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
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