[Haskell-cafe] Why Maybe exists if there is Either?
vlatko.basic at gmail.com
Thu Jan 9 16:36:06 UTC 2014
But instance declarations wouldn't be needed because we already have all the
instances for Either. The point would be to have them unified.
But it is a problem that there are no data constructor synonyms in Haskell. So
at least pattern matching wouldn't be possible the simple way. Maybe
ViewPatterns could (partially) solve that.
-------- Original Message --------
Subject: Re: [Haskell-cafe] Why Maybe exists if there is Either?
From: Artyom Kazak <yom at artyom.me>
To: haskell-cafe at haskell.org
Date: 09.01.2014 16:23
> Besides, even defining
> type Maybe a = Either () a
> in standard library wouldn’t be the same as
> data Maybe a = Nothing | Just a
> since in Haskell 98 type synonyms aren’t allowed in instance declarations, which
> means that programmers would still have to remember that `Maybe` is actually
> `Either ()` under-the-hood every time when writing an instance.
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