private ProgramObject parseLowerOrderExpression()
{
ProgramObject expression;
ProgramObject tmp;
expression = parseHigherOrderExpression();
while (currentToken.tokenType != TokenType.Then &&
currentToken.tokenType != TokenType.Eol &&
currentToken.tokenType != TokenType.Eof)
{
switch (currentToken.tokenType)
{
case TokenType.And:
tmp = expression;
currentToken = lexer.nextToken();
expression = new LeftAnd(tmp, parseHigherOrderExpression());
break;
case TokenType.Or:
tmp = expression;
currentToken = lexer.nextToken();
expression = new LeftOr(tmp, parseHigherOrderExpression());
break;
case TokenType.Xor:
tmp = expression;
currentToken = lexer.nextToken();
expression = new LeftXor(tmp, parseHigherOrderExpression());
break;
case TokenType.OParenthesis:
currentToken = lexer.nextToken();
expression = parseParenthesis();
break;
case TokenType.CParenthesis:
return(expression);
default:
throw new UnexpectedTokenException(currentToken.value);
}
}
return(expression);
}
private ProgramObject parseHigherOrderExpression()
{
ProgramObject expression = null;
ProgramObject s;
if (currentToken.tokenType == TokenType.Not || currentToken.tokenType == TokenType.Symbol)
{
s = parseSymbol();
switch (currentToken.tokenType)
{
case TokenType.And:
currentToken = lexer.nextToken();
expression = new LeftAnd(s, parseHigherOrderExpression());
break;
case TokenType.Or:
case TokenType.Xor:
case TokenType.Then:
case TokenType.OParenthesis:
case TokenType.CParenthesis:
case TokenType.Eol:
case TokenType.Eof:
expression = s;
break;
}
}
else if (currentToken.tokenType == TokenType.OParenthesis)
{
currentToken = lexer.nextToken();
expression = parseParenthesis();
}
else
{
throw new UnexpectedTokenException(currentToken.value);
}
return(expression);
}