diff -r 412556272333 -r 9ce78065f68d progs/compile.scala
--- a/progs/compile.scala	Fri Oct 25 14:55:31 2019 +0100
+++ b/progs/compile.scala	Fri Oct 25 17:23:23 2019 +0100
@@ -120,7 +120,7 @@
 
 
 // environments 
-type Env = Map[String, String]
+type Env = Map[String, Int]
 
 // arithmetic expression compilation
 def compile_aexp(a: AExp, env : Env) : String = a match {
@@ -150,8 +150,7 @@
 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.toString
+    val index = if (env.isDefinedAt(x)) env(x) else env.keys.size
     (compile_aexp(a, env) ++ i"istore $index", env + (x -> index))
   } 
   case If(b, bl1, bl2) => {
@@ -180,8 +179,7 @@
     (i"iload ${env(x)}" ++ 
      i"invokestatic XXX/XXX/write(I)V", env)
   case Read(x) => {
-    val index = if (env.isDefinedAt(x)) env(x) else 
-                    env.keys.size.toString
+    val index = if (env.isDefinedAt(x)) env(x) else env.keys.size
     (i"invokestatic XXX/XXX/read()I" ++ 
      i"istore $index", env + (x -> index))
   }