listToMaybe package:slist

Returns Nothing on an empty list or Just a where a is the first element of the slist.

Examples

Basic usage:

>>> slistToMaybe mempty
Nothing

>>> slistToMaybe (one 42)
Just 42

>>> slistToMaybe (cons 1 $ cons 2 $ one 3)
Just 1

Laws :

slistToMaybe . maybeToList ≡ id

Reverse is right only on singleton/empty lists

maybeToList . slistToMaybe {empty, singleton slist} ≡ {empty, singleton slist}