Pretty-printing Lua datastructures

The following code is (yet another) pretty printer, useful for debugging because it tries to avoid clutter. To dump the contents of var, type pretty("var",var). This version deals with all types of data and knows how to deal with cycles.

  -- This was extracted from utility code in "util.lua".
  -- 23/02/2001 jcw@equi4.com

  -- pretty displays a value, properly dealing with tables and cycles
  local displayvalue=
    function (s)
      if not s or type(s)=='function' or type(s)=='userdata' then
        s=tostring(s)
      elseif type(s)~='number' then
        s=gsub(format('%q',s),'^"([^"\']*)"$',"'%1'")
      end
      return s
    end
  local askeystr=
    function (u,s)
      if type(u)=='string' and strfind(u,'^[%w_]+$') then return s..u end
      return '['..%displayvalue(u)..']'
    end
  local horizvec=
    function (x,n)
      local o,e='',''
      for i=1,getn(x) do
        if type(x[i])=='table' then return end
        o=o..e..%displayvalue(x[i])
        if strlen(o)>n then return end
        e=','
      end
      return '('..o..')'
    end
  local horizmap=
    function (x,n)
      local o,e='',''
      for k,v in x do
        if type(v)=='table' then return end
        o=o..e..%askeystr(k,'')..'='..%displayvalue(v)
        if strlen(o)>n then return end
        e=','
      end
      return '{'..o..'}'
    end
  function pretty(p,x,h,q)
    if not p then p,x='globals',globals() end
    if type(x)=='table' then
      if not h then h={} end
      if h[x] then
        x=h[x]
      else
        if not q then q=p end
        h[x]=q
        local s={}
        for k,v in x do tinsert(s,k) end
        if getn(s)>0 then
          local n=75-strlen(p)
          local f=getn(s)==getn(x) and %horizvec(x,n)
          if not f then f=%horizmap(x,n) end
          if not f then
            sort(s,function (a,b)
                     if tag(a)~=tag(b) then a,b=tag(b),tag(a) end
                     return a<b
                   end)
            for i=1,getn(s) do
              if s[i] then
                local u=%askeystr(s[i],'.')
                pretty(p..u,x[s[i]],h,q..u)
                p=strrep(' ',strlen(p))
              end
            end
            return
          end
          x=f
        else
          x='{}'
        end
      end
    else
      x=%displayvalue(x)
    end
    print(p..' = '..x)
  end

To display all globals, type "pretty()".