbol that can be substituted by single terminal, for example
// a := A | B (this is alias)
// a := A B (this is not an alias)
// we start with terminals, because they serve as aliases too (to themselves)
DynamicDictionary <SYMBOL_ENUM, HashSet <SYMBOL_ENUM> > term_aliases = result.Terminals
.Select(it => Tuple.Create(it, new HashSet <SYMBOL_ENUM>(new[] { it })))
.ToDefaultDynamicDictionary();
// this is not cover set algorithm!
while (true)
{
int count = term_aliases.Count;
foreach (SYMBOL_ENUM non_term in result.NonTerminals.Where(it => !term_aliases.ContainsKey(it)))
{
bool found = true;
foreach (Production <SYMBOL_ENUM, TREE_NODE> prod in result.FilterByLhs(non_term))
{
if (prod.RhsSymbols.Count != 1 || !term_aliases.ContainsKey(prod.RhsSymbols.Single()))
{
found = false;
break;
}
}
if (found)
{
term_aliases[non_term].AddRange(result.FilterByLhs(non_term).Select(it => term_aliases[it.RhsSymbols.Single()]).Flatten());
}
}
if (count == term_aliases.Count)
{
break;
}
}
// check the placement of error token in every error production
foreach (Production <SYMBOL_ENUM, TREE_NODE> prod in productions)
{
IEnumerable <SYMBOL_ENUM> error_symbols = prod.RhsSymbols.Where(it => it.Equals(result.SyntaxErrorSymbol));
if (error_symbols.Any())
{
new_productions.Add(prod);
}
else if (error_symbols.Count() > 1)
{
throw new ArgumentException("Only one syntax error token per production: " + prod.PositionDescription);
}
else
{
int idx = prod.RhsSymbols.IndexOf(result.SyntaxErrorSymbol);
if (idx != prod.RhsSymbols.Count - 2)
{
throw new ArgumentException("Syntax error token has to be next to last: " + prod.PositionDescription);
}
SYMBOL_ENUM recovery_symbol = prod.RhsSymbols[idx + 1];
if (!term_aliases.ContainsKey(recovery_symbol))
{
throw new ArgumentException("There has to be a terminal or alias non-terminal after syntax error token: " + prod.PositionDescription);
}
else if (result.NonTerminals.Contains(recovery_symbol))
{
foreach (SYMBOL_ENUM term in term_aliases[recovery_symbol])
{
new_productions.Add(new Production <SYMBOL_ENUM, TREE_NODE>(
symbolsRep,
prod.LhsNonTerminal,
prod.Recursive,
prod.RhsSymbols.SkipTail(1).Concat(term), // replacing aliased terminal
prod.UserAction,
prod.IdentityOuterFunctionParamIndex));
}
}
else
{
new_productions.Add(prod);
}
}
}
return(new_productions);
}
