maybe is:module

The Maybe type, and associated operations.

The Maybe type.

The MaybeT monad transformer extends a monad with the ability to exit the computation without returning a value. A sequence of actions produces a value only if all the actions in the sequence do. If one exits, the rest of the sequence is skipped and the composite action exits. For a variant allowing a range of exception values, see Control.Monad.Trans.Except.

The strict variant of the standard Haskell Maybe type and the corresponding variants of the functions from Data.Maybe. Note that in contrast to the standard lazy Maybe type, the strict Maybe type is not an applicative functor, and therefore also not a monad. The problem is the homomorphism law, which states that

pure f <*> pure x = pure (f x)  -- must hold for all f

This law does not hold for the expected applicative functor instance of Maybe, as this instance does not satisfy pure f <*> pure _|_ = pure (f _|_) for f = const.

Utility functions to work with Maybe data type as monad.

TextShow instance for Maybe. Since: 2

A carrier for an Empty effect, indicating failure with a Nothing value. Users that need access to an error message should use the Fail effect. Note that Empty effects can, when they are the last effect in a stack, be interpreted directly to a Maybe without a call to runEmpty.

Utility functions to work with Maybe data type as monad.

Symbolic option type, symbolic version of Haskell's Maybe type.

Extend Maybe by common operations for the Maybe type. Note: since this module is usually imported unqualified, we do not use short names, but all names contain Maybe, Just, or 'Nothing.

The Maybe type, and associated operations.

Maybe type

This module provides tools for defining Maybe configuration types.

Bidirectional version of Data.Maybe.

An Automaton with Maybe or MaybeT in its monad stack can terminate execution at any step.

The Maybe monad is very versatile. It can stand for default arguments, for absent values, and for (nondescript) exceptions. The latter viewpoint is most natural in the context of MSFs.