diff -r 1f4e81950ab4 -r 9476086849ad progs/comb2.scala
--- a/progs/comb2.scala	Mon Nov 14 15:50:42 2016 +0000
+++ b/progs/comb2.scala	Sat Jan 07 14:52:26 2017 +0000
@@ -1,3 +1,6 @@
+// A parser and evaluator for the while language
+// 
+
 import scala.language.implicitConversions
 import scala.language.reflectiveCalls
 
@@ -125,12 +128,12 @@
 
 // boolean expressions
 lazy val BExp: Parser[String, BExp] = 
-  ((AExp ~ "=" ~ AExp) ==> { case ((x, y), z) => Bop("=", x, z): BExp } || 
-   (AExp ~ "!=" ~ AExp) ==> { case ((x, y), z) => Bop("!=", x, z): BExp } || 
-   (AExp ~ "<" ~ AExp) ==> { case ((x, y), z) => Bop("<", x, z): BExp } || 
-   (AExp ~ ">" ~ AExp) ==> { case ((x, y), z) => Bop(">", x, z): BExp } || 
-   ("true" ==> ((_) => True: BExp)) || 
-   ("false" ==> ((_) => False: BExp)) ||
+  ((AExp ~ "=" ~ AExp) ==> { case ((x, y), z) => Bop("=", x, z):BExp } || 
+   (AExp ~ "!=" ~ AExp) ==> { case ((x, y), z) => Bop("!=", x, z):BExp } || 
+   (AExp ~ "<" ~ AExp) ==> { case ((x, y), z) => Bop("<", x, z):BExp } || 
+   (AExp ~ ">" ~ AExp) ==> { case ((x, y), z) => Bop(">", x, z):BExp } || 
+   ("true" ==> ((_) => True:BExp )) || 
+   ("false" ==> ((_) => False:BExp )) ||
    ("(" ~ BExp ~ ")") ==> { case ((x, y), z) => y})
 
 lazy val Stmt: Parser[String, Stmt] =
@@ -149,7 +152,7 @@
    (Stmt ==> ((s) => List(s))))
 
 
-Block.parse_all("x2:=5")
+Stmt.parse_all("x2:=5")
 Block.parse_all("{x:=5;y:=8}")
 Block.parse_all("if(false)then{x:=5}else{x:=10}")
 
@@ -193,4 +196,4 @@
 
 def eval(bl: Block) : Env = eval_bl(bl, Map())
 
-eval(Block.parse_all(fib).head)("result")
+println(eval(Block.parse_all(fib).head)("result"))