diff -r cc3f7908b942 -r e6868bd2942b while.scala
--- a/while.scala	Wed Nov 21 07:28:28 2012 +0000
+++ b/while.scala	Wed Nov 21 09:04:11 2012 +0000
@@ -1,12 +1,13 @@
 
 //:load matcher.scala
+//:load parser3.scala
 
 // some regular expressions
-val SYM = RANGE("""ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz_""")
+val SYM = RANGE("ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz_")
 val DIGIT = RANGE("0123456789")
 val ID = SEQ(SYM, STAR(ALT(SYM, DIGIT))) 
 val NUM = PLUS(DIGIT)
-val KEYWORD = ALTS("skip", "while", "do", "if", "then", "else", "begin", "end", "true", "false") 
+val KEYWORD = ALTS("skip", "while", "do", "if", "then", "else", "true", "false") 
 val SEMI: Rexp = ";"
 val OP: Rexp = ALTS(":=", "=", "+", "-", "*")
 val WHITESPACE = PLUS(RANGE(" \n"))
@@ -15,7 +16,7 @@
 val BEGIN: Rexp = "{"
 val END: Rexp = "}"
 
-// for classifying the strings that have been recognised
+// tokens for classifying the strings that have been recognised
 abstract class Token
 case object T_WHITESPACE extends Token
 case object T_SEMI extends Token
@@ -28,7 +29,6 @@
 case class T_NUM(s: String) extends Token
 case class T_KWD(s: String) extends Token
 
-
 val lexing_rules: List[Rule[Token]] = 
   List((KEYWORD, (s) => T_KWD(s.mkString)),
        (ID, (s) => T_ID(s.mkString)),
@@ -53,14 +53,16 @@
 case class If(a: BExp, bl1: Block, bl2: Block) extends Stmt
 case class While(b: BExp, bl: Block) extends Stmt
 case class Assign(s: String, a: AExp) extends Stmt
+
 case class Var(s: String) extends AExp
 case class Num(i: Int) extends AExp
 case class Aop(o: String, a1: AExp, a2: AExp) extends AExp
+
 case object True extends BExp
 case object False extends BExp
 case class Bop(o: String, a1: AExp, a2: AExp) extends BExp
 
-
+// atomic parsers
 case class TokParser(tok: Token) extends Parser[List[Token], Token] {
   def parse(ts: List[Token]) = ts match {
     case t::ts if (t == tok) => Set((t, ts)) 
@@ -91,12 +93,12 @@
   (F ~ T_OP("*") ~ T) ==> { case ((x, y), z) => Aop("*", x, z): AExp } || F
 lazy val F: Parser[List[Token], AExp] = 
   (T_LPAREN ~> AExp <~ T_RPAREN) || 
-  IdParser ==> ((s) => Var(s)) || 
-  NumParser ==> ((i) => Num(i))
+  IdParser ==> Var || 
+  NumParser ==> Num
 
 lazy val BExp: Parser[List[Token], BExp] = 
   (AExp ~ T_OP("=") ~ AExp) ==> { case ((x, y), z) => Bop("=", x, z): BExp } || 
-  (T_KWD("true") ==> ((_) => True: BExp)) || 
+  (T_KWD("true") ==> ((_) => True)) || 
   (T_KWD("false") ==> ((_) => False: BExp))
 
 lazy val Stmt: Parser[List[Token], Stmt] =
@@ -113,43 +115,58 @@
   (T_BEGIN ~> Stmts <~ T_END) || 
   (Stmt ==> ((s) => List(s)))
 
+
+// examples
 val p1 = "x := 5"
 val p1_toks = Tok.fromString(p1) 
 val p1_ast = Block.parse_all(p1_toks)
 println(p1_toks)
 println(p1_ast)
 
+val p1a = "{ x := 5; y := 8}"
+val p1a_toks = Tok.fromString(p1a) 
+val p1a_ast = Block.parse_all(p1a_toks)
+println(p1a_ast)
+
 val p2 = "5 = 6"
 val p2_toks = Tok.fromString(p2) 
 val p2_ast = BExp.parse_all(p2_toks)
-println(p2_toks)
 println(p2_ast)
 
 val p2a = "true"
 val p2a_toks = Tok.fromString(p2a) 
 val p2a_ast = BExp.parse_all(p2a_toks)
-println(p2a_toks)
 println(p2a_ast)
 
 val p3 = "if true then skip else skip"
 val p3_toks = Tok.fromString(p3) 
 val p3_ast = Stmt.parse_all(p3_toks)
-println(p3_toks)
 println(p3_ast)
 
 val p3a = "if true then x := 5 else x := 10"
 val p3a_toks = Tok.fromString(p3a) 
 val p3a_ast = Stmt.parse_all(p3a_toks)
-println(p3a_toks)
 println(p3a_ast)
 
 val p3b = "if false then x := 5 else x := 10"
 val p3b_toks = Tok.fromString(p3b) 
 val p3b_ast = Stmt.parse_all(p3b_toks)
-println(p3b_toks)
 println(p3b_ast)
 
+val p4 = """{ x := 5;
+              y := 3;
+              r := 0;
+              while y = 0 do {
+                 r := r + x;
+                 y := y - 1
+              } 
+            }"""
+val p4_toks = Tok.fromString(p4) 
+val p4_ast = Block.parse_all(p4_toks)
+println(p4_ast)
 
+
+// interpreter
 type Env = Map[String, Int]
 
 def eval_bexp(b: BExp, env: Env) : Boolean = b match {