How to spawn stuff in PICO-8 with a function

add_something.p8

-- create a table to hold your objects
coins ={}

--now you can add things into here by hand, but you can also make a functionnsonyou can call that point

function add_coin(xpos, ypos)
  -- now lets make a temporary local table to hold the coins atrributes, you want position mainly
  local coin = {
    x = xpos,
    y = ypos
  }
  -- you now have a coin object but no way to track it as it will die once you exit the function. Lets add it tonthe global table. add(tablename, value)
  add(coins, coin)
end

-- now you can iterate over your coins inside the coin table with any for cycle. If you want to deletenobjects you generally want to go backwards. In update
function update_coins()
  for i=#coins,1,-1 do
    -- this will make i go from the size of the coins table to 1
    --you can grab elements from the table in an easy way
    local coin = coins[i]
    -- this will put each coin inside coins into this coin variable 1 by 1, you can now move them if you want
    coin.y +=1
    -- now for example delete them if they are offscreen
    if coin.y > 128 then
      del(coins, coin)
    end
  end
  --[[
  yoiu can do the same with a for all in() cycle
    for coin in all(coins) do
      coin.y +=1
      -- now for example delete them if they are offscreen
      if coin.y > 128 then
        del(coins, coin)
      end
    end
  ]]--
end

-- now in draw you can do
function draw_coins()
  for i=#coins,1,-1 do
    local coin = coins[i]
    -- you now known where it is on the screen
    print("◆", coin.x, coin.y,9)
  end
end
-- with all this setup you csn just add a coin whenever you want with, where the two numbers all the positions
function _update()
  if btnp(4) then
    add_coin(rnd(128), rnd(128))
  end
  update_coins()
end

function _draw()
  cls()
  draw_coins()
  
end

Do you want add a bullet, that goes forward? Modify the update so it is:

coin.x += 2

and remove the coin.y modification now it is moving from side to side just like a bullet!

More PICO-8 Tutorials: https://github.com/Achie72/kofi-articles/blob/main/README.md#pico-8-tutorials

If you would like to read more like this, feel free to checkout my Ko-fi articles, with many devlogs and code rundowns like this!
https://github.com/Achie72/kofi-articles