F# Compiler Services

Compiler Services: Notes on FSharp.Core.dll

Shipping an FSharp.Core with your application

When building applications or plug-in components which use FSharp.Compiler.Service.dll, you will normally also include a copy of FSharp.Core.dll as part of your application.

For example, if you build a HostedCompiler.exe, you will normally place an FSharp.Core.dll (say alongside your HostedCompiler.exe.

If doing dynamic compilation and execution you may also need to include an FSharp.Core.optdata and FSharp.Core.sigdata, see below for guidance.

Binding redirects for your application

The FSharp.Compiler.Service.dll component depends on FSharp.Core Normally your application will target a later version of FSharp.Core, and you will need a binding redirect to ensure that other versions of FSharp.Core forward to the final version of FSharp.Core.dll your application uses. Binding redirect files are normally generated automatically by build tools. If not, you can use one like this (if your tool is called HostedCompiler.exe, the binding redirect file is called HostedCompiler.exe.config)

Some other dependencies may also need to be reconciled and forwarded.

<?xml version="1.0" encoding="utf-8" ?>
      <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
          <assemblyIdentity name="FSharp.Core" publicKeyToken="b03f5f7f11d50a3a" culture="neutral"/>
          <bindingRedirect oldVersion="" newVersion=""/>
          <assemblyIdentity name="System.Collections.Immutable" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
          <bindingRedirect oldVersion="" newVersion="" />

Which FSharp.Core and .NET Framework gets referenced in compilation?

The FSharp.Compiler.Service component can be used to do more or less any sort of F# compilation. In particular you can reference an explicit FSharp.Core and/or framework assemblies in the command line arguments (different to the FSharp.Core and a .NET Framework being used to run your tool).

To target a specific FSharp.Core and/or .NET Framework assemblies, use the --noframework argument and the appropriate command-line arguments:

let fsharpCorePath = 
    @"C:\Program Files (x86)\Reference Assemblies\Microsoft\FSharp\.NETFramework\v4.0\\FSharp.Core.dll"
let errors2, exitCode2 = 
    [| "fsc.exe"; "--noframework"; 
       "-r"; fsharpCorePath; 
       "-r"; @"C:\Windows\Microsoft.NET\Framework\v4.0.30319\mscorlib.dll"; 
       "-o"; fn3; 
       "-a"; fn2 |])

You will need to determine the location of these assemblies. The easiest way to locate these DLLs in a cross-platform way and convert them to command-line arguments is to crack an F# project file.
Alternatively you can compute SDK paths yourself, and some helpers to do this are in the tests for FSharp.Compiler.Service.dll.

What about if I am processing a script or using GetCheckOptionsFromScriptRoot

If you do not explicitly reference an FSharp.Core.dll from an SDK location, or if you are processing a script using FsiEvaluationSession or GetCheckOptionsFromScriptRoot, then an implicit reference to FSharp.Core will be made by the following choice:

  1. The version of FSharp.Core.dll statically referenced by the host assembly returned by System.Reflection.Assembly.GetEntryAssembly().

  2. If there is no static reference to FSharp.Core in the host assembly, then

    • For FSharp.Compiler.Service 0.x series, a reference to FSharp.Core version is added
    • For FSharp.Compiler.Service 1.3.1.x (F# 3.1 series), a reference to FSharp.Core version is added
    • For FSharp.Compiler.Service 1.4.0.x (F# 4.0 series), a reference to FSharp.Core version is added

Do I need to include FSharp.Core.optdata and FSharp.Core.sigdata?

If your compilation arguments explicitly reference an FSharp.Core.dll from an SDK location, then FSharp.Core.sigdata and FSharp.Core.optdata should be alongside the DLL (if these files are not installed, then that's a bug in the F# SDK installation). If your compilation arguments are always making an explicit reference, then you should not include FSharp.Core.optdata and FSharp.Core.sigdata as part of your application.

If you are relying on an implicit reference (e.g. for script processing, see above), this means your tool may reference the FSharp.Core.dll that is part of your application. In this case, you may either get an error that FSharp.Core.optdata and FSharp.Core.sigdata are not found alongside FSharp.Core.dll. If you want to implicitly reference the FSharp.Core.dll you are including in your application, then also add FSharp.Core.sigdata and FSharp.Core.optdata as two additional files to your application. When using CompileToDynamicAssembly, this problem can also manifest itself as a stack overflow during assembly resolution.

Tools that dynamically compile and execute code (e.g. a HostedExecution.exe) often make an implicit reference to FSharp.Core.dll, which means they normally also include FSharp.Core.optdata and FSharp.Core.sigdata.


In this design note we have discussed three things:

  • which FSharp.Core.dll is used to run your compilation tools
  • how to configure binding redirects for the FSharp.Core.dll used to run your compilation tools
  • which FSharp.Core.dll and/or framework assemblies are referenced during the checking and compilations performed by your tools.
Multiple items
type LiteralAttribute =
  inherit Attribute
  new : unit -> LiteralAttribute

Full name: Microsoft.FSharp.Core.LiteralAttribute

new : unit -> LiteralAttribute
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