Fwiw, this was proposed back then in 2014, you can find the libraries thread and the patch over at - https://mail.haskell.org/pipermail/libraries/2014-November/024383.html - https://gitlab.haskell.org/ghc/ghc/-/issues/9816 respectively. It might also be worth pointing out the function added to `base` originated from my package `int-cast` - https://hackage.haskell.org/package/int-cast-0.2.0.0/docs/Data-IntCast.html which provides the means to have compile-time verified "safe" (and also a slightly weaker lossless "iso"morphic) integer conversions without requiring O(n^2) instances. I typically use `int-cast` for critical code where I need more assurance and want to prove that my integer conversions are safe. -- hvr Mikolaj Konarski writes:

This doesn't work when the target type is, e.g., Double (Num, but not Integral), but thank you for the tip, I've already used it in my code to fail when wrapping, etc., would occur for integral types.

On Thu, Aug 13, 2020 at 3:10 PM Andrew Lelechenko wrote:

...

...

From: Edward Kmett

fromIntegralMaybe :: (Integral a, Num b) => a -> Maybe b fromIntegralMaybe = fromIntegerMaybe . toInteger

I’m late to the party, so might be missing something. Did someone already proposed using http://hackage.haskell.org/package/base-4.14.0.0/docs/Data-Bits.html#v:toInt..., which has a very similar signature?

toIntegralSized :: (Integral a, Integral b, Bits a, Bits b) => a -> Maybe b

No need for O(n^2) instances and it is already in `base`.

Best regards, Andrew _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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Herbert, now I'm a fan of your package. However, I'm getting this when trying to intCast Int64 to Rational: engine-src/Game/LambdaHack/Common/Time.hs:265:19: error: … • Couldn't match type ‘int-cast-0.2.0.0:Data.IntCast.IsIntBaseSubType ('int-cast-0.2.0.0:Data.IntCast.FixedIntTag 64) (int-cast-0.2.0.0:Data.IntCast.IntBaseType Rational)’ with ‘'True’ arising from a use of ‘intCast’ • In the expression: intCast :: Int64 -> Rational In the first argument of ‘(*)’, namely ‘(intCast :: Int64 -> Rational) v’ In the second argument of ‘($)’, namely ‘(intCast :: Int64 -> Rational) v * s’ On Thu, Aug 13, 2020 at 6:54 PM Ben Franksen wrote:

Am 13.08.20 um 17:48 schrieb Herbert Valerio Riedel:

...

It might also be worth pointing out the function added to `base` originated from my package `int-cast`

- https://hackage.haskell.org/package/int-cast-0.2.0.0/docs/Data-IntCast.html

which provides the means to have compile-time verified "safe" (and also a slightly weaker lossless "iso"morphic) integer conversions without requiring O(n^2) instances.

This is pretty cool. Thanks for sharing.

Cheers Ben

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