Rash thoughts about .NET, C#, F# and Dynamics NAV.

Today I released FAKE 2.12 with a lot of small bug fixes and improvements. The biggest feature is that we now use NancyFx for FAKE.Deploy. A big thanks to all of the 60 contributors.

What’s new?

• Add getDependencies to NugetHelper #373
• Add more F# friendly functions for IO.Path #374
• SourceLink support #345
• NancyFx instead of ASP.NET MVC for FAKE.Deploy #376 – big thanks to @MorganPersson
• Allows to execute processes as unit tests #379
• Allow to run MsTest test in isolation #367
• Fixed Nuget.packSymbols #366
• Fixed bug in SemVer parser #364
• New title property in Nuspec parameters #359
• Added option to disabled FAKE’s automatic process killing #357
• Better AppyVeyor integration #353, #345
• Added ability to define custom MSBuild loggers #352
• Fix for getting the branch name with Git >= 1.9 #351
• Added functions to write and delete from registry #350
• NUnit NoThread, Domain and StopOnError parameters #349
• Add support for VS2013 MSTest #346
• Lots of small fixes

Getting started

If you new to FAKE you should read the getting started guide or clone the F# ProjectScaffold.

Go and grab the bits

Feel free to contact me if you need help for the upgrade.

As part of a longer process of making FSharpx better maintainable I created a new project called FSharp.Configuration. It contains type providers for the configuration of .NET projects:

• AppSettings (extracted from FSharpx)
• ResX (by Phil Trelford)
• Yaml (by Vasily Kirichenko)

Additonal information:

• Nuget package
• Source code (Apache 2.0 License)

Please tell me what you think.

I’m happy to annouce the new release of the FSharpx.Collections package on nuget.

Most important changes:

• We extracted all collections into a new repositiory.
• We have documentation and samples (even for C#).
• PersistentVector<T> doesn’t require equality constraints on T.
• We did some basic performance tests.
• We added PersistentHashMap.
• The build process uses FAKE and FSharp.Formatting via the FSharp.ProjectScaffold.

Please tell me if it works for you.

In earlier posts I showed how we can use F# type providers to access Dynamics NAV 2009 via Web Services and Dynamics NAV 2013 via OData. This time I want to point to a new type provider which allows Dynamics NAV data access directly via the SQL Server. The new type provider aims to be a replacement for C/Front.NET and gives a much nicer API.

It’s already available on nuget and has documentation with a “getting started guide”.

Christian Clausen and Bent Rasmussen released their second static analysis tool for Dynamics NAV called Prism. This time it has more features and it’s even faster than Supervision.

“Load time for Developers Toolkit for a typical full database is approximately 25 minutes which compares to Prism’s 20 seconds. Load time is a serious productivity and/or quality killer, as people will either work with old objects in Developers Toolkit, wait another 25 minutes to reprocess the objects, or even decide to just go ahead and change code without understanding how the current code is actually working.”

[project page]

The biggest new feature is “Find usages”:

Check out the project page and watch the presentation at the Community for F# which gives some details about the implementation.

Until yesterday I thought I would be the only person on this planet who plays with a combination of F# and Dynamics NAV. Turned out I was wrong.

Christian Clausen and Bent Rasmussen created a really really cool static analysis tool for Dynamics NAV written in F#. For those who worked with the Dynamics NAV Developer’s Toolkit this is your new friend:

“Supervision is a free software program which can transform C/AL object text files into color-coded hyper-linked interactive HTML files.

The purpose of Supervision is to give Microsoft Dynamics NAV developers an easy and intuitive way to browse C/AL source code which provides better insight into the semantics of C/AL programs.”

[Project page]

Some of the features are:

• Produces HTML/JavaScript code from Microsoft Dynamics NAV text export files
• Usages of user-defined functions, variables, parameters, fields, system-defined variables, and object types link to their declaration
• Usages of C/AL system functions link to official Microsoft C/AL language documentation
• Code coloring
• It’s blazing-fast

Check out the project page and watch the presentation at the Community for F# which gives some details about the implementation.

Triggered by a short tweet by Tomas Petricek and a blog post by Don Syme I had a couple of conservations about null as a value, Null as a type (Nothing in Scala), the null object pattern and the Maybe monad (or Option type in F#). I decided to share my opinion on this topic in order to help others to make their own opinion.

Part I – Null as a value

Unfortunately most programming languages have some kind of null pointer. We are now even at a point where some people claim that Tony Hoare’s famous billion dollar mistake costs actually a billion dollar per year.

But before we start to think about solutions to the null pointer problem let us first see where null values might come in handy.

Uninitialized values

In a statement oriented language like C# it is sometimes not that easy to represent uninitialized state.

As you can see we forgot to initialize peter in the missing "else-branch" which might lead to a NullReferenceException. There are a couple of things we can do to prevent this from happening. First of all we should omit the explicit initialization with null:

In this case the C# compiler throws an error telling us "Use of unassigned local variable ‘peter’".

In expression oriented languages like F# the problem doesn’t exist. We usually write initializations like this:

There is no way to forget the else branch since the types don’t match.

Unknown values

Consider a search function which tries to find a Person in a list:

Unknown values are probably the most common cause for the introduction of nulls and in contrast to uninitialized values they have much more global effects.

Solutions to unknown values

1. Using explicit exceptions

One easy solution to get rid of the nulls is to make the exception explicit:

One benefit here is that we have a concrete exception which is telling us what went wrong. Unfortunately nothing forces us to handle this exception in the calling method. This means the program can still crash. Another problem is that if we use try/catch as a control flow statement (i.e. use it very very often) then we might slow down our program.

And there is still a philosophical question: is it really an exception if we don’t have a person in our repository?

2. Using out parameters and returning bools

If we want to make the result of our search a little more explicit we can also introduce a boolean return value:

This is a pattern which is actually used everywhere in the .NET framework, so it must be good right?!

Just a simple question here: What did we gain exactly? If we forget to check for nulls why would we remember to check the bool?

There is another interesting observation here. Due to the introduction of out parameters we also introduce the uninitialized value problem in every calling method, which is bizarre.

3. Null object pattern

“In object-oriented computer programming, a Null Object is an object with defined neutral ("null") behavior. The Null Object design pattern describes the uses of such objects and their behavior (or lack thereof).”

Wikipedia

So obviously this makes only sense in a context where objects have observable behavior. So let’s add some behavior to our Person class:

Let’s look at this solution for a moment.

• Pro: Implementation of missing behavior is trivial
• Pro: We don’t introduce null values –> we won’t get NullReferenceExceptions
• Pro: The name of the class carries information about the reason for the null value
• Cons: In order to to get rid of the Person(string name, int age) constructor in the null-object we had to introduce an interface
• Cons: In order to use the interface we had to modify the Person class. This might be a real problem if we don’t have access to the source. We would need some kind of ad-hoc polymorphism like Haskell’s type classes, Scala’s Traits or Clojure’s Protocols (read more about the expression problem)
• Cons: Everything we want to do with Persons has to be part of the IPerson interface or we have to fall back to explicit runtime type tests, because there is no way to get to the data:

  

• Cons: Without ad-hoc polymorphism the Person class is getting more and more complex over time since we are adding all the behavior to it. Compare it with our starting point where it was a simple data representation. We totally lost that.
• Cons: Errors/bugs might appear as normal program execution. [see Fowler, Martin (1999). Refactoring pp. 261]

Don’t use this approach it’s really not a good solution.

4. The Option type (a.k.a. Maybe monad)

The option type is a way to push the idea from 2. “returning bools” into the type system. There are lots of tutorials about the option type on the web, but for now it’s enough to know that it is something which is based on the following idea:

In order to allow pattern matching in C# we introduce a small helper:

With this idea we can get rid of all null values in the program, we don’t have to introduce an IPerson interface, the null case is type checked and the best thing is it’s really easy to create functions like IsOlderThan12:

Please don’t implement the option type yourself. Even in C# it’s much easier to just reference FSharp.Core.dll and use FSharpx (read 10 reasons to use the F# runtime in your C# app).

Of course this is only the tip of the iceberg. If you read more about the option type you will see that its monadic behavior allows all kinds of awesome applications (e.g. LINQ, folds, map, …).

5. The Either type

One of the benefits of the null object pattern above was that it allows to encode the reason for the missing value. In some cases we need the same thing for the maybe monad. So let’s try to capture the reason in the None case:

Now we can use this in the TryFindPerson method:

As with the option type please don’t rewrite this stuff yourself. There is a Choice type in F# which helps to capture this idea and Mauricio has a couple of blog posts which explain how to use it from C# (of course FSharpx is helping here again).

6. The (singleton) list monad

The option type captures the idea that we can either have one value or nothing. We can do the same thing with List<T>:

Of course this uses only a small subset of the power of IEnumerable<T> but I wanted to show the similarity to the maybe monad. You can read more about the “poor man’s option type” on Mauricio’s blog.

Conclusion

We saw a couple of very different solutions to get rid of null values. Normally I’d only use the option type or the either type (if I need to carry the reason). In some very rare situations (e.g. C# only projects) I would also use singleton lists.

I wouldn’t use the other solutions. They are potentially dangerous, especially if your project gets bigger.

I would be happy to read your opinions.

There was a lot of confusion about the document type providers in the last couple of months. The reason was Tomas Petricek and Co. worked on an improved version in the FSharp.Data project and most people lost track which feature was in which project.

In order to make things clearer I removed the Freebase, CSV, JSON and XML type providers from the fsharpx project. From now on they are only in the FSharp.Data project (on github and nuget).

I hope this doesn’t make things worse and I apologize for the confusion. On the bright side you now get a couple of new features and a really cool documentation.

You can read more about this on Tomas’s blog.

The current version of FAKE contains two tasks for Xamarins xpkg format. These are already used in Daniel Nauck’s Portable.Licensing project (read more about this project).

Sample usage:

Thank you Daniel for this contribution.

"Portable.Licensing is a cross platform open source software licensing framework which allows you to implement licensing into your application or library.

It is targeting the Portable Class Library and thus runs on nearly every .NET/Mono profile including Silverlight, Windows Phone, Windows Store App, Xamarin.iOS, Xamarin.Android, Xamarin.Mac and XBox 360. Use it for your Desktop- (WinForms, WPF, etc.), Console-, Service-, Web- (ASP.NET, MVC, etc.), Mobile (Xamarin.iOS, Xamarin.Android) or even LightSwitch applications."

[Project site]

Yep, you read this correct. This project gives you a free licensing tool for all .NET/mono platforms including stuff like Android and iOS. It’s hosted on github and already on nuget and the Xamarin store, so it’s pretty easy to use – even from F#.

Create a license

There is a really good documentation on the github project page (and there is even a sample implementation for a License Manager app), but just to give you a small glimpse:

Make sure to keep the private key private and distribute the public key with your app.

Validate a license

So try it out and don’t forget to thank Daniel Nauck for this awesome new tool.