Yes, how can i miss that... It's working now, but still it works only for the first element of the list. It prints the result only for the first string. Now when it's operational, i have just to modify it to be working for all of the elements of the list. If i run the program right now, the results are:
Main> p ["2*3","4/2"] 6 I'm not so sure, if i have to modify the caller function only, or i have to modify both the caller function and the exact function that makes the parsing? 2011/6/25 Jack Henahan <jhena...@uvm.edu>: > The error in ghci is > > Couldn't match expected type `Int' with actual type `[a0]' > In the expression: [] > In an equation for `p': p [] = [] > > You've defined p as [String] -> Int, but then your base case is p [] = []. [] > is not an Int. I changed it to 0 and it'll compile, at least, but I'm not > sure if that's the effect you're after. > > http://hpaste.org/48324 > Edited code (really just indentation changes and the change from p [] = [] to > p [] = 0) > > On Jun 25, 2011, at 3:19 PM, Stoyan Peev wrote: > >> 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 > > > > > > -- Поздрави, Стоян Пеев _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
