/*
* by Ali R+ SARAL
* Please indicate my name if you copy my work.
*/
package nbParse;
import com.sun.xml.internal.fastinfoset.util.CharArray;
import java.nio.CharBuffer;
import java.util.HashMap;
import java.util.Map;
import java.util.Stack;
/**
*
* @author Ali Riza SARAL
*/
public class LRparser {
public enum Symbols {
TS_ONE, // +
TS_EOS, // $
TS_INVALID, // invalid token
// Non-terminal symbols:
NTS_S, // S
NTS_E
}
public enum States {
ST_ZERO,
ST_ONE,
ST_TWO,
ST_THREE
}
Symbols lexer(char c) {
switch (c) {
case '1':
return Symbols.TS_ONE;
case '$':
return Symbols.TS_EOS;
case 'E':
return Symbols.NTS_E;
default:
return Symbols.TS_INVALID;
}
}
public static void main(String[] args) {
LRparser lrparser = new LRparser();
StringBuilder p = new StringBuilder("111$"); // input buffer
int ppointer = 0;
int state = 0;
//initialize the symbol stream cursor
ppointer = 0;
boolean reduced = false;
for (ppointer = 0; ppointer < p.length(); ppointer++) {
if (reduced) {
ppointer = 0;
reduced = false;
}
System.out.println("\np[" + ppointer + "]= " + p.charAt(ppointer));
System.out.println("lexer(p(ppointer))= " + lrparser.lexer(p.charAt(ppointer)));
System.out.println("state= " + state);
System.out.println("p= " + p.toString());
switch (state) {
case 0:
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_ONE) {
System.out.println("1. shift one state 0");
state = 1;
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_EOS) {
System.out.println("none");
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.NTS_E) {
System.out.println("goto state 2");
state = 2;
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_INVALID) {
System.out.println("invalid input");
return;
}
break;
case 1:
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_ONE) {
System.out.println("1. shift one state 1");
state = 1;
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_EOS) {
System.out.println("reduce 2 ");
p.deleteCharAt(ppointer - 1);
p.insert(ppointer - 1, 'E');
state = 0;
ppointer = 0;
reduced = true;
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.NTS_E) {
System.out.println("goto state 3");
state = 3;
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_INVALID) {
System.out.println("invalid input");
return;
}
break;
case 2:
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_ONE) {
System.out.println("none state 2.1");
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_EOS) {
System.out.println("accept ");
state = 0;
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.NTS_E) {
System.out.println("none state 2.3");
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_INVALID) {
System.out.println("invalid input");
return;
}
break;
case 3:
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_ONE) {
System.out.println("none state 3.1");
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_EOS) {
System.out.println("reduce 1 ");
p.deleteCharAt(ppointer - 2);
state = 0;
ppointer = 0;
reduced = true;
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.NTS_E) {
System.out.println("none state 3.3");
}
if (lrparser.lexer(p.charAt(ppointer)) == Symbols.TS_INVALID) {
System.out.println("invalid input");
return;
}
break;
default:
System.out.println("Parsing table default");
return;
}
}
System.out.println("Finished parsing");
return;
}
}
Output:
run:
p[0]= 1
lexer(p(ppointer))= TS_ONE
state= 0
p= 111$
1. shift one state 0
p[1]= 1
lexer(p(ppointer))= TS_ONE
state= 1
p= 111$
1. shift one state 1
p[2]= 1
lexer(p(ppointer))= TS_ONE
state= 1
p= 111$
1. shift one state 1
p[3]= $
lexer(p(ppointer))= TS_EOS
state= 1
p= 111$
reduce 2
p[0]= 1
lexer(p(ppointer))= TS_ONE
state= 0
p= 11E$
1. shift one state 0
p[1]= 1
lexer(p(ppointer))= TS_ONE
state= 1
p= 11E$
1. shift one state 1
p[2]= E
lexer(p(ppointer))= NTS_E
state= 1
p= 11E$
goto state 3
p[3]= $
lexer(p(ppointer))= TS_EOS
state= 3
p= 11E$
reduce 1
p[0]= 1
lexer(p(ppointer))= TS_ONE
state= 0
p= 1E$
1. shift one state 0
p[1]= E
lexer(p(ppointer))= NTS_E
state= 1
p= 1E$
goto state 3
p[2]= $
lexer(p(ppointer))= TS_EOS
state= 3
p= 1E$
reduce 1
none state 3.3
p[0]= E
lexer(p(ppointer))= NTS_E
state= 0
p= E$
goto state 2
p[1]= $
lexer(p(ppointer))= TS_EOS
state= 2
p= E$
accept
Finished parsing
BUILD SUCCESSFUL (total time: 0 seconds)
