If you only have F# 3.1 installed on a machine, but need to use a compiled application that requires F# 3.0, here's what you can do.

This post uses a particular application, Zero29, as an example in order to explain a problem and one possible solution. However, the post isn't about Zero29, but rather about a particular F# DLL hell.

Currently, I'm repaving one of my machines, which is always a good idea to do regularly, because it's a great remedy against works on my machine syndrome. This machine doesn't yet have a lot of software, but it does have Visual Studio 2013 and F# 3.1.

Working with a code base, I wanted to use Zero29 to incement the version number of the code, so first I executed:

$ packages/Zero29.0.4.1/tools/Zero29 -l

which promptly produced this error message:

Unhandled Exception: System.IO.FileNotFoundException:
Could not load file or assembly
'FSharp.Core, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
or one of its dependencies. The system cannot find the file specified.
   at Ploeh.ZeroToNine.Program.main(String[] argv)

On one level, this makes sense, because Zero29 0.4.1 was compiled against F# 3.0 (which corresponds to FSharp.Core

On another level, this is surprising, since I do have F# 3.1 (FSharp.Core on my machine. Until the error message appeared, I had lived with the naïve assumption that when you install F# 3.1, it would automatically add redirects from FSharp.Core to, or perhaps make sure that FSharp.Core was also available. Apparently, I've become too used to Semantic Versioning, which is definitely not the versioning scheme used for F#.

Here's one way to address the issue.

Although Zero29 is my own (and contributors') creation, I didn't want to recompile it just to deal with this issue; it should also be usable for people with F# 3.0 on their machines.

Even though it's a compiled program, you can still add an application configuration file to it, so I created an XML file called Zero29.exe.config, placed it alongside Zero29.exe, and added this content:

<?xml version="1.0" encoding="utf-8"?>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <assemblyIdentity name="FSharp.Core"
        <bindingRedirect oldVersion=""

This solved the problem, although I now have the derived problem that this new file isn't part of the Zero29 NuGet package, and I don't know if it's going to ruin my colleagues' ability to use Zero29 if I check it into source control...

Another option may be to add the redirect to machine.config, instead of an application-specific redirect, but I have no desire to manipulate my machine.config files if I can avoid it, so I didn't try that.

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Thursday, 30 January 2014 18:39:00 UTC


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