private GdlVariable ParseVariable(Lexer lexer)
{
int token = lexer.Token();
// Make sure we actually got an identifier
if (token <= 255)
ReportError("? token must be followed by an identifier token in variable parsing");
return GdlVariable.GetGdlVariable(_symbolTable, token);
}
private GdlList ParseList(Lexer lexer)
{
var arr = new List<GdlExpression>();
int token;
while ((token = lexer.Token()) != ')')
{
if (token == Lexer.Eof)
{
ReportError("Unexpected end of file in parseList");
}
// put this token back, and parse the expression
lexer.Unget(token);
arr.Add(ParseExpression(lexer));
}
// Convert the ArrayList to an array, and return a new GdlList object.
return new GdlList(_symbolTable, arr.ToArray());
}
private static void ReportError(String str, Lexer lexer = null)
{
string message = lexer != null
? string.Format("Parser error (line {0}): {1}", lexer.GetLineNumber(), str)
: string.Format("Parser error: {0}", str);
throw new ApplicationException(message);
}
private GdlExpression ParseExpression(Lexer lexer)
{
// Get the token:
int t = lexer.Token();
// If it's a (, then we must have a new expression
if (t == '(')
return ParseList(lexer);
// If it's an identifier, then we have an atom
if (t > 255)
return new GdlAtom(_symbolTable, t);
// If it's a question mark, then we have a variable
if (t == '?')
return ParseVariable(lexer);
ReportError("Expression: can't handle token " + t + " (char: " + (char)t + ")");
return null;
}
public GdlList Parse(TextReader input)
{
var lexer = new Lexer(input, _symbolTable);
// Top-level is a list of expressions.
var exprs = new List<GdlExpression>();
while (true)
{
int t = lexer.Token();
if (t == -1)
break;
lexer.Unget(t);
exprs.Add(ParseExpression(lexer));
}
return new GdlList(_symbolTable, exprs.ToArray());
}
