"Elvis" operator (?:) as a reverse infix form of "fromMaybe"

[Dan Burton]

Oh, you're right, my mistake.


-- Dan Burton


On Sat, Oct 12, 2013 at 12:53 PM, Nikita Volkov
<nikita.y.volkov at gmail.com>wrote:

> Dan Burton, `maybeA <|> maybeB |> c` has type `Maybe a`, while `maybeA ?:
> maybeB ?: c` has type `a`. The sole purpose of `?:` is in extracting a
> value from `Maybe`, not lifting to it.
>
>
> 2013/10/12 Dan Burton <danburton.email at gmail.com>
>
>> It's not a completely different thing, it's the very same thing, but more
>> general.
>>
>> -- Dan Burton
>>
>>
>> On Sat, Oct 12, 2013 at 12:41 PM, Nikita Volkov <
>> nikita.y.volkov at gmail.com> wrote:
>>
>>> John Lato, you're offering a completely different thing and I would
>>> totally vote against it. Please don't flood.
>>>
>>>
>>> 2013/10/12 John Lato <jwlato at gmail.com>
>>>
>>>> I'd prefer it if we had an operator in Control.Applicative such as
>>>>
>>>>   |> :: Alternative f => f a -> a -> f a
>>>>   l |> r = l <|> pure r
>>>>
>>>> if it doesn't already exist, this would generalize fromMaybe, and
>>>> complicated cases could be written as
>>>>
>>>>   maybeA <|> maybeB |> c
>>>>
>>>> but even this could be easily written using <|> and pure, so I'm not
>>>> sure it pulls its weight.
>>>>
>>>> John L.
>>>>
>>>>
>>>> On Sat, Oct 12, 2013 at 7:40 AM, Nikita Volkov <
>>>> nikita.y.volkov at gmail.com> wrote:
>>>>
>>>>> I suggest to include this operator in "Data.Maybe" and "Prelude".
>>>>>
>>>>> *Implementation:*
>>>>>
>>>>>     (?:) :: Maybe a -> a -> a
>>>>>     maybeA ?: b = fromMaybe b maybeA
>>>>>
>>>>> *Use cases:*
>>>>>
>>>>>     1.
>>>>>         maybeValue ?: error "Value is unexpectedly empty. This is a
>>>>> bug."
>>>>>
>>>>>     instead of
>>>>>
>>>>>         fromMaybe (error "Value is unexpectedly empty. This is a
>>>>> bug.") maybeValue
>>>>>
>>>>>     2.
>>>>>         maybeA ?: maybeB ?: c
>>>>>
>>>>>     instead of
>>>>>
>>>>>         fromMaybe (fromMaybe c maybeB) maybeA
>>>>>
>>>>> *Name collisions:*
>>>>>
>>>>>     Hayoo search gives only 6 collisions with 5 hardly fundamental
>>>>> libraries.
>>>>>
>>>>>
>>>>>
>>>>> * The nickname and the operator itself are inspired by the ones from
>>>>> Groovy language.
>>>>>
>>>>> ** The symbols of the operator are a reminder of plain old ternary
>>>>> construct.
>>>>>
>>>>> *** To understand the nickname look at the operator as on emoticon.
>>>>>
>>>>>
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>>>>>
>>>>>
>>>>
>>>
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>>
>
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