F# source code formatter, inspired by scalariform for Scala, ocp-indent for OCaml and PythonTidy for Python.
This project aims at formatting F# source files based on a given configuration. Fantomas will ensure correct indentation and consistent spacing between elements in the source files. We assume that the source files are parsable by F# compiler before feeding into the tool. Fantomas follows the formatting guideline being described in A comprehensive guide to F# Formatting Conventions.
The project is developed with the following use cases in mind:
-
Reformatting an unfamiliar code base. It gives readability when you are not the one originally writing the code. To illustrate, the following example
type Type = TyLam of Type * Type | TyVar of string | TyCon of string * Type list with override this.ToString () = match this with | TyLam (t1, t2) -> sprintf "(%s -> %s)" (t1.ToString()) (t2.ToString()) | TyVar a -> a | TyCon (s, ts) -> s
will be rewritten to
```fsharp
type Type =
| TyLam of Type * Type
| TyVar of string
| TyCon of string * Type list
override this.ToString() =
match this with
| TyLam(t1, t2) -> sprintf "(%s -> %s)" (t1.ToString()) (t2.ToString())
| TyVar a -> a
| TyCon(s, ts) -> s
```
-
Converting from verbose syntax to light syntax. Feeding a source file in verbose mode, Fantomas will format it appropriately in light mode. This might be helpful for code generation since generating verbose source files is much easier. For example, this code fragment
let Multiple9x9 () = for i in 1 .. 9 do printf "\n"; for j in 1 .. 9 do let k = i * j in printf "%d x %d = %2d " i j k; done; done;; Multiple9x9 ();;
is reformulated to ```fsharp let Multiple9x9() = for i in 1..9 do printf "\n" for j in 1..9 do let k = i * j printf "%d x %d = %2d " i j k
Multiple9x9()
```
- Formatting F# signatures, especially those generated by F# compiler and F# Interactive.
For more complex examples, please take a look at F# outputs of 20 language shootout programs and 10 CodeReview.SE source files.
You can fork this repo and compile the project with F# 3.0/.NET framework 4.0. Alternatively, Fantomas is also available via a NuGet package which contains both the library and the command line interface. For detailed guidelines, please read Fantomas: How to use.
FantomasWeb, implemented by Taha Hachana, is accessible at http://fantomasweb.apphb.com/. Please try out Fantomas on this nice website and provide feedbacks.
Ivan Towlson is developing Fantomas extension under fsharp-vs-commands project.
The code base is written in F# 3.0/.NET framework 4.0. The solution file can be opened in Visual Studio 2012 and MonoDevelop or Xamarin Studio. NuGet is used to manage external packages. The test project depends on FsUnit and NUNit. However, the library project and command line interface have no dependency on external packages.
We have tried to be careful in testing the project. There are 145 unit tests and 30 validated test examples, but it seems some corner cases of the language haven't been covered. Feel free to suggests tests if they haven't been handled correctly.
Due to limited information in F# ASTs, beware of current drawbacks:
- Inline comments and multiline comments are lost. Only XML doc comments are preserved.
- Compiler directives are lost.
There are a few reasons to choose the name as such. First, it starts with an "F" just like many other F# projects. Second, Fantomas is my favourite character in the literature. Finally, Fantomas means "ghost" in French; coincidentally F# ASTs and formatting rules are so mysterious to be handled correctly.
Would like to contribute? Read the formatting conventions and the Usage notes and discuss on the issues. You can fork the GitHub repository and send a pull request.
We would like to gratefully thank the following people for their contributions.
The library and tool are available under Apache 2.0 license. For more information see the License file.