F# Programming

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Declaring Values and Functions - This article will show you how to declare simple functions, how to use type inference, and how to read F#'s 'arrow' notation.
Pattern Matching Basics - Pattern matching is used for control flow. Its conceptually similar to a switch statement in other languages, but orders of magnitude more powerful.
Recursion and Recursive Functions - A recursive function is a special type of function which calls itself.
Higher Order Functions - Higher order functions take and return functions as values. Combined with currying, it allows programmers to write powerful and expressive programs.

Immutable Data Structures

"Data structure" is a fancy word which refers to anything that helps programmers group and represent related values in useful, logical units. F# has a number of built-in data structures which include tuples, records, lists, unions, and a number of others.

Option Types - Option types are simple, lightweight data structures which are commonly used to represent successful or failed computation.
Tuples and Records - Tuples and records are simple data structures which allow programmers to group related values together into a single unit.
Lists - A list represents an ordered group of values. F#'s List library has extensive support for manipulating and working with lists.
Sequences - Sequence expressions represent sequences of data computed on-demand.
Sets and Maps - Sets are conceptually similar to lists, except they cannot hold duplicate items. Maps allows programmers to relate keys to values and find items in the collection very efficiently.
Discriminated Unions - Discriminated unions represent a finite, well-defined set of choices. Discriminated unions are often the tool of choice building up more complicated data structures including linked lists and a wide range of trees.

Imperative Programming

F# is an "impure" programming language, meaning it allows programmers to write functions with side-effects and mutable state, very similar to the programming style used by imperative programming languages such as C# and Java.

Mutable Data - By default, variables in F# are immutable. However, F# supports mutable variables through mutable fields and ref cells.
Control Flow - Decision making and Loops.
Arrays - Arrays are ubiquitous mutable data structure used in imperative programming languages.
Mutable Collections - Lists and Dictionaries.
Basic I/O - Reading and writing to files and the console window.
Exception Handling - Exception handling allows programmers to catch and handle errors whenever an application enters an invalid state.

Object Oriented Programming

F# is a CLI/.NET programming language. CLI is an object-oriented platform. One of the most important features of F# is its ability to mix and match styles: since the .NET platform is Object Oriented, with F#, you often work with objects.

Operator Overloading - C#-like operator overloading.
Classes - classes and objects are the foundation of object-oriented programming (OOP). They are used to model actions, processes, and any conceptual entities in applications.
Inheritance - inheritance makes OOP code reusable. It allows programmers to create classes which inherit features from another class and add its own modifications.
Interfaces - interfaces abstract away the implementation details of a class by defining a template of methods an object must implement and expose publicly.
Events - events allow classes to send and receive messages between one another.
Modules and Namespaces - modules and namespaces are used to organize classes into groups of related functionality.

F# Advanced

F# is easy enough for beginners to learn as their first language, yet it provides a powerful set of tools which can be appreciated by experienced developers. This section describes advanced syntactic constructs and techniques often used in F# programs.

Units of Measure - Units of measure attach metadata to floats, which allows floats to represent kilograms, pounds, Newtons, hectares, and so on.
Caching - Techniques to store computed values for efficient future retrieval. Also called Memoization.
Active Patterns - Active patterns allow programmers to wrap ad hoc values and objects in union-like structures for use in pattern matching.
Advanced Data Structures - Overview of techniques used to implement immutable data structures.
Reflection - Reflection allows programmers to inspect types and metadata in objects.
Quotations - Quotations convert arbitrary F# code into an abstract syntax tree.
Computation Expressions - Similar to monads in Haskell, computation expressions are used to simplify code written continuation-passing style.

Multi-threaded and Concurrent Applications

Multi-threading is becoming increasingly important with the development of multi-core processors. Functional programmers can take advantage of immutable data structures to make massively scalable, concurrent applications that are simple and easy to write.

Async Workflows - F#'s async primitive is fundamental for writing functional, simple multi-threaded code.
MailboxProcessor Class - Mailboxes are used to implement "message-passing concurrency," a style of concurrent programming used in massively parallel applications consisting of 10s or 1000s of independent nodes.

F# Tools

Lexing and Parsing - FsLex and FsYacc, lexer/parser generators based on the GNU Bison family of generators, are used to implement custom grammars and domain-specific languages in F#.