/// <summary>
/// Looks up the specified symbol by scanning the scoped symbol table, starting from the current scope.
/// </summary>
/// <param name="symbol">Symbol to look up in the scope symbol table.</param>
/// <param name="value">Indexed value matching the specified symbol. The outer index represents the scope relative to the current scope, with a value of -1 representing the global scope. The inner index represents the index in the declaring symbol table.</param>
/// <returns>true if the symbol was found; otherwise, false.</returns>
public bool TryLookup(TSymbol symbol, out Indexed <Indexed <TValue> > value)
{
var level = 0;
Indexed <TValue> res;
foreach (var table in _environment)
{
if (table.TryGetValue(symbol, out res))
{
value = new Indexed <Indexed <TValue> >(res, level);
return(true);
}
level++;
}
if (GlobalScope.TryGetValue(symbol, out res))
{
value = new Indexed <Indexed <TValue> >(res, -1);
return(true);
}
value = default;
return(false);
}
/// <summary>
/// Gets the symbol table entry associated with the specified symbol.
/// </summary>
/// <param name="symbol">Symbol to look up in the symbol table.</param>
/// <param name="value">Indexed value matching the specified symbol.</param>
/// <returns>true if the symbol was found; otherwise, false.</returns>
public bool TryGetValue(TSymbol symbol, out Indexed <TValue> value)
{
if (_table.TryGetValue(symbol, out Indexed <TValue> state))
{
value = state;
return(true);
}
value = default;
return(false);
}
/// <summary>
/// Adds an entry to the symbol table.
/// </summary>
/// <param name="symbol">Symbol to add to the table.</param>
/// <param name="value">Value to associate to the symbol.</param>
/// <returns>Indexed entry in the symbol table.</returns>
public Indexed <KeyValuePair <TSymbol, TValue> > Add(TSymbol symbol, TValue value)
{
if (_table.ContainsKey(symbol))
{
throw new InvalidOperationException(string.Format(CultureInfo.InvariantCulture, "Symbol table already contains symbol '{0}'.", symbol));
}
var res = new Indexed <TValue>(value, _table.Count);
_table[symbol] = res;
var entry = new KeyValuePair <TSymbol, TValue>(symbol, value);
_ordered.Add(entry);
return(new Indexed <KeyValuePair <TSymbol, TValue> >(entry, res.Index));
}
/// <summary>
/// Looks up the specified symbol by following the symbol table's parent chain.
/// </summary>
/// <param name="symbol">Symbol to look up in the symbol table and its parents.</param>
/// <param name="value">Indexed value matching the specified symbol. The outer index represents the scope relative to the current table. The inner index represents the index in the declaring symbol table.</param>
/// <returns>true if the symbol was found; otherwise, false.</returns>
public bool TryLookup(TSymbol symbol, out Indexed <Indexed <TValue> > value)
{
var level = 0;
var table = this;
while (table != null)
{
if (table.TryGetValue(symbol, out Indexed <TValue> res))
{
value = new Indexed <Indexed <TValue> >(res, level);
return(true);
}
table = table.Parent;
level++;
}
value = default;
return(false);
}
/// <summary> /// Determines whether this value equals to the specified indexed value. /// Two indexed values matches if both their index and object are equal. /// </summary> /// <param name="other">Other indexed value to compare this value to.</param> /// <returns>true if both indexed values are equal; otherwise, false.</returns> public bool Equals(Indexed <T> other) => Index == other.Index && EqualityComparer <T> .Default.Equals(Value, other.Value);
