[Haskell-cafe] Cabal dependencies

[José Lopes]

Thanks!

On 06-10-2012 23:07, Yuras Shumovich wrote:
> On Sat, 2012-10-06 at 22:40 +0200, José Lopes wrote:
>> OK. Got it!
>>
>> Do you have any suggestions to install xmobar in this particular case?
> In case of executables I usually rm -rf ~/.ghc, cabal install,
> and rm -rf ~/.ghc again. Executables are still here (in ~/.cabal/bin),
> but all libraries are lost. Warning: it may break your development
> environment, so make sure you know what you are doing.
>
> Better solution could be sandbox tools like cabal-dev. They alloy you to
> setup development environment per project.
>
>> Thanks,
>> José
>>
>> On 06-10-2012 19:08, Yuras Shumovich wrote:
>>> On Sat, 2012-10-06 at 18:25 +0200, José Lopes wrote:
>>>> OK.
>>>>
>>>> But, wouldn't it be possible for xmobar to use mtl-2.0.1.0 and for
>>>> parsec to use mtl-2.1.1, while xmobar would use this parsec version?
>>>> In this case, I am assuming that mtl-2.0.1.0 and mtl-2.1.1 are
>>>> considered two different libraries.
>>> Usually it leads to "strange" compilation errors.
>>>
>>> E.g.
>>> Package A:
>>>     data AA = AA String
>>>     func0 :: Int -> AA
>>>     func0 n = AA $ replicate n "A"
>>>     func1 :: AA -> Int
>>>     func1 (AA str) = length str
>>>
>>> Package B:
>>>     import A
>>>     func2 :: AA -> Int
>>>     func2 aa = func1 + 1
>>>
>>> Package C:
>>>
>>>     import A
>>>     import B
>>>     func3 :: Int -> Int
>>>     func3 n = func2 $ func0 n
>>>
>>> If C and B are compiled with different versions of C,
>>> then func3 will not compile. Compiler will say that
>>> AA returned by func0 doesn't match AA expected by func2
>>>
>>> More real examples:
>>> http://stackoverflow.com/questions/11068272/acid-state-monadstate-instance-for-update
>>> http://stackoverflow.com/questions/12576817/couldnt-match-expected-type-with-actual-type-error-when-using-codec-bmp/12577025#12577025
>>>
>>>
>>>> Thanks,
>>>> José
>

-- 
José António Branquinho de Oliveira Lopes
Instituto Superior Técnico
Technical University of Lisbon