IsNull: A typeclass to determine if a given value is null.

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A typeclass to determine if a given foldable type (or other) is empty ~ null ~ invalid. The definition is intentionally vague, to cover types from Either to Text and Sets.


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Versions 0.3.0.0, 0.3.0.0, 0.4.0.0
Change log None available
Dependencies base (>=4.5 && <4.8), base-compat (==0.5.*), bytestring (>=0.10.0 && <1.0), containers (==0.5.*), text (>=0.11.3 && <1.3) [details]
License BSD-3-Clause
Author João Cristóvão
Maintainer jmacristovao@gmail.com
Category Data
Home page https://github.com/jcristovao/IsNull
Source repo head: git clone https://github.com/jcristovao/IsNull
Uploaded by jcristovao at 2014-05-08T09:40:55Z

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Readme for IsNull-0.3.0.0

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IsNull

A typeclass to determine if a given container is null.

Strongly inspired by mono-traversable, but with a simpler goal: supporting IsNull and nested IsNull operations.

Supported functions:

isNull :: a -> Bool

notNull :: a -> Bool

-- | Nested isNull
isNullN :: (Foldable f) => f a -> Bool

-- | Monadic isNull
isNullM :: Monad m => m a -> m Bool

-- | Monadic Nested isNull
isNullNM :: (Monad m, Foldable f) => m (f a) -> m Bool


-- | Alternative <|> operator does not always operate as choice,
-- at least not in an intuitive way (for example with lists).
-- This one does:
<\> :: a -> a -> a

The N stands for (non-recursive) nested, such that:


isNullN (Just "abc") == False
isNullN (Just ""   ) == True
isNullN (Nothing   ) == True

While the isNull function is equivalent to (==) mempty for most of the instances, not all Foldables are monoids, and not all monoids mempty means null:

Bugs, suggestions and comments are most welcomed!