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Example: F# Script Demo

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Scripts:

Use this example when you want to try F# scripting inside Revit.

  • F#
  • NuGet
  • Revit

The script​

main_script.fsx references NuGet packages, loads a local module, then asks you to pick an element and prints its metadata. This is the start of the file; the repository version continues with geometry examples using geometry3Sharp and NetTopologySuite:

main_script.fsx
#r "C:/Program Files/Autodesk/Revit 2025/RevitAPI.dll"
#r "C:/Program Files/Autodesk/Revit 2025/RevitAPIUI.dll"
#r "nuget: Newtonsoft.Json"
#r "nuget: geometry3Sharp"
#r "nuget: NetTopologySuite"

#load "./modules/Processor.fsx"

open Autodesk.Revit.Attributes
open Autodesk.Revit.UI
open Autodesk.Revit.UI.Selection
open Demo
open Newtonsoft.Json
open System

[<Transaction(TransactionMode.Manual)>]
type ShowMessageCommand() =
    interface IExternalCommand with
        member _.Execute(commandData, _message, _elements) =
            let text = Processor.getDialogText commandData
            TaskDialog.Show("F# Script", text) |> ignore

            let uiDoc = commandData.Application.ActiveUIDocument
            let selectRef = uiDoc.Selection.PickObject(ObjectType.Element)
            let element = uiDoc.Document.GetElement(selectRef.ElementId)

            Console.WriteLine(element.GetType())
            Console.WriteLine(element.Name)
            Console.WriteLine(element.Category)

            let o = {| X = 2; Y = "Hello" |}
            Console.WriteLine $"%s{JsonConvert.SerializeObject o}"

            Result.Succeeded
Packages are resolved for you

The three #r "nuget: …" lines are all it takes. The first run is slower while packages restore; later runs reuse the cache. See NuGet Dependencies.

The complete scripts are in the repository: main_script.fsx and selection_script.fsx.

What It Shows​

  • referencing Revit API assemblies;
  • referencing NuGet packages from a script;
  • loading local F# modules;
  • creating an IExternalCommand;
  • selecting a Revit element;
  • printing element metadata;
  • trying computational geometry packages such as geometry3Sharp and NetTopologySuite.

Run​

  1. Open Revit 2025 or adjust the #r paths for your installed Revit version.
  2. Add the FSharpScriptDemo folder as a script folder.
  3. Run main_script.fsx.
  4. Select an element when prompted.
  5. Review the trace panel output.

First run may take longer because NuGet packages need to be resolved.

What To Edit​

Common edits:

  • Change Revit API reference paths for another Revit version.
  • Add F# helper code under modules/.
  • Try a smaller set of NuGet packages while debugging.
  • Replace selection with a collector when you do not need user input.

Troubleshooting​

SymptomCheck
Revit API reference not foundupdate #r paths
NuGet package failscheck package name/version and network access
selection cancelsESC/cancel is expected to stop the command
command not discoveredfile name must end with script.fsx