Re: heads-up: Haskell updates

[Mark H Weaver]

Ricardo Wurmus <address@hidden> writes:

> Mark H Weaver <address@hidden> writes:
>
>> I suppose if one reads the error message literally:
>>
>>   Control/Monad/Trans/Resource/Internal.hs:302:10: error:
>>       • Could not deduce (MonadBase IO (Strict.StateT s m))
>>           arising from the superclasses of an instance declaration
>>         from the context: MonadResource m
>>           bound by the instance declaration
>>           at Control/Monad/Trans/Resource/Internal.hs:302:10-63
>>       • In the instance declaration for
>>           ‘MonadResource (Strict.StateT s m)’
>>
>> "Could not deduce" might be interpreted to include the case where we
>> failed for lack of sufficient memory.  They might have written the code
>> to catch any error at all, including out of memory errors, and report
>> the failure with this error message.
>
> I think that’s a misunderstanding.  The cause for the error is earlier
> when it complains that some packages depend on different versions of the
> “transformers” package.  “StateT” is a monad transformer.
>
> I think that “ghc-pkg” fails, which leads to some other version of the
> transformers package (maybe a default included with GHC) to be used.  In
> the case where ghc-pkg does not fail (as on my laptop) the proper
> version is used, so there are no problems finding the expected
> instances.

Ah, okay, that sounds plausible.  I confess that my previous message was
somewhat rushed, without much investigation or thought behind it.
Apologies for the noise.

     Regards,
       Mark