diff --git a/compiler/src/prog8/compiler/functions/BuiltinFunctions.kt b/compiler/src/prog8/compiler/functions/BuiltinFunctions.kt
index dba87f73e..ba7bb0fef 100644
--- a/compiler/src/prog8/compiler/functions/BuiltinFunctions.kt
+++ b/compiler/src/prog8/compiler/functions/BuiltinFunctions.kt
@@ -366,7 +366,7 @@ private fun builtinLen(args: List<Expression>, position: Position, program: Prog
             NumericLiteralValue.optimalInteger(arraySize, args[0].position)
         }
         DataType.STR -> {
-            val refLv = target.value as StringLiteralValue
+            val refLv = target.value as? StringLiteralValue ?: throw CannotEvaluateException("len", "stringsize unknown")
             NumericLiteralValue.optimalInteger(refLv.value.length, args[0].position)
         }
         DataType.STRUCT -> throw SyntaxError("cannot use len on struct, did you mean sizeof?", args[0].position)
diff --git a/compiler/src/prog8/optimizer/StatementOptimizer.kt b/compiler/src/prog8/optimizer/StatementOptimizer.kt
index 16b1f2046..c4b49e3df 100644
--- a/compiler/src/prog8/optimizer/StatementOptimizer.kt
+++ b/compiler/src/prog8/optimizer/StatementOptimizer.kt
@@ -20,7 +20,7 @@ internal class StatementOptimizer(private val program: Program,
                                   private val errors: IErrorReporter,
                                   private val functions: IBuiltinFunctions,
                                   private val compTarget: ICompilationTarget,
-                                  private val asmFileLoader: (filename: String, source: Path)->String
+                                  asmFileLoader: (filename: String, source: Path)->String
 ) : AstWalker() {
 
     private val noModifications = emptyList<IAstModification>()
@@ -296,18 +296,6 @@ internal class StatementOptimizer(private val program: Program,
         return noModifications
     }
 
-    override fun after(whenStatement: WhenStatement, parent: Node): Iterable<IAstModification> {
-        // remove empty choices
-        class ChoiceRemover(val choice: WhenChoice) : IAstModification {
-            override fun perform() {
-                whenStatement.choices.remove(choice)
-            }
-        }
-        return whenStatement.choices
-                .filter { !it.statements.containsCodeOrVars() }
-                .map { ChoiceRemover(it) }
-    }
-
     override fun after(jump: Jump, parent: Node): Iterable<IAstModification> {
         // if the jump is to the next statement, remove the jump
         val scope = jump.definingScope()
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index a71c000a0..50a4c48b5 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -2,8 +2,11 @@
 TODO
 ====
 
+- compiler error for double when labels
+
 - add sound to the cx16 tehtriz
 
+- add const arrays and cost strings
 - hoist all variable declarations up to the subroutine scope *before* even the constant folding takes place (to avoid undefined symbol errors when referring to a variable from another nested scope in the subroutine)
 - optimize swap of two memread values with index, using the same pointer expression/variable, like swap(@(ptr+1), @(ptr+2))
 - optimize several inner loops in gfx2 (highres 4 color mode)
diff --git a/examples/cx16/tehtriz.p8 b/examples/cx16/tehtriz.p8
index 37a0a1c21..3de5cb93d 100644
--- a/examples/cx16/tehtriz.p8
+++ b/examples/cx16/tehtriz.p8
@@ -6,6 +6,7 @@
 ;   shows next piece
 ;   staged speed increase
 ;   TODO:  replicate the simple sound effects from the C64 version
+;          how to do this on the Vera PSG without a ADSR envelope...?
 
 
 %target cx16
diff --git a/examples/test.p8 b/examples/test.p8
index 060185a4c..81d0a1a3d 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -7,40 +7,21 @@ main {
 ;   $1F9C0 - $1F9FF 	PSG registers
 
     sub start() {
-        uword xx = &b2.zz
-        xx=&b3.zz
-        xx=&b4.zz
-        xx=&b5.zz
 
-        txt.print_uwhex(&main, true)
-        txt.nl()
-        txt.print_uwhex(&b2, true)
-        txt.nl()
-        txt.print_uwhex(&b3, true)
-        txt.nl()
-        txt.print_uwhex(&b4, true)
-        txt.nl()
-        txt.print_uwhex(&b5, true)
-        txt.nl()
+        ubyte xx = '?'
+        when xx {
+            'a' -> txt.print("a\n")
+            'b' -> txt.print("b\n")
+            '?' -> {
+            }
+            else -> txt.print("else\n")
+        }
+
+;        uword freq = 1181
+;        cx16.vpoke(1, $f9c0, lsb(freq))
+;        cx16.vpoke(1, $f9c1, msb(freq))
+;        cx16.vpoke(1, $f9c2, %11111111)     ; volume
+;        cx16.vpoke(1, $f9c3, %11000000)     ; triangle waveform
     }
 }
 
-b2 {
-    str zz="hello"
-}
-
-b3 $4001 {
-    str zz="bye"
-}
-
-b4 {
-    %option align_word
-
-    str zz="wut"
-}
-
-b5 {
-    %option align_page
-
-    str zz="wut2"
-}