Re: Proposal: Export String from Data.String (and two related proposals)

On Wed, Nov 17, 2010 at 4:06 PM, Bas van Dijk wrote:

On Wed, Nov 17, 2010 at 9:46 PM, Duncan Coutts wrote:

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If we accept 3 then in the spirit of  "export a symbol from as few modules as possible", you may expect a fourth proposal: Unexport the String operations: lines, words, unlines and unwords from Data.List. However I think this will break lots of programs. I have no problem also discussing this one though.

Yeah, I agree in principle, but probably best to leave that for later.

It obviously needs to go through a deprecation phase.

It would be great if we could {-# DEPRECATE #-} an export?

So something like:

module Data.List  (  ...  {-# DEPRECATE lines "Exported from Data.String instead" #-}  , lines  ...  ) where ... lines = ... ...

Alternatively, we could just {-# DEPRECATE #-} the functions in Data.List and define equivalently named new ones in Data.String.

I thought about this, and I even thought it was a great idea, until I realized that it would be a real bummer for anyone importing both Data.List and Data.String - they would get an error from the compiler unless they specifically hid the functions in question from one of the imports. There is a similar (but perhaps easier to solve?) problem with the deprecated export - the compiler would need to not warn on use of the function if it is imported from multiple sources and at least one of the sources exports it non-deprecated. Antoine