haskell

问题 For instance if I would like to read the source code for the default curry function in Prelude, where do I refer? Is there a way to read it's implementation? I tried to search it in Hoogle, but it doesn't give the exact implementation, just the input and output types. I am using GHCI on stack to run haskell.- Hoogle curry 回答1: Like @Lee mentioned in the comments, there is a link for source for many of the functions on hackage. Following this will take you to the source code for curry : -- |

问题 For instance if I would like to read the source code for the default curry function in Prelude, where do I refer? Is there a way to read it's implementation? I tried to search it in Hoogle, but it doesn't give the exact implementation, just the input and output types. I am using GHCI on stack to run haskell.- Hoogle curry 回答1: Like @Lee mentioned in the comments, there is a link for source for many of the functions on hackage. Following this will take you to the source code for curry : -- |

问题 For instance if I would like to read the source code for the default curry function in Prelude, where do I refer? Is there a way to read it's implementation? I tried to search it in Hoogle, but it doesn't give the exact implementation, just the input and output types. I am using GHCI on stack to run haskell.- Hoogle curry 回答1: Like @Lee mentioned in the comments, there is a link for source for many of the functions on hackage. Following this will take you to the source code for curry : -- |

问题 I'm having an issue in which my parser for if-blocks (and Do-While blocks because the problem is the same) won't terminate upon the parsing of the string "fi". An If-Block takes the form of: if P -> p [] Q -> q fi If I use Text.Parsec 's string parser to parse "fi" like how I used it to parse "if" to even enter the loop, the program halts. When I print out what should be evaluated its not even there so the program doesn't even enter the If-Block when it is ended with "fi" . When I remove the

问题 This question already has an answer here : Type Inference in Haskell for functions (1 answer) Closed 1 year ago . I'm preparing for my exams but there is something I can't understand. functions: tw f x = f (f x) f x y = (y, x) I am able to determine the type of 'f' which is f :: t1 -> t -> (t, t1) but can't determine the type of 'tw'. Supposed type of tw: tw :: (t -> t) -> t -> t thanks! 回答1: Let us analyze the function tw : tw f x = f (f x) tw takes as parameters f and x . At the moment we

问题 I've always wondered how the Haskell exception system fits in with the whole "Pure functional language" thing. For example see the below GHCi session. GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Prelude> head [] *** Exception: Prelude.head: empty list Prelude> :t head head :: [a] -> a Prelude> :t error error :: [Char] -> a Prelude> error "ranch" *** Exception: ranch CallStack (from HasCallStack): error, called at <interactive>:4:1 in interactive:Ghci1 Prelude> The type of

问题 Take for example the class Functor : class Functor a instance Functor Maybe Here Maybe is a type constructor. But we can do this in two other ways: Firstly, using multi-parameter type classes: class MultiFunctor a e instance MultiFunctor (Maybe a) a Secondly using type families: class MonoFunctor a instance MonoFunctor (Maybe a) type family Element type instance Element (Maybe a) a Now there's one obvious advantage of the two latter methods, namely that it allows us to do things like this:

问题 I've tried googling but come up short. I am furthering my Haskell knowledge by reading some articles and I came across one that uses a syntax I've never seen before. An example would be: reconstruct node@(Node a b c l r) parent@(Node b d le ri) I've never seen these @'s before. I tried searching online for an answer but came up short. Is this simply a way to embed tags to help make things clearer, or do they have an actual impact on the code? 回答1: It is used in pattern matching. Now node

问题 In a functional language, functions are first class citizens and thus calling them is not the only thing I can do. I can also store them away. Now when I have a language, which is strict by default, then I am still not forced to evaluate a function call. I have the option to store the function and its parameters e.g. in a tuple for later evaluation. So instead of x = f a b c I do something like x = (f,a,b,c) And later, I can evaluate this thing with something like eval (f,a,b,c) = f a b c

问题 I have the following code which works fine unless the file has utf-8 characteres : module Main where import Ref main = do text <- getLine theInput <- readFile text writeFile ("a"++text) (unlist . proc . lines $ theInput) With utf-8 characteres I get this: hGetContents: invalid argument (invalid byte sequence) Since the file I'm working with has UTF-8 characters, I would like to handle this exception in order to reuse the functions imported from Ref if possible. Is there a way to read a UTF-8