1.  local operators = {
        ["+"] = function(a, b)
           return a + b
        end,
        ["-"] = function(a ,b)
           return a - b
        end,
        ["*"] = function(a ,b)
           return a * b
        end,
        ["/"] = function(a, b)
           return a / b
        end
     }
    
     local NUMBER_PATTERN = "^%s*([+-]?%d*%.?%d+)"
     local OPERATOR_PATTERN = "^%s*(.)"
     local END_PATTERN = "^%s*$"
     local NUMBER_ERROR = "No valid number at position %d"
     local OPERATOR_ERROR = "Unrecognized operator at position %d: '%s'"
    
     local errorState = false
    
     local function reportError(message)
        print(message)
        errorState = true
     end
    
    
     local function calculate(number1, ...)
        if errorState then
           return
        end
    
        for i = 1, select("#", ...), 2 do
           print(select(i, ...))
           local operator, number2 = select(i, ...)
           number1 = operators[operator](number1, number2)
        end
    
        return number1
     end
    
     local function getpairs(message, start)
        local _, operatorFinish, operator = message:find(OPERATOR_PATTERN, start)
        local operatorFunction = operators[operator]
        if not operatorFunction then
           reportError(OPERATOR_ERROR:format(start, operator))
           return
        end
        operatorFinish = operatorFinish + 1
        local _, numberFinish, number = message:find(NUMBER_PATTERN, operatorFinish)
        if not number then
           reportError(NUMBER_ERROR:format(operatorFinish))
           return
        end
        numberFinish = numberFinish + 1
        if message:match(END_PATTERN, numberFinish) then
           return operatorFunction, number
        else
           return operatorFunction, number, getpairs(message, numberFinish)
        end
     end
    
    
     local function tokenize(message)
        local _, finish, number = message:find(NUMBER_PATTERN)
        if not number then
           reportError(NUMBER_ERROR:format(1))
           return
        end
        finish = finish + 1
        if message:match(END_PATTERN, finish) == "" then
           return number
        else
           return number, getpairs(message, finish)
        end
     end
    
    
     SLASH_SIMPLECALC1 = "/calculate"
     SLASH_SIMPLECALC2 = "/calc"
     SlashCmdList["SIMPLECALC"] = function(message)
        errorState = false
        print(calculate(tokenize(message)))
     end
    

    When I do a simple command: /calculate 1 + 2 I get the following error

     Message: Interface\AddOns\UiMisc\UiMisc.lua:38: attempt to call field '?' (a nil value)
     Time: 07/04/10 02:38:56
     Count: 2
     Stack: Interface\AddOns\UiMisc\UiMisc.lua:38: in function <Interface\AddOns\UiMisc\UiMisc.lua:30>
     Interface\AddOns\UiMisc\UiMisc.lua:88: in function `?'
     Interface\FrameXML\ChatFrame.lua:4049: in function `ChatEdit_ParseText'
     Interface\FrameXML\ChatFrame.lua:3660: in function `ChatEdit_SendText'
     Interface\FrameXML\ChatFrame.lua:3698: in function `ChatEdit_OnEnterPressed'
     [string "*:OnEnterPressed"]:1: in function <[string "*:OnEnterPressed"]:1>
    
     Locals: number1 = "1"
     (for index) = 1
     (for limit) = 2
     (for step) = 2
     i = 1
     operator = <function> defined @Interface\AddOns\UiMisc\UiMisc.lua:2
     number2 = "2"
     (*temporary) = nil
     (*temporary) = "1"
     (*temporary) = "2"
     (*temporary) = "attempt to call field '?' (a nil value)"
     errorState = false
     operators = <table> {
      - = <function> defined @Interface\AddOns\UiMisc\UiMisc.lua:5
      / = <function> defined @Interface\AddOns\UiMisc\UiMisc.lua:11
      + = <function> defined @Interface\AddOns\UiMisc\UiMisc.lua:2
      * = <function> defined @Interface\AddOns\UiMisc\UiMisc.lua:8
     }
    

    Also curious what happens when you do a return of a function that returns more than one argument.

    so for example. "return somevariable, x()" and if x() returns more than one argument how does that effect the return somevariable, x() ?

    There's an issue with the bolding of the text in the second code block on page 343. You also need to edit the two lines within the for statement from the previous version. As listed on that page, the calculate function should be this:

     local function calculate(number1, ...)
        if errorState then
           return
        end
    
        print(number1, ...)
    
        for i = 1, select("#", ...), 2 do
           local operator, number2 = select(i, ...)
           number1 = operator(number1, number2)
        end
    
        return number1
     end
    

    Also curious what happens when you do a return of a function that returns more than one argument.

    so for example. "return somevariable, x()" and if x() returns more than one argument how does that effect the return somevariable, x() ?

    The semantics of multiple return values are discussed early on in the book, check the table of contents. In this case, as long as the thing returning multiple values is at the end of a return list, all of those values will be returned.. same as usual.

    Thanks, works now.