[NTG-context] supp-ran.lua makes code unable to work in ConTeXt

[Aditya Mahajan]

On Sat, 2 May 2020, Hans Hagen wrote:

> On 5/1/2020 11:38 PM, Aditya Mahajan wrote:
>> On Fri, 1 May 2020, Hans Hagen wrote:
>> 
>>> On 5/1/2020 6:12 AM, Jairo A. del Rio wrote:
>>>> I've adapted the following code to make mazes in LuaLaTeX and ConTeXt: 
>>>> https://www.rosettacode.org/wiki/Maze_generation#Lua
>>>> 
>>>> I defined a modified version to make content visible to TeX and I saved 
>>>> in a file named maze.lua:
>>>> 
>>>> function make_maze_tex(w, h, m)
>>>>    w = w or 16
>>>>    h = h or 8
>>>> 
>>>>    local map = initialize_grid(w*2+1, h*2+1)
>>>> 
>>>>    function walk(x, y)
>>>>      map[y][x] = false
>>>> 
>>>>      local d = { 1, 2, 3, 4 }
>>>>      shuffle(d)
>>>>      for i, dirnum in ipairs(d) do
>>>>        local xx = x + dirs[dirnum].x
>>>>        local yy = y + dirs[dirnum].y
>>>>        if map[yy] and map[yy][xx] then
>>>>          map[avg(y, yy)][avg(x, xx)] = false
>>>>          walk(xx, yy)
>>>>        end
>>>>      end
>>>>    end
>>>> 
>>>>    walk(math.random(1, w)*2, math.random(1, h)*2)
>>>> 
>>>> ...ext/tex/texmf-context/tex/context/base/mkiv/supp-ran.lua:30: C stack 
>>>> overflow Why does it happen? I guess it has something to do with 
>>>> math.randomseed, but I don't know how to avoid this error message.
>>> no, it's just lua running out of stack space so it depends on the binary 
>>> (and als the initial random value)
>> 
>> But why is it running out of stack? Isn't the walk function tail 
>> recursive, in which case it should not cause a stack overflow 
>> (https://www.lua.org/pil/6.3.html).
> not really tail recursive: that is only true when it's the last action and 
> return is used and it nests very deep
>
> function foo(...)
>  ...
>  return foo(...)
> end
>
> versus
>
> function foo(...)
>  ...
>  if something then
>     foo(...)
>  end
> end

Thanks for the clarification.

If you or anyone else is going to play around with generating mazes,
definitely take a look at http://www.mazesforprogrammers.com/

and the live demos here: 
https://weblog.jamisbuck.org/2011/2/7/maze-generation-algorithm-recap

Aditya