diff --git a/lua-temp/tests.lua b/lua-temp/tests.lua
index ca81f94..e04aafc 100755
--- a/lua-temp/tests.lua
+++ b/lua-temp/tests.lua
@@ -341,7 +341,7 @@ do TEST "VM: GC strings"
 end
 
 do TEST "VM: arrays"
-    local vm = VM.new():set_debug(true):load(assemble [[
+    local vm = VM.new():load(assemble [[
         .func 0
             newa
             pushi   10
@@ -359,4 +359,42 @@ do TEST "VM: arrays"
     assert_eq(vm.heap:size(), 1)
 end
 
+do TEST "VM: arrays GC"
+    local vm = VM.new():load(assemble [[
+        .func 0
+            pushn
+            newa
+            pushi   10
+            seti    0
+            pop
+            gc
+            ret
+    ]]):call(0)
+
+    assert_eq(vm.heap:size(), 0)
+end
+
+do TEST "VM: GC items (1st level)"
+    local vm = VM.new():set_debug(true):load(assemble [[
+        .const
+            0: "Hello "
+            1: "world"
+        .func 0
+            pushn
+            newa
+            pushc   0
+            pushc   1
+            sum
+            seti    0
+            gc
+            pop
+            ret
+    ]]):call(0)
+
+    pprint(vm.heap)
+    print(vm:debug_heap())
+    assert_eq(vm.heap:size(), 0)
+end
+-- TODO - arrays gc items
+
 print('End.')
diff --git a/lua-temp/tyche-vm.lua b/lua-temp/tyche-vm.lua
index 1057613..92458a8 100644
--- a/lua-temp/tyche-vm.lua
+++ b/lua-temp/tyche-vm.lua
@@ -365,7 +365,7 @@ function VM:format_value(v)
     if v.type == 'integer' or v.type == 'real' then
         return tostring(v.value)
     elseif v.type == 'string' then
-        return self_:extract_string(v)
+        return '"' .. self:_extract_string(v) .. '"'
     elseif v.type == 'array' then
         local array = self:_extract_array(v)
         local tbl = {}
@@ -376,7 +376,7 @@ function VM:format_value(v)
     elseif v.type == 'nil' then
         return 'nil'
     else
-        print('warning: cannot convert from type ' .. v.type)
+        print('warning: cannot convert from type ' .. tostring(v.type))
         return pprint.pformat(v)
     end
 end
@@ -396,7 +396,15 @@ end
 function VM:debug_heap()
     local ss = { "Heap:\n" }
     for k,v in pairs(self.heap.items) do
-        table.insert(ss, string.format("  [%X] = %s", k, pprint.pformat(v)))
+        if type(v) == 'string' then
+            table.insert(ss, string.format('  [%X] = "%s"', k, v))
+        elseif type(v) == 'table' then
+            table.insert(ss, string.format('  [%X] = [', k))
+            local t = {}; for _,vv in ipairs(v) do t[#t+1] = self:format_value(vv) end
+            table.insert(ss, table.concat(t, ", ") .. ']')
+        else
+            error('Unsupported type in heap')
+        end
         table.insert(ss, "\n")
     end
     return table.concat(ss)