calculator.lua

Calculator = {}

function Calculator:new (o, input) -- the "account" example at http://www.lua.org/cgi-bin/demo made me think that you could just make classes, didn't realise the importance of all this boilerplate
  o = o or {name=name}
  setmetatable(o, self)
  self.__index = self
  
  self.input = input
  self.calculation = "(%d+) ?([+-/*]) ?(%d+)" -- not sure if i'm a fan of lua not supporting all regex features - http://lua-users.org/wiki/PatternsTutorial - but i suspect the benefits will be obvious after more digging
  
  return o
end

function Calculator:result () -- forgot the brakcets here - debugging that was confusing
  local first_num, method, last_num = string.match(self.input, self.calculation) -- was pleased to see you could do this

  if method == "+" then -- seems dumb that "then" is required
    return first_num + last_num
  elseif method == "-" then
    return first_num - last_num
  elseif method == "*" then
    return first_num * last_num
  elseif method == "/" then
    return first_num / last_num
  end
end

print(Calculator:new(nil, "1 + 1"):result()) -- 2 <-- i'm spoiled by ruby. forgot the method call braces() for ages.
print(Calculator:new(nil, "22 + 14"):result()) -- 36
print(Calculator:new(nil, "22 - 14"):result()) -- 8
print(Calculator:new(nil, "10 / 5"):result()) -- 2
print(Calculator:new(nil, "10 * 5"):result()) -- 500
print(Calculator:new(nil, "10 / 9"):result()) -- 1.1111111111111 <-- cool, didn't expect it to do floats automatically. it also parsed the string correctly.

Where's the support for multiple operators and order of operations?