Runfs

This is a demonstrator (work in progress), made to investigate if and how the "dotnet run app.cs" functionality can be provided for F#.

You can use it to directly run an F# .fs source file. So, if you want to build a small tool, you don't need to bother with projects and folders and artifacts any more. You rather just create your source file and run it with runfs.

The source file can contain directives to reference libraries and to influence the build process, see section Directives.

Important: runfs is not about F# scripts (.fsx files) that can be run by dotnet fsi. See below.

Usage

dotnet tool install [-g] runfs
dotnet runfs app.fs

Directives

The following directives (source lines) are recognized by runfs:

• #r_package "[email protected]" - references package pp, version 1.0.0
• #r_sdk "[email protected]" - references an sdk
• #r_property "myprop=42" - sets a build property
• #r_project "xyz.fsproj" - references a project
• #r_dll "mylib.dll" - references a library
• #r_source "utilities.fs" - references a source file

The above directive syntax is preliminary and made to work with the current F# compiler (the parser accepts and ignores them). Ideally, the syntax defined for "dotnet run app.cs" should be reused, like #:package [email protected], but this needs a compiler fix first.

How does runfs relate to fsi?

	dotnet runfs app.fs	dotnet fsi app.fsx
F# grammar	implementationFile grammar (full F# grammar)	interaction grammar (limited script grammar)
reference resolution	dotnet build	custom, dependence on the package tool
startup time initial run	2 sec	2 sec
startup time subsequent runs	100 ms	2 sec
conversion to F# project	easy (dotnet runfs --convert app.fs)	add namespaces / modules, create project file, move references to project file ...
availability	needs dotnet tool install runfs (until re-implemented into dotnet run)	available with sdk
maintainability	a small modular tool	a huge complex dinosaur
editor support	none yet	Ionide/FSAC, VS, Rider

(The timings are "order of magnitude" and depending on many factors)

fsi interactive

All of the above is not related to fsi interactive mode, which can be used in both cases with snippets from the source file ('alt Enter').

Learnings

The main goal of this project is to investigate viability of dotnet run app.fs and to create clarity on requirements and missing pieces.

I started by looking into extending the sdk code to accomodate F# input. This would have meant, however, to work with some particularly ugly (in my eyes) C# code. So, I chose to create an independent tool for the investigation, reproducing the functionality as closely as possible.

Main learnings

• This has to be about running .fs files, not scripts.
• A small compiler change is needed to allow for the directive format.
• The most important missing piece is editor support.

TODOs

Runfs

• investigate if the "compile only" shortcut can be replicated for F#
• add more tests, possibly Rid-package, fix case sensitivity issue in Directives.fs
• implement --convert

Elsewhere

• propose and possibly implement a compiler change so that the 'dotnet run app.cs' syntax for directives can be used
• Ionide/FSAC support
• collect feedback for an eventual dotnet run app.fs

HOWTOs

(just for my future self)

Create a release

• Create the feature / fix on a new branch
• Update Version and PackageReleaseNotes in Runfs.fsproj
• Create PR, wait for CI test, merge it
• Switch to main, git pull
• git tag V.V.V && git push --tags, where V.V.V is the version
• This should create the package and push it to nuget