Re: pairs and ipairs

[rzvxa <rzvxa@...>]

Can it be done in a strategy pattern? for example, each type can implement its iterator via its iter function and you can use it based on the type you are iterating.
for example, something like this can be done:

function loopTeXObj(obj)

    for k, v in obj.iter() do

        -- something

    end

    -- or

   -- itr can be a global function that detects your type and injects the strategy function for it

   -- itr can simply be a look up table

    for k, v in iter(obj) do

        -- something

    end

end

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------- Original Message -------
On Sunday, October 22nd, 2023 at 3:20 PM, Hans van der Meer <havdmeer@ziggo.nl> wrote:

Francisco, thank you very much for pointing this out. Sets me on track.

As suggested by some, I add a little bit of information to illustrate why and in what context my question arose.

I am programming for the ConTeXt (a TeX variant) typesetting programming environment. There is exchange of values from the TeX main program body to the embedded Lua in this system and vice versa. It brings its own peculiarities. More often than not parameters are exchanged from TeX to Lua as strings. So some limitations one must take for granted. Or otherwise clutter the interface with different macro's for string or bare value exchange. I have learnt to live with those limitations.

Programming of data structures in the TeX language (although formally a Turing machine) can be done, but is a pain in the ass, so to speak. Therefore I am doing that on ConteXt's Lua side.

In order to handle data structures like arrays and records in TeX I am aiming for a few object oriented modules for each of these two. It then seemed natural to traverse each of them in their own way.

On 22 Oct 2023, at 13:27, Francisco Olarte <folarte@peoplecall.com> wrote:

May be having apairs() to will make more sense, but anyway, due to how
they work ( returning values plus a function ) building a Xpairs
functions is easy,  just do it:

function inext(t,i) i=i+1 ; v=t[i]; if v then return i,v end end
function zpairs(t) return inext, t, -1 end -- like ipairs, but start at 0.

You can trivially iterate through the string only:

function snext(t,k)

local v; k,v=next(t,k)
while k~= nil do
  if type(k)=="string" then return k,v end
  k,v = next(t,k)
end
end

function spairs(t) return snext, t, nil end
a={1,2,b=3,[{}]=4,c=5,6,7}
for i,v in spairs(a) do print(i,v) end

b    3
c    5

Francisco Olarte.

yours sincerely

dr. Hans van der Meer