local _tl_compat; if (tonumber((_VERSION or ''):match('[%d.]*$')) or 0) < 5.3 then local p, m = pcall(require, 'compat53.module'); if p then _tl_compat = m end end; local table = _tl_compat and _tl_compat.table or table; local ForthStack = {}



 Stack = {}






function Stack:push(val)
   self.top = self.top + 1
   table.insert(self.contents, val)
end
function Stack:pop()
   self.top = self.top - 1
   if self.top < 0 then
      error("Stack underflow")
   end
   return table.remove(self.contents)
end
local stack_mt = { __index = Stack }
function Stack:new()
   return setmetatable({ contents = {}, top = 0 }, stack_mt)
end



function ForthStack.add(stack)
   local a = stack:pop()
   local b = stack:pop()
   if type(a) == "number" and type(b) == "number" then
      local c = a + b
      stack:push(c)
   else
      error("invalid operands for add operation!")
   end
end
function ForthStack.dot(s)
   print(s:pop())
end
local s = Stack:new()
s:push(1)
s:push(4)
ForthStack.add(s)
print(ForthStack.dot(s))



return ForthStack