F# compiler guide

Welcome to the F# compiler and tools repository! This guide discusses the F# compiler source code and implementation from a technical point of view.

Documentation Topics

• Overview
• Coding Standards
• Compiler Startup Performance
• Debug Emit
• Diagnostics
• Notes on FSharp.Core
• F# Interactive Code Emit
• Large inputs and stack overflows
• Memory usage
• Optimizations
• Equality optimizations
• Runtime async
• Project builds
• Tooling features

Edit the source for these docs. The docs are published automatically daily fsharp.github.io/fsharp-compiler-docs/ by this repo.

Key Folders

• src/Compiler/Utilities - various utilities, largely independent of the compiler

• src/Compiler/Facilities - various items of functionality specific to the compiler

• src/Compiler/AbstractIL - the Abstract IL library used for .NET IL

• src/Compiler/SyntaxTree - the SyntaxTree, parsing and lexing

• src/Compiler/TypedTree - the TypedTree, and utilities associated with it

• src/Compiler/Checking - checking logic

• src/Compiler/Optimize - optimization and "lowering" logic

• src/Compiler/CodeGen - IL code generation logic

• src/Compiler/Driver - compiler options, diagnostics and other coordinating functionality

• src/Compiler/Symbols - symbols in the public API to the compiler

• src/Compiler/Service - the incremental compilation and build logic, plus editor services in the public API to the compiler

• src/Compiler/Interactive - the components forming the interactive REPL and core of the notebook engine

• src/FSharp.Core - the core library

• tests - the tests

• vsintegration - the Visual Studio integration

Resources for learning

• Channel: F# Software Foundation compiler sessions

• Video: Learn me some F# Compiler, an online chat with Vlad and Don

• Video: Understanding the F# Optimizer, and online chat with Vlad and Don

• Video: Lexer and Parser, an online chat with Vlad and Don

• Video: Resumable State Machines, an online chat with Vlad and Don

• Video: The Typechecker, an online chat with Vlad and Don

• Video: FSharp.Compiler.Service, an online chat with Vlad and Don

Tools to help work with the compiler

• sharplab.io can be used to decompile code.

• fantomas-tools can be used to view the Untyped Abstract Syntax Tree.

Attribution

This document is based on an original document published in 2015 by the F# Software Foundation. It has since been updated substantially.