Oh, you're right, my mistake.
-- Dan Burton
On Sat, Oct 12, 2013 at 12:53 PM, Nikita Volkov
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
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
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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