ghci

Suppose I am given a source file called MyModule.hs and inside it the module declaration is module My.Module where ... (note: not module MyModule where ... ). I am not permitted to alter this source file or change the directory structure where the file resides. From reading some docs about importing...

I am following https://en.wikibooks.org/wiki/Haskell/Understanding_monads/State , and randomIO prints an integer in ghci directly. Given its type is polymorphic, how does ghci know it's Int here? Are there some special rules for type inference in ghci ? GHCi> :m System.Random GHCi> :t randomIO...

I need to write on a module to be run on GHCi, with a function composition to the same function. This (The classic fog(x) = f(g(x)) ) runs: (.) f g = (\x -> f (g x)). The problem appears when I try to write it like this (.) f f = (\x -> f (f x)). (fof(x) = f(f(x))) GHCi says: "Conflicting...

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...

I was thinking it would be nice to set up my global GHCI config such that my commonly-used imports occur automatically when the packages that provide them are present. I tried adding this to ~/.ghc/ghci.conf : :set -XCPP #ifdef MIN_VERSION_containers import Data.Set (Set) import qualified Data.Set...

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 =...

Look at this output from ghci: Prelude> :t Data.Map.lookup Data.Map.lookup :: Ord k => k -> Data.Map.Map k a -> Maybe a Prelude> :t flip Data.Map.lookup flip Data.Map.lookup :: Ord a => Data.Map.Map a a1 -> a -> Maybe a1 Prelude> let look = flip Data.Map.lookup Loading package array-0.3.0.2 ......

Following an example in http://en.wikibooks.org/wiki/Haskell/Beginning Prelude> let abs x = if x < 0 then -x else x Prelude> abs 5 5 Prelude> abs -3 <interactive>:1:6: No instance for (Num (a0 -> a0)) arising from the literal `3' Possible fix: add an instance declaration for (Num (a0 -> a0)) In the...

Let's say you want to use your own show function (for example, let show = take 1000 . Prelude.show ). How can you allow ghci to use that for printing instead of the built in show ? Lee You can define your own interactive print function e.g: module BetterPrint betterPrint a = putStrLn (take 1000 $...

When I do something simple in ghci, like the following: let x = 7 + 2 I expect ghci to give a response of the type that x holds, like: x :: Integer When I run ghci, I do not get that the above line. How do I get that response? To show types automatically use :set +t : μ> :set +t μ> let x = 7 + 2 x :...