Traverse (ComputerCraft)

-- Copyright © 2021 LoganDark
--
-- Permission is hereby granted, free of charge, to any person obtaining a copy
-- of this software and associated documentation files (the "Software"), to deal
-- in the Software without restriction, including without limitation the rights
-- to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-- copies of the Software, and to permit persons to whom the Software is
-- furnished to do so, subject to the following conditions:
--
-- The above copyright notice and this permission notice shall be included in
-- all copies or substantial portions of the Software.
--
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-- SOFTWARE.

local next = next
local type = type

return function(start, callback)
    local stack = {
        data = {start, next(start)},
        len = 1,
        seen = {[start] = true}
    }

    while stack.len > 0 do
        local tblIdx = stack.len * 2 - 1
        local keyIdx = tblIdx + 1

        local tbl = stack.data[tblIdx]
        local key = stack.data[keyIdx]

        if key == nil then
            stack.len = stack.len - 1
            stack.data[stack.len * 2 + 1] = nil

            if stack.len > 0 then
                stack.data[keyIdx - 2] = next(stack.data[tblIdx - 2], stack.data[keyIdx - 2])
            end
        else
            local value = tbl[key]

            callback(value, key, tbl, stack)

            if type(value) == 'table' and not stack.seen[value] then
                stack.seen[value] = true
                stack.data[stack.len * 2 + 1] = value
                stack.data[stack.len * 2 + 2] = next(value)
                stack.len = stack.len + 1
            else
                stack.data[keyIdx] = next(tbl, key)
            end
        end
    end
end

--[[ Example usage:
local traverse = require('traverse')

traverse(_G, function(v, k, tbl, stack)
    local keys = {}

    for i = 2, stack.len * 2, 2 do
        keys[i / 2] = stack.data[i]
    end

    print(table.unpack(keys, 1, stack.len))
    os.sleep(0.05)
end) ]]