362 lines
12 KiB
Java
362 lines
12 KiB
Java
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//This file is part of SECONDO.
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//Copyright (C) 2004, University in Hagen, Department of Computer Science,
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//Database Systems for New Applications.
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//SECONDO is free software; you can redistribute it and/or modify
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//it under the terms of the GNU General Public License as published by
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//the Free Software Foundation; either version 2 of the License, or
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//(at your option) any later version.
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//SECONDO is distributed in the hope that it will be useful,
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//but WITHOUT ANY WARRANTY; without even the implied warranty of
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//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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//GNU General Public License for more details.
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//You should have received a copy of the GNU General Public License
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//along with SECONDO; if not, write to the Free Software
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//Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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import java.io.*;
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import java.net.*;
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import java.util.*;
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import jpl.JPL;
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import jpl.Atom;
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import jpl.Query;
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import jpl.Term;
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import jpl.Variable;
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import jpl.fli.*;
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import jpl.Compound;
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import jpl.List;
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class PrologParser{
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private class Scanner{
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public Scanner(String i){
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input = i;
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nextStart=0;
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length=input.length();
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}
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int getNext(){
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int state = 0;
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int startPos = nextStart;
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int pos = nextStart;
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char c=' ';
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while(pos<length){
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c = input.charAt(pos);
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switch(state){
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case(0) : if(isWhiteSpace(c)){
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pos++;
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}
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else if(c=='\"'){
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startPos=pos;
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pos++;
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state=1;
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}else if( c=='\''){
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startPos=pos;
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pos++;
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state=2;
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}else if(c=='('){
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nextStart=pos+1;
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value="(";
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return OPENBRACKET1;
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}else if(c=='['){
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nextStart=pos+1;
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value="[";
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return OPENBRACKET2;
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}else if(c==')'){
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nextStart=pos+1;
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value=")";
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return CLOSEBRACKET1;
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}else if(c==']'){
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nextStart=pos+1;
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value="]";
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return CLOSEBRACKET2;
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}else if (isUpperCase(c)){
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startPos=pos;
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state=3;
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pos++;
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}else{
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startPos=pos;
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pos++;
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state=4;
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}
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break;
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case(1) : if(c=='\"'){ // string found
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nextStart=pos+1;
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value = input.substring(startPos,pos+1);
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return ATOM;
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}else{
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pos++;
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}
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break;
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case(2) : if(c=='\''){ // founc a complex atom
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nextStart=pos+1;
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value = input.substring(startPos+1,pos);
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return ATOM;
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} else{
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pos++;
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}
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break;
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case(3) : if(isSeparator(c)){
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nextStart=pos;
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value = input.substring(startPos,pos);
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return VARIABLE;
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}else{
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pos++;
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}
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break;
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case(4) : if(isSeparator(c)){
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nextStart=pos;
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value = input.substring(startPos,pos);
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return ATOM;
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}else{
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pos++;
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}
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break;
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}
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}
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// end of input
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nextStart = length;
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switch(state){
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case(0) : value ="";
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return EOI;
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case(1) : value ="unclosed string literal";
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return ERROR;
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case(2) : value ="unclosed atom";
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return ERROR;
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case(3) : value = input.substring(startPos);
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return VARIABLE;
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case(4) : value = input.substring(startPos);
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return ATOM;
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}
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value = "unexpected end";
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return ERROR;
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}
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/** returns the next token
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* in the next getNext command the same token is returned
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* the value is updated
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*/
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public int preview(){
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int oldStart = nextStart;
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int Token = getNext();
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nextStart = oldStart;
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return Token;
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}
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/** returns true if c is upper case */
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private boolean isUpperCase(char c){
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return c>='A' && c <='Z';
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}
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/** returns true if c is a separator without meaning*/
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private boolean isWhiteSpace(char c){
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return c==' ' | c=='\n' | c=='\t' | c==',' | c==';' | c==':' | c=='|';
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}
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/** returns true if c is a character which indicates the end of a atom or a variable */
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private boolean isSeparator(char c){
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return isWhiteSpace(c) | c=='(' | c==')' | c=='[' | c==']' | c=='\"' | c=='\'';
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}
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/** return the value of the last getNext or preview command */
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public String getValue(){
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return value;
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}
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private String value;
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private int nextStart;
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private String input;
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private int length;
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private int EOI = 0; // end of input
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private int ATOM = 1;
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private int VARIABLE = 2;
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private int OPENBRACKET1 = 3; // (
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private int OPENBRACKET2 = 4; // [
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private int CLOSEBRACKET1 = 5; // )
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private int CLOSEBRACKET2 = 6; // ]
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private int ERROR = -1;
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} // class scanner
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/** the method constructs a prolog query from given input
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* if the string is not a valid query, null is returned
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* all
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*/
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public Query parse(String Input,Vector Variables){
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if(Variables==null)
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Variables = new Vector();
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Variables.clear();
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pos = 0;
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ErrorMessage="";
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if(Input==null){
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ErrorMessage="null is not allowed as input ";
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return null;
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}
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Scan = new Scanner(Input);
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Token = Scan.getNext();
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if(Token != Scan.ATOM){
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ErrorMessage="prolog command must begin with an atom";
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return null;
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}
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Atom Command = new Atom(Scan.getValue());
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int P = Scan.preview();
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Vector V;
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if (P==Scan.OPENBRACKET1){
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P = Scan.getNext(); // read over the bracket
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V = getArgumentList(Variables,Scan.CLOSEBRACKET1);
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}
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/*else if(P==Scan.OPENBRACKET2){
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P = Scan.getNext();
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V = getArgumentList(Variables,Scan.CLOSEBRACKET2);
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}*/
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else
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V = getArgumentList(Variables,Scan.EOI);
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P=Scan.preview();
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if(P!=Scan.EOI){
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ErrorMessage="input after end of command found";
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return null;
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}
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if(V==null) // an error is occured
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return null;
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Term[] args= new Term[V.size()];
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for(int i=0;i<V.size();i++)
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args[i] = (Term) V.get(i);
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return new Query(Command,args);
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}
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/** construct one of atom, float, integer, long from the string **/
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private Term getSimpleTerm(String value){
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try{
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int v = Integer.parseInt(value);
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return new jpl.Integer(v);
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}catch(Exception e){}
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try{
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long v = Long.parseLong(value);
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return new jpl.Long((int)v);
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}catch(Exception e){}
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try{
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double v = Double.parseDouble(value);
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return new jpl.Float(v);
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}catch(Exception e){}
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if(value.startsWith("\"") && value.endsWith("\"")){
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return new jpl.String(value.substring(1,value.length()-2));
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}
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return new jpl.Atom(value);
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}
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private Vector getArgumentList(Vector Variables,int EndToken){
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int T = Scan.getNext();
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Vector result = new Vector();
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while(T!=EndToken){ // add the next argument into the Vector
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if(T==Scan.VARIABLE){
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NamedVariable Var = new NamedVariable(Scan.getValue());
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int index = Variables.indexOf(Var);
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if(index<0){ // a new Variable
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result.add(Var.getTerm());
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Variables.add(Var);
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}else{
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result.add(Variables.get(index));
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}
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}else if(T==Scan.ATOM){
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String value = Scan.getValue();
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int P = Scan.preview();
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if(P==Scan.OPENBRACKET1){
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Atom A = new Atom(Scan.getValue());
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int dummy = Scan.getNext(); // read the open bracket
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Vector sublist = getArgumentList(Variables,Scan.CLOSEBRACKET1);
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if(sublist==null) // error in parsing sublist
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return null;
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Term[] args = new Term[sublist.size()];
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for(int i=0;i<sublist.size();i++)
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args[i] = (Term) sublist.get(i);
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result.add(new Compound(A,args));
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} else{
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result.add(getSimpleTerm(value));
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}
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}else if(T==Scan.OPENBRACKET2){ // indicating a prolog list
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Vector sublist = getArgumentList(Variables,Scan.CLOSEBRACKET2);
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if(sublist==null) // error in parsing sublist
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return null;
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if(sublist.size()==0)
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result.add(List.NIL); // found a empty list
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else{
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List L = new List((Term)sublist.get(sublist.size()-1),List.NIL); // build a list
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for(int i=sublist.size()-2;i>=0;i--){
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L = new List( (Term) sublist.get(i),L);
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}
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result.add(L);
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}
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} else {
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if(T==Scan.ERROR)
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ErrorMessage=Scan.getValue();
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else
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ErrorMessage="error in building argument list"+T;
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return null;
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}
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T = Scan.getNext();
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}
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return result;
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}
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// for tests only
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public static void main(String[] args){
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System.out.println("only a test for the prolog parser");
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System.out.println("type in your prolog command and the resulting query is printed out");
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try{
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BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
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PrologParser P = new PrologParser();
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String line;
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Query Q;
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while(!(line=in.readLine()).equals("exit")){
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Q = P.parse(line,null);
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if(Q==null){
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System.out.println("error in parsing command: "+P.ErrorMessage);
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}else
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System.out.println("=> "+Q);
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}
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}
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catch(Exception e){
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e.printStackTrace();
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}
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}
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private int Token;
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private int pos; // position in input-stream
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private Vector arguments;
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private Scanner Scan;
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public String ErrorMessage="";
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}
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