private bool TryParseSequence(Cursor <Cobject> current, out SequenceLiteral sequence)
{
if (!Equals(current.Item, Symbol.LeftParent))
{
sequence = null;
return(false);
}
using (Scanner.LevelUp())
{
current.Advance();
IEnumerable <Cobject> Loop()
{
while (current && !Equals(current.Item, Symbol.RightParent))
{
yield return(ParseObject(current));
}
}
sequence = SequenceLiteral.From(Loop().ToList());
if (!current)
{
throw new ParserException("unbalanced `(´ in input");
}
Debug.Assert(Equals(current.Item, Symbol.RightParent));
current.Advance();
return(true);
}
}
private Cobject ParseObject(Cursor <Cobject> current)
{
if (TryParseSequence(current, out var sequence))
{
return(sequence);
}
if (TryParseDefiner(current, out var binder))
{
return(binder);
}
if (TryParseAssigner(current, out var assigner))
{
return(assigner);
}
if (current.Item is Symbol symbol && current.Next && Equals(current.Next.Item, Symbol.ToBind))
{
current.Advance(); // symbol
current.Advance(); // ':='
var value = ParseObject(current);
return(Special.Define(symbol, value));
}
if (Equals(current.Item, Symbol.Quoter))
{
current.Advance();
if (!current)
{
throw new ParserException($"dangling `{Symbol.Quoter}´ at end of input");
}
return(SequenceLiteral.Quote(ParseObject(current)));
}
if (Equals(current.Item, Symbol.RightParent))
{
throw new ParserException($"unbalanced `{Symbol.RightParent}´ in input");
}
var @object = current.Item;
current.Advance();
return(@object);
}
private bool TryParseSymbolSequence(Cursor <Cobject> current, out SequenceLiteral sequence)
{
if (TryParseSequence(current, out sequence))
{
if (sequence.IsEmpty())
{
throw new ParserException($"objects sequence `{sequence}´ should contain at least one symbol");
}
if (!sequence.AllSymbols())
{
throw new ParserException($"objects sequence `{sequence}´ should only contain symbols");
}
return(true);
}
sequence = null;
return(false);
}
