diff -r 05cfce0fdef7 -r 8865f4f2be59 progs/compile.scala
--- a/progs/compile.scala	Thu Nov 14 01:21:02 2019 +0000
+++ b/progs/compile.scala	Thu Nov 14 13:17:02 2019 +0000
@@ -118,6 +118,9 @@
     def l(args: Any*): String = sc.s(args:_*) ++ ":\n"
 }
 
+// this allows you to write things like
+// i"add" and l"Lable"
+
 
 // environments 
 type Env = Map[String, Int]
@@ -132,16 +135,17 @@
 // arithmetic expression compilation
 def compile_aexp(a: AExp, env : Env) : String = a match {
   case Num(i) => i"ldc $i"
-  case Var(s) => i"iload ${env(s)}"
+  case Var(s) => i"iload ${env(s)} \t\t; $s"
   case Aop(op, a1, a2) => 
     compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ compile_op(op)
 }
 
 // boolean expression compilation
+//  - the jump-label is for where to jump if the condition is not true
 def compile_bexp(b: BExp, env : Env, jmp: String) : String = b match {
   case True => ""
   case False => i"goto $jmp"
-  case Bop("=", a1, a2) => 
+  case Bop("==", a1, a2) => 
     compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ i"if_icmpne $jmp"
   case Bop("!=", a1, a2) => 
     compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ i"if_icmpeq $jmp"
@@ -153,8 +157,8 @@
 def compile_stmt(s: Stmt, env: Env) : (String, Env) = s match {
   case Skip => ("", env)
   case Assign(x, a) => {
-    val index = if (env.isDefinedAt(x)) env(x) else env.keys.size
-    (compile_aexp(a, env) ++ i"istore $index", env + (x -> index))
+    val index = env.getOrElse(x, env.keys.size)
+    (compile_aexp(a, env) ++ i"istore $index \t\t; $x", env + (x -> index))
   } 
   case If(b, bl1, bl2) => {
     val if_else = Fresh("If_else")
@@ -179,12 +183,12 @@
      l"$loop_end", env1)
   }
   case Write(x) => 
-    (i"iload ${env(x)}" ++ 
+    (i"iload ${env(x)} \t\t; $x" ++ 
      i"invokestatic XXX/XXX/write(I)V", env)
   case Read(x) => {
-    val index = if (env.isDefinedAt(x)) env(x) else env.keys.size
+    val index = env.getOrElse(x, env.keys.size) 
     (i"invokestatic XXX/XXX/read()I" ++ 
-     i"istore $index", env + (x -> index))
+     i"istore $index \t\t; $x", env + (x -> index))
   }
 }
 
@@ -266,6 +270,11 @@
        Write("minus1"))                 //  write minus1
 
 
+// the compiled file as string
+//
+//println(compile(fib_test, "fib"))
+
+
 compile_run(fib_test, "fib")