[Haskell-beginners] question about shared data types

[David Virebayre]

> I've been including newtype Foo in a Common.hs module that is included in
both

Ah, you alredy did that, I didn't see it. Sorry for the noise.



2013/4/29 David Virebayre <dav.vire+haskell at gmail.com>

> What about making a third module that defines and exports Foo ?
>
> David.
>
>
> 2013/4/29 Ian Knopke <ian.knopke at gmail.com>
>
>> Hi everyone,
>>
>> I have two modules that share a common data type in their respective data
>> structures:
>>
>> package Aaa where
>>
>>       newtype Foo = Foo String
>>
>>       data Bar = Bar {
>>           barFoo :: [Foo]
>>       } deriving (Show, Eq)
>>       ...
>>
>> package Bbb where
>>
>>       newtype Foo = Foo String
>>
>>       data Quux = Quux {
>>           quuxFoo :: [Foo]
>>       } deriving (Show, Eq)
>>       ...
>>
>> Both modules require the Foo newtype defined. However, in all other
>> respects they are separate modules that can be used independently.
>>
>> Defining the newtype Foo twice, as above, throws a compilation error
>> (ambigious reference). Importing one module inside another breaks
>> independence. I've been including newtype Foo in a Common.hs module that is
>> included in both, as I would in C or C++. This sort of thing can easily get
>> more complicated as the program grows however.
>>
>> I was wondering if the Haskell community has a better solution to this
>> that I've overlooked.
>>
>>
>> Ian Knopke
>>
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>>
>
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