1. Posted by galvin on Sun, 04 Jul 2010 06:40:00 
     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() ?

  2. Posted by jnwhiteh on Sun, 04 Jul 2010 08:56:30

    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.

  3. Posted by galvin on Sun, 04 Jul 2010 21:48:15

    Thanks, works now.