diff -r ac7a7a9048c6 -r db329a4d2bc0 exps/token1.scala
--- a/exps/token1.scala	Wed Jan 30 12:28:44 2019 +0000
+++ b/exps/token1.scala	Thu Jan 31 09:07:50 2019 +0000
@@ -20,25 +20,6 @@
 
 type Bits = List[Bit]
 
-abstract class Action
-case object ST extends Action
-case object NST extends Action
-case object AL extends Action
-
-abstract class PartialValue
-case object Plhdr extends PartialValue
-case object STS extends PartialValue
-case object ENDSTS extends PartialValue
-case class Ch(c: Char) extends PartialValue
-case object Empt extends PartialValue
-case object Seque extends PartialValue
-case class Posi(i: Int) extends PartialValue
-case class RECRD(x: String) extends PartialValue
-case object ALTSTART extends  PartialValue
-case object ALTEND extends PartialValue
-case object RIG extends PartialValue
-case object LEF extends PartialValue
-
 abstract class Rexp 
 case object ZERO extends Rexp
 case object ONE extends Rexp
@@ -61,7 +42,7 @@
 case class ASEQ(bs: Bits, r1: ARexp, r2: ARexp) extends ARexp 
 case class ASTAR(bs: Bits, r: ARexp) extends ARexp 
 
-
+// abbreviations
 def AALT(bs: Bits, r1: ARexp, r2: ARexp) = AALTS(bs, List(r1, r2))
 
 abstract class Val
@@ -72,8 +53,8 @@
 case class Right(v: Val) extends Val
 case class Stars(vs: List[Val]) extends Val
 case class Rec(x: String, v: Val) extends Val
-case class Pos(i: Int, v: Val) extends Val
-case object Prd extends Val
+
+
    
 // some convenience for typing in regular expressions
 def charlist2rexp(s : List[Char]): Rexp = s match {
@@ -124,221 +105,43 @@
 }
 
 internalise(("a" | "ab") ~ ("b" | ""))
-val action_stack = scala.collection.mutable.ArrayBuffer.empty[Action]
-val next_stack = scala.collection.mutable.ArrayBuffer.empty[Int]
-val regx_stack = scala.collection.mutable.ArrayBuffer.empty[Rexp]
-val pv_stack = scala.collection.mutable.ArrayBuffer.empty[PartialValue]
-var top = 0
-//st is the global var stack, made with a linked list?
-@tailrec
-def decode_stack(sp: Int, bs: Bits): Unit = {
-if(action_stack.isEmpty){
-  return 
-}
-val action = action_stack.last
-action_stack.trimEnd(1)
-val r = regx_stack.last
-regx_stack.trimEnd(1)
-if(action == ST)//we have the rest of the star to finish(ST -> STAR)
-{
-  bs match {
-    case Z::bs => {//pv -> partial value  Each grid in a stack does not hold a whole value but a partial one.
-      pv_stack(sp) = ENDSTS
-      if(next_stack.isEmpty)
-        return 
-      val n = next_stack.last
-      next_stack.trimEnd(1)
-      decode_stack(n, bs)
+
+def decode_aux(r: Rexp, bs: Bits) : (Val, Bits) = (r, bs) match {
+  case (ONE, bs) => (Empty, bs)
+  case (PRED(f), C(c)::bs) => (Chr(c), bs)
+  case (ALTS(r::Nil), bs) => decode_aux(r, bs)
+  case (ALTS(rs), bs) => bs match {
+    case Z::bs1 => {
+      val (v, bs2) = decode_aux(rs.head, bs1)
+      (Left(v), bs2)
     }
-    case S::bs => {
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 1
-      }
-      next_stack += (sp + 1)
-      regx_stack += r  
-      action_stack += ST
-      pv_stack.insert(sp + 1, Plhdr)
-      action_stack += NST
-      regx_stack += r 
-      decode_stack(sp, bs)
-    }
-    case _ => println("Sequence not decodable")
-  }
-
-}
-else if(action == NST){
-  (r, bs) match{
-    case (ONE, bs) => {
-      pv_stack(sp) = Empt
-      if(next_stack.isEmpty)
-        return 
-      val n = next_stack.last
-      next_stack.trimEnd(1)
-      decode_stack(n, bs)
-    }
-    case (PRED(f), C(c)::bs) => {
-      pv_stack(sp) = Ch(c)
-      if(next_stack.isEmpty)
-        return 
-      val n = next_stack.last
-      next_stack.trimEnd(1)
-      decode_stack(n, bs)
-    }
-    case (ALTS(rs), Z::bs1) => {
-      pv_stack(sp) = ALTSTART
-      pv_stack.insert(sp + 1, LEF)
-      pv_stack.insert(sp + 2, Plhdr)
-      pv_stack.insert(sp + 3, ALTEND)
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 3
-      }
-      regx_stack += rs.head
-      action_stack += NST
-      decode_stack(sp + 2, bs1)
+    case S::bs1 => {
+      val (v, bs2) = decode_aux(ALTS(rs.tail), bs1)
+      (Right(v), bs2)			
     }
-    case (ALTS(rs), S::bs1) => {
-      pv_stack(sp) = ALTSTART
-      pv_stack.insert(sp + 1, RIG)
-      pv_stack.insert(sp + 2, Plhdr)
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 2
-      }
-      regx_stack += ALTS(rs.tail)
-      action_stack += AL
-      decode_stack(sp + 2, bs1)		
-    }
-      /*
-      val le = rs.length
-      val det = bs.take(le - 1)
-      val chosen =  det.indexWhere(_ == Z)
-      action_stack += NST
-      pv_stack.insert(sp + 1, Plhdr)
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 1
-      }
-      if(chosen ==  -1){
-        pv_stack(sp) = Posi(le)
-        regx_stack += rs(le - 1)
-        decode_stack(sp + 1, bs.drop(le - 1))
-      }
-      else{
-        pv_stack(sp) = Posi(chosen + 1)
-        regx_stack += rs(chosen)
-        decode_stack(sp + 1, bs.drop(chosen + 1))
-      }*/
-    case (SEQ(r1, r2), bs) => {
-      action_stack += NST
-      action_stack += NST
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 2
-      }
-      next_stack += (sp + 2)
-      regx_stack += r2
-      regx_stack += r1
-      pv_stack.insert(sp + 1, Plhdr)
-      pv_stack.insert(sp + 2, Plhdr)
-      pv_stack(sp) = Seque
-      decode_stack(sp + 1, bs)
-    }
-    case (STAR(r1), S::bs) => {
-      action_stack += ST
-      regx_stack += r1
-      action_stack += NST
-      regx_stack += r1
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 2
-      }
-      next_stack += sp + 2
-      pv_stack(sp) = STS
-      pv_stack.insert(sp + 1, Plhdr)
-      pv_stack.insert(sp + 1, Plhdr)
-      decode_stack(sp + 1, bs)
-    }
-    case (STAR(_), Z::bs) => {
-      pv_stack(sp) = STS 
-      pv_stack.insert(sp + 1, ENDSTS)
-      if(next_stack.isEmpty)
-        return 
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 1
-      }
-      val n = next_stack.last
-      next_stack.trimEnd(1)
-      decode_stack(n, bs)
-    }
-    case (RECD(x, r1), bs) => {
-      pv_stack(sp) = RECRD(x)
-      pv_stack.insert(sp + 1, Plhdr)
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 1
-      }
-      action_stack += NST
-      regx_stack += r1
-      decode_stack(sp + 1, bs)
-    }//shouldn't go beyond this point
-    case (_, _) => println("Error with NST")
+  }
+  case (SEQ(r1, r2), bs) => {
+    val (v1, bs1) = decode_aux(r1, bs)
+    val (v2, bs2) = decode_aux(r2, bs1)
+    (Sequ(v1, v2), bs2)
+  }
+  case (STAR(r1), S::bs) => {
+    val (v, bs1) = decode_aux(r1, bs)
+    val (Stars(vs), bs2) = decode_aux(STAR(r1), bs1)
+    (Stars(v::vs), bs2)
+  }
+  case (STAR(_), Z::bs) => (Stars(Nil), bs)
+  case (RECD(x, r1), bs) => {
+    val (v, bs1) = decode_aux(r1, bs)
+    (Rec(x, v), bs1)
   }
 }
-else{//action is AL
-  r match {
-    case (ALTS(r1::Nil)) => {
-      pv_stack.insert(sp + 1, ALTEND)
-      for(i <- 0 to next_stack.length - 1){
-        next_stack(i) = next_stack(i) + 1
-      }
-      action_stack += NST
-      regx_stack += r1
-      decode_stack(sp, bs)
-    }
-    case (ALTS(rs)) => {
-      bs match {
-        case (Z::bs1) => {
-          pv_stack(sp) = LEF
-          pv_stack.insert(sp + 1, ALTEND)
-          pv_stack.insert(sp + 1, Plhdr)
-          for(i <- 0 to next_stack.length - 1){
-            next_stack(i) = next_stack(i) + 2
-          }
-          regx_stack += rs.head
-          action_stack += NST
-          decode_stack(sp + 1, bs1)
-        }
-        case (S::bs2) => {
-          pv_stack(sp) = RIG
-          pv_stack.insert(sp + 1, Plhdr)
-          for(i <- 0 to next_stack.length - 1){
-            next_stack(i) = next_stack(i) + 1
-          }
-          regx_stack += ALTS(rs.tail)
-          action_stack += AL
-          decode_stack(sp + 1, bs2)
-        }
-        case _ => println("Not decodable")
-      }
-    }
-    case (rs) => println(r,bs)
-  }
-}
-}
-//advantage: may decode chunks of bits
-def decode(r: Rexp, bs: Bits) = {
-  action_stack.clear()
-  next_stack.clear()
-  regx_stack.clear()
-  pv_stack.clear()
 
-  action_stack += NST
-  regx_stack += r
-  pv_stack += Plhdr
-
-  decode_stack(0, bs)
-}
-/*
 def decode(r: Rexp, bs: Bits) = decode_aux(r, bs) match {
   case (v, Nil) => v
   case _ => throw new Exception("Not decodable")
 }
-*/
+
 
 //erase function: extracts the regx from Aregex
 def erase(r:ARexp): Rexp = r match{
@@ -405,7 +208,7 @@
     case AZERO :: rs1 => flats(rs1)
     case AALTS(bs, rs1) :: rs2 => rs1.map(fuse(bs, _)) ::: flats(rs2)
     case r1 :: rs2 => r1 :: flats(rs2)
-  }
+}
 
 def simp(r: ARexp): ARexp = r match {
   case ASEQ(bs1, r1, r2) => (simp(r1), simp(r2)) match {
@@ -462,19 +265,6 @@
 }
 
 
-def vsize(v: Val): Int = v match {
-  case Empty => 1
-  case Chr(c) => 1
-  case Sequ(v1, v2) => vsize(v1) + vsize(v2) + 1
-  case Left(v1) => vsize(v1) + 1
-  case Right(v1) => vsize(v1) + 1
-  case Stars(vs) => vs.map(vsize(_)).sum + 1
-  case Rec(x, v1) => vsize(v1) + 1
-  case Pos(i, v1) => vsize(v1) + 1
-  case Prd => 1
-}
-
-
 // Lexing Rules for a Small While Language
 
 //symbols
@@ -528,25 +318,16 @@
 
 // Some Tests
 //============
-def compute_and_print(r: Rexp, s: String){
-  //println(r)
-  //println(s)
-  lexing_simp(r, s)
-  println(pv_stack)
-}
+
 println("simple tests:")
-/*
+
 println(lexing_simp((SYM.%), "abcd"))
 println(lexing_simp(((SYM.%) | NUM), "12345"))
 println(lexing_simp((WHILE_REGS), "abcd"))
 println(lexing_simp((WHILE_REGS), "12345"))
-println(lexing_simp((WHILE_REGS), "\nwrite \"Fib\";"))
-*/
-compute_and_print((SYM.%), "abcd")
-compute_and_print(((SYM.%) | NUM), "12345")
-compute_and_print((WHILE_REGS), "abcd")
-compute_and_print((WHILE_REGS), "12345")
-compute_and_print((WHILE_REGS), "\nwrite \"Fib\";")
+println(lexing_simp((WHILE_REGS), """write "Fib";"""))
+
+
 
 def time[T](code: => T) = {
   val start = System.nanoTime()
@@ -585,14 +366,3 @@
   //time(lex_simp(internalise(WHILE_REGS), (prog2 * i).toList))
 }
 
-
-/*
-def recurseTest(i:Int):Unit={
-   try{
-      recurseTest(i+1)
-   } catch { case e:java.lang.StackOverflowError => 
-      println("Recursion depth on this system is " + i + ".")
-   }
-}
-recurseTest(0)
-*/
\ No newline at end of file