LanguageExt.Sys

LanguageExt.Sys is the a wrapper around the System namespace IO functions and is part of the language-ext functional programming framework.

The framework uses and abuses the features of C# to provide a pure functional-programming 'Base Class Library' that, if you squint, can look like extensions to the language itself. The desire here is to make programming in C# much more robust by helping the engineer's inertia flow in the direction of declarative and pure functional code rather than imperative.

Using these techniques for large code-bases can bring tangible benefits to long-term maintenance by removing hidden complexity and by easing the engineer's cognitive load.

Features

Functional effects and IO

Location	Feature	Description
Core	IO<A>	A synchronous and asynchronous side-effect: an IO monad
Core	Eff<A>	A synchronous and asynchronous side-effect with error handling
Core	Eff<RT, A>	Same as Eff<A> but with an injectable runtime for dependency-injection: a unit testable IO monad
Core	Pipes	A clean and powerful stream processing system that lets you build and connect reusable streaming components
Core	StreamT	less powerful (than Pipes), but easier to use streaming effects transformer

Atomic concurrency and collections

Location	Feature	Description
Core	Atom<A>	A lock-free atomically mutable reference for working with shared state
Core	Ref<A>	An atomic reference to be used in the transactional memory system
Core	AtomHashMap<K, V>	An immutable HashMap with a lock-free atomically mutable reference
Core	AtomSeq<A>	An immutable Seq with a lock-free atomically mutable reference
Core	VectorClock<A>	Understand distributed causality
Core	VersionVector<A>	A vector clock with some versioned data
Core	VersionHashMap <ConflictV, K, V>	Distrubuted atomic versioning of keys in a hash-map

Immutable collections

Location	Feature	Description
Core	Arr<A>	Immutable array
Core	Seq<A>	Lazy immutable list, evaluate at-most-once - very, very fast!
Core	Iterable<A>	Wrapper around IEnumerable with support for traits - enables the higher-kinded traits to work with enumerables.
Core	Lst<A>	Immutable list - use Seq over Lst unless you need InsertAt
Core	Map<K, V>	Immutable map
Core	Map<OrdK, K, V>	Immutable map with Ord constraint on K
Core	HashMap<K, V>	Immutable hash-map
Core	HashMap<EqK, K, V>	Immutable hash-map with Eq constraint on K
Core	Set<A>	Immutable set
Core	Set<OrdA, A>	Immutable set with Ord constraint on A
Core	HashSet<A>	Immutable hash-set
Core	HashSet<EqA, A>	Immutable hash-set with Eq constraint on A
Core	Que<A>	Immutable queue
Core	Stck<A>	Immutable stack

Optional and alternative value monads

Location	Feature	Description
Core	Option<A>	Option monad
Core	OptionT<M, A>	Option monad-transformer
Core	Either<L,R>	Right/Left choice monad
Core	EitherT<L, M, R>	Right/Left choice monad-transformer
Core	Fin<A>	Error handling monad, like Either<Error, A>
Core	FinT<M, A>	Error handling monad-transformer
Core	Try<A>	Exception handling monad
Core	TryT<M, A>	Exception handling monad-transformer
Core	Validation<FAIL ,SUCCESS>	Validation applicative and monad for collecting multiple errors before aborting an operation
Core	ValidationT<FAIL, M, SUCCESS>	Validation applicative and monad-transformer

State managing monads

Location	Feature	Description
Core	Reader<E, A>	Reader monad
Core	ReaderT<E, M, A>	Reader monad-transformer
Core	Writer<W, A>	Writer monad that logs to a W constrained to be a Monoid
Core	WriterT<W, M, A>	Writer monad-transformer
Core	State<S, A>	State monad
Core	StateT<S, M, A>	State monad-transformer

Parser combinators

Location	Feature	Description
Parsec	Parser<A>	String parser monad and full parser combinators library
Parsec	Parser<I, O>	Parser monad that can work with any input stream type

Pretty

Location	Feature	Description
Core	Doc<A>	Produce nicely formatted text with smart layouts

Differencing

Location	Feature	Description
Core	Patch<EqA, A>	Uses patch-theory to efficiently calculate the difference (Patch.diff(list1, list2)) between two collections of A and build a patch which can be applied (Patch.apply(patch, list)) to one to make the other (think git diff).

Traits

The traits are major feature of v5+ language-ext that makes generic programming with higher-kinds a reality. Check out Paul's series on Higher Kinds to get a deeper insight.

Location	Feature	Description
Core	MonoidK<F>	A monoid on applicative functors
Core	Applicative<F>	Applicative functor
Core	Eq<A>	Ad-hoc equality trait
Core	Fallible<F>	Trait that describes types that can fail
Core	Foldable<T>	Aggregation over a structure
Core	Functor<F>	Functor Map
Core	Has<M, TRAIT>	Used in runtimes to enable DI-like capabilities
Core	Hashable<A>	Ad-hoc has-a-hash-code trait
Core	Local<M, E>	Creates a local environment to run a computation
Core	Monad<M>	Monad trait
Core	MonadT<M, N>	Monad transformer trait
Core	Monoid<A>	A monoid is a type with an identity Empty and an associative binary operation +
Core	MonoidK<M>	Equivalent of monoids for working on higher-kinded types
Core	Mutates<M, OUTER_STATE, INNER_STATE>	Used in runtimes to enable stateful operations
Core	Ord<A>	Ad-hoc ordering / comparisons
Core	Range<SELF, NumOrdA, A>	Abstraction of a range of values
Core	Readable<M, Env>	Generalised Reader monad abstraction
Core	SemigroupK<F>	A semigroup on functors
Core	Semigroup<A>	Provides an associative binary operation +
Core	SemigroupK<M>	Equivalent of semigroups for working with higher-kinded types
Core	Stateful<M, S>	Generalised State monad abstraction
Core	Traversable<T>	Traversable structures support element-wise sequencing of Applicative effects
Core	Writable<M, W>	Generalised Writer monad abstraction

Value traits

These work a little like NewType but they impart semantic meaning and some common operators for the underlying value.

Location	Feature	Description
Core	DomainType<SELF, REPR>	Provides a mapping from SELF to an underlying representation: REPR
Core	Identifier <SELF>	Identifiers (like IDs in databases: PersonId for example), they are equivalent to DomaintType with equality.
Core	VectorSpace<SELF, SCALAR>	Scalable values; can add and subtract self, but can only multiply and divide by a scalar. Can also negate.
Core	Amount <SELF, SCALAR>	Quantities, such as the amount of money in USD on a bank account or a file size in bytes. Derives VectorSpace, IdentifierLike, DomainType, and is orderable (comparable).
Core	LocusLike <SELF, SCALAR, DISTANCE>	Works with space-like structures. Spaces have absolute and relative distances. Has an origin/zero point and derives DomainType, IdentifierLike, AmountLike and VectorSpace. DISTANCE must also be an AmountLike<SELF, REPR, SCALAR>.