First I am using WinHugs. that's the code i made so far but it's still not working:
http://hpaste.org/48318 Error: ERROR file:.\kursovazadacha.hs:36 - Type error in explicitly typed binding *** Term : p *** Type : [String] -> [a] *** Does not match : [String] -> Int I'm still breaking down somewhere ... 2011/6/25 Daniel Patterson <lists.hask...@dbp.mm.st>: > what haskell compiler are you using? And what does the "include" line do? > > That does not look like a GHC error message (the only compiler I'm familiar > with), but it seems like it is saying that you should not have the extra > newlines between the function type signature and declaration. - that's only > my guess, based on the assumption that the whitespace is being converted to a > syntax with explicit semilcolon line terminations. > > now, looking at the actual code, the type of the parse function is [a] -> > [a]. This means that you can parse a list of anything into a list of > anything, which doesnt make much sense. This should probably be [String] -> > [String] (you are parsing a list of strings to a list of strings, yes?). Now > the base case of parse (the first case) makes sense, but look at the second > case. parse is being given a list of elements (which you have used pattern > matching to decompose, but the whole argument, (x:xs), is a list of > elements). You are then passing that, unchanged, to eval. This means that > eval must take the same type. Does it? how would you apply eval to each > element in that list, instead of just applying it to the whole list? > > On Jun 24, 2011, at 4:31 PM, Stoyan Peev wrote: > >> I found the library myself, and i already put the code in that site: >> >> http://hpaste.org/48277 >> >> >> >> That's what i have tried to do for making the task by calling the one >> string function by another one: >> >> include kursovazadacha >> >> parse :: [a] -> [a] >> >> parse [] = [] >> >> parse (x:xs) = eval (x:xs) >> >> >> The error from the compiler: >> >> ERROR file:.\list.hs:3 - Syntax error in declaration (unexpected `;', >> possibly due to bad layout) >> >> >> On Fri, Jun 24, 2011 at 11:20 PM, Daniel Patterson >> <lists.hask...@dbp.mm.st> wrote: >>> What have you tried to do in order to make it work for the list, and what >>> error results? What is confusing about the error message? More generally, >>> how could you transform an operation on a single string into one that does >>> the same thing to a list of strings? You've probably talked about higher >>> order functions in your class - would any of the common ones (filter, map, >>> foldr) be helpful here? Would any encapsulate what you are trying to do? >>> >>> If you include these kinds of things, I think you'll find this community >>> to be very helpful; without that (showing what your thought process is, why >>> it isn't working, what seems confusing about what the haskell compiler is >>> telling you, etc), you are not going to get help here. People here are very >>> friendly and willing to help people learn; this is not a place to come to >>> get an assignment finished :) >>> >>> Also, could you put the library you are using (I'm assuming that this is >>> provided by your university) and the code on somewhere like hpaste.org, so >>> that the formatting is not messed up by email, and it is syntax highlighted? >>> >>> On Jun 24, 2011, at 3:57 PM, Stoyan Peev wrote: >>> >>>> Hello all, >>>> >>>> I am experiencing some issues to do my course task in university. >>>> >>>> I have to write a calculator- function in Haskell. The function >>>> argument is a list of strings and also form such list, as each string >>>> of the argument made definite action: >>>> - If the string has the form of an arithmetic _expression_ - calculate >>>> this _expression_. The string result becomes part of the list-result. >>>> If the _expression_ contains a variable which is not assigned value, >>>> the result is displayed "undefined". >>>> - If the string has the form- Name = value calculated from the last >>>> _expression_ is assigned to the variable with the corresponding name >>>> in the list, and in the result list is formed a string with type >>>> - If there is not a calculated _expression_ to be assigned to form a >>>> string "no value". >>>> - If the string is non-blank, but there is a species different from >>>> the above two case, form the string "error". >>>> - If the string is empty, incl. when it contains only spaces, in the >>>> result there is not form a string. >>>> >>>> Expressions consist of integers without sign variables, operations + >>>> (Addition), - (subtraction), * (multiplication) and / (divide) and >>>> parentheses. Where no brackets, the operations are performed from left >>>> to right, but * and / precede the + and -. Implementation of any >>>> operation gives integer; in the division rejected the fractional part, >>>> if any. >>>> Variables have names of one letter - from the Latin small letter. In >>>> the beginning, end or between the elements of each row can have spaces >>>> - they are irrelevant to its correctness. >>>> Example: the list-argument >>>> ["3 +7 / 2" "2 + x", "= s", "2 * s +4", "", "2 + +4 / 5] >>>> function should provide a result-list >>>> ["6", "undefined", "s = 6", "16", "error"]. >>>> >>>> >>>> I say another person have the same task, but he didn't do anything. I >>>> started doing this task myself but i get stuck in the middle. Then i >>>> started searching for something that could help me and find out you :) >>>> >>>> The code i have written so far uses the library file "Parsing.lhs" >>>> but what i have written is taking those actions that i already >>>> described, only for a string. I cannot modify it to work for list of >>>> string, and complete the whole task. >>>> >>>> I'll be glad to finish the task myself, but i am going to need some help. >>>> >>>> Here is the code i have already written: >>>> >>>> >>>> import Parsing >>>> >>>> expr :: Parser Int >>>> expr = do t <- term >>>> do symbol "+" >>>> e <- expr >>>> return (t+e) >>>> +++ do symbol "-" >>>> e <- expr >>>> return (t-e) >>>> +++ return t >>>> term :: Parser Int >>>> term = do f <- factor >>>> do symbol "*" >>>> t <- term >>>> return (f * t) >>>> +++ do symbol "/" >>>> t <- term >>>> return (f-t) >>>> +++ return f >>>> factor :: Parser Int >>>> factor = do symbol "(" >>>> e <- expr >>>> symbol ")" >>>> return e >>>> +++ natural >>>> eval :: String -> Int >>>> eval xs = case (parse expr xs) of >>>> [(n,[])] -> n >>>> [(_,out)] -> error ("undefined") >>>> [] -> error "error" >>>> >>>> >>>> >>>> Thanks all in advance :) >>>> >>>> -- >>>> Best Wishes >>>> Stoyan Peev >>>> >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> Haskell-Cafe@haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >>> >> >> >> >> -- >> Поздрави, >> Стоян Пеев > > -- Поздрави, Стоян Пеев _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
