Fesh 0.33.1-net9

This is a prerelease version of Fesh.

There is a newer version of this package available.
See the version list below for details.

dotnet add package Fesh --version 0.33.1-net9

NuGet\Install-Package Fesh -Version 0.33.1-net9

This command is intended to be used within the Package Manager Console in Visual Studio, as it uses the NuGet module's version of Install-Package.

<PackageReference Include="Fesh" Version="0.33.1-net9" />

For projects that support PackageReference, copy this XML node into the project file to reference the package.

<PackageVersion Include="Fesh" Version="0.33.1-net9" />
                    

                            Directory.Packages.props

<PackageReference Include="Fesh" />
                    

                            Project file

For projects that support Central Package Management (CPM), copy this XML node into the solution Directory.Packages.props file to version the package.

paket add Fesh --version 0.33.1-net9

The NuGet Team does not provide support for this client. Please contact its maintainers for support.

#r "nuget: Fesh, 0.33.1-net9"

#r directive can be used in F# Interactive and Polyglot Notebooks. Copy this into the interactive tool or source code of the script to reference the package.

#:package Fesh@0.33.1-net9

#:package directive can be used in C# file-based apps starting in .NET 10 preview 4. Copy this into a .cs file before any lines of code to reference the package.

#addin nuget:?package=Fesh&version=0.33.1-net9&prerelease
                    

                            Install as a Cake Addin

#tool nuget:?package=Fesh&version=0.33.1-net9&prerelease
                    

                            Install as a Cake Tool

The NuGet Team does not provide support for this client. Please contact its maintainers for support.

Logo

Fesh

code size

Fesh is an F# Editor & Scripting Host.
On Windows.

It is designed for embedding F# as application scripting tool.
But it works standalone just as well.

Screenshot

It is based on the excellent AvalonEdit, that is why it only works on Windows (for now).
The editor supports F# 10 and has modern IDE features like semantic syntax highlighting, type-info and autocomplete.
Unlike a typical F# REPL this editor has the input and the output in two separate windows.
Just like Don Syme always wanted it.
You can even color the output with Fesher.

Contrary to most F# editors, it uses FSharp.Compiler.Service in the same process as the UI.
There is no separate language server or FSI process.
Therefore, Fesh can easily be hosted in other apps to create an embedded application scripting tool.
This was in fact the primary motivation for creating Fesh.
It is public since 2024.
But I started prototyping it in 2017. I used it for scripting in Rhino3D professionally since 2019.
Initially I used the Tsunami F# editor, like seen in my talk on the Louvre Abu Dhabi Dome.
But it is no longer available. So I created Fesh.

For hosting there is the nuget package Fesh. See hosting examples Fesh.Rhino and Fesh.Revit.

Features

Syntax Highlighting

Initial static syntax highlighting is done via AvalonEdit's regex based highlighting.
See SyntaxHighlightingFSharp.xshd.
The F# Compiler Service provides additional semantic highlighting.
If you want different colors go to the menu: About → Open and watch SyntaxHighlighting in VS Code.
You will see any changes upon every save in VS Code.

Auto complete

Auto complete works on enter and dot, also when typing in the middle of a word.

Type info

The type info includes the inferred signature.
All of the xml docs and information about the path of the containing assembly.

Status bar

The statusbar at the bottom shows compiler error count, click on it to scroll to the first error.

Selection highlighting

Selected text is highlighted in both code and output window. The count is shown in the status bar.

Drag and drop

Drag any file or folder into the editor to get the full path as a string at the cursor position.
For *.dlls it will be at the top and prefixed with #r.
For *.fsx it will be at the top and prefixed with #load.

Font

The default font is Cascadia Mono.
Besides italic it also supports a cursive script mode. Fesh is using cursive for comments.
To enable ligatures set the font to Cascadia Code.
You can change the font in the 'Settings.txt' file at %APPDATA%\Local\Fesh\Settings\Standalone\Settings.txt.
Or via the menu: About → Open Settings Folder.

How to install the Standalone App

Installer

The recommended way is to run the Setup.exe from Releases.
Fesh will automatically offer to update itself when a new version is available.
There is a .NET 10 and a .NET 4.8 version. Apart from the runtime they are the same.

The installer is created with Velopack and digitally signed.

No admin rights are required to install or run the app.
The app will be installed in \AppData\Local\Fesh.
And will save its settings in \AppData\Roaming\Fesh.
A shortcut will be created on the desktop.

There is also a portable package in each release.
Extract that zip and place it wherever you'd like.
It has identical functionality to the installed app,
but keeps its Settings folder in the same directory.
There is a ".portable" file in the folder to indicate that.
It will also automatically offer to update itself when a new version is available.

Build from source

Build from the source with:

dotnet build FeshStandalone.fsproj

You will still get notifications about new releases, but you have to install them manually.

How to host Fesh in another app

Use the nuget package Fesh.
Or, to build the Fesh nuget package run:

dotnet build FeshHosting.fsproj

Release Notes

For changes in each release see the CHANGELOG.md

License

Fesh is licensed under the MIT License.

Product	Compatible and additional computed target framework versions.
.NET	net9.0-windows7.0 is compatible. net10.0-windows was computed.

Compatible target framework(s)

Included target framework(s) (in package)

Learn more about Target Frameworks and .NET Standard.

net9.0-windows7.0
- AvalonLog (>= 0.20.0)
- Fittings (>= 0.10.0)
- FSharp.Compiler.Service (>= 43.9.303)
- FSharp.Core (>= 9.0.303)
- Microsoft.VisualBasic (>= 10.3.0)
- System.Private.Uri (>= 4.3.2)
- Velopack (>= 0.0.1298)

NuGet packages

This package is not used by any NuGet packages.

GitHub repositories

This package is not used by any popular GitHub repositories.

Version	Downloads	Last Updated
0.33.2	31	10/1/2026
0.33.2-net9	28	10/1/2026
0.33.2-net8	32	10/1/2026
0.33.2-net472	32	10/1/2026
0.33.2-net10	0	10/2/2026
0.33.1	29	10/1/2026
0.33.1-net9	30	10/1/2026
0.33.1-net8	26	10/1/2026
0.33.1-net472	28	10/1/2026
0.33.0	34	10/1/2026
0.33.0-net9	35	10/1/2026
0.33.0-net8	29	10/1/2026
0.33.0-net472	31	10/1/2026
0.32.3	150	5/23/2026
0.32.3-net9	121	5/23/2026
0.32.3-net8	196	5/23/2026
0.32.3-net472	186	5/23/2026
0.32.2-net9	113	5/10/2026
0.32.2-net8	134	5/10/2026
0.32.2-net472	141	5/10/2026

### Changed

- 'Reset FSI' asks before cancelling a running evaluation, the log is only cleared if the reset starts
- switching between sync and async FSI mode cancels the running evaluation (after confirmation)
- hosting API: new field `firstLine` on `EvalData`, new `Fsi.TryReset()` that returns if the reset was started

### Fixed

- 'Close and Delete File' deleting the file even when closing the tab was canceled
- 'Rename/Move' deleting the file when the name was kept or only its casing was changed
- file not being watched anymore after the "deleted or renamed" message, so a file that exists again was not noticed
- 'Save Incrementing' dropping the character before a single trailing digit, e.g. `test1.fsx` was saved as `tes2.fsx`
- possible endless loop in selection highlighting when the selection gets cleared while searching
- possible crash when the list of recently used files is accessed from several threads
- crash on Delete or Backspace in a rectangular selection on the first line
- crash on swapping the last word of a document to the right
- jump to the wrong line after a runtime error when only a part of the script was evaluated or when the error is in a file loaded via `#load`
- marking of evaluated code not being cleared on 'Reset FSI'
- closing the window shutting down the dispatcher of the UI thread instead of the one of the FSI thread
- tab shown as unsaved after saving a document that got tabs or LF line endings via paste
- font size of tooltips and completion window not using the saved size on startup
- event handlers of the scrollbar error markers piling up on every tab switch