Features Added in F# Language Versions

F# 1.0

Discriminated unions
Records
Tuples
Pattern matching
Type abbreviations
Object expressions
Structs
Signature files
Imperative programming
Modules (no functors)
Nested modules
.NET Interoperability

F# 1.1

Interactive environment
Object programming
Encapsulation Extensions

F# 2.0

Active patterns
Units of measure
Sequence expressions
Asynchronous programming
Agent programming
Extension members
Named arguments
Optional arguments
Array slicing
Quotations
Native interoperability
Computation expressions

F# 3.0

Type providers
LINQ query expressions
CLIMutable attribute
Triple-quoted strings
Auto-properties
Provided units-of-measure

F# 3.1

Named union type fields
Extensions to array slicing
Type inference enhancements

F# 4.0

printf on unitized values
Extension property initializers
Non-null provided types
Primary constructors as functions
Static parameters for provided methods
printf interpolation
Extended #if grammar
Multiple interface instantiations
Optional type args
Params dictionaries

F# 4.1

Struct tuples which inter-operate with C# tuples
Struct annotations for Records
Struct annotations for Single-case Discriminated Unions
Underscores in numeric literals
Caller info argument attributes
Result type and some basic Result functions
Mutually referential types and modules within the same file
Implicit Module syntax on modules with shared name as type
Byref returns, supporting consuming C# ref-returning methods
Error message improvements
Support for fixed

F# 4.5

Versioning alignment of binary, package, and language
Support for Span<'T> and related types
Ability to produce byref returns
The voidptr type
The inref<'T> and outref<'T> types to represent readonly and write-only byrefs
IsByRefLike structs
IsReadOnly structs
Extension method support for byref<'T>/inref<'T>/outref<'T>
match! keyword in computation expressions
Relaxed upcast with yield in F# sequence/list/array expressions
Relaxed indentation with list and array expressions
Enumeration cases emitted as public

F# 4.6

Anonymous records
ValueOption module functions

F# 4.7

Compiler support for LangVersion
Implicit yields
No more required double underscore (wildcard identifier)
Indentation relaxations for parameters passed to constructors and static methods