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Nested "Maybe"

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This group is looking quiet, but you never know...

Recently I wanted a type that adds another alternative to Maybe,
specifically an approximate result, so I wrote (somewhat without
thinking)

  data Approximate a = Roughly a | Maybe a

Haskell does not complain about the type (after all, it just looks like
I'm defining a constructor called Maybe) but, equally obviously, I can't
write a function like this

  f a | a < 0     = Nothing
      | a > 10000 = Roughly (sqrt a)
      | otherwise = Just (a / 2)

without type errors.  I can nest the Maybe in a new type:

  data Approximate a = Roughly a | Exactly (Maybe a)

  f a | a < 0     = Exactly Nothing
      | a > 10000 = Roughly (sqrt a)
      | otherwise = Exactly (Just (a / 2))

but I can't help wondering if I'm missing a neater way to do this.

-- 
Ben.

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Thread

Nested "Maybe" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-09 22:13 +0100
  Re: Nested "Maybe" Paul Rubin <no.email@nospam.invalid> - 2021-04-09 14:24 -0700
    Re: Nested "Maybe" Paul Rubin <no.email@nospam.invalid> - 2021-04-09 14:27 -0700
  Re: Nested "Maybe" Mark Carroll <mtbc@bcs.org> - 2021-04-09 17:33 -0400

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