Description
The Maybe type, and associated operations.
DocumentationThe Maybe type encapsulates an optional value. A value of type Maybe aa (represented as Just aNothing). 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.
maybe :: b -> (a -> b) -> Maybe a -> bSource
The maybe function takes a default value, a function, and a Maybe value. If the Maybe value is Nothing, the function returns the default value. Otherwise, it applies the function to the value inside the Just and returns the result.
mapMaybe :: (a -> Maybe b) -> [a] -> [b]Source
The mapMaybe function is a version of map which can throw out elements. In particular, the functional argument returns something of type Maybe bNothing, no element is added on to the result list. If it just Just bb is included in the result list.
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