On Tue, Oct 18, 2016 at 8:56 PM, Rustom Mody <rustompm...@gmail.com> wrote: > One thing probably is correct in what you are saying (if you are saying!): > The IO monad cannot be programmed at the vanilla user/programmer level but > must > be hardwired into the system (for an FPL of course; for python its all demo > anyway)
That's about right. (And yeah, I'm fine with the Python demos being a bit forced - it's a lot easier than all of us trying to learn Haskell syntax. Though I do appreciate the examples of the Haskell equivalents, where we get to see how clean it looks in actual usage.) So what that really means is: 1) In actual Haskell code (as opposed to standard library code), there are certain restrictions, including that your functions must be pure. 2) Standard library code is allowed to play fast and loose with the rules. 3) This makes Haskell actually useful, instead of being an interesting research project. For comparison, Python has similar rules: 1) In actual Python code, there are certain restrictions, including that your object references must be perfectly maintained. 2) Standard library code is allowed to play fast and loose (eg making weakrefs that don't count as actual references, or releasing the GIL while doing heavy computation, etc). 3) This makes Python actually perform fast, instead of being a pure and naive byte-code interpreter. In each case, I absolutely agree with the third point. There is nothing wrong with sacrificing a bit of purity in order to gain a ton of practicality, especially if you can bury the sacrifice away in some deep corner of the language. However, it is patently false to claim that all of CPython could be implemented using equivalent Python code; for instance, you would have no way of ever creating the top-of-tree loop wherein 'object' is an instance of 'type', and 'type' is a subclass of 'object'. In the same way, I think, it is patently false to claim that Haskell is purely functional - but the I/O monads are a crucial feature in making the language useful. Just please, stop trying to claim that it's purely functional. It isn't. It's imperative with functional paint. (Unless I'm flat wrong in my analysis, of course, in which case I'm happy to be corrected in my understanding.) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
