Re: [Haskell-cafe] Ord methods too strict?

The implementation of the Ord instance for Bool is derived

So my argument would be—doesn’t this mean that we need to do cleverer deriving or at least have a hand-written instance?

As for the justification, perhaps it's too much of a special case for only one value of an enumeration to compare to undefined without crashing

This is not just about crashing. (I’m using `undefined` as a way of making strictness explicit.) `False >= veryExpensiveComputation` should return `True` immediately without any unnecessary computation. Also it doesn’t seem like a special case: this makes sense for any partially ordered Type with a top and/or bottom element.

perhaps it inhibits optimisation opportunities.

That doesn’t seem very likely to me, I would rather think the contrary (see above): doing unnecessary work can hardly make a program run faster. V

On 2 Jan 2019, at 11:37, Tom Ellis wrote:

On Wed, Jan 02, 2019 at 09:47:15AM +0000, V.Liepelt wrote:

...

I am surprised to find that `False <= undefined = undefined`.

What justifies (<=) to be strict in both arguments?

The implementation of the Ord instance for Bool is derived, as you can see here:

https://www.stackage.org/haddock/lts-12.1/ghc-prim-0.5.2.0/src/GHC-Classes.h...

As for the justification, perhaps it's too much of a special case for only one value of an enumeration to compare to undefined without crashing, and perhaps it inhibits optimisation opportunities.

Tom _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.