handle backreferences and linked lists in puke

updatedshmup.p8

@@ -45,7 +45,9 @@ function mknew(tt, more)
  end
 end
 
-linked_list = {}
+-- intrusive singly-linked list.
+-- cannot be nested!
+linked_list = {is_linked_list=true}
 mknew(linked_list, function(x)
   x.next=nil
   x.tail=x
@@ -288,17 +290,39 @@ function fadescreen()
  end
 end
 
-function puke(item, indent)
+-- puke emits a verbose string
+-- describing item, indented to
+-- the specified depth (0 by
+-- default). used for table
+-- debugging. table-type keys
+-- are not legible here
+function puke(item, indent, seen)
+ if (type(item) ~= "table") return tostr(item)
+ 
+ seen = seen or {}
+ if (seen[item]) return "<<PREV>>"
+ seen[item] = true
+ 
  indent = indent or 0
- local pfx = ""
+ local pfx = "\n"
  for _=1,indent do
   pfx ..= " "
  end
- if (type(item) ~= "table") return pfx..tostr(item)
- ret = pfx.."{"
- pfx = "\n"..pfx
+
+ if item.is_linked_list then
+  local ret,n = "linked_list <",0
+  item:strip(function(x)
+   n += 1
+   local masked_x = {next="<<...>>"}
+   setmetatable(masked_x, {__index=x})
+   ret ..= pfx..tostr(n)..": "..masked_x
+  end)
+  return ret..pfx..">"
+ end
+
+ local ret = "{"
  for k, v := pairs(item) do
-  ret ..= pfx..tostr(k)..": "..puke(v, indent+1)
+  ret ..= pfx..tostr(k)..": "..puke(v, indent+1, seen)
  end
  return ret..pfx.."}"
 end