Computer science

import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; import java.util.Scanner; /* * Simple Compiler * <Program1> -> ( <VarDefinition> | <AssignmentStatement> ) {[ <VarDefinition> | <AssignmentStatement> ] } <varDefinition> -> var <varName>; <varName> -> (a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w){0|1|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w} <AssignmentStatement> -> <varname> = <ExpressionStatement>; <ExpressionStatement> -> [<varname1> | <constant>] { + [<varname2> | <constant>] }; * * */ private class simpleCompiler { // <Program1> -> (<VarDefinition> | <Assignment> | <ForStatment>) {(<VarDefinition> | <AssignmentStatement> | <ForStatment>) } // NEED TO TRANSLATE THIS EBNF to BNF (non left-recursive) // <Program1> -> (<VarDefinition> | <AssignmentStatement>) <Program2> // <Program2> -> epsilon | (<VarDefinition> | <AssignmentStatement>) <Program2> public static String linecode = ""; public static int lineIndex = 0; public static int columnIndex = 0; public static boolean Program1() { System.out.println("Enter <Program1> -> (<VarDefinition> | <AssignmentStatement>) <Program2>"); if (varDefinition() || (AssignmentStatement())) { } else { System.out.println("Exit <Program1> -> (<VarDefinition> | <AssignmentStatement>) <Program2> FAIL"); return false; } boolean isProgram2 = Program2(); if (isProgram2) { System.out.println("Exit <Program1> -> (<VarDefinition> | <AssignmentStatement>) <Program2> SUCCESS"); System.out.println("Compilation succeeded!"); return true; } else { System.out.println("Exit <Program1> -> (<VarDefinition> | <AssignmentStatement>) <Program2> FAIL"); System.out.println("Compilation failed"); return false; } } public static boolean Program2() { System.out.println("Enter <Program2> -> epsilon | (<VarDefinition> | <AssignmentStatement>) <Program2> "); String nextSymbol = getNextSymbol(); if ((nextSymbol == null) || (nextSymbol.trim().equals(""))) { System.out.println("EXIT <Program2> -> epsilon | (<VarDefinition> | <AssignmentStatement>) <Program2> SUCCESS"); return true; } else { if (varDefinition() || (AssignmentStatement())) { } else { return false; } return Program2(); } } // <varDefinition> -> var <varName>; public static boolean varDefinition() { // scan the next symbol // if it is a variable, good // otherwise, back the cursor System.out.println("Enter <varDefinition> -> var <varName>;"); int startIndex = columnIndex; String nextSymbol = getNextSymbol(); if (nextSymbol!=null) { if (nextSymbol.equals("var")) { // good, get next Symbol nextSymbol = getNextSymbol(); boolean isVarNameSemicolon = varNameSemicolon(nextSymbol); if (isVarNameSemicolon) { System.out.println("Exit <varDefinition> -> var <varName>; SUCCESS"); return true; } else { columnIndex = startIndex; System.out.println("Exit <varDefinition> -> var <varName>; FAIL"); return false; } } else { columnIndex = startIndex; System.out.println("Exit <varDefinition> -> var <varName>; FAIL"); return false; } } else { System.out.println("Exit <varDefinition> -> var <varName>; FAIL"); return false; } } // <varName> -> [a-z]{[a-z01]}; public static boolean varNameSemicolon(String variable) { System.out.println("Enter <varName> -> (a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w){0|1|a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w}; "); int lastindex = variable.length()-1; int variableIndex = 0; if ((variable.charAt(variableIndex) >= 'a') && (variable.charAt(variableIndex) <= 'z')) { // continue variableIndex++; // check the net while ( (variableIndex <= lastindex) && (((variable.charAt(variableIndex) >= 'a') && (variable.charAt(variableIndex) <= 'z')) || (variable.charAt(variableIndex) == ';') || (variable.charAt(variableIndex) == '0') || (variable.charAt(variableIndex) == '1'))) { variableIndex++; if (variable.charAt(variableIndex) == ';') { if (variableIndex == lastindex) { // GOOD, RETURN SUCCESS System.out.println("EXIT <varName> -> [a-z]{[a-z01]}; SUCCESS"); return true; } else { int currentColumn = columnIndex - variable.length() + variableIndex; System.out.println("Error at line " + lineIndex + " column " + (currentColumn+1)); return false; } } } if (variableIndex <= lastindex) { int currentColumn = columnIndex - variable.length() + variableIndex; System.out.println("Error at line " + lineIndex + " column " + (currentColumn + 1)); return false; } } else { int currentColumn = columnIndex - variable.length() + variableIndex; System.out.println("Error at line " + lineIndex + " column " + (currentColumn + 1)); return false; } return true; } public static String getNextSymbol() { System.out.println("Enter GetNextSymbol " + linecode + " " + columnIndex); while (linecode.charAt(columnIndex) == ' '){ columnIndex++; } if (linecode.charAt(columnIndex) == '\n') { System.out.println("No more symbol."); return null; } String curSymbol = "" + linecode.charAt(columnIndex); columnIndex++; while ((linecode.charAt(columnIndex) != '\n') && (linecode.charAt(columnIndex) != ' ')) { curSymbol += linecode.charAt(columnIndex); columnIndex++; } System.out.println("Exit GetNextSymbol " + curSymbol); return curSymbol; } // <AssignmentStatement> -> <varname> = <ExpressionStatement>; public static boolean AssignmentStatement() { System.out.println("<AssignmentStatement> -> <varname> = <ExpressionStatement>;"); int startIndex = columnIndex; String nextSymbol = getNextSymbol(); String variable = nextSymbol; //TODO: Implement this BNF int currentColumn = columnIndex - variable.length(); System.out.println("Error at line " + lineIndex + " column " + (currentColumn + 1)); columnIndex = startIndex; return false; } public static void main(String[] args) { // read content from a text file BufferedReader reader; try (Scanner sc = new Scanner(System.in)){ // Create a Scanner object System.out.println("Enter your file name"); reader = new BufferedReader(new FileReader(sc.next())); linecode = reader.readLine(); // NOTE THAT THE FOLLOWING SOLUTION ASSUMES that EACH LINE // FOLLOWS THE RULE // This is NOT the best solution // This solution cannot recognize the following program as correct // var myCount; var // secondCount; while (linecode != null) { //System.out.println(line); // read next line lineIndex++; // print out this line linecode += '\n'; System.out.println("Read: " + linecode); // handle each line to see whether it is a correct statement boolean isCorrectLineCode = Program1(); if (!isCorrectLineCode) { System.out.println("EXIT ... Compilation failed"); break; } linecode = reader.readLine(); columnIndex = 0; } reader.close(); } catch (IOException e) { e.printStackTrace(); } } }