What about making a third module that defines and exports Foo ?

David.

2013/4/29 Ian Knopke <ian.knopke@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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