If the most used extensions are theoretically sound and improve software developed with them, they should be included in the next Haskell standard.

I think that may be oversimplifying the issue. For example, there are cases such as FunDeps and TypeFamilies where -- probably -- precisely one should end up in the language, but we're not sure which -- or maybe there's some other solution yet to be found which is better than both. We're never going to find out which it is unless people write a lot of code using both extensions (and that code gets onto Hackage). However, adding both to the standard at this stage would probably mean removing one or both later, which causes even bigger problems. When an extension is no longer supported,

or another Haskell compiler must be used, this may lead to a lot of maintenance work.

I think there's a degree of "common knowledge" out there that some extensions (FD's and TypeFamilies included) are here for the foreseeable future -- i.e. they're pretty stable and certainly the compiler isn't going to forget about them soon. Others are maybe more experimental or obsolete. I agree that if that information isn't clearly written down somewhere, it should be. Packages, using rejected extensions, should be redesigned or shunned

(marked as such in Hackage).

It might be useful to have a commonly used "Portability" entry on Hackage, as in Haddock (unless there is one?). But, usually code that uses rejected extensions will also have ceased to compile a long time ago, which you can see in Hackage. If you have a counterexample that would help. Regards, Freddie On 19 April 2012 22:50, Henk-Jan van Tuyl wrote:

L.S.,

Many libraries on Hackage use language extensions, or depend on other libraries that use extensions. When an extension is no longer supported, or another Haskell compiler must be used, this may lead to a lot of maintenance work.

To prevent an extreme amount of maintenance, I try to avoid using language extensions, but many libraries on Hackage use them.

My proposal is: Make an inventory, of the most used language extensions (based on the number of Hackage downloads of packages depending directly or indirectly on them). If the most used extensions are theoretically sound and improve software developed with them, they should be included in the next Haskell standard.

Packages, using rejected extensions, should be redesigned or shunned (marked as such in Hackage).

Regards, Henk-Jan van Tuyl

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