ghci

问题 Defining a function signature in Haskell's interpreter GHCi doesn't work. Copying an example from this page: Prelude> square :: Int -> Int <interactive>:60:1: error: • No instance for (Show (Int -> Int)) arising from a use of ‘print’ (maybe you haven't applied a function to enough arguments?) • In a stmt of an interactive GHCi command: print it Prelude> square x = x * x How can I declare a function signature and then give function definition in Haskell interactively? also: why can't I simply

问题 I'm using Haskell 2010.1.0.0.1 with GHC 6. Typing :t at the GHCi prompt followed by the name of a function shows us the type of the function. Is there a way to view the function definition as well? 回答1: Not currently. The closest command to what you want is :info :info name ... Displays information about the given name(s). For example, if name is a class, then the class methods and their types will be printed; if name is a type constructor, then its definition will be printed; if name is a

问题 I have a Haskell program using the FFI to import C++ functions. I'm using Windows. When I compile to an executable or to a DLL, this works. But when I load a module in GHCI, this doesn't always work: sometimes this works, sometimes I get Access violation in generated code when reading 0000000000000000 whenever I call a function from the module (even if this function has nothing to do with the C++). Do you know how to prevent that? 来源： https://stackoverflow.com/questions/47849032/access

问题 I'm running a servant server and another background thread (via async ) in gchi . When I press Ctrl+c on the GHCi prompt, the servant server shuts down properly, but my background thread keeps running. Only quitting the entire GHCi session seems to really terminate it. Two questions: Is this behaviour only because I'm in GHCi? If I compiled a binary, ran it, and then pressed Ctrl+C on it, would the background-thread still keep running? How do I solve for this properly? 回答1: Is this behaviour

问题 I'm running a servant server and another background thread (via async ) in gchi . When I press Ctrl+c on the GHCi prompt, the servant server shuts down properly, but my background thread keeps running. Only quitting the entire GHCi session seems to really terminate it. Two questions: Is this behaviour only because I'm in GHCi? If I compiled a binary, ran it, and then pressed Ctrl+C on it, would the background-thread still keep running? How do I solve for this properly? 回答1: Is this behaviour

问题 How does history management work in GHCI or other Haskell-based REPLs? Since Haskell is a pure language, I guess it's implemented using a monad, perhaps the state monad. Kindly note I'm a beginner in Haskell, so please provide a detailed explanation rather than just linking to the source. 回答1: This is a simplified example of how a program might keep a history of commands entered by the user. It basically has the same structure as the number guessing game, so once you understand that you

问题 How does history management work in GHCI or other Haskell-based REPLs? Since Haskell is a pure language, I guess it's implemented using a monad, perhaps the state monad. Kindly note I'm a beginner in Haskell, so please provide a detailed explanation rather than just linking to the source. 回答1: This is a simplified example of how a program might keep a history of commands entered by the user. It basically has the same structure as the number guessing game, so once you understand that you

问题 Using the low-level GNU Science Library bindings Bindings.Gsl.RandomNumberGeneration, I'm running into this odd type behavior in GHCi where binding changes return type from a peek into GHC.Prim.Any . I'm trying to understand why since I can't use the c'rng_alloc unless I retain the type of pointer to an rng . For eample: λ> :t c'gsl_rng_alloc c'gsl_rng_alloc :: Ptr C'gsl_rng_type -> IO (Ptr C'gsl_rng) λ> :t p'gsl_rng_mt19937 p'gsl_rng_mt19937 :: Ptr (Ptr gsl_rng_type) λ> :t peek p'gsl_rng

问题 I am a novice in Haskell. Here's some simple code: module Src ( -- The 'Answer' type isn't exported Shape(Circle), -- i.e 'Rectangle' data constructor isn't exported Point(..), area, nudge ) where data Answer = Yes | No deriving (Show) data Point = Point Float Float deriving (Show) data Shape = Circle Point Float | Rectangle Point Point deriving (Show) area :: Shape -> Float area (Circle _ r) = pi * r ^ 2 area (Rectangle (Point x1 y1) (Point x2 y2)) = (abs $ x2 - x1) * (abs $ y2 - y1) nudge:

问题 I want to make a Haskell script to read files in my /home folder. However there are many files named with Chinese characters, and Haskell and Ghci cannot manage it. It seems Haskell and Ghci aren't good at displaying UTF-8 characters. Here is what I encountered: Prelude> "让Haskell或者Ghci能正确显示汉字并且读取汉字命名的文档" "\35753Haskell\25110\32773Ghci\33021\27491\30830\26174\31034\27721\23383\24182\19988\35835\21462\27721\23383\21629\21517\30340\25991\26723" 回答1: Prelude> putStrLn "\35753Haskell\25110