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/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package parser;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
/**
*
* @author edwajohn
*/
public class Util {
public static final String EPSILON = "EPSILON";
public static final String EOF = "$";
public static HashMap<String, HashSet<String>> computeFirst(ArrayList<String> symbols, HashSet<String> terminals, ArrayList<Rule> rules) {
HashMap<String, HashSet<String>> first = new HashMap<>();
for (String symbol : symbols) {
first.put(symbol, new HashSet<>());
}
for (String terminal : terminals) {
first.get(terminal).add(terminal);
}
// Algorithm 3.7
boolean changed = true;
while (changed) {
changed = false;
for (Rule rule : rules) {
ArrayList<String> rhsSymbols = rule.getRhs();
HashSet<String> rhs = new HashSet<>();
final String B0 = rhsSymbols.get(0);
rhs.addAll(noEpsilon(first.get(B0)));
boolean stop = !first.get(B0).contains(EPSILON);
for (int i = 0; !stop && i < rhsSymbols.size() - 1; ++i) {
final String B = rhsSymbols.get(i + 1);
rhs.addAll(noEpsilon(first.get(B0)));
stop = !first.get(B).contains(EPSILON);
}
if (!stop) {
rhs.add(EPSILON);
}
final String A = rule.getLhs();
if (!first.get(A).containsAll(rhs)) {
first.get(A).addAll(rhs);
changed = true;
}
}
}
// System.out.println("\n");
// for (String symbol : symbols) {
// final String A = symbol;
// System.out.println("FIRST(" + A + ") = " + first.get(A));
// }
return first;
}
public static HashMap<String, HashSet<String>> computeFollow(
ArrayList<String> symbols, HashSet<String> terminals, ArrayList<Rule> rules,
HashMap<String, HashSet<String>> first) {
HashMap<String, HashSet<String>> follow = new HashMap<>();
for (String symbol : symbols) {
follow.put(symbol, new HashSet<>());
}
follow.get(rules.get(0).getLhs()).add(EOF);
boolean changed = true;
while (changed) {
changed = false;
for (Rule rule : rules) {
HashSet<String> trailer = new HashSet<>(follow.get(rule.getLhs()));
final ArrayList<String> rhsSymbols = rule.getRhs();
for (int i = rhsSymbols.size() - 1; i >= 0; --i) {
final String Bi = rhsSymbols.get(i);
if (!terminals.contains(Bi)) {
if (!follow.get(Bi).containsAll(trailer)) {
follow.get(Bi).addAll(trailer);
changed = true;
}
if (first.get(Bi).contains(EPSILON)) {
trailer.addAll(noEpsilon(first.get(Bi)));
} else {
trailer = first.get(Bi);
}
} else {
trailer = first.get(Bi);
}
}
}
}
// System.out.println("\n");
// for (String symbol : symbols) {
// if (!terminals.contains(symbol)) {
// System.out.println("FOLLOW(" + symbol + ") = " + follow.get(symbol));
// }
// }
return follow;
}
public static HashMap<Rule, HashSet<String>> computeFirstPlus(
ArrayList<String> symbols, HashSet<String> terminals, ArrayList<Rule> rules,
HashMap<String, HashSet<String>> first, HashMap<String, HashSet<String>> follow) {
HashMap<Rule, HashSet<String>> firstPlus = new HashMap<>();
for (Rule rule : rules) {
final String A = rule.getLhs();
final String B = rule.getRhs().get(0);
HashSet<String> firstPlusA = new HashSet<>();
if (!first.get(B).contains(EPSILON)) {
firstPlusA.addAll(first.get(B));
} else {
firstPlusA.addAll(first.get(B));
firstPlusA.addAll(follow.get(A));
}
firstPlus.put(rule, firstPlusA);
}
// System.out.println("\n");
// for (Rule rule : rules) {
// System.out.println("FIRST+(" + rule + ") = " + firstPlus.get(rule));
// }
return firstPlus;
}
private static HashSet<String> noEpsilon(final HashSet<String> set) {
HashSet<String> s = new HashSet<>(set);
s.remove(EPSILON);
return s;
}
}
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