Bug fixes:

Catching Indentation Errors.
	A typo on regex of Identifiers
	Potential fixes on allowing function body with only definations. (not applied)
TODO:
	Allowing a program to have interleaving definations and statements?

src/main/jflex/chocopy/pa1/ChocoPy.jflex

@@ -1,6 +1,7 @@
 package chocopy.pa1;
 import java_cup.runtime.*;
 import java.util.ArrayList;
+import java.util.Iterator;
 %%
 
 /*** Do not change the flags below unless you know what you are doing. ***/
@@ -37,6 +38,7 @@ import java.util.ArrayList;
     private int str_l = 0, str_c = 0; //Start location of a string.
     /*A stack that keeps track of the spaces in each Indentation Level*/
     private ArrayList<Integer> stack = new ArrayList<Integer>(20); 
+    private boolean indentErrorUnchecked = true;
     /** Return a terminal symbol of syntactic category TYPE and no
      *  semantic value at the current source location. */
     private Symbol symbol(int type) {
@@ -63,6 +65,15 @@ import java.util.ArrayList;
         if(stack.isEmpty()) return 0;
         return stack.get(stack.size() - 1);
     }
+    private boolean find(int indent){
+      if(indent == 0) return true;
+      Iterator<Integer> it = stack.iterator();
+      while(it.hasNext()){
+         if(it.next() == indent)
+            return true;
+      }
+      return false;
+    }
 %}
 
 /* Macros (regexes used in rules below) */
@@ -72,7 +83,7 @@ LineBreak  = \r|\n|\r\n
 
 IntegerLiteral = 0|[1-9][0-9]* // Accroding to the manual, 00+ is illeagal
 StringLiteral = ([^\"\\]|(\\\")|(\\t)|(\\r)|(\\n)|(\\\\))+ // \n, \r, \t, \\, \" and Anything except \ and " 
-Identifiers = (_|[a-z]|[A-Z])(_|[a-z]|[A-Z][0-9])* 
+Identifiers = (_|[a-z]|[A-Z])(_|[a-z]|[A-Z]|[0-9])* 
 Comments = #[^\r\n]*
 %%
 //YYINITIAL state is where we're dealing with indentations.
@@ -135,7 +146,18 @@ if True:
           AFTER state.
           */ 
           pop();
-          return symbol(ChocoPyTokens.DEDENT, currIndent);
+          if(top() < currIndent)
+          {
+            currIndent = top();
+            return symbolFactory.newSymbol("<bad indentation>", ChocoPyTokens.UNRECOGNIZED,
+              new ComplexSymbolFactory.Location(yyline + 1, yycolumn - 1),
+              new ComplexSymbolFactory.Location(yyline + 1,yycolumn + yylength()),
+              currIndent);
+          }
+          return symbolFactory.newSymbol(ChocoPyTokens.terminalNames[ChocoPyTokens.DEDENT], ChocoPyTokens.DEDENT,
+            new ComplexSymbolFactory.Location(yyline + 1, yycolumn - 1),
+            new ComplexSymbolFactory.Location(yyline + 1,yycolumn + yylength()),
+            currIndent);
       }
       /*Otherwise, we will start dealing with the rest 
         of the line after indentation in AFTER state. */
@@ -159,7 +181,7 @@ if True:
 <AFTER> {
 
   /* Delimiters. */
-  {LineBreak}                 {  yybegin(YYINITIAL); currIndent = 0;return symbol(ChocoPyTokens.NEWLINE);}
+  {LineBreak}                 {  yybegin(YYINITIAL); currIndent = 0;indentErrorUnchecked = true; return symbol(ChocoPyTokens.NEWLINE);}
   ":"                         { return symbol(ChocoPyTokens.COLON); }
   ","                         { return symbol(ChocoPyTokens.COMMA); }