--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/html.scala	Sat Jun 15 09:23:18 2013 -0400
@@ -0,0 +1,99 @@
+
+//:load matcher.scala
+
+// some regular expressions
+val SYM = RANGE("""ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz.,!?-{[()]}':;%0123456789""")
+val WORD = PLUS(SYM)
+
+val BTAG = SEQS("<", WORD, ">") 
+val ETAG = SEQS("</", WORD, ">")
+
+val WHITESPACE = PLUS(RANGE(" \n"))
+
+// for classifying the strings that have been recognised
+abstract class Token
+case object T_WHITESPACE extends Token
+case class T_WORD(s: String) extends Token
+case class T_ETAG(s: String) extends Token
+case class T_BTAG(s: String) extends Token
+case class T_NT(s: String, rhs: List[Token]) extends Token
+
+val lexing_rules: List[Rule[Token]] = 
+  List((BTAG, (s) => T_BTAG(s.mkString)),
+       (ETAG, (s) => T_ETAG(s.mkString)),
+       (WORD, (s) => T_WORD(s.mkString)),
+       (WHITESPACE, (s) => T_WHITESPACE))
+
+// the tokenizer
+val T = Tokenizer(lexing_rules)
+
+// width for printing
+val WIDTH = 60
+
+
+def interpret(ts: List[Token], c: Int, ctr: List[String]) : Unit= ts match {
+  case Nil => println(Console.RESET)
+  case T_WHITESPACE::rest => print(Console.RESET + " "); interpret(rest, c + 1, ctr)
+  case T_WORD(s)::rest => {
+    val newstr = Console.RESET + ctr.reverse.mkString + s
+    if (c + s.length < WIDTH) {
+      print(newstr);
+      interpret(rest, c + s.length, ctr)
+    }
+    else {
+      print("\n" + newstr)
+      interpret(rest, s.length, ctr)
+    } 
+  }
+  case T_BTAG("<p>")::rest => print("\n"); interpret(rest, 0, ctr)
+  case T_ETAG("</p>")::rest => print("\n"); interpret(rest, 0, ctr)
+  case T_BTAG("<b>")::rest => interpret(rest, c, Console.BOLD :: ctr)
+  case T_BTAG("<a>")::rest => interpret(rest, c, Console.UNDERLINED :: ctr)
+  case T_BTAG("<cyan>")::rest => interpret(rest, c, Console.CYAN :: ctr)
+  case T_BTAG("<red>")::rest => interpret(rest, c, Console.RED :: ctr)
+  case T_BTAG("<blink>")::rest => interpret(rest, c, Console.BLINK :: ctr)
+  case T_ETAG(_)::rest => interpret(rest, c, ctr.tail)
+  case _::rest => interpret(rest, c, ctr)
+}
+ 
+val test_string = """
+<b>MSc Projects</b>
+
+<p>
+start of paragraph. <cyan> a <red>cyan</red> word</cyan> normal again something longer.
+</p> 
+
+
+ <p><b>Description:</b>  
+  <a>Regular expressions</a> are extremely useful for many text-processing tasks such as finding patterns in texts,
+  lexing programs, syntax highlighting and so on. Given that regular expressions were
+  introduced in 1950 by <a>Stephen Kleene</a>, you might think 
+  regular expressions have since been studied and implemented to death. But you would definitely be mistaken: in fact they are still
+  an active research area. For example
+  <a>this paper</a> 
+  about regular expression matching and partial derivatives was presented this summer at the international 
+  PPDP'12 conference. The task in this project is to implement the results from this paper.</p>
+
+  <p>The background for this project is that some regular expressions are 
+  <a>evil</a>
+  and can stab you in the back; according to
+  this <a>blog post</a>.
+  For example, if you use in <a>Python</a> or 
+  in <a>Ruby</a> (probably also in other mainstream programming languages) the 
+  innocently looking regular expression a?{28}a{28} and match it, say, against the string 
+  <red>aaaaaaaaaa<cyan>aaaaaaa</cyan>aaaaaaaaaaa</red> (that is 28 as), you will soon notice that your CPU usage goes to 100%. In fact,
+  Python and Ruby need approximately 30 seconds of hard work for matching this string. You can try it for yourself:
+  <a>re.py</a> (Python version) and 
+  <a>re.rb</a> 
+  (Ruby version). You can imagine an attacker
+  mounting a nice <a>DoS attack</a> against 
+  your program if it contains such an evil regular expression. Actually 
+  <a>Scala</a> (and also Java) are almost immune from such
+  attacks as they can deal with strings of up to 4,300 as in less than a second. But if you scale
+  the regular expression and string further to, say, 4,600 as, then you get a 
+  StackOverflowError 
+  potentially crashing your program.
+  </p>
+"""
+
+interpret(T.fromString(test_string), 0, Nil)