diff -r f5214da1976e -r 8067d0a8ba04 progs/comb2.scala
--- a/progs/comb2.scala	Sun Jul 28 21:10:39 2019 +0100
+++ b/progs/comb2.scala	Tue Jul 30 20:19:40 2019 +0100
@@ -110,7 +110,7 @@
 
 // boolean expressions with some simple nesting
 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 } || 
    (AExp ~ ">" ~ AExp) ==> { case ((x, y), z) => Bop(">", x, z): BExp } ||
@@ -120,7 +120,7 @@
    ("false" ==> ((_) => False: BExp )) ||
    ("(" ~ BExp ~ ")") ==> { case ((x, y), z) => y}
 
-// statements
+// statement / statements
 lazy val Stmt: Parser[String, Stmt] =
   (("skip" ==> ((_) => Skip: Stmt)) ||
    (IdParser ~ ":=" ~ AExp) ==> { case ((x, y), z) => Assign(x, z): Stmt } ||
@@ -133,6 +133,7 @@
   (Stmt ~ ";" ~ Stmts) ==> { case ((x, y), z) => x :: z : Block } ||
   (Stmt ==> ((s) => List(s) : Block))
 
+// blocks (enclosed in curly braces)
 lazy val Block: Parser[String, Block] =
   (("{" ~ Stmts ~ "}") ==> { case ((x, y), z) => y} || 
    (Stmt ==> ((s) => List(s))))
@@ -142,19 +143,20 @@
 Block.parse_all("{x:=5;y:=8}")
 Block.parse_all("if(false)then{x:=5}else{x:=10}")
 
-val fib = """{n := 10;
-              minus1 := 0;
-              minus2 := 1;
-              temp := 0;
-              while (n > 0) do {
+val fib = """n := 10;
+             minus1 := 0;
+             minus2 := 1;
+             temp := 0;
+             while (n > 0) do {
                  temp := minus2;
                  minus2 := minus1 + minus2;
                  minus1 := temp;
                  n := n - 1
-              };
-              result := minus2}""".replaceAll("\\s+", "")
+             };
+             result := minus2""".replaceAll("\\s+", "")
 
-Block.parse_all(fib)
+Stmts.parse_all(fib)
+
 
 // an interpreter for the WHILE language
 type Env = Map[String, Int]
@@ -198,7 +200,7 @@
 
 // parse + evaluate fib program; then lookup what is
 // stored under the variable result 
-println(eval(Block.parse_all(fib).head)("result"))
+println(eval(Stmts.parse_all(fib).head)("result"))
 
 
 // more examles
@@ -208,20 +210,20 @@
 println("Factors")
 
 val factors =  
-   """{n := 12;
+   """n := 12;
       f := 2;
       while (f < n / 2 + 1) do {
         if ((n / f) * f == n) then  { write(f) } else { skip };
         f := f + 1
-      }}""".replaceAll("\\s+", "")
+      }""".replaceAll("\\s+", "")
 
-eval(Block.parse_all(factors).head)
+eval(Stmts.parse_all(factors).head)
 
 // calculate all prime numbers up to a number 
 println("Primes")
 
 val primes =  
-   """{end := 100;
+   """end := 100;
       n := 2;
       while (n < end) do {
         f := 2;
@@ -232,6 +234,6 @@
         };
         if (tmp == 0) then { write(n) } else { skip };
         n  := n + 1
-      }}""".replaceAll("\\s+", "")
+      }""".replaceAll("\\s+", "")
 
-eval(Block.parse_all(primes).head)
+eval(Stmts.parse_all(primes).head)