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

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

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 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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