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| package org.apache.hivemind.conditional; |
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| import org.apache.hivemind.util.Defense; |
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| public class Parser |
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| { |
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| private String _input; |
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| |
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| private Lexer _lexer; |
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| private Token _nextToken; |
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| private boolean _onDeck; |
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| private static final Evaluator NOT_EVALUATOR = new NotEvaluator(); |
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| private static final Evaluator OR_EVALUATOR = new OrEvaluator(); |
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| private static final Evaluator AND_EVALUATOR = new AndEvaluator(); |
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| public Node parse(String input)
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| { |
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| Defense.notNull(input, "input");
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| try
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| { |
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| _input = input;
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| _lexer = new Lexer(input);
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| Node result = expression();
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| Token token = next();
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| if (token != null)
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| throw new RuntimeException(ConditionalMessages.unparsedToken(token, _input));
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| return result;
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| } |
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| finally |
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| { |
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| _input = null;
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| _nextToken = null;
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| _lexer = null;
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| _onDeck = false;
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| } |
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| } |
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| private Token next()
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| { |
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| Token result = _onDeck ? _nextToken : _lexer.next();
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| _onDeck = false;
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| _nextToken = null;
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| return result;
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| } |
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| private Token match(TokenType expected)
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| { |
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| Token actual = next();
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| if (actual == null)
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| throw new RuntimeException(ConditionalMessages.unexpectedEndOfInput(_input));
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| if (actual.getType() != expected)
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| throw new RuntimeException(ConditionalMessages.unexpectedToken(expected, actual
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| .getType(), _input)); |
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| return actual;
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| } |
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| private Token peek()
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| { |
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| if (! _onDeck)
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| { |
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| _nextToken = _lexer.next();
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| _onDeck = true;
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| } |
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| return _nextToken;
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| } |
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| private TokenType peekType()
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| { |
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| Token next = peek();
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| return next == null ? null : next.getType();
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| } |
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| private boolean isPeek(TokenType type)
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| { |
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| return peekType() == type;
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| } |
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| private Node expression()
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| { |
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| Node lnode = term();
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| if (isPeek(TokenType.OR))
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| { |
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| next();
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| Node rnode = expression();
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| return new NodeImpl(lnode, rnode, OR_EVALUATOR);
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| } |
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| if (isPeek(TokenType.AND))
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| { |
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| next();
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| Node rnode = expression();
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| return new NodeImpl(lnode, rnode, AND_EVALUATOR);
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| } |
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| return lnode;
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| } |
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| private Node term()
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| { |
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| if (isPeek(TokenType.OPAREN))
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| { |
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| next();
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| Node result = expression();
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| match(TokenType.CPAREN);
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| return result;
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| } |
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| if (isPeek(TokenType.NOT))
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| { |
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| next();
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| match(TokenType.OPAREN);
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| Node expression = expression();
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| match(TokenType.CPAREN);
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| return new NodeImpl(expression, null, NOT_EVALUATOR);
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| } |
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| if (isPeek(TokenType.PROPERTY))
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| { |
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| next();
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| Token symbolToken = match(TokenType.SYMBOL);
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| Evaluator ev = new PropertyEvaluator(symbolToken.getValue());
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| return new NodeImpl(ev);
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| } |
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| if (isPeek(TokenType.CLASS))
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| { |
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| next();
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| Token symbolToken = match(TokenType.SYMBOL);
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| Evaluator ev = new ClassNameEvaluator(symbolToken.getValue());
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| return new NodeImpl(ev);
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| } |
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| throw new RuntimeException(ConditionalMessages.unparsedToken(next(), _input));
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| } |
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| } |