Re: supp-ran.lua makes code unable to work in ConTeXt

[Hans Hagen <j.hagen@xs4all.nl>]

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

Hans

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
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