F# Basics 
This section is suitable for complete beginners to F# and Functional Programming in general.
- Getting Set Up - Installing F# on Windows, Linux and Mac.
- Basic Concepts - A lightweight crash course in functional programming concepts.
Working With Functions 
F# is a functional programming language. Not surprisingly, functions are a big part of the language, and mastering them is the first step to becoming an effective F# developer.
- 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 a 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 contructs 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 10s of 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#.
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- F# Language Reference on MSDN Library
- F# Homepage on Microsoft Research
- Microsoft F# Developer Center
- Real-World F# Articles on MSDN
- Language Specification
- Language Specification PDF
- F# Component Design Guidelines
- F# Component Design Guidelines PDF
- hubFS F# Community
- fpish community-driven events and learning material
- Community for F# monthly, virtual user group
- F# Snippets
- Try F# online
- Using the F# Language for Teaching
- Cross-platform and other F# extensions
- F# source code and community projects on GitHub
- F# cross-platform packages and samples
- The F# Survival Guide
- F# for fun and profit
- F-Sharp Wiki (No longer available)
- Objective Caml
- F# for game development
- Learning F# Through Game Development with XNA