Lexer.java

// Kimberley Ni and Eylul Oktay

import java.util.ArrayList;

public class Lexer {
	public static final String specials = "()\\ ;.λ="; // special characters

	/*
	 * A lexer (or "tokenizer") converts an input into tokens that
	 * eventually need to be interpreted.
	 * 
	 * Given the input
	 * (\bat .bat flies)cat λg.joy! )
	 * you should output the ArrayList of strings
	 * [(, \, bat, ., bat, flies, ), cat, \, g, ., joy!, )]
	 *
	 */
	public ArrayList<String> tokenize(String input) {
		ArrayList<String> tokens = new ArrayList<String>();

		String tokenStr = "";
		for (int i = 0; i < input.length(); i++) {
			String letter = input.substring(i, i + 1);

			// Tokenize as individual: special characters held in constant String variable specials
			if (specials.contains(letter)) {
				if (!tokenStr.equals("")) {
					tokens.add(tokenStr);
					tokenStr = ""; // reset
				}
				if (letter.equals(";")) // comment; at this point don't need to process further
					return tokens;
				else if (!letter.equals(" "))
					tokens.add(letter);
			} else {
				tokenStr += letter;
			}
			
		}

		if (!tokenStr.equals("")) // cleans up any last tokens
			tokens.add(tokenStr);

		return tokens;
	}
}