diff -r 98370b96c1c5 -r 3c1107984b41 turing.scala
--- a/turing.scala	Thu Feb 21 14:27:14 2013 +0000
+++ b/turing.scala	Thu Feb 21 14:49:26 2013 +0000
@@ -21,7 +21,7 @@
 
 
 
-abstract class Cell {
+sealed abstract class Cell {
   def * (n: Int) : List[Cell] = n match {
     case 0 => Nil
     case n => this :: this * (n - 1)
@@ -30,7 +30,7 @@
 case object Bk extends Cell { override def toString = "0" }
 case object Oc extends Cell { override def toString = "1" }
 
-abstract class Action
+sealed abstract class Action
 case object WBk extends Action
 case object WOc extends Action
 case object R extends Action
@@ -144,7 +144,7 @@
 
 
 // Abacus machines
-abstract class AInst 
+sealed abstract class AInst 
 case class Inc(n: Int) extends AInst
 case class Dec(n: Int, l: Int) extends AInst
 case class Goto(l: Int) extends AInst
@@ -181,7 +181,6 @@
     case (Some(Goto(l)), _) => AConfig(l, cf.regs)
   }  
 
-  
   def steps(cf: AConfig, n: Int) : AConfig = n match {
     case 0 => cf
     case n => steps(step(cf), n - 1)
@@ -220,42 +219,45 @@
 
 
 // Abacus to TM translation
-type Layout = List[Int]
-
 def layout(p: AProg) = p.map(_ match {
   case Inc(n) => 2 * n + 9 
   case Dec(n, _) => 2 * n + 16 
   case Goto(n) => 1
 })
 
-def start(ly: Layout, n: Int) = ly.take(n).sum + 1
+def start(p: AProg, n: Int) = layout(p).take(n).sum + 1
 
-val TMInc = TM(List((WOc, 1), (R, 2), (WOc, 3), (R, 2), (WOc, 3), (R, 4), 
-                    (L, 7), (WBk, 5), (R, 6), (WBk, 5), (WOc, 3), (R, 6),
-                    (L, 8), (L, 7), (R, 9), (L, 7), (R, 10), (WBk, 9)))
+def compile_Inc(s: Int, n: Int) = {
+  val TMInc = TM(List((WOc, 1), (R, 2), (WOc, 3), (R, 2), (WOc, 3), (R, 4), 
+                      (L, 7), (WBk, 5), (R, 6), (WBk, 5), (WOc, 3), (R, 6),
+                      (L, 8), (L, 7), (R, 9), (L, 7), (R, 10), (WBk, 9)))
+  TMFindnth(n).shift(s - 1) ++ TMInc.shift(2 * n).shift(s - 1)
+}
 
-val TMDec = TM(List((WOc, 1), (R, 2), (L, 14), (R, 3), (L, 4), (R, 3),
-                    (R, 5), (WBk, 4), (R, 6), (WBk, 5), (L, 7), (L, 8),
-                    (L, 11), (WBk, 7), (WOc, 8), (R, 9), (L, 10), (R, 9),
-                    (R, 5), (WBk, 10), (L, 12), (L, 11), (R, 13), (L, 11),
-                    (R, 17), (WBk, 13), (L, 15), (L, 14), (R, 16), (L, 14),
-                    (R, 0), (WBk, 16)))
-
-def TMINC(s: Int, n: Int) = (TMFindnth(n) ++ TMInc.shift(2 * n)).shift(s - 1)
+def compile_Dec(s: Int, n: Int, e: Int) = {
+  val TMDec = TM(List((WOc, 1), (R, 2), (L, 14), (R, 3), (L, 4), (R, 3),
+                      (R, 5), (WBk, 4), (R, 6), (WBk, 5), (L, 7), (L, 8),
+                      (L, 11), (WBk, 7), (WOc, 8), (R, 9), (L, 10), (R, 9),
+                      (R, 5), (WBk, 10), (L, 12), (L, 11), (R, 13), (L, 11),
+                      (R, 17), (WBk, 13), (L, 15), (L, 14), (R, 16), (L, 14),
+                      (R, 0), (WBk, 16)))
+  TMFindnth(n).shift(s - 1) ++ TMDec.shift(2 * n).shift(s - 1).adjust(e)
+}
 
-def TMDEC(s: Int, n: Int, e: Int) = TMFindnth(n).shift(s - 1) ++ TMDec.shift(2 * n).shift(s - 1).adjust(e)
-
-def TMGOTO(n: Int) = TM(List((Nop, n), (Nop, n)))
+def compile_Goto(s: Int) = {
+  val TMGoto = TM(List((Nop, 1), (Nop, 1)))
+  TMGoto.shift(s - 1)
+}
 
-def compile(ly: Layout, s: Int, i: AInst) = i match {
-  case Inc(n) => TMINC(s, n)
-  case Dec(n, e) => TMDEC(s, n, start(ly, e))
-  case Goto(e) => TMGOTO(start(ly, e))
+def compile(p: AProg, s: Int, i: AInst) = i match {
+  case Inc(n) => compile_Inc(s, n)
+  case Dec(n, e) => compile_Dec(s, n, start(p, e))
+  case Goto(e) => compile_Goto(start(p, e))
 }
 
 def tms(p: AProg) = {
-  val ss = (0 until p.length).map (start(layout(p),_))
-  (ss zip p).map{case (n, i) => compile(layout(p), n, i)}
+  val ss = (0 until p.length).map (start(p,_))
+  (ss zip p).map{case (n, i) => compile(p, n, i)}
 }
 
 def toTM(p: AProg) = tms(p).reduceLeft(_ ++ _)