[Haskell-beginners] Different behaviors between GHC 7.6.3 and 7.8.3

[Emilio De Camargo Francesquini]

Hello,

That, however, does not explain why

Prelude> :force x
x = _

did not evaluate "x". I finally found the related bug and apparently it is
indeed a known problem: https://ghc.haskell.org/trac/ghc/ticket/9046

Thanks!

Emilio

2014-10-01 9:02 GMT-03:00 Henk-Jan van Tuyl <hjgtuyl at chello.nl>:

> On Tue, 30 Sep 2014 17:33:51 +0200, Emilio De Camargo Francesquini <
> francesquini at gmail.com> wrote:
>
> :
>
>> GHCi, version 7.8.3: http://www.haskell.org/ghc/  :? for help
>> Loading package ghc-prim ... linking ... done.
>> Loading package integer-gmp ... linking ... done.
>> Loading package base ... linking ... done.
>> Prelude> let x = 3 + 4
>> Prelude> :print x
>> x = (_t1::Num a => a)
>> Prelude> :force x
>> x = _
>> Prelude> print _t1
>> ghc: panic! (the 'impossible' happened)
>>   (GHC version 7.8.3 for x86_64-unknown-linux):
>>     tcTyVarDetails a{tv atm} [tv]
>>
>> Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
>>
>>
>> Is it really a bug or is it something I really shouldn't be doing?
>>
>
> It seems to me that _t1 is a temporary name, therefore it is not
> meaningful to print _t1; GHCi should give a message telling that _t1 is not
> defined, not a panic message. It is best to write a bug report for this.
>
> Regards,
> Henk-Jan van Tuyl
>
>
> --
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