(Harry is @ DevTeach in Vancounver with his family this week. He was hoping to still do Morning Coffee posts, but that’s turned out to be infeasible. So instead, you get a series of pre-written posts about F#.)

It’s not all puppy dogs and ice cream with F#. Here are a few things that I didn’t like about the lanugage.

Linear Scoping

In C#, a given piece of code is able to call any function it wants to (limited by CAS and visibility of course). If I define two functions, the first can call the second even thought the compiler has never seen the second function when it’s parsing the first.

F# has linear scoping like C++ does. You can’t call functions that haven’t already been defined in the file (or a previous file that’s already been fed to the compiler). This makes writing mutually recursive functions (A calls B, B calls C, C calls A) fairly annoying. Typically, in F# we declare functions with “let”. But in the Additive function above, we’re declaring the function with “and”. By using “and”, we’re basically chaining together function declarations into a logical unit. Then, you mark the first function declaration in the chain as recursive, and now those methods are enabled for mutual recursion. Not exactly intuitive.

Frankly, I like C#’s ability to bind to methods that haven’t been declared yet. I wonder if this is an intrinsic issue with FP or F# scoping rules, or if it’s something they could fix if they took the time.

No Method Overloading

In my CheckForToken method, I use a string type to hold the token I’m looking for, since tokens can often be multi-character. However, for one character tokens, this is over kill. Not just in terms of creating a string object to contain just one character, but also in how I pattern match the token against the input string. If we’re only looking for one character, we can skip recursion entirely. Yet there’s no way to define two functions called Token that have different signatures.

Given type inference, this isn’t surprising, but it’s still a little annoying for folks coming from C# land.

Limited VS support

More evidence of a rotted brain. F#’s integration into VS is limited at best. It does syntax highlighting and debugging, but that’s about it. The problem I keep running into is that I have two projects – my main project and my test project. Even though I’ve define the test project as being dependent on the main project, it doesn’t automatically compile the test project when I change the main project. So I keep doing something like fix a bug, recompile, then run NUnit to see if the light turned green. It doesn’t, because I haven’t rebuilt the test project and it’s still referencing the old version of the main project. Now that it’s a “real” product, I’m hoping to see better integration into VS08. Maybe even an F# Express that leverages the new VS08 shell?

(Harry is @ DevTeach in Vancounver with his family this week. He was hoping to still do Morning Coffee posts, but that’s turned out to be infeasible. So instead, you get a series of pre-written posts about F#.)

Significant Whitespace

If you’re a Python programmer, you already know this one. Instead of delineating code blocks explicit with curly braces or begin/end keywords, F# uses whitespace. Code blocks are indented relative to their parent. This enforces readability standards as well as conciseness. You can see that in the code Additive function above. Technically, this is optional in F# if you specify the #light compiler option, but pretty much all the docs and books assume this by default.

Custom Operators

This is minor, but cool nonetheless. Many languages let you overload existing operators like + and *. However, F# goes a step further and also lets you create custom operators. You just pick a combination of symbols that isn’t already being used and define a function for it. For example, in my parsing code I wanted a simple way to adorn my input parse strings in my tests so that I could later easily change their type if I changed the type of NextChar and CheckForToken as described above. I defined the “double bang” operator !!. Currently, double bang converts a string into a character list, but originally it simply returned the string since I had written my Char and Token classes in terms of string.