F# Library Reference

This section provides detailed documentation for the F# language's core libraries and types. Explore the namespaces and members to leverage the full power of F# for functional programming.

Introduction

The F# standard library offers a rich set of data structures, algorithms, and utilities designed to support functional programming paradigms. It builds upon the .NET Base Class Library (BCL) and provides F#-idiomatic ways to work with collections, computation expressions, asynchronous programming, and more.

Namespaces

System

This namespace contains fundamental types and operations, many of which are commonly used in F# development.

`System.String`

Represents an immutable sequence of characters.

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`System.Int32`

Represents a 32-bit signed integer.

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`System.Collections.Generic.IEnumerable<T>`

Represents a collection that can be enumerated.

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Microsoft.FSharp.Collections

Provides F#-specific collection types optimized for functional programming.

`FSharpList<T>`

Represents an immutable singly-linked list.

Efficient for prepending and recursive processing.

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`FSharpSet<T>`

Represents an immutable set data structure.

Ensures uniqueness of elements.

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`FSharpMap<TKey, TValue>`

Represents an immutable map (dictionary) data structure.

Maps keys to values in an immutable fashion.

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Microsoft.FSharp.Control

Contains types for asynchronous programming and event handling.

`Async<T>`

Represents an asynchronous computation.

Provides mechanisms for composing and executing asynchronous operations.

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`Choice<T1, T2>`

Represents a value that can be one of two distinct types.

Useful for representing success/failure or alternative outcomes.

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Microsoft.FSharp.Core

The core F# library, containing fundamental types, functions, and modules.

`Unit`

Represents the absence of a value, analogous to void in imperative languages but used in a functional context.

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`fst`

Extracts the first element of a pair.

val fst : ('T1 * 'T2) -> 'T1 See Full Details

`snd`

Extracts the second element of a pair.

val snd : ('T1 * 'T2) -> 'T2 See Full Details

`id`

The identity function: returns its input unchanged.

val id : 'a -> 'a See Full Details

Microsoft.FSharp.Linq

Provides support for Language Integrated Query (LINQ) in F#.

`Query<T>`

Represents a LINQ query.

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Types

F# provides various types to represent data effectively. Explore common types like:

Tuples: For grouping multiple values of potentially different types.
Records: For creating immutable data structures with named fields.
Discriminated Unions: For representing data that can take on one of several distinct forms.
<'T> Seq: For lazy sequences of elements.
<'T> List: For immutable singly-linked lists.

Functions

Functions are first-class citizens in F#. The library includes a wide array of utility functions for:

You can also explore the comprehensive .NET API Browser for all available types and members.