This library builds on top of the FSharp.Compiler.Service library and provides a nice API for F# script integration. It provides APIs to push values into and to get values from scripts. Additionally it adds some extension methods missing from the FSharp.Compiler.Service API.

fsharp, scripting, compiler, host
Install-Package Yaaf.FSharp.Scripting -Version 1.7.1




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The Yaaf.FSharp.Scripting library can be installed from NuGet:
PM> Install-Package Yaaf.FSharp.Scripting

Include as source file


You can include the functionality directly into your application by using paket source files:


github matthid/Yaaf.FSharp.Scripting src/source/Yaaf.FSharp.Scripting/YaafFSharpScripting.fs


File: YaafFSharpScripting.fs 

See for details.


The YaafFSharpScripting.fs source code file is included in the nuget package as well. You can find it in content/YaafFSharpScripting.fs. By adding the source code file (as reference) to your project you don't need to add a nuget dependency (Yaaf.FSharp.Scripting) to your final package.

Quick intro

This library tries to improve the scripting capabilities of FSharp.

It builds on top of FSharp.Compiler.Service but provides a nice an clean API:

open Yaaf.FSharp.Scripting
use fsiSession = ScriptHost.CreateNew()
fsiSession.Reference (@"C:\MyAssembly.dll")
fsiSession.Open ("MyAssembly")

// hook 25 into the session with name test (ie "let test = 25")
// this works with any object
fsiSession.Let "test" 25

// Get a value out of the evaluator
let v = fsiSession.EvalExpression<int> "test"
assert (v = 25)

// Try to get a value (with handling error cases)
match fsiSession.Handle<int> fsiSession.EvalExpression "test" with
| InvalidExpressionType e -> 
  // not of type int
  // e.Value contains the result object, e.ExpectedType the expected type (int in this case)
| InvalidCode e -> 
  // couldn't get app value (compiler error, not defined or exception in the running code)
  // e.Input is the given text, e.Result is the compiler or the script output
  // Note: script exceptions are written as strings within e.Result
| Result r -> 
  // r is the value.

// Get the output of the snippet
let v = fsiSession.EvalInteractionWithOutput """printf "test" """
assert (v.Output.ScriptOutput = "test")

// Get the error message of the compilation
try fsiSession.EvalInteraction """ Some_Invalid_F# """
with :? FsiEvaluationException ev ->
    printfn "FSI said: %s" ev.Result.Error.FsiOutput
    printfn "Complete Error: %O" ev

// Load scripts
fsiSession.EvalScript "Script.fsx"

The library also provides some nice members which are missing in FSharp.Compiler.Service:

open Yaaf.FSharp.Scripting
open Microsoft.FSharp.Compiler.SourceCodeServices

// A Assembly -> FSharpEntity mapping (extension) function
let fsAssembly = FSharpAssembly.FromAssembly typeof<MyType>.Assembly

// A extension method to find the entity type
let fsType = fsAssembly.Value.FindType typeof<MyType>

And some extensions for System.Type to get the FSharp type name

// with concrete types.
let def = typeof<option<int>>
test <@ def.Name = "FSharpOption`1" @>
test <@ def.Namespace = "Microsoft.FSharp.Core" @>

test <@ def.FSharpParamList = "<System.Int32>" @>
test <@ def.FSharpFullName = "Microsoft.FSharp.Core.Option" @>
test <@ def.FSharpFullNameWithTypeArgs = "Microsoft.FSharp.Core.Option<System.Int32>" @>
test <@ def.FSharpName = "Option" @>

// With typedefs.
let def = typedefof<option<int>>
test <@ def.Name = "FSharpOption`1" @>
test <@ def.FullName = "Microsoft.FSharp.Core.FSharpOption`1" @>

test <@ def.FSharpParamList = "<_>" @>
test <@ def.FSharpFullName = "Microsoft.FSharp.Core.Option" @>
test <@ def.FSharpFullNameWithTypeArgs = "Microsoft.FSharp.Core.Option<_>" @>
test <@ def.FSharpName = "Option" @>

Examples and configuration overview