[Haskell-cafe] Re: Maybe to Either -- is there a better way?

Ertugrul Soeylemez es at ertes.de
Tue Aug 3 08:09:20 EDT 2010

Tom Davies <tgdavies at gmail.com> wrote:

> I find it convenient sometimes to convert a Maybe value to an Either
> thus (excuse the syntax, it's CAL, not Haskell):
> maybeToEither :: a -> Maybe b -> Either a b;
> maybeToEither errorValue = maybe (Left errorValue) (\x -> Right x);

As a side note, this is perfectly valid Haskell code, even though it's
quite verbose.  The equivalent:

  maybeToEither :: a -> Maybe b -> Either a b
  maybeToEither leftValue = maybe (Left leftValue) Right

Honestly I find this better than the completely points-free variants
posted in the other subthread.  They demonstrate overusing points-free


nightmare = unsafePerformIO (getWrongWife >>= sex)

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