Learning some Fantomas AST

Made a test encoder/decored for a simple namespace declaration with Fantomas OAK Ast, see fantomas tools page

given

Oak (1,0-1,15)
        ModuleOrNamespaceNode (1,0-1,15)
            ModuleOrNamespaceHeaderNode (1,0-1,15)
                MultipleTextsNode (1,0-1,9)
                    namespace (1,0-1,9)
                IdentListNode (1,10-1,15)
                    A (1,10-1,11)
                    B (1,12-1,13)
                    C (1,14-1,15)

it will output A.B.C (lowered)

you can run it as dotnet fsi script.fsx or in vscode with dotnet sdk installed. cheers!

let oakAst = 
    "hello.one.two"
    |> FantomasWriter.makeNamespace  []

oakAst 
|> FantomasReader.extractNsFromOak 
|> Option.iter (printfn "NAMESPACE: %s")

Fabulous.AST

if you want to make your life easier and drop the custom write part for Oak, you can make use of the awesome Fabulous.AST DSL nuget package

#r "nuget:Fabulous.AST"

open System
open Fabulous.AST
open type Fabulous.AST.Ast

// using Fabulous.AST life becomes easier for writing oak
let oakAst = 
    Ast.Oak(){
        Ast.Namespace("hello.one.two") {}
    }
    |> Gen.mkOak

Here a Gist of It

	#r "nuget:Fantomas.Core"
	open Fantomas.Core
	open Fantomas.Core.SyntaxOak
	open Fantomas.FCS.Text
	open System
	(** `namespace A.B.C` : https://fsprojects.github.io/fantomas-tools
	Oak (1,0-1,15)
	ModuleOrNamespaceNode (1,0-1,15)
	ModuleOrNamespaceHeaderNode (1,0-1,15)
	MultipleTextsNode (1,0-1,9)
	namespace (1,0-1,9)
	IdentListNode (1,10-1,15)
	A (1,10-1,11)
	B (1,12-1,13)
	C (1,14-1,15)
	*)
	module FantomasWriter =
	let text v = SingleTextNode(v, Range.Zero)
	let toMultipleTexts lst = MultipleTextsNode(lst |> Seq.map text |> Seq.toList ,Range.Zero)
	let toIdentList (lst: string seq) =
	let ll =
	lst
	|> Seq.map (fun l ->
	let content = l |> text
	if l = "." then
	content |> IdentifierOrDot.KnownDot
	else
	content |> IdentifierOrDot.Ident
	)
	|> Seq.toList
	if ll.Length > 0 then
	IdentListNode(ll, Range.Zero) |> Some
	else
	None
	let makeModuleOrNamespaceHeaderNode (nameSpaceString: string) =
	let ns = nameSpaceString.ToLower().Trim().Split([|'.'|])
	if ns.Length > 0 then
	ModuleOrNamespaceHeaderNode(
	None,
	None,
	[ "namespace" ] |> toMultipleTexts,
	None,
	false,
	ns |> toIdentList,
	Range.Zero) |> Some
	else
	None
	let makeNamespace (nameSpaceString: string) decls =
	let nsOpt = makeModuleOrNamespaceHeaderNode nameSpaceString
	Oak([],
	[
	ModuleOrNamespaceNode(nsOpt, decls, Range.Zero)
	], Range.Zero)
	module FantomasReader =
	let extractNs (iln: IdentListNode) =
	iln.Content
	|> List.collect (fun iod ->
	match iod with
	| IdentifierOrDot.Ident(stn) -> [ stn.Text ]
	| _ -> []
	)
	|> fun l ->
	if l.Length > 0 then
	String.Join('.',l) |> Some
	else
	None
	// Define a function to extract the namespace from an Oak AST
	let extractNsFromOak (oak: Oak) =
	oak.ModulesOrNamespaces.Head.Header
	|> Option.bind (
	fun header ->
	match header.LeadingKeyword.Content with
	| [x] when x.Text = "namespace" ->
	header.Name
	|> Option.bind extractNs
	| _ -> None
	)
	// Example usage
	let oakAst = FantomasWriter.makeNamespace "hello.one.two" []
	oakAst
	|> FantomasReader.extractNsFromOak
	|> Option.iter (printfn "NAMESPACE: %s")

view raw fantomas_extract_namespace_oak.fsx hosted with ❤ by GitHub