001 /*
002 * Created on Sep 15, 2003 by Ravi Mohan
003 *
004 */
005 package aima.logic.propositional.parsing;
006
007 import java.util.ArrayList;
008 import java.util.List;
009
010 import aima.logic.common.LogicTokenTypes;
011 import aima.logic.common.ParseTreeNode;
012 import aima.logic.common.Parser;
013 import aima.logic.common.Token;
014 import aima.logic.propositional.parsing.ast.AtomicSentence;
015 import aima.logic.propositional.parsing.ast.BinarySentence;
016 import aima.logic.propositional.parsing.ast.FalseSentence;
017 import aima.logic.propositional.parsing.ast.MultiSentence;
018 import aima.logic.propositional.parsing.ast.Sentence;
019 import aima.logic.propositional.parsing.ast.Symbol;
020 import aima.logic.propositional.parsing.ast.TrueSentence;
021 import aima.logic.propositional.parsing.ast.UnarySentence;
022
023 /**
024 * @author Ravi Mohan
025 *
026 */
027
028 public class PEParser extends Parser {
029
030 public PEParser() {
031 lookAheadBuffer = new Token[lookAhead];
032 }
033
034 @Override
035 public ParseTreeNode parse(String inputString) {
036 lexer = new PELexer(inputString);
037 fillLookAheadBuffer();
038 return parseSentence();
039 }
040
041 private TrueSentence parseTrue() {
042
043 consume();
044 return new TrueSentence();
045
046 }
047
048 private FalseSentence parseFalse() {
049 consume();
050 return new FalseSentence();
051
052 }
053
054 private Symbol parseSymbol() {
055 String sym = lookAhead(1).getText();
056 consume();
057 return new Symbol(sym);
058 }
059
060 private AtomicSentence parseAtomicSentence() {
061 Token t = lookAhead(1);
062 if (t.getType() == LogicTokenTypes.TRUE) {
063 return parseTrue();
064 } else if (t.getType() == LogicTokenTypes.FALSE) {
065 return parseFalse();
066 } else if (t.getType() == LogicTokenTypes.SYMBOL) {
067 return parseSymbol();
068 } else {
069 throw new RuntimeException(
070 "Error in parseAtomicSentence with Token " + lookAhead(1));
071 }
072 }
073
074 private UnarySentence parseNotSentence() {
075 match("NOT");
076 Sentence sen = parseSentence();
077 return new UnarySentence(sen);
078 }
079
080 private MultiSentence parseMultiSentence() {
081 consume();
082 String connector = lookAhead(1).getText();
083 consume();
084 List<Sentence> sentences = new ArrayList<Sentence>();
085 while (lookAhead(1).getType() != LogicTokenTypes.RPAREN) {
086 Sentence sen = parseSentence();
087 // consume();
088 sentences.add(sen);
089 }
090 match(")");
091 return new MultiSentence(connector, sentences);
092 }
093
094 private Sentence parseSentence() {
095 if (detectAtomicSentence()) {
096 return parseAtomicSentence();
097 } else if (detectBracket()) {
098 return parseBracketedSentence();
099 } else if (detectNOT()) {
100 return parseNotSentence();
101 } else {
102
103 throw new RuntimeException("Parser Error Token = " + lookAhead(1));
104 }
105 }
106
107 private boolean detectNOT() {
108 return (lookAhead(1).getType() == LogicTokenTypes.CONNECTOR)
109 && (lookAhead(1).getText().equals("NOT"));
110 }
111
112 private Sentence parseBracketedSentence() {
113
114 if (detectMultiOperator()) {
115 return parseMultiSentence();
116 } else {
117 match("(");
118 Sentence one = parseSentence();
119 if (lookAhead(1).getType() == LogicTokenTypes.RPAREN) {
120 match(")");
121 return one;
122 } else if ((lookAhead(1).getType() == LogicTokenTypes.CONNECTOR)
123 && (!(lookAhead(1).getText().equals("Not")))) {
124 String connector = lookAhead(1).getText();
125 consume(); // connector
126 Sentence two = parseSentence();
127 match(")");
128 return new BinarySentence(connector, one, two);
129 }
130
131 }
132 throw new RuntimeException(
133 " Runtime Exception at Bracketed Expression with token "
134 + lookAhead(1));
135 }
136
137 private boolean detectMultiOperator() {
138 return (lookAhead(1).getType() == LogicTokenTypes.LPAREN)
139 && ((lookAhead(2).getText().equals("AND")) || (lookAhead(2)
140 .getText().equals("OR")));
141 }
142
143 private boolean detectBracket() {
144 return lookAhead(1).getType() == LogicTokenTypes.LPAREN;
145 }
146
147 private boolean detectAtomicSentence() {
148 int type = lookAhead(1).getType();
149 return (type == LogicTokenTypes.TRUE)
150 || (type == LogicTokenTypes.FALSE)
151 || (type == LogicTokenTypes.SYMBOL);
152 }
153 }