B F# overview

This appendix explores the basic syntax of F#, which is an established general-purpose functional first language with object-oriented programming (OOP) support. In fact, F# embraces the .NET common language infrastructure (CLI) object model, which allows the declaration of interfaces, classes, and abstract classes. Furthermore, F# is a statically and strongly typed language, which means that the compiler can detect the data type of variables and functions at compile time. F#’s syntax is different from C-style languages, such as C#, because curly braces aren’t used to delimit blocks of code. Moreover, whitespace rather than commas and indentation is important to separate arguments and delimit the scope of a function body. In addition, F# is a cross-platform programming language that can run inside and outside the .NET ecosystem.

The let binding

In F#, let is one of the most important keywords that binds an identifier to a value, which means giving a name to value (or, bind a value to a name). It’s defined as let <identifier> = <value>.

The let bindings are immutable by default. Here are a few code examples:

let myInt = 42
let myFloat = 3.14
let myString = "hello functional programming" 
let myFunction = fun number -> number * number

As you can see from the last line, you can name a function by binding the identifier myFunction to the lambda expression fun number -> number * number.

Understanding function signatures in F#

Creating mutable types: mutable and ref

Functions as first-class types

Composition: pipe and composition operators

Delegates

Comments

Open statements

Basic data types

Special string definition

Tuple

Record types

Discriminated unions

Pattern matching

Active patterns

Collections

Arrays

Sequences (seq)

Lists

Sets

Maps

Loops

Classes and inheritance

Abstract classes and inheritance

Interfaces

Object expressions

Casting

Units of measure

Event module API reference

Learn more