Thsi has been mentioned before. One issue is that the CLI, and the .NET Framework don't have any notion of purity. So you'd be pretty limited in what you can do in pure code.
There is something called "Code Contracts" that's being added to .NET 4 (I think) to address some of the shortcomings of the .NET type system (like non-null references). F# could possibly pick up on some of those to help static analysis.
Having it fully throughout the system would require extending the type system to encompass purity. I doubt this will happen anytime soon.
Thank you for this. I was not aware this had been raised before and am pleased that I'm not the only one who would like this feature. I'm not so sure lack of framework support would matter too much as it would be methods I wrote myself or in the FSharp-specific libraries that I would want to reason about.
I will look into code contracts.
Thanks again.
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I have always considered that one of the main benefits of functional programming is that programs are relatively easy to reason about. This is largely due to referential transparency and associated properties such as immutability. Knowing that a function is 'pure' in this sense would gives programmers confidence in reasoning about it and using it in a multi-threaded context. For understandable pragmatic reasons F# does not require all functions to be pure.
Would it be possible to add a 'pure' modifier to function definitions that the compiler checks. For example, I would like to be able to write:
let pure my_func = ...
and if the function uses mutable data or other impure features, a compilation error would result. This check would require the compiler to check that any functions called by my_func are also pure.
As a slight sideline, the 'pure' keyword would be analagous to the const modifier for methods in C++ (sadly there is no equivalent in c#).
Your thoughts would be appreciated.