private ValueExpression EvaluateVariableExpression(IExpression expr)
{
VariableExpression variableExpr = (VariableExpression)expr;
return(_variables.TryGetValue(variableExpr.Name, out double value)
? new ValueExpression(value)
: throw LangException.UnassignedVariable(variableExpr));
}
private string ReadIdentifier(ISourceText stream)
{
const char identifierTerminator = '}';
StringBuilder builder = new StringBuilder("{", 12);
stream.MoveNext();
if (char.IsLetter(stream.Current) || stream.Current == '_')
{
builder.Append(stream.Current);
stream.MoveNext();
}
else
{
Token token = new Token(TokenType.Unknown, stream.Current.ToString(), stream.Position);
throw LangException.UnexpectedToken(token, TokenType.Identifier);
}
while (stream.Current != identifierTerminator)
{
if (char.IsLetterOrDigit(stream.Current) || stream.Current == '_')
{
builder.Append(stream.Current);
stream.MoveNext();
}
else
{
Token token = new Token(TokenType.Unknown, stream.Current.ToString(), stream.Position);
throw LangException.UnexpectedToken(token, identifierTerminator);
}
}
builder.Append(stream.Current);
stream.MoveNext();
string text = builder.ToString();
if (text.Length == 2)
{
Token token = new Token(TokenType.Unknown, identifierTerminator.ToString(), stream.Position - 1);
throw LangException.UnexpectedToken(token, identifierTerminator);
}
return(text);
}
private IExpression ParsePrimaryExpression()
{
switch (_currentToken.Type)
{
case TokenType.Number:
return(new ConstantExpression(Take().Text));
case TokenType.Identifier:
VariableExpression rep = new VariableExpression(Take().Text);
_variables.Add(rep.Name);
return(rep);
case TokenType.OpenParen:
return(ParseGroupingExpression());
default:
throw LangException.UnexpectedToken(_currentToken);
}
}
private string ReadNumber(ISourceText stream)
{
StringBuilder builder = new StringBuilder(8);
bool hasDot = false;
while (true)
{
if (stream.Current == '.')
{
if (!hasDot)
{
hasDot = true;
builder.Append(stream.Current);
stream.MoveNext();
}
else
{
Token token = new Token(TokenType.Unknown, stream.Current.ToString(), stream.Position);
throw LangException.UnexpectedToken(token, TokenType.Number);
}
}
else if (char.IsDigit(stream.Current))
{
builder.Append(stream.Current);
stream.MoveNext();
}
else
{
break;
}
}
char peeked = stream.Peek(-1);
if (peeked == '.')
{
Token token = new Token(TokenType.Unknown, peeked.ToString(), stream.Position);
throw LangException.UnexpectedToken(token, TokenType.Number);
}
return(builder.ToString());
}
private Token Match(TokenType tokenType)
{
return(_currentToken.Type == tokenType
? Take()
: throw LangException.UnexpectedToken(_currentToken, tokenType));
}