empty package:base

The identity of <|>

Prepares an empty write buffer. This lets the device decide how to set up a write buffer: the buffer may need to point to a specific location in memory, for example. This is typically used by the client when switching from reading to writing on a buffered read/write device. There is no corresponding operation for read buffers, because before reading the client will always call fillReadBuffer.

The empty CallStack.

Identity of mappend

>>> "Hello world" <> mempty
"Hello world"

Check whether a given MVar is empty. Notice that the boolean value returned is just a snapshot of the state of the MVar. By the time you get to react on its result, the MVar may have been filled (or emptied) - so be extremely careful when using this operation. Use tryTakeMVar instead if possible.

Create an MVar which is initially empty.

List of elements of a structure, from left to right.

>>> toNonEmpty (Identity 2)
2 :| []

A NonEmpty list is one which always has at least one element, but is otherwise identical to the traditional list type in complexity and in terms of API. You will almost certainly want to import this module qualified.

Non-empty (and non-strict) list type.

nonEmpty efficiently turns a normal list into a NonEmpty stream, producing Nothing if the input is empty.