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

[Nikita Volkov]

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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