Java Programming:

Look through the Language Description and build a list of keywords. Add a HashMap to your Lexer class and initialize all the keywords. Change your lexer so that it checks each string before making the WORD token and creates a token of the appropriate type if the work is a key word. When the exact type of a token is known (like "WHILE"), you should NOT fill in the value string, the type is enough. For tokens with no exact type (like "hello"), we still need to fill in the token's string. Finally, rename "WORD" to "IDENTIFIER". Similarly, look through the Language Description for the list of punctuation. A hash map is not necessary or helpful for these - they need to be added to your state machine. Be particularly careful about the multi-character operators like := or >=. These require a little more complexity in your state machine. See the comment state machine example for an idea on how to implement this. Strings and characters will require some additions to your state machine. Create "STRINGLITERAL" and "CHARACTERLITERAL" token types. These cannot cross line boundaries. Note that we aren't going to build in escaping like Java does ( " This is a double quote\" that is inside a string" or '\''). Comments, too, require a bit more complexity in your state machine. When a comment starts, you need to accept and ignore everything until the closing comment character. Assume that comments cannot be nested - {{this is invalid} and will be a syntax error later}. Remember, though, that comments can span lines, unlike numbers or words or symbols; no token should be output for comments. Your lexer should throw an exception if it encounters a character that it doesn't expect outside of a comment, string literal or character literal. Create a new exception type that includes a good error message and the token that failed. Ensure that the ToString method prints nicely. An example of this might be:

ThisIsAnIdentifier 123 ! {

Add "line number" to your Token class. Keep track of the current line number in your lexer and populate each Token's line number; this is straightforward because each call to lex() will be one line greater than the last one. The line number should be added to the exception, too, so that users can fix the exceptions.

Finally, indentation. This is not as bad as it seems. For each line, count from the beginning the number of spaces and tabs until you reach a non-space/tab. Each tab OR four spaces is an indentation level. If the indentation level is greater than the last line (keep track of this in the lexer), output one or more INDENT tokens. If the indentation level is less than the last line, output one or more DEDENT tokens (obviously you will need to make new token types). For example:

1 { indent level 0, output NUMBER 1 }

a { indent level 1, output an INDENT token, then IDENTIIFIER a }

b { indent level 2, output an INDENT token, then IDENTIFIER b }

c { indent level 4, output 2 INDENT tokens, then IDENTIFIER c }

2 { indent level 0; output 4 DEDENT tokens, then NUMBER 2 }

Be careful of the two exceptions:

If there are no non-space/tab characters on the line, don't output an INDENT or DEDENT and don't change the stored indentation level.

If we are in the middle of a multi-line comment, indentation is not considered.

Note that end of file, you must output DEDENTs to get back to level 0.

Your exception must be called SyntaxErrorException and be in its own file. Unterminated strings or characters are invalid and should throw this exception, along with any invalid symbols. There are errors in the lexer and shank files. Please fix those errors and make sure all three files run correctly without any error. There must be no error at all. Below are the lexer, shank, and token files. Attached is the rubric as well. Make sure to include the SyntaxErrorException as well.

Lexer.java

package mypack;

import java.util.HashMap;

import mypack.Token.TokenType;

public class Lexer { private static final int INTEGER_STATE = 1; private static final int DECIMAL_STATE = 2; private static final int IDENTIFIER_STATE = 3; private static final int SYMBOL_STATE = 4; private static final int ERROR_STATE = 5; private static final int STRING_STATE = 6; private static final int CHAR_STATE = 7; private static final int COMMENT_STATE = 8;

private static final char EOF = (char) -1;

private static String input; private static int index; private static char currentChar; private static int lineNumber = 1; private static int indentLevel = 0; private static int lastIndentLevel = 0;

private static HashMap keywords = new HashMap() {{ put("while", TokenType.WHILE); put("if", TokenType.IF); put("else", TokenType.ELSE); put("print", TokenType.PRINT); }};

private static HashMap symbols = new HashMap() {{ put('+', TokenType.PLUS); put('-', TokenType.MINUS); put('*', TokenType.MULTIPLY); put('/', TokenType.DIVIDE); put('=', TokenType.EQUALS); put(':', TokenType.COLON); put(';', TokenType.SEMICOLON); put('(', TokenType.LEFT_PAREN); put(')', TokenType.RIGHT_PAREN); put('{', TokenType.LEFT_BRACE); put('}', TokenType.RIGHT_BRACE); put('', TokenType.GREATER_THAN); }};

public Lexer(String input) { Lexer.input = input; index = 0; currentChar = input.charAt(index); }

private void nextChar() { index++; if (index >= input.length()) { currentChar = EOF; } else { currentChar = input.charAt(index); } }

private void skipWhiteSpace() { while (Character.isWhitespace(currentChar)) { nextChar(); } }

private int getIndentLevel() { int level = 0; int i = index; char c = input.charAt(i); while (c == ' ' || c == '\t') { if (c == '\t') { level += 1; } else if (c == ' ') { level += 1; } i++; if (i >= input.length()) { break; } } return level; } }

Shank.java

package mypack;

import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; import java.util.List;

public class Shank { public static void main(String[] args) { if (args.length != 1) { System.out.println("Error: Exactly one argument is required."); System.exit(0); } String filename = args[0];

try { List lines = Files.readAllLines(Paths.get(filename));

for (String line : lines) { try { Lexer lexer = new Lexer(line); List tokens = lexer.lex(line);

for (Token token : tokens) { System.out.println(token); } } catch (Exception e) { System.out.println("Exception: " + e.getMessage()); } } } catch (IOException e) { System.out.println("Error: Could not read file '" + filename + "'."); } } }

Token.java

package mypack;

public class Token { public enum TokenType { WORD, NUMBER, SYMBOL }

public TokenType tokenType; private String value; public Token(TokenType type, String val) { this.tokenType = type; this.value = val; } public TokenType getTokenType() { return this.tokenType; } public String toString() { return this.tokenType + ": " + this.value; } }