Maybe -package:strict

The Maybe type encapsulates an optional value. A value of type Maybe a either contains a value of type a (represented as Just a), or it is empty (represented as Nothing). Using Maybe is a good way to deal with errors or exceptional cases without resorting to drastic measures such as error. The Maybe type is also a monad. It is a simple kind of error monad, where all errors are represented by Nothing. A richer error monad can be built using the Either type.

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 Maybe type encapsulates an optional value. A value of type Maybe a either contains a value of type a (represented as Just a), or it is empty (represented as Nothing). Using Maybe is a good way to deal with errors or exceptional cases without resorting to drastic measures such as error. The Maybe type is also a monad. It is a simple kind of error monad, where all errors are represented by Nothing. A richer error monad can be built using the Either type.

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.

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 encapsulates an optional value. A value of type Maybe a either contains a value of type a (represented as Just a), or it is empty (represented as Nothing). Using Maybe is a good way to deal with errors or exceptional cases without resorting to drastic measures such as error. The Maybe type is also a monad. It is a simple kind of error monad, where all errors are represented by Nothing. A richer error monad can be built using the Either type.

The Maybe type, and associated operations.

Maybe type