F# Language Specification

Overview

This is an initiative to create a more complete and community-maintainable F# spec.

This will be no small task, but we believe it is worthwhile and we count on community contributions.

We foresee three phases:

1. Convert the latest official spec to markdown and create the structure and tools to make it community-maintainable. This is done.
2. Add the post-4.1 features as documented in the RFCs to the spec. Our goal: a complete F# 10 spec.
3. Make spec update part of new feature development so that an up-to-date spec can be released with every new major compiler release.

Process

The spec is in the end closely coupled to the language design and therefore needs a) strong community contributions and b) a clearly defined final responsibility, which will be similar to the one of the language design process.

We foresee the following types of contributions:

• Issues and/or PRs for bug fixes.
• PRs for integration of an accepted and implemented RFC.
• Issues for proposing and discussing smaller or larger improvements to the spec
• PRs for such improvements, once the discussion converges and/or is decided by the team in charge

All PRs need to be accepted by two team reviewers for merging.

Repository structure

The sources are the markdown files for the chapters (clauses) in the spec directory. Run build to create a new complete spec (including ToC and updated reference links) in your artifacts directory.

At certain points, releases are created and published in the releases directory.

F# Language Features RFCs

Version	Feature ID	Feature with RFC Link	Status
F# 4.0	N/A	Auto Quotation	This was already covered (see § 8.13.7.3 and the FSharp.Core documentation)
F# 4.0	N/A	Class Names As Functions	done
F# 4.0	N/A	Core Library Functions	This was replaced by the RFC "List, Seq, Array Additions", see below
F# 4.0	N/A	Extended If Grammar	This was already covered (see §3.3)
F# 4.0	N/A	Extension Property Initializers	This was already covered (see §14.4, item 4, 5th bullet, second sub-bullet, second sentence)
F# 4.0	N/A	List, Seq, Array Additions	This is documented in the FSharp.Core documentation. FSharp.Core functionality is not documented in detail in this spec, except as needed for reference (see §18)
F# 4.0	N/A	Microsoft Optional	Both library documentation and spec were adapted already.
F# 4.0	N/A	Multi-Interface Instantiation
F# 4.0	N/A	Non-Null Provided Types
F# 4.0	N/A	Printf Units of Measure
F# 4.0	N/A	Static Method Arguments
F# 4.1	FS-1002	Cartesian Product for Collections
F# 4.1	FS-1004	Result Type	done
F# 4.1	FS-1005	Underscores in Numeric Literals	done
F# 4.1	FS-1006	Struct Tuples	done
F# 4.1	FS-1007	Additional Option Module Functions
F# 4.1	FS-1008	Struct Records
F# 4.1	FS-1009	Mutually Referential Types and Modules in Single Scope
F# 4.1	FS-1010	Add Map.count
F# 4.1	FS-1012	Caller Info Attributes
F# 4.1	FS-1013	Enable Reflection Functionality on Portable Profiles
F# 4.1	FS-1014	Struct Discriminated Unions
F# 4.1	FS-1015	Support for fixed
F# 4.1	FS-1016	Unreserve Keywords
F# 4.1	FS-1017	Fix SRTP Constraint Parsing
F# 4.1	FS-1018	Adjust Extensions Method Scope
F# 4.1	FS-1019	Implicitly Add the Module Suffix
F# 4.1	FS-1020	ByRef Returns
F# 4.1	FS-1025	Improve Record Type Inference
F# 4.1	FS-1027	Complete Optional DefaultParameterValue
F# 4.1	FS-1029	Implement IReadOnlyCollection in list
F# 4.1	FS-1040	Enum Match
F# 4.5	FS-1047	Match Bang
F# 4.5	FS-1053	Span
F# 4.5	FS-1054	Undent List Args
F# 4.5	FS-1055	Subsumption for Yield in Sequence Expression
F# 4.5	FS-1058	Make Enum Cases Public
F# 4.6	FS-1030	Anonymous Records
F# 4.7	FS-1046	Wildcard Self Identifiers
F# 4.7	FS-1069	Implicit Yields
F# 4.7	FS-1070	Offside Relaxations
F# 5.0	FS-1001	String Interpolation
F# 5.0	FS-1003	Nameof Operator
F# 5.0	FS-1031	Allow Implementing Same Interface at Different Generic Instantiations
F# 5.0	FS-1063	Support LetBang and AndBang for Applicative Functors
F# 5.0	FS-1068	Open Type Declaration
F# 5.0	FS-1071	Witness Passing Quotations
F# 5.0	FS-1074	Default Interface Member Consumption
F# 5.0	FS-1075	Nullable Interop
F# 5.0	FS-1077	3D/4D Fixed Index Slicing
F# 5.0	FS-1077	Tolerant Slicing
F# 5.0	FS-1080	Float32 Without Dot
F# 5.0	FS-1082	Uint Type Abbreviation
F# 5.0	FS-1085	Nameof Pattern
F# 5.0	FS-1089	Allow String Everywhere
F# 6.0	FS-1039	Struct Representation for Active Patterns
F# 6.0	FS-1056	Allow Custom Operation Overloads
F# 6.0	FS-1087	Resumable Code
F# 6.0	FS-1091	Extend Units of Measure	done
F# 6.0	FS-1093	Additional Conversions
F# 6.0	FS-1097	Task Builder
F# 6.0	FS-1098	Inline If Lambda
F# 6.0	FS-1099	List Collector
F# 6.0	FS-1100	Printf Binary
F# 6.0	FS-1102	Discards on Use Bindings
F# 6.0	FS-1104	Struct Representations
F# 6.0	FS-1105	Non-variable Patterns to the Right of As Patterns
F# 6.0	FS-1107	Allow Attributes After the Module Keyword
F# 6.0	FS-1108	Undentation Frenzy
F# 6.0	FS-1109	Additional Intrinsics for the NativePtr Module
F# 6.0	FS-1110	Index Syntax
F# 6.0	FS-1111	RefCell Op Information Messages
F# 6.0	FS-1113	Insert Remove Update Functions
F# 6.0	FS-1114	ML Compat Revisions
F# 7.0	FS-1024	Simplify Constrained Call Syntax
F# 7.0	FS-1083	SRTP Type No Whitespace
F# 7.0	FS-1096	Map Min Max KeyValue
F# 7.0	FS-1123	Result Module Parity with Option
F# 7.0	FS-1124	Interfaces with Static Abstract Members
F# 7.0	FS-1126	Allow Lower Case DU Cases when RequireQualifiedAccess is Specified
F# 7.0	FS-1127	Init Only and Required Properties
F# 7.0	FS-1131	NoCompilerInliningAttribute
F# 7.0	FS-1133	Arithmetic in Literals
F# 8.0	FS-1011	Warn on Recursive Without Tail Call
F# 8.0	FS-1081	Extended Fixed Bindings
F# 8.0	FS-1128	Allow Static Members in Interfaces
F# 8.0	FS-1129	Shorthand Anonymous Unary Functions
F# 8.0	FS-1132	Better Interpolated Triple Quoted Strings
F# 8.0	FS-1134	Try With in Sequence Expressions
F# 8.0	FS-1136	Constraint Intersection Syntax
F# 9.0	FS-1060	Nullable Reference Types
F# 9.0	FS-1079	Union Properties Visible
F# 9.0	FS-1140	Boolean Returning and Return Type Directed Partial Active Patterns
F# 9.0	FS-1144	Empty Bodied Computation Expressions
F# 9.0	FS-1147	Non-String Directive Args

FSharp.Core RFCs

Version	Feature ID	Feature with RFC Link	Status
FSharp.Core 4.4.3.0	FS-1028	Implement Async.StartImmediateAsTask
FSharp.Core 4.4.3.0	FS-1036	Consistent Slicing
FSharp.Core 4.4.3.0	FS-1041	IReadOnly
FSharp.Core 4.4.3.0	FS-1042	Add Seq.transpose
FSharp.Core 4.4.3.0	FS-1044	Add NativePtr.toByRef
FSharp.Core 4.5.0.0	FS-1045	Func to FSharpFunc Overloads
FSharp.Core 4.5.0.0	FS-1050	TryGetValue Map
FSharp.Core 4.5.0.0	FS-1057	ValueOption
FSharp.Core 4.5.0.0	FS-1059	Improve Async Stack Traces
FSharp.Core 4.6.0	FS-1065	ValueOption Parity
FSharp.Core 4.6.0	FS-1066	tryExactlyOne
FSharp.Core 4.7.0	FS-1067	Async Sequential
FSharp.Core 8.0	FS-1130	Array Parallel Collection Functions More Regular
FSharp.Core 9.0	FS-1135	Random Functions for Collections
FSharp.Core 9.0	FS-1145	C# Collection Expression Support for Lists and Sets