Re: Unexpected error

[Peter Cawley <lua@...>]

That code shouldn't work with the latest version of Lua (5.1).
Specifically, the line:
for k,v in self do n[k] = v end
Uses a feature which was deprecated in 5.0, and has been removed in
5.1, and hence when executed, that line should be giving you this
error:
line 14: attempt to call a table value
A version of that line changed to be compatible with Lua 5.1 is:
for k,v in pairs(self) do n[k] = v end
If instead of changing it, you commented out that line, then you would
get the error message which you stated:
line 80: attempt to call method 'pushright' (a nil value)

Also, the line numbers in your error message do not correlate with the
source file which you included - line 46 does not call pushright, nor
is it part of the test function.

On Sun, Sep 20, 2009 at 5:34 PM, Christopher Eykamp <chris@eykamp.com> wrote:
> I'm trying to run some pretty basic code, and am getting an unexpected and
> confusing error.  I'm hoping that more experienced eyes can tell me what's
> wrong.  This is standard code that was previously published, which I have
> not modified in any way.  I am running the latest version of Lua.
>
> Here is the error:
> C:\>lua listtest.lua
> lua: listtest.lua:46: attempt to call method 'pushright' (a nil value)
> stack traceback:
>         listtest.lua:46: in function 'test'
>         listtest.lua:72: in main chunk
>         [C]: ?
>
> C:\>
>
> Here is the code:
>
> -- $Id: lists.lua,v 1.6 2001/01/13 22:04:18 doug Exp $
> -- http://www.bagley.org/~doug/shootout/
> -- implemented by: Roberto Ierusalimschy
>
> --------------------------------------------------------------
> -- List module
> -- defines a prototipe for lists
> --------------------------------------------------------------
>
> List = {first = 0, last = -1}
>
> function List:new ()
>   local n = {}
>   for k,v in self do n[k] = v end
>   return n
> end
>
> function List:length ()
>   return self.last - self.first + 1
> end
>
> function List:pushleft (value)
>   local first = self.first - 1
>   self.first = first
>   self[first] = value
> end
>
> function List:pushright (value)
>   local last = self.last + 1
>   self.last = last
>   self[last] = value
> end
>
> function List:popleft ()
>   local first = self.first
>   if first > self.last then error"list is empty" end
>   local value = self[first]
>   self[first] = nil  -- to allow collection
>   self.first = first+1
>   return value
> end
>
> function List:popright ()
>   local last = self.last
>   if self.first > last then error"list is empty" end
>   local value = self[last]
>   self[last] = nil  -- to allow collection
>   self.last = last-1
>   return value
> end
>
> function List:reverse ()
>   local i, j = self.first, self.last
>   while i<j do
>     self[i], self[j] = self[j], self[i]
>     i = i+1
>     j = j-1
>   end
> end
>
> function List:equal (otherlist)
>   if self:length() ~= otherlist:length() then return nil end
>   local diff = otherlist.first - self.first
>   for i1=self.first,self.last do
>     if self[i1] ~= otherlist[i1+diff] then return nil end
>   end
>   return 1
> end
>
> -----------------------------------------------------------
> -----------------------------------------------------------
>
> -- Some tests
>
> function test ()
>   local SIZE = 10000
>   -- create a list with elements 1..SIZE
>   local l1 = List:new()
>   for i=1,SIZE do
>     l1:pushright(i)
>   end
>   -- creates a copy of l1
>   local l2 = l1:new()
>   -- remove each individual item from left side of l2 and
>   -- append to right side of l3 (preserving order)
>   local l3 = List:new()
>   while l2:length() > 0 do
>     l3:pushright(l2:popleft())
>   end
>   -- remove each individual item from right side of l3 and
>   -- append to right side of l2 (reversing list)
>   while l3:length() > 0 do
>     l2:pushright(l3:popright())
>   end
>   -- reverse l1 in place
>   l1:reverse()
>   -- compare Li1 and Li2 for equality
>   -- and return length of the list
>   if not l1:equal(l2) then return nil
>   else return l1:length()
>   end
> end
>
> N = tonumber((arg and arg[1])) or 1
> for i=1, N do
>   result = test()
> end
> print(result)
>
>