ListT -package:ghc-internal

A generator with side-effects.

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Not on Stackage, so not searched. List transformer

Not on Stackage, so not searched. Trees and monadic trees expressed as monadic lists where the underlying monad is a list

The listToMaybe function returns Nothing on an empty list or Just a where a is the first element of the list.

Examples

Basic usage:

>>> listToMaybe []
Nothing

>>> listToMaybe [9]
Just 9

>>> listToMaybe [1,2,3]
Just 1

Composing maybeToList with listToMaybe should be the identity on singleton/empty lists:

>>> maybeToList $ listToMaybe [5]
[5]

>>> maybeToList $ listToMaybe []
[]

But not on lists with more than one element:

>>> maybeToList $ listToMaybe [1,2,3]
[1]

Returns an array of the threads started by the program. Note that this threads which have finished execution may or may not be present in this list, depending upon whether they have been collected by the garbage collector.

List the Haskell threads of the current process.

Convert a list into an array.