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What are the pitfalls of using FlexibleContexts and FlexibleInstances?


What are the pitfalls of using FlexibleContexts and FlexibleInstances?

By : naveen sharma
Date : December 01 2020, 04:55 PM
hope this fix your issue I once stumbled upon the following. Answering this question, I first tried this code:
code :


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Are Haskell FlexibleInstances a stable extension to the language?

Are Haskell FlexibleInstances a stable extension to the language?


By : Doug Allen
Date : March 29 2020, 07:55 AM
hope this fix your issue What is the problem with FlexibleInstances in Haskell? Why are they not included in Haskell 2010? Were implementations of FlexibleInstances simply not stable enough for inclusion into a standard or are deeper concerns connected to FlexibleInstances? Is it safe to use them? Will they likely be included in Haskell Prime? ,
Is it safe to use them?
ghc-7.10: Non type-variable argument (Use FlexibleContexts to permit this)

ghc-7.10: Non type-variable argument (Use FlexibleContexts to permit this)


By : user3118086
Date : March 29 2020, 07:55 AM
What is the FlexibleContexts extension good for? Could you please explain it using a simple example?

What is the FlexibleContexts extension good for? Could you please explain it using a simple example?


By : Chris Pickering
Date : March 29 2020, 07:55 AM
like below fixes the issue Without FlexibleContexts all typeclass constraints on function definitions must have type variables. For example:
code :
add :: Num a => a -> a -> a 
add = (+)
intAdd :: Num Int => Int -> Int -> Int 
intAdd = (+)
class Shower a b where
  myShow :: a -> b

doSomething :: Shower a String => a -> String
doSomething = myShow
Using Char does not compile without FlexibleContexts

Using Char does not compile without FlexibleContexts


By : Atik Patel
Date : March 29 2020, 07:55 AM
I hope this helps . , The reason is actually in the error message.
code :
Non type-variable argument in the constraint: 
  MArray a0 Char m (Use FlexibleContexts to permit this)
drawLine :: MArray a Char m => ...
drawLine :: (Num n, MArray a n m) => ...
Keep getting (Use FlexibleContexts to permit this) Error In Simple Haskell Function

Keep getting (Use FlexibleContexts to permit this) Error In Simple Haskell Function


By : WenWu.You
Date : March 29 2020, 07:55 AM
it helps some times You can solve this by either enabling FlexibleContexts as it suggests, or by changing your function to work on something more general than lists.
The issue is that Haskell does not allow non-type variable things in a context. If you write out the types of your functions (which you should be doing anyway), you get
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