I'm sure he did, but I figured I should take the opportunity to point out other ways to use those names. On May 21, 2016 9:09 AM, "Christopher Allen" wrote:

I think Edward meant fromJust given the context.

Sent from my iPhone

On May 21, 2016, at 6:58 AM, David Feuer wrote:

No one wants to remove fromMaybe. In fact, it could serve as a template for total fromLeft and fromRight:

fromLeft :: b -> (a -> b) -> Either a x -> b fromRight :: b -> (a -> b) -> Either x a -> b On May 21, 2016 8:55 AM, "Edward Kmett" wrote:

I'm personally -1 on this.

A large portion of the community is vehemently against adding new partial functions, and they have to share base with the rest of us. I'd say more people want to remove fromMaybe, head, tail, etc. than want to double down on the pattern at this time.

-Edward

On Fri, May 20, 2016 at 4:08 PM, Anton Felix Lorenzen wrote:

...

When working with Either, I am often missing two simple functions: fromRight :: Either a b -> b fromLeft :: Either a b -> a

It has been implemented a couple of times: http://hayoo.fh-wedel.de/?query=fromRight

But I don't want to depend on yet another library for such a basic function.

Could it be added?

Anton _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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Ah, yes, we want fromLeft and fromRight, but with types fromLeft :: a -> Either a b -> a fromRight :: b -> Either a b -> b where the first argument is the "default", like fromLeft a (Right b) = a Then you can write fromLeft impossible e where `impossible` does a controlled crash of your program. (See fromMaybe.) --Andreas On 21.05.2016 15:16, Edward Kmett wrote:

Sorry, I meant fromJust.

On Sat, May 21, 2016 at 8:58 AM, David Feuer mailto:david.feuer@gmail.com> wrote:

No one wants to remove fromMaybe. In fact, it could serve as a template for total fromLeft and fromRight:

fromLeft :: b -> (a -> b) -> Either a x -> b fromRight :: b -> (a -> b) -> Either x a -> b

On May 21, 2016 8:55 AM, "Edward Kmett" mailto:ekmett@gmail.com> wrote:

I'm personally -1 on this.

A large portion of the community is vehemently against adding new partial functions, and they have to share base with the rest of us. I'd say more people want to remove fromMaybe, head, tail, etc. than want to double down on the pattern at this time.

-Edward

On Fri, May 20, 2016 at 4:08 PM, Anton Felix Lorenzen mailto:anfelor@posteo.de> wrote:

When working with Either, I am often missing two simple functions: fromRight :: Either a b -> b fromLeft :: Either a b -> a

It has been implemented a couple of times: http://hayoo.fh-wedel.de/?query=fromRight

But I don't want to depend on yet another library for such a basic function.

Could it be added?

Anton _______________________________________________ Libraries mailing list Libraries@haskell.org mailto:Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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-- Andreas Abel <>< Du bist der geliebte Mensch. Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden andreas.abel@gu.se http://www2.tcs.ifi.lmu.de/~abel/

On Sat, May 21, 2016 at 2:06 PM, Andreas Abel wrote:

Ah, yes, we want fromLeft and fromRight, but with types

fromLeft :: a -> Either a b -> a fromRight :: b -> Either a b -> b

where the first argument is the "default", like

If anything is added, then +1 for these versions. Very strong -1 for adding partial functions. -- Live well, ~wren

The main annoyance with the total versions is that the existing fromJust has the wrong convention. Oh well. Consistency is overrated. -Edward On Sun, May 29, 2016 at 9:00 PM, Michael Burge wrote:

+1 on the total versions.

On Sat, May 28, 2016 at 5:48 PM, wren romano wrote:

...

On Sat, May 21, 2016 at 2:06 PM, Andreas Abel wrote:

...

Ah, yes, we want fromLeft and fromRight, but with types

fromLeft :: a -> Either a b -> a fromRight :: b -> Either a b -> b

where the first argument is the "default", like

If anything is added, then +1 for these versions.

Very strong -1 for adding partial functions.

-- Live well, ~wren _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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On 30.05.2016 09:29, lennart spitzner wrote:

For the lazy; `either` defines:

...

Data.Either.Combinators.fromLeft :: a -> Either a b -> a

This is the thing we want. -- Andreas Abel <>< Du bist der geliebte Mensch. Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden andreas.abel@gu.se http://www2.tcs.ifi.lmu.de/~abel/

lennart spitzner writes:

...

...

...

Data.Either.Combinators.fromLeft :: a -> Either a b -> a

This is the thing we want.

Oh indeed, derp; still had the first suggestion in mind. (b -> (a -> b) -> Either ..)

On this one i am neutral.

How should we address the part where we don't want to promote Partiality Oriented Programming? -- с уважениeм / respectfully, Косырев Сергей

It is a minor annoyance, not a -1. The fromLeft and fromRight there got merged in from another package when we started consolidating. I've never really given them conscious thought, but on the plus side, I'd get to just re-export the combinators from base in Data.Either.Combinators avoiding conflicts. I'm a weak +1 on adding the total versions that Wren espoused above. -Edward On Mon, May 30, 2016 at 3:29 AM, lennart spitzner < lsp@informatik.uni-kiel.de> wrote:

On 30/05/16 03:40, Edward Kmett wrote:

...

The main annoyance with the total versions is that the existing fromJust has the wrong convention.

Oh well. Consistency is overrated.

So you don't mind the breaking change in the `either` package?

For the lazy; `either` defines:

...

Data.Either.Combinators.fromLeft :: a -> Either a b -> a Data.Either.Combinators.fromLeft' :: Either a b -> a (~Right similarly)

Also, packages `MissingH` and `extra` define the consistent

...

fromLeft :: Either a b -> a

(don't know if user numbers of those count as significant in any way.)

-1 on both partial and inconsistent total