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@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@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@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@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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