/// <summary>
/// Returns the next token to be used by the parser.
/// </summary>
/// <returns></returns>
public PrologToken Next()
{
if (_peeked == true)
{
_current = _lookahead;
_peeked = false;
return(_current);
}
PrologToken tok = new PrologToken(PrologToken.EOF, _line, _col);
string val = "";
while (_ch != EOF)
{
/* comment encountered */
if (_ch == '%')
{
while (_input.Read() != '\n')
{
}
NextCharacter();
continue;
}
if (_ch == '/')
{
_ch = (char)_input.Peek();
if (_ch == '*')
{
// Comment started
_input.Read();
while (true)
{
_ch = (char)_input.Peek();
if (_ch == '*')
{
_input.Read();
_ch = (char)_input.Peek();
if (_ch == '/')
{
_input.Read();
NextCharacter();
break;
}
else
{
//_input.Read();
}
}
else
{
_input.Read();
}
}
}
else
{
_ch = '/';
}
}
if (_ch == '_')
{
tok.Kind = PrologToken.ATOM;
tok.StringValue = _ch.ToString();
_current = tok;
NextCharacter();
return(tok);
}
/* Recognizes: numbers */
if (Char.IsDigit(_ch))
{
tok.Kind = PrologToken.ATOM;
while (Char.IsDigit(_ch))
{
val += _ch.ToString();
NextCharacter();
}
tok.IntValue = Int32.Parse(val);
tok.StringValue = val;
_current = tok;
return(tok);
}
/* Recognizes: identifiers, not, mod */
else if (Char.IsLetter(_ch))
{
tok.Kind = PrologToken.ATOM;
while (Char.IsLetterOrDigit(_ch) || _ch == '_')
{
val += _ch.ToString();
NextCharacter();
}
if (Char.IsUpper(val, 0) || val[0] == '_' || val == "_")
{
tok.Kind = PrologToken.VARIABLE;
}
tok.StringValue = val;
_current = tok;
return(tok);
}
else if (Char.IsPunctuation(_ch) || Char.IsSymbol(_ch))
{
tok.Kind = PrologToken.ATOM;
val += _ch.ToString();
switch (val)
{
case ",":
tok.Kind = PrologToken.COMMA;
NextCharacter();
break;
case "|":
tok.Kind = PrologToken.LIST_SEP;
NextCharacter();
break;
case "(":
tok.Kind = PrologToken.LPAREN;
NextCharacter();
break;
case ")":
tok.Kind = PrologToken.RPAREN;
NextCharacter();
break;
case "[":
tok.Kind = PrologToken.LBRACKET;
NextCharacter();
break;
case "]":
tok.Kind = PrologToken.RBRACKET;
NextCharacter();
break;
case "!":
tok.Kind = PrologToken.STRING;
NextCharacter();
break;
case ".":
tok.Kind = PrologToken.DOT;
NextCharacter();
break;
case "'":
tok.Kind = PrologToken.STRING;
NextCharacter();
while (_ch != '\'')
{
val += _ch.ToString();
NextCharacter();
}
NextCharacter();
//val = val.Remove(0,1);
val += "'";
tok.StringValue = val;
_current = tok;
break;
case "\"":
tok.Kind = PrologToken.STRING;
NextCharacter();
while (_ch != '"')
{
val += _ch.ToString();
NextCharacter();
}
NextCharacter();
//val = val.Remove(0,1);
val += "\"";
tok.StringValue = val;
_current = tok;
break;
//default:
// Error("Invalid token: " + val);
// break;
}
if (tok.Kind != PrologToken.ATOM)
{
tok.StringValue = val;
if (tok.Kind == PrologToken.STRING)
{
tok.Kind = PrologToken.ATOM;
}
_current = tok;
return(tok);
}
val = "";
while ((Char.IsPunctuation(_ch) || Char.IsSymbol(_ch)) && _ch != '(')
{
val += _ch.ToString();
NextCharacter();
}
tok.StringValue = val;
_current = tok;
return(tok);
}
NextCharacter();
}
_current = tok;
return(tok);
}
/// <summary>
/// Returns the next token to be used by the parser.
/// </summary>
/// <returns></returns>
public PrologToken Next()
{
if(_peeked == true)
{
_current = _lookahead;
_peeked = false;
return _current;
}
PrologToken tok = new PrologToken(PrologToken.EOF, _line, _col);
string val = "";
while(_ch != EOF)
{
/* comment encountered */
if(_ch == '%')
{
while(_input.Read() != '\n')
{
}
NextCharacter();
continue;
}
if (_ch == '/')
{
_ch = (char)_input.Peek();
if (_ch == '*')
{
// Comment started
_input.Read();
while (true)
{
_ch = (char)_input.Peek();
if (_ch == '*')
{
_input.Read();
_ch = (char)_input.Peek();
if (_ch == '/')
{
_input.Read();
NextCharacter();
break;
}
else
{
//_input.Read();
}
}
else
{
_input.Read();
}
}
}
else
{
_ch = '/';
}
}
if(_ch == '_')
{
tok.Kind = PrologToken.ATOM;
tok.StringValue = _ch.ToString();
_current = tok;
NextCharacter();
return tok;
}
/* Recognizes: numbers */
if(Char.IsDigit(_ch))
{
tok.Kind = PrologToken.ATOM;
while(Char.IsDigit(_ch))
{
val += _ch.ToString();
NextCharacter();
}
tok.IntValue = Int32.Parse(val);
tok.StringValue = val;
_current = tok;
return tok;
}
/* Recognizes: identifiers, not, mod */
else if(Char.IsLetter(_ch))
{
tok.Kind = PrologToken.ATOM;
while(Char.IsLetterOrDigit(_ch) || _ch == '_')
{
val += _ch.ToString();
NextCharacter();
}
if(Char.IsUpper(val, 0) || val[0] == '_' || val == "_")
{
tok.Kind = PrologToken.VARIABLE;
}
tok.StringValue = val;
_current = tok;
return tok;
}
else if(Char.IsPunctuation(_ch) || Char.IsSymbol(_ch))
{
tok.Kind = PrologToken.ATOM;
val += _ch.ToString();
switch(val)
{
case ",":
tok.Kind = PrologToken.COMMA;
NextCharacter();
break;
case "|":
tok.Kind = PrologToken.LIST_SEP;
NextCharacter();
break;
case "(":
tok.Kind = PrologToken.LPAREN;
NextCharacter();
break;
case ")":
tok.Kind = PrologToken.RPAREN;
NextCharacter();
break;
case "[":
tok.Kind = PrologToken.LBRACKET;
NextCharacter();
break;
case "]":
tok.Kind = PrologToken.RBRACKET;
NextCharacter();
break;
case "!":
tok.Kind = PrologToken.STRING;
NextCharacter();
break;
case ".":
tok.Kind = PrologToken.DOT;
NextCharacter();
break;
case "'":
tok.Kind = PrologToken.STRING;
NextCharacter();
while(_ch != '\'')
{
val += _ch.ToString();
NextCharacter();
}
NextCharacter();
//val = val.Remove(0,1);
val += "'";
tok.StringValue = val;
_current = tok;
break;
case "\"":
tok.Kind = PrologToken.STRING;
NextCharacter();
while (_ch != '"')
{
val += _ch.ToString();
NextCharacter();
}
NextCharacter();
//val = val.Remove(0,1);
val += "\"";
tok.StringValue = val;
_current = tok;
break;
//default:
// Error("Invalid token: " + val);
// break;
}
if(tok.Kind != PrologToken.ATOM)
{
tok.StringValue = val;
if(tok.Kind == PrologToken.STRING)
tok.Kind = PrologToken.ATOM;
_current = tok;
return tok;
}
val = "";
while((Char.IsPunctuation(_ch) || Char.IsSymbol(_ch)) && _ch != '(')
{
val += _ch.ToString();
NextCharacter();
}
tok.StringValue = val;
_current = tok;
return tok;
}
NextCharacter();
}
_current = tok;
return tok;
}
