Re: Deprecate Foldable for Either

This would have to be determined and triggered at the use site of `f' since `f :: Foldable t => t a -> Int'. As long as you stay generic the user of your function will decide whether he wants the warning. If you choose to specialize your function to a 2-tuple you would get the warning. Adam On Sun, 19 Mar 2017 at 17:14 wrote:

Is there a clear way to implement this instance warning? I.e. given:

f x = 2 * length x

Can we guarantee at compile time that "f" will never be passed a 2-tuple?

Tom

El 18 mar 2017, a las 20:04, Adam Bergmark escribió:

I'm on the fence about the instance existing. I'm +1 for a warning, and thus would be +1 on keeping the instance. +1 on making the warning opt-in and +1 keeping it out of -Wall.

On Sun, 19 Mar 2017 at 00:51 wrote:

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El 18 mar 2017, a las 16:01, Lana Black escribió:

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On 18/03/17 19:49, Henning Thielemann wrote:

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On Sat, 18 Mar 2017, Carter Schonwald wrote:

for what?

A warning if someone e.g. calls 'length (a,b)', or more generally, if certain instances are used. _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

Please no. Many of us like our code Wall-clean while still being able to write polymorphic functions. Adding more warnings that are often triggered by correct code (redundant constraints, anyone?) only leads to more headache.

You could make that an hlint rule on the other hand.

Can it be a hlint rule? It seems quite difficult to predict that "length" will not ever be passed e.g. a 2-tuple in the general case, within hlint.

I would also favor a warning, and happily have -Wall not include it (though I'd prefer inclusion).

Tom

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