We provide the data type NonEmpty that allows to store a list-like structure
with at least or exactly n elements,
where n is fixed in the type in a kind of Peano encoding
and is usually small.
The datatype is intended to increase safety
by making functions total that are partial on plain lists.
E.g. on a non-empty list, head and tail are always defined.
There are more such data types like Optional and Empty.
Together with NonEmpty you can define a list type
for every finite set of admissible list lengths.
The datatype can be combined with Lists, Sequences and Sets
(from the containers package).
The package needs only Haskell 98.
Similar packages:
semigroups, semigroupoids:
restricted to lists, minimum number of elements: 1,
provides more type classes tailored to the use of non-empty lists.
NonEmptyList:
restricted to lists, minimum number of elements: 1
NonEmpty:
restricted to lists, minimum number of elements: 1,
designed for unqualified use of identifiers
Cardinality:NeverEmptyList
mono-traversable:Data.MinLen:
allows to specify a minimum number of elements using type families
and works also for monomorphic data structures like ByteString
Stream:
Lists that contain always infinitely many elements.
fixed-length:
Uses the data structure of this package
and defines a closed-world class for fixed-length lists
and an according index type.
fixed-list:
Uses the same data structure as this package
but is intended for fixing the number of elements in a list.
Requires multi-parameter type classes with functional dependencies.
