Sokoban movement (slidable check)

local function move(map, startX, startY, dX, dY)
    local targetX, targetY = startX + dX, startY + dY
    if not map[targetX][targetY] then return startX, startY; end
    if map[targetX][targetY].isBox then
        local slideX, slideY = targetX + dX, targetY + dY
        if not (map[slideX] and map[slideX][slideY] and map[slideX][slideY].isWalkable) then return startX, startY; end
    end
end